Patterns of Climate Change Across Scotland: Technical Report

Final Report Project CC03

Patterns of climate change across Scotland: technical report

May 2006

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Research contractor This document was produced by:

Claire Barnett and Matthew Perry Met Office, FitzRoy Road, Exeter, Devon, EX1 3PB, United Kingdom

Jo Hossell, Greg Hughes and Chris Procter Woodthorne, Wergs Road Wolverhampton, WV6 8TQ United Kingdom

The report should be referenced as: Barnett, C., J. Hossell, M. Perry, C. Procter and G. Hughes (2006) Patterns of climate change across Scotland: Technical Report. SNIFFER Project CC03, Scotland & Northern Ireland Forum for Environmental Research, 102pp.

SNIFFER’s project manager SNIFFER’s project manager for this contract is:

Noranne Ellis, Scottish Natural Heritage

SNIFFER’s project steering group members are:

June Graham, Scottish Environment Protection Agency (SEPA) Helen McKay, Forestry Commission Peter Singleton, Scottish Environment Protection Agency (SEPA) Guy Winter, Scottish Executive

SNIFFER First Floor, Greenside House, 25 Greenside Place, EDINBURGH EH1 3AA

Company No: SC149513 Scottish Charity: SCO22375 www.sniffer.org.uk

EXECUTIVE SUMMARY

CC03: Patterns of climate change across Scotland, March 2006

Project funders/partners: Scotland and Northern Ireland Forum for Environmental Research (SNIFFER), Scottish Executive, Scottish Environment Protection Agency (SEPA), Scottish Natural Heritage (SNH) and the Forestry Commission.

Background to research

The Scottish mainland and Scottish Isles warmed by 0.69°C and 0.64°C respectively, over the period 1861-2000 (Jones and Lister, 2004). Precipitation patterns have also altered, generally producing drier summer and wetter winters but there has also been an increased frequency of heavy rain events (Mayes, 1996; Smith, 1995). Generalised annual values at a national level can mask significant regional and seasonal variations. In order to plan for adaptation to climate change there is a need to know the degree of change in specific locations across the seasons. Only then can potential future trends for that locality be considered in the context of the latest UK Climate Impacts Programme (UKCIP) climate change scenarios.

Objectives of research

The aim of this study is to collate records of observed data in order to provide an up to date assessment of how the climate of Scotland has changed, not just giving a nationally averaged result but identifying regional patterns of change. This study provides a benchmark against which future change can be measured. The analysis of trends shows how far Scotland’s climate has altered. It also places the predicted future climate of Scotland within the context of changes already observed. It thereby provides information essential to those considering the need to adapt to the impacts of climate change in Scotland. A stakeholder survey was conducted in order to ensure the capture of key variables. The findings of the study are presented in summary form as a Handbook, with the full details of the analysis being given in this technical handbook.

When descriptions of our changing climate are presented in terms of nationally averaged annual mean statistics, significant regional and seasonal variations can be masked. This technical report describes the analysis of a number of high-resolution datasets. These are based upon data from a dense network of observing stations that has been gridded using some of the latest data regression and interpolation techniques. The datasets include temperature and precipitation from 1914 to 2004, sunshine from 1929 to 2004, and a range of other variables, such as mean sea level and snow cover, from 1961. A number of quantities based upon either temperature or rainfall, such as growing season length and rainfall intensity, have also been derived. These datasets have been analysed in order to identify patterns of change in the Scottish climate over time and space.

Key findings

• Since 1914 average temperatures in Scotland have risen by 0.5°C. Northern Scotland has warmed at a slower rate than the rest of the country, with average increases in temperature only being significant in spring. In northern Scotland, there has been little change in winter temperatures since 1914. • Temperatures have increased in every season and in all parts of Scotland since 1961. This has been the fastest period of warming observed over the 1914 to 2004 period analysed in this

i study. Since 1961 average spring, summer and winter temperatures have risen by more than 1°C. • Since 1961 average daily maximum temperatures have been increasing at a faster rate than average minimum, or night time, temperatures in Scotland. Globally, over approximately the same period, it is minimum temperatures that have increased at the faster rate. It is interesting to note that conversely the trend in Scotland over the 1914 to 2004 period also has the minimum temperatures increasing at the faster rate. • Scotland has become wetter since 1961, with an average increase of almost sixty percent in winter months in northern and western Scotland. For the majority of the country there has not been a large-scale significant change in average summer rainfall although some parts of north west Scotland have become up to forty five percent drier in summer. Contrary to the Scottish national trend, Aberdeenshire has seen little change in precipitation in winter months although this is compensated for in this region by a significant increase in precipitation in autumn (September-November). • Heavy rainfall events have increased significantly in winter, particularly in northern and western regions. • The snow season has shortened across the country since 1961, with the season starting later and finishing earlier in the year. The greatest reductions have occurred in northern and western Scotland. • Since 1961 there has been more than a twenty-five percent reduction in the number of days of frost (both air and ground frost) across the country. At the same time, the growing season length has increased significantly, with the greatest change occurring at the beginning of the season. • Inconsistent methods for observing cloud data and the challenges of analysing wind observations have meant that identification of any trends or patterns of change in these quantities has not been possible in this study. Further, more complex, data analysis techniques would be required for such an undertaking. • The majority of the analysis presented here is based upon data for 1961 to 2004. Longer data records for temperature and precipitation have allowed trends over this time to be put into the context of a long period. The study highlights the fact that since 1961 both annual mean temperature and precipitation have increased at a faster rate than at any other time in the ninety years considered. • The trends identified since 1961 are not always consistent with those that might be expected based upon the future climate of Scotland projected by climate models, although evidence of such trends often exists in the longer record, i.e. the 1914 to 2004 dataset. This underlines the fact that caution is required when drawing conclusions about trends and climate change based upon a relatively short data period.

This study is focused upon the identification of trends in Scottish climate and providing the regional and spatial detail that national averages mask. The study does not seek to explain, or attribute a cause, for identified trends. Although some of the trends identified are consistent with projected future climate for Scotland, it is not possible to say that the trends are evidence of man-made, i.e. anthropogenic, climate change. However, many of the trends identified are significant and therefore beyond the range expected from natural variability. Whether or not the changes are due to anthropogenic climate change it is clear that these observed trends are often comparable with those predicted for the future. This means that Scotland already has experience of the impact of such changes and is therefore well placed to plan the necessary adaptation measures for the future.

Key words: Scotland, climate change, observed trends

ii SNIFFER Project CC03: Patterns of climate change across Scotland: technical report May 2006

TABLE OF CONTENTS

EXECUTIVE SUMMARY ...... i

1. INTRODUCTION...... 1

2. OBSERVED TRENDS IN SCOTTISH CLIMATE ...... 3

2.1. Data analysis...... 6 2.2. Temperature...... 7 2.3. Rainfall ...... 24 2.4. Snow and frost ...... 34 2.5. Sunshine ...... 42 2.6. Cloud...... 45 2.7. Mean sea level pressure ...... 46 2.8. Wind ...... 48

3. PREDICTED FUTURE CHANGE IN SCOTTISH CLIMATE ...... 51

3.1. Observed trends in Scottish climate: the UKCIP02 context ...... 51 3.1.1 Temperature...... 51 3.1.2 Precipitation...... 52 3.1.3 Snowfall...... 53 3.1.4 Sunshine ...... 53 3.1.5 Mean sea level pressure ...... 53 3.1.6 Wind ...... 53

4. CONCLUSIONS...... 55

5. REFERENCES...... 57

iii SNIFFER Project CC03: Patterns of climate change across Scotland: technical report May 2006

List of Tables

Table 1 Average number of stations included per month in the gridded dataset. 5 Table 2 Mean temperature changes (°C), 1961 to 2004 and 1914 to 2004 8 Table 3 24-hour maximum temperature changes (°C), 1961 to 2004 and 1914 to 2004 10 Table 4 24-hour minimum temperature changes (°C), 1961 to 2004 and 1914 to 2004 10 Table 5 Mean diurnal temperature range changes (°C), 1961 to 2004 13 Table 6 Changes in annual temperature indices, 1961 to 2004: (a) heating degree 15 days (%), (b) growing degree days (%), (c) growing season length (days), and (d) extreme temperature range (°C) Table 7 Changes in summer and winter half-year heat and cold wave durations 22 (days), 1961 to 2003 Table 8 Changes in total precipitation amount (%), 1961 to 2004 and 1914 to 2004 25 Table 9 Changes in days of heavy rain ≥ 10 mm, 1961 to 2004 28 Table 10 Changes in annual precipitation indices, 1961 to 2004: (a) maximum 31 consecutive dry days (days), (b) mean rainfall intensity, (c) maximum 5-day precipitation amount (%) Table 11 Changes in days of snow cover (%), 1961/62 to 2004/05 24 Table 12 Changes in days of air frost (%) 1096/62 to 2004/05 36 Table 13 Changes in days of ground frost (%), 1961/62 to 2004/05 37 Table 14 Changes in the dates of the first and last ground frost, 1961 to 2005 41 Table 15 Changes in total sunshine hours (%), 1961 to 2004 and 1929 to 2004 42 Table 16 Changes in percentage cloud cover, 1961 to 2004 45 Table 17 Changes in mean sea level pressure (hPa), 1961 to 2004 46

iv SNIFFER Project CC03: Patterns of climate change across Scotland: technical report May 2006

List of Figures

Figure 1 Location of observing sites (January 2001) for data used in the 4 construction of the Met Office gridded datasets. Figure 2 Map of Scotland showing boundaries of the three regions as defined 7 in this study (North, West and East Scotland). Figure 3 Annual mean temperature (°C) for Scottish regions, 1914 to 2004. 8 Figure 4 Gridded change for mean temperature (°C), based on a linear trend from 9 1961 to 2004 (a) spring, (b) summer, (c) autumn and (d) winter. Figure 5 Annual average 24-hour maximum temperature (°C) for Scottish regions, 11 1914 to 2004 Figure 6 Annual average 24-hour minimum temperature (°C) for Scottish regions, 11 1914 to 2004. Figure 7 Gridded change for 24-hour maximum temperature (°C), based on a linear 12 trend from 1961 to 2004 (a) summer and (b) winter. Figure 8 Gridded change for 24-hour minimum temperature (°C), based on a linear 13 trend from 1961 to 2004 (a) summer and (b) winter. Figure 9 Annual mean diurnal temperature range (°C) for Scottish regions, 14 1961 to 2004. Figure 10 Annual heating degree days for Scottish regions, 1961 to 2003. 16 Figure 11 Annual growing degree days for Scottish regions, 1961 to 2003. 17 Figure 12 Annual growing season length (days) for Scottish regions, 1961 to 2004 17 Figure 13 Growing season start date for Scottish regions, 1961 to 2004. 18 Figure 14 Growing season end date for Scottish regions, 1961 to 2004. 18 Figure 15 Annual extreme temperature range (°C) for Scottish regions, 1961 to 2003 19 Figure 16 Gridded change for (a) growing degree days (%) and (b) heating degree 19 days based upon a linear trend from 1961 to 2003 Figure 17 Gridded change for extreme temperature range (°C) based upon a linear 20 trend from 1961 to 2003 Figure 18 Gridded change for growing season length (days) based upon a linear 21 trend from 1961 to 2004 Figure 19 Gridded change for (a) start and (b) end of the growing season (days) 22 based upon a linear trend from 1961 to 2004 Figure 20 Winter half-year cold wave duration (days) for Scottish regions, 1961/62 to 23 2003/04. Figure 21 Summer half-year heat wave duration (days) for Scottish regions, 1961 to 23 2003. Figure 22 Gridded change for (a) winter half-year cold wave duration (days) and 24 (b) summer half-year heat wave duration (days) based upon a linear trend from 1961 to 2003 Figure 23 Annual precipitation amount (mm) for Scottish regions, 1914 to 2004. 26 Figure 24 Climatology of annual mean rainfall amounts (mm) for Scotland, 1961 to 2004 26 Figure 25 Gridded change in precipitation (%), based upon a linear trend from 1961 27 to 2004: (a) spring, (b) summer, (c) autumn, (d) winter. Figure 26 Annual days of heavy rain ≥10mm for Scottish regions, 1961 to 2004 28 Figure 27 Gridded change in days of heavy rain ≥10mm, based on a linear trend 30 from 1961 to 2004: (a) spring, (b) summer, (c) autumn, (d) winter. Figure 28 Annual maximum consecutive dry days for Scottish regions, 1961 to 2004 31 Figure 29 Annual mean rainfall intensity (mm/day) for Scottish regions, 1961 to 2004 32 Figure 30 Annual maximum 5-day precipitation amount (mm) for Scottish regions, 32 1961 to 2004 Figure 31 Gridded change for annual maximum consecutive dry days, based on a 33 linear trend from 1961 to 2004

v SNIFFER Project CC03: Patterns of climate change across Scotland: technical report May 2006

Figure 32 Gridded change (%) for (a) annual rainfall intensity on days ≥1mm 34 rainfall, and (b) annual maximum 5-day precipitation amount, based upon a linear trend from 1961 to 2004 Figure 33 Climatology of number of days of snow cover for Scotland, 1961 to 1990. 35 Spring (upper panel) and autumn (lower panel) Figure 34 Annual days of snow cover for Scottish regions, 1961/62 to 2004/05 36 Figure 35 Annual days of air frost for Scottish regions, 1961/62 to 2004/05 37 Figure 36 Annual days of ground frost for Scottish regions, 1961/62 to 2004/05 38 Figure 37 Gridded change for (a) annual days of air frost and (b) days of snow cover, 39 based on a linear trend from 1961 to 2004 Figure 38 Gridded change for days of ground frost based upon a linear trend from 40 1961 to 2004: (a) spring, (b) summer, (c) autumn and (d) winter Figure 39 Date of the first ground frost (in days since August 1st), 1960 to 2005, at 41 four Scottish stations. Figure 40 Date of the last ground frost before the end of July (in days since August 1st), 42 1961 to 2005, at four Scottish stations. Figure 41 Annual sunshine hours for Scottish regions, 1929 to 2004 43 Figure 42 Gridded change for sunshine, based on a linear trend from 1961 to 2004: 44 (a) spring, (b) summer, (c) autumn, (d) winter Figure 43 Annual percentage cloud cover for Scottish regions, 1961 to 2004 45 Figure 44 Annual mean sea level pressure (hPa) for Scottish regions, 1961 to 2004 47 Figure 45 Gridded change for annual average mean sea level pressure (hPa), 48 based on a linear trend from 1961 to 2004: (a) summer, (b) winter Figure 46 Annual mean wind speed (knots) for three Scottish stations: Lerwick, 49 Tiree and Leuchars (values estimated from Turnhouse prior to 1969), 1957 to 2004 Figure 47 Annual mean wind speed (knots) for Scottish regions, 1969 to 2004. 49 Figure 48 Annual days of gale for three Scottish stations: Lerwick, Tiree and 50 Leuchars (values estimated from Turnhouse prior to 1969), 1957 to 2004

vi SNIFFER Project CC03: Patterns of climate change across Scotland: technical report May 2006

Appendices

Appendix 1 Data availability scoping study...... 59 Appendix 2 A brief discussion of uncertainty in climate modelling...... 87 Appendix 3 Glossary...... 91

vii SNIFFER Project CC03: Patterns of climate change across Scotland: technical report May 2006

viii SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

1. INTRODUCTION

Over recent decades the scientific community has amassed a wealth of observational data. The last one hundred years have been a period of rapid climate change, partly in response to human influences. Social, economic, industrial, and land use developments all contribute to human impact on our climate, locally, nationally and globally. The changes already observed have had, and continue to have, impacts on many aspects of society, including health, agriculture, water resources and energy demand. In order to make appropriate plans for the future it is vital to investigate observed changes in climate. In doing so, models of past and present climate can be validated and scenarios of future climate put into the context of any change already recorded.

Of the national climate trends studies conducted to date most have made use of data from a small number of stations with long historical records (e.g. Begert et al., 2005). Some authors have combined data from several stations to create a single series for a country (e.g. Hanna et al., 2004, for Iceland). In a study of UK climate, Jones and Lister (2004) have shown that the Scottish mainland and Scottish Isles warmed by 0.69°C and 0.64°C respectively over the period 1861 to 2000. Over a similar period, it can be shown that precipitation patterns over Scotland have altered (Osborn et al., 2000): summers have become drier and winters wetter. There has also been an increased frequency of heavy rain events (Mayes, 1996; Smith, 1995). However, annual average figures for Scotland can mask significant regional and seasonal variations.

As the evidence of climate change has increased, so has our understanding of the Earth’s climate, and improvements have been made to the mathematical models used to simulate it. Using climate models it has now been determined that not all of the changes observed can be attributed to natural causes and that a man-made, or anthropogenic, component can be discerned (IPCC, 2001). It is now possible to detect the signals of such anthropogenic changes at not only a global scale but also regionally (Stott et al., 2003; Stott, 2003).

In order to plan for adaptation to climate change there is a need to know the degree of change already experienced in specific locations throughout the seasons. It is also necessary to consider observed trends for that locality in the context of potential future trends suggested by the latest UK Climate Impacts Programme (UKCIP) climate change scenarios (Hulme et al., 2002). This is true for all sectors of society and business, whether for the management of land, water resources, nature conservation, or building and maintenance of infrastructures. There have been a number of publications that consider the changing climate of the UK or its regions (e.g. Kerr et al., 1999; Hulme et al., 2002; Jenkins et al., 2003; etc). Although some of these publications have focused upon Scotland, there is still the need for one publication to present a consistent analysis of available Scottish data and to place observed trends of change into the context of the latest climate model predictions. This study seeks to resolve this need.

The analysis presented here provides an assessment of climate data for the whole of Scotland that has been collated to show seasonal and regional trends for a range of variables. It places these trends in the context of climate model predictions of Scotland’s

1 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006 future climate (taken from the UKCIP02 scenarios, Hulme et al., 2002), and briefly discusses uncertainties associated with these predictions.

This technical report is structured as follows. Section 2 focuses upon observed changes in Scottish climate. It begins with a description of the framework for the analysis and then, in section 2.1, discusses the datasets used and the analysis methods employed. Trends in temperature, including derived quantities such as growing season length and heat wave duration, are presented in section 2.2. Analysis of precipitation variables, again including some derived variables, is shown in section 2.3, which is followed by trends in snow and frost in section 2.4. Changes in sunshine and cloud are given in sections 2.5 and 2.6. The analysis of observed change concludes with a presentation of trends in mean sea level pressure (section 2.7) and wind (section 2.8). In section 3 predicting the future climate of Scotland is discussed, and the trends identified in the analysis of historical data are placed in the context of the UK Climate Impacts Programme 2002 scenarios (Hulme et al., 2002). Concluding remarks are given in section 4. A handbook is also available which summarises the findings described in this technical report.

2 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

2. OBSERVED TRENDS IN SCOTTISH CLIMATE

There are many sources of observed climate data for Scotland. Records for particular variables at individual locations are available from a wide range of sources for differing periods of time (see Appendix 1). A number of these datasets have been collated into gridded datasets using spatial interpolation techniques. Datasets are often available free of charge, often under a licence agreement although access to some requires a fee. This study, for ease of accessibility for the reader, relies upon datasets that are readily available to the general public, although these have been supplemented by datasets available to the authors. The use of accessible data ensures that the analysis may be readily updated in the future.

Initially, a scoping study sought to identify relevant climate datasets and to assess their availability, plus suitability, for the proposed analysis. In addition, a survey was undertaken to assess what derived variables (in addition to standard temperature and precipitation datasets) would be of most interest to a range of stakeholders across Scotland. The scoping study report, including the dataset listings, is presented in Appendix 1. The majority of gridded datasets identified are available from 1961 until the end of 2004, although there are exceptions to this. In particular, much longer records exist for temperature, rainfall and sunshine. To assess whether trends can be detected in observed records of Scottish climate, it is highly desirable to use as long a data record as possible. On the other hand, using a consistent period of history for all variables allows a comprehensive picture of change, and any inter-dependencies, to be identified most clearly. For this reason, all data were analysed for the period 1961 to 2004 (or less where records are not available throughout the full period). However, where longer records exist these were also analysed and presented alongside the 1961 to 2004 analysis. Where gridded datasets do not exist or are difficult to interpret due to inhomogenities in the data (e.g. a change in instrumentation or observing site) individual site records were used.

The Met Office has a historical database containing observations of weather elements. These observations come from an irregularly spaced and gradually evolving network of meteorological stations across the United Kingdom. From this dataset a consistent series of climatic statistics have been produced which enables comparisons to be made across space and time. In order to do this, methods were developed to create gridded datasets from the station data.

The analysis process used geographical information system (GIS) capabilities to combine multiple regression, based on factors such as altitude, terrain shape and nearby sea or urban areas, with inverse-distance-weighted interpolation of the regression residuals. A verification of the gridded results compared with observed values was also undertaken. The full method is described in Perry and Hollis (2005a; 2005b). Although the gridded datasets have been verified using independent observations, they are the result of interpolation techniques and therefore the maps of trends derived from this data should be taken only as indicative of local patterns of change as the techniques employed to construct the datasets from point location data may influence the finer detail of the patterns.

The Met Office dataset is notable for the range of climate elements included: gridded data sets at 5km by 5km resolution over the UK have been produced for 36 monthly or annual climate variables, for the period 1961-2000. The start date of 1961 was chosen because there is a significant increase in the availability of digitised data from this point. A number of these variables are routinely updated with the latest month while several other variables have been updated to 2004 for this study.

The density of the station network varies between elements. An example of the distribution of stations in the observing network is shown in Figure 1 below. The left hand panel shows the

3 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006 location of sites which recorded temperature and/or precipitation in January 2001. The location of sites that recorded pressure and/or sunshine is given in the right-hand panel. This is a snapshot of the status of the network in January 2001 but it must be noted that the number of stations within the network changes over time. For example, the number of sunshine stations reached a peak of one hundred in the early 1970s but has since been reduced, such that there were only forty eight in Scotland in January 2001 (as seen in Figure 1). The network of precipitation recording stations is of the highest density average while the distribution of pressure and sunshine observing sites is of the lowest density for the variables included in the gridded dataset. Networks are comparatively sparse in certain areas, especially those that are sparsely populated, e.g. the Scottish Highlands.

Figure 1 - Location of observing sites (January 2001) for data used in the construction on the Met Office gridded datasets. Precipitation and temperature sites are shown in the left-hand panel. Sites recording sunshine and/or pressure are shown in the right-hand panel.

All available monthly meteorological data are used in the construction of the dataset in order to make maximum use of the information available and ensure that the most accurate possible representation of the climate can be made for each month. Consequently, the network of stations used changes slightly each month, and the methods used are designed specifically to minimise the impact of these changes on the consistency of the datasets through time. Table 1 shows, by variable, the average number of stations included in a month of the dataset. The average number of stations for the variables available before 1961 is also given, clearly showing the increase in available digitised data since this time.

4 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

Table 1 - Average number of stations included per month in the gridded dataset.

Climate variable Pre-1961 1961 onwards Precipitation 102 740 Days of rain >= 10 mm n/a 693 Rainfall intensity / greatest 5-day rainfall n/a 458 Air temperature 76 158 Annual consecutive dry days n/a 145 Annual extreme temperature range n/a 141 Heating and growing degree days n/a 126 Days of snow cover n/a 106 Sunshine 59 75 Heat and cold wave duration n/a 52 Mean sea level pressure / cloud n/a 19

The values of climate variables at locations between observing stations can be estimated to a good degree of accuracy, producing detailed and representative maps of the Scottish climate. Spatial and temporal variability and trends in climate can be investigated using the results of the gridding, which provides a consistent set of data. It must be noted however that accuracy varies and is dependent on the nature of the variable plus the density and representivity of the station network. Errors are highest in areas of sparse station coverage, particularly the highlands of Scotland, which are also areas of complex mountainous terrain. Localised effects on climate such as frost hollows, and effects caused by soil type and forests, have not been taken into account. Additionally the methods used to generate the dataset have not been optimised for complex variables such as wind. The difficulties in identifying trends in a number of variables presented in this report are discussed in each relevant section.

It is recognised that globally averaged temperatures have increased over the last century but that the increase has not been a linear one (IPCC, 2001). During the first half of the twentieth century observed global mean temperatures increased. This was followed by a decreasing trend throughout the fifties and sixties before temperatures once again began to rise, although at a faster rate than seen previously. Also, while nine of the ten warmest years observed (based on global average figures) have been within the last decade the warmest individual year globally occurred in 1998. Subsequent years have failed to exceed this record temperature although 2005 recorded the second warmest annual mean global temperature and the warmest northern hemisphere annual mean on record. The record temperatures of 1998 are likely to be due, in part, to a prolonged El Niño event. El Niño Southern Oscillation (ENSO) is one of a number of cycles, including sun spot activity, which combine to produce the variability that naturally occurs on a number of different time scales within our weather and climate. Natural variability also results in the record breaking annual mean temperatures occurring regionally in different years, for example, 2003 was the warmest year that has been observed in Scotland.

In order to minimise the signal of this natural variability, climatologies are constructed from long-term average of weather, typically thirty years. The World Meteorological Organisation (WMO) publishes updated climatologies every decade. Currently the most widely used of these WMO climatological periods is 1961 to 1990. This is the period used to define a ‘baseline’ or ‘control’ climate for many climate modelling studies, including those in the Intergovernmental Panel on Climate Change’s Third Assessment Report (IPCC, 2001) and the United Kingdom Climate Impacts Programme Climate Change Scenarios for the United Kingdom (UKCIP02, Hulme et al., 2002). The 1971 to 2000 climatology is also available. Where it aids understanding a climatology is included in this text. More images are also available from the Met Office website (www.metoffice.gov.uk). Further details of the mapped climatological variables available are given in the scoping study report (see Appendix 1).

5 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

2.1. Data analysis

The analysis is presented in a three-tier manner:

• Firstly, linear trends were calculated for each variable for Scotland as a whole and for three regions (e.g. Figure 2). This was done for annual and seasonal mean periods. The seasons used in this work are as follows: December, January and February (DJF, winter); March, April and May (MAM, spring); June, July and August (JJA, summer); and September, October, and November (SON, autumn). The three regions are the same as those typically used by the Met Office to generate descriptions of regional weather and climate. Each region encompasses an area of similar climatic characteristics. For the purposes of this report they have been termed North, West and East Scotland1. A linear regression equation was calculated for each dataset and then the trend was calculated from the gradient parameter (i.e. the rate of change) multiplied by the length of the data period to provide a clear change value since the start of the period. The Mann-Kendall test was then used to show whether significant changes have occurred. Where these trends are statistically significant they are shown as either bold (significant at the 1% level) or italic (significant at the 5% level) type (e.g. Table 2). Significance at the 1% level is equivalent to saying that there is a confidence level of 99% that the identified trend cannot be explained by natural variability. Equally, significance at the 5% level equates to 95% confidence that the trend is beyond that which could be explained by natural variability. Where text is in neither bold nor italic font then there is less than 95% confidence that a trend exists. It is possible that trends may be identified with less stringent significance/confidence criteria, however these have not been explored here.

• Secondly, graphs of the time-series for each variable were produced for each of the three regions of Scotland. These demonstrate the inter-annual variability that exists in each variable and include a smoothed version of the data as an indication of the longer-term trends and variations (see Figure 3 for an example).

• Finally, where appropriate, a map of observed trends was produced showing the spatial variation not apparent from the national average figures often presented elsewhere. (See Figure 4 as an example).

The time series data were smoothed by applying a triangular-shaped kernel filter, with 14 terms either side of each target point2. This non-parametric filter, effectively a running mean with weighting, enables the long-term fluctuations in the climate to be clearly seen without assuming that the trend follows a stated model. It was applied to the regional data in order that changes in different parts of Scotland could be compared.

The data were analysed for trends using linear regression, and the significance of trends was tested using the non-parametric Mann-Kendall tau test3 (Sneyers, 1990). Care needs to be taken when interpreting results from linear trends as the assumption of a linear trend is not always valid. However, the trends do often approximate to linear, and the combination of

1 The convention is taken that only when discussing one of the three regions, as defined for this study, is a capital letter used, i.e. North Scotland. The capital letter is not used when describing areas of the mapped changes, i.e. northern Scotland.

2 The kernel filter is a non-parametric smoothing technique, where, in this case, each point is replaced by a weighted average of the target point and 14 points on either side, with the weights being determined by a triangular-shaped kernel centred on the target point.

3 The Mann-Kendall test is a rank-based non-parametric test. For each value in the series, the number of preceding values which exceed it is calculated, and this is used to gain evidence for the existence of a trend in the data series.

6 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006 linear trends with the Mann-Kendall significance test has been widely used in the analysis of climate trends (e.g. Domroes and El-Tantawi, 2005; Shen et al., 2005).

Figure 2 - Map of Scotland showing boundaries of the three regions as defined in this study (North, West and East Scotland).

As with the regional and national series, linear trends were also calculated for series within each individual 5km x 5km grid cell of the gridded datasets. This enabled the mapping of changes in climate variables over the period of study, so that the spatial differentiation of changes can be clearly seen.

The analysis methods described here are consistent with the methods being used by the Met Office in an on-going analysis of trends in UK climate.

2.2. Temperature

Records of temperature are probably the most frequently analysed of all meteorological records. Some of the longest records of weather variables are for temperature. The Met Office gridded dataset covers the period 1914 to 2004. Seasonal and annual changes in mean temperature (°C) for three regions of Scotland are presented below (Table 2). It can be seen that the increase in temperature observed since 1961 is statistically significant in each region and every season, with the exception of winter in North Scotland. The trends since 1914 have not been as large, although annual average temperature for the whole of Scotland

7 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006 has increased significantly. At a regional level there have been significant temperature rises since 1914, particularly in East and West Scotland where temperatures have risen from an annual average of approximately 6.7°C (East Scotland) and 7.8°C (West Scotland) to 7.5°C and 8.3°C respectively. The apparent inconsistency between these two sets of figures, with the fact that more of the regions and seasons show significant trends during the later (shorter) period, suggests a more rapid rise in temperatures over this later part of the twentieth century. This can also be seen in Figure 3, which presents the ninety-year time- series of annual mean temperatures for the regions (1914 to 2004).

Table 2 - Mean Temperature changes (°C), 1961 to 2004 and 1914 to 2004. Statistically significant trends are shown in bold (significant at the 1% level) or italic (significant at the 5% level) type.

1961-2004 1914-2004 North East West North East West Scotland Scotland Scotland Scotland ScotlandScotland Scotland Scotland Spring 1.03 1.23 1.20 1.14 0.59 0.83 0.66 0.69 Summer 1.06 1.12 1.08 1.08 0.50 0.59 0.43 0.51 Autumn 0.64 0.68 0.66 0.66 0.46 0.85 0.68 0.64 Winter 1.03 1.39 1.31 1.22 0.02 0.45 0.33 0.24 Annual 0.92 1.08 1.04 1.00 0.37 0.66 0.51 0.50

Figure 3 - Annual mean temperature (°C) for Scottish regions, 1914 to 2004, with smoothed curve. The vertical dashed line marks the position of 1961.

Annual Mean temperature for the three Scottish districts, with 30-year smooth filter, 1914-2004

9.0

8.5

8.0

7.5 N Scotland E Scotland 7.0 W Scotland

6.5 Mean (deg temperature C)

6.0

5.5

1914 1917 1920 1923 1926 1929 1932 1935 1938 1941 1944 1947 1950 1953 1956 1959 1962 1965 1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004

The pattern of Scottish regional temperature change (Figure 3), where the weighted running mean is shown by the smoothed curve, is very similar to that seen in the global mean temperature time-series (not shown). Here there is an increase throughout the first half of the twentieth century, then a decrease throughout the fifties and sixties before rising once again toward the end of the century. It is also clear that average annual temperature in each region is now higher than at any other time in this record, i.e. since 1914. The inter-annual, or year- by-year, variation in temperatures is also apparent in Figure 3. It is interesting to note that whilst the West Scotland region is slightly milder than the other two, that all three regions see very similar inter-annual variation across the period, i.e. when one region experiences a warm or cold year so do the other two. The mapped trends in seasonal mean temperature for the period 1961 to 2004 are presented in Figure 4. It can be seen that average seasonal temperatures have increased everywhere in Scotland during this period, although the

8 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006 increases are smallest during autumn and largest in southern and eastern Scotland in winter. Results from this study concur with the results of Jones and Lister (2004), which demonstrated that there has been a significant increase in annual mean temperature over the whole of the UK during the last century.

Figure 4 - Gridded change for mean temperature (°C) from 1961 to 2004, based on a linear trend: a) spring (MAM), b) summer (JJA), c) autumn (SON) and d) winter (DJF).

9 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

The 24-hour or daily maximum and minimum temperature datasets also exhibit a warming trend. The changes for 24-hour maximum temperature are tabulated for each region and season below (Table 3). As previously, trends for 1961 to 2004 are shown alongside those calculated from 1914 to 2004. In the 1961 to 2004 period each region shows a statistically significant increase in maximum temperature. Moreover, increases in daily maximum temperature have been consistently greater than those in the mean temperature. However, the same is not true of the full ninety-year record. Significance is found in the annual mean figures but not consistently in the seasonal means (only spring in North and East Scotland, autumn in East Scotland and winter in West Scotland). In addition, since 1914 it is only in North Scotland that daily maximum temperatures have increased at a faster rate than daily mean temperatures.

Table 3 - 24-hour maximum temperature changes (°C), for 1961 to 2004 and 1914 to 2004. Statistically significant trends are shown in bold (significant at the 1% level) or italic (significant at the 5% level) type.

1961-2004 1914-2004 North East West North East West Scotland Scotland Scotland Scotland Scotland Scotland Scotland Scotland Spring 1.16 1.41 1.35 1.29 0.70 0.71 0.48 0.64 Summer 1.11 1.14 1.12 1.12 0.58 0.37 0.20 0.40 Autumn 0.85 0.83 0.83 0.84 0.58 0.66 0.46 0.57 Winter 1.16 1.51 1.47 1.36 0.41 0.58 0.42 0.47 Annual 1.14 1.29 1.25 1.21 0.59 0.60 0.41 0.54

Changes in 24-hour minimum (effectively night-time) temperatures present a more complex pattern of change (Table 4). As with maximum temperatures all increases since 1961 are significant, although some increases are at a slower rate than for mean temperatures. Since 1914 there has been a significant upward trend (at the one percent level) in night-time minimum temperatures in the East and West of Scotland in all seasons except for winter. These trends are for warming at a rate faster than the mean temperature. In contrast to this, the average winter minimum temperatures have decreased in North Scotland since 1914, although none of the winter trends over this period are statistically significant.

Table 4 - 24-hour minimum temperature changes (°C), for 1961 to 2004 and 1914 to 2004. Statistically significant trends are shown in bold (significant at the 1% level) or italic (significant at the 5% level) type.

1961-2004 1914-2004 North East West North East West Scotland Scotland Scotland Scotland Scotland Scotland Scotland Scotland Spring 0.89 1.08 1.07 1.00 0.46 1.00 0.94 0.76 Summer 1.07 1.18 1.11 1.12 0.30 0.80 0.65 0.55 Autumn 0.55 0.64 0.56 0.58 0.39 1.12 0.99 0.79 Winter 0.96 1.32 1.22 1.15 -0.37 0.35 0.22 0.02 Annual 0.94 1.13 1.06 1.03 0.22 0.84 0.73 0.56

Comparing the data in Tables 3 and 4 it is clear that since 1961 daytime maximum temperatures have increased at a faster rate than night-time minimum temperatures. This is contrary to the global trend identified in the IPCC Third Assessment Report (IPCC, 2001). The IPCC report, based upon analysis of data from 1950 to 1993, showed that, on average, night-time daily minimum temperatures increased at approximately twice the rate of daytime daily maximum temperatures. It is interesting to note that extending the period of analysis back to 1914 shows that the warming trends in maximum and minimum temperature in the

10 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

East and West Scotland regions are more like the global average reported by the IPCC (2001).

As with mean temperature the pattern of warming, cooling and then warming again can be seen in the regional time-series of both the annual mean 24-hour minimum and maximum temperature time-series (Figures 5 and 6). The rate of change in maximum temperature is similar in each region but minimum temperatures in North Scotland are increasing at a slower rate than in the other two regions. East Scotland has moved from an annual climate with lower night-time minimum temperatures than North Scotland to one which experiences very similar annual means.

Figure 5 - Annual average 24-hour maximum temperature (°C) for Scottish regions, 1914 to 2004, with smoothed curve. The vertical dashed line marks the position of 1961.

12.5

12.0

11.5

11.0 Scotland N 10.5 Scotland E Scotland W 10.0

9.5 Maximum temperature (deg C)

9.0

8.5

14 18 26 30 38 42 50 54 62 66 74 78 86 90 98 02 9 9 922 9 9 934 9 9 946 9 9 958 9 9 970 9 9 982 9 9 994 9 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2

Figure 6 - Annual average 24-hour minimum temperature (°C) for Scottish regions, 1914 to 2004, with smoothed curve. The vertical dashed line marks the position of 1961.

6.0

5.5

5.0

4.5

Scotland N 4.0 Scotland E Scotland W

3.5

Minimum temperature (deg C) (deg temperature Minimum 3.0

2.5

2.0

4 2 18 3 46 6 66 74 94 02 914 9 922 9 942 9 950 954 9 9 970 9 978 982 990 9 998 0 1 1 1 1926 1930 1 1938 1 1 1 1 1958 1 1 1 1 1 1 1986 1 1 1 2

11 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

Maps of trends in the gridded data (1961 to 2004) are shown for the winter (December- February) and summer (June-August) seasons for 24-hour maximum temperature and 24- hour minimum temperature in Figures 7 and 8. Typically the greatest rises in temperature have occurred in the winter rather than summer season. Winter patterns of change for both are similar to that of mean temperature (Figure 4). In particular, the most rapid warming trends are in southern Scotland in the winter season. Parts of northern Scotland have seen relatively little increase in minimum temperatures over the 1961 to 2004 period. Minimum temperatures have increased during summer months at a faster rate in northern, eastern and southern Scotland than in central areas or the Highlands. In contrast, the rise in summer daily maximum temperatures has been relatively uniform across the country except for the Shetland Islands, where a cooling has been recorded.

Figure 7 - Gridded change for 24-hour maximum temperature (°C), based on a linear trend from 1961 to 2004: a) summer quarter, b) winter quarter

12 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

Figure 8 - Gridded change for 24-hour minimum temperature (°C), based on a linear trend from 1961 to 2004: a) summer quarter, b) winter quarter.

With maximum temperatures increasing at a faster rate than minimum temperatures since 1961, it is likely that the daily, or diurnal, temperature range (DTR) will also have increased. This is indeed the case as can be seen the regionally averaged changes in DTR for 1961 to 2004 (Table 5). With the exception of the summer season in East Scotland the diurnal temperature range has increased in all regions and seasons. Summer increases are modest for all regions and not statistically significant. However, North Scotland has seen significant increases in DTR during the autumn season and significant increases have occurred in the winter season across the country as a whole. The time-series of diurnal temperature range for the regions since 1961 clearly shows that the three regions are well correlated, indicating that patterns of change are likely to be large scale (Figure 9).

Table 5 - Mean diurnal temperature range changes (°C), 1961 to 2004. Statistically significant trends are shown in bold (significant at the 1% level) or italic (significant at the 5% level) type.

North East West Scotland Scotland Scotland Scotland Spring 0.30 0.24 0.27 0.27 Summer 0.09 -0.06 0.01 0.02 Autumn 0.46 0.24 0.32 0.35 Winter 0.45 0.30 0.37 0.38 Annual 0.33 0.19 0.23 0.26

13 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

Figure 9 - Annual mean diurnal temperature range (°C) for Scottish regions, 1961 to 2004, with smoothed curve.

8.0

7.5

7.0 N Scotland E Scotland W Scotland 6.5

6.0 Diurnal temperature range (deg C) (deg range temperature Diurnal

5.5

65 77 83 91 01 963 971 981 987 989 995 1961 1 19 1967 1969 1 1973 1975 19 1979 1 19 1985 1 1 19 1993 1 1997 1999 20 2003

In addition to temperature records, a number of temperature related variables can be derived for each year. These variables have particular significance for several sectors and can be better related to direct climate impacts. The derived temperature variables analysed in this report are:

• Heating degree-days (HDD)4. This is an indicator of household consumption of heat energy. The base temperature for calculation of a heating degree day is 15.5°C, such that if the mean temperature were below 15.5°C then the value of the HDD for that individual day would be 15.5°C minus the mean temperature. For example, if a day has a mean temperature of 13.5°C this is equivalent to 2.0 heating degree days. This figure represents the energy input required to keep a building at a constant temperature. Typical figures at the start of the 1961 to 2004 period were approximately 3200 HDD per annum for North and East Scotland, and 2900 HDD per annum for West Scotland.

• Growing degree-days (GDD)5. This is an accumulated sum for mean temperatures above a threshold assumed to represent the temperature above which plants are photosynthetically active. In this report, a threshold of 5°C is used and the calculation is very similar to that of HDD. For example, if mean temperature for a day is 7.5°C this equates to 2.5 growing degree days. Typical values in the early 1960’s were approximately 950 GDD per annum in North Scotland, 1000 GDD per annum in East Scotland and 1150 GDD per annum in West Scotland.

• Growing season start (GSS). This is the start date for the growing season (calculated as Julian days), where the growing season is assumed to start on the 5th consecutive day with a mean temperature of 5°C or greater. During the 1960s the typical start date for the growing season was 12th April in East Scotland, 10th April in North Scotland and 29th March in West Scotland

4 Heating Degree Days = ∑ (15.5 – daily T_mean) for T_mean < 15.5 °C 5 Growing Degree Days = ∑ (daily T_mean – 5) for T_mean > 5 °C.

14 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

• Growing season end (GSE). This is the end date for the growing season (calculated in Julian days), where the growing season is assumed to end on the 5th consecutive day with a mean temperature of 5°C or less. During the 1960s the typical end date for the growing season was 10th November in East Scotland, 12th November in the North and 20th November in the West.

• Growing season length (GSL)6. This is the number of days between the start and end of the growing season i.e. GSE-GSS. In the early 1960s typical values were a growing season of approximately 213 days in East Scotland, 217 days in North Scotland and 237 days in the West.

• Extreme Temperature Range (ETR) is defined as the range between the highest maximum and lowest minimum temperature within each year.

• Cold wave duration7 is calculated for a half-year period, either winter or summer. In this study, it is defined to be the total length of periods of at least 6 days, during the summer half- year (April to September) or winter half-year (October to March), when the minimum temperature is at least 3°C less than the 1961-1990 average for that day.

• Heat wave duration8. This is also is calculated for half-year periods. It is defined as the total length of periods of at least 6 days, during either the summer half-year or winter half- year, when the maximum temperature exceeds the 1961-1990 average for that day by at least 3°C.

Changes in some of these derived quantities since 1961 are presented in Table 6. It can be seen that in all areas of Scotland the number of heating degree days have decreased significantly. There has also been a significant increase in the number of growing degree days, and an associated increase in the length of the growing season. These changes are likely to be primarily due to the significant increases in both minimum and mean temperatures in the spring although increases in autumn temperatures will contribute.

Table 6 - Changes in annual temperature indices: a) heating degree days, 1961 to 2003 (%), b) growing degree days, 1961 to 2003 (%), c) growing season length, 1961 to 2004 (days), d) growing season start, 1961 to 2004 (days), e) growing season end, 1961 to 2004 (days) and f) extreme temperature range, 1961 to 2003 (°C). Statistically significant trends are shown in bold (significant at the 1% level) or italic (significant at the 5% level) type.

North East West Scotland Scotland Scotland Scotland Heating Degree Days (%) -9.2 -10.7 -11.3 -10.2 Growing Degree Days (%) 23.7 22.5 21.1 22.5 Growing Season Length (days) 31.1 32.5 36.7 33.2 Growing Season Start (days9) -19.6 -20.6 -22.4 -20.7 Growing Season End (days) 11.5 12.0 14.4 12.5 Extreme Temperature Range (°C) 0.0 -3.4 -2.2 -1.8

6 Growing Season Length = period (days) bounded by daily T_mean > 5 °C and < 5 °C for > 5 days 7 Cold Wave Duration = ∑ days with 1961-1990 daily normal - daily T_min > 3 °C for ≥ 6 consecutive days 8 Heat Wave Duration = ∑ days with daily T_max – 1961-1990 daily normal > 3 °C for ≥ 6 consecutive days 9 A negative number of days indicates a date earlier in the year, i.e. growing season starting earlier in the year.

15 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

The contribution of the higher temperatures is confirmed by the trends in growing season start and end dates (Table 6). As previously noted, during the 1960s the typical start date for the growing season was 12th April in East Scotland, 10th April in North Scotland and 29th March in West Scotland. At the same time, the typical end date for the growing season was 10th November in East Scotland, 12th November in the North and 20th November in the West. The growing season is now starting almost three weeks earlier in North and East Scotland, and more than three weeks earlier in the West. Whilst the growing season is also ending later, it is by less than two weeks in the North and East and just over two weeks in the West. The changes to the start and end of the growing season are statistically significant in all regions.

The changes indicated by the extreme temperature range (ETR) are not straightforward to interpret (Table 6). These trends are not significant and, in fact, ETR appears to be reducing. This would suggest that the increase in the lowest minimum temperature each year is occurring at a faster rate than the increase in the highest maximum temperature. However, it should also be noted that the result is not significant so it may simply be “noise” within the data resulting from natural variability in extremes.

Figures 10 to 15 show time-series for these derived temperature variables since 1961. It is clear that in each case the regions show similar inter-annual variability indicating that the causal factors are likely to be large scale. However, the maps of trends presented in Figure 16 to 19 show that there is considerable spatial variation in the trends, often related largely to topography.

Figure 10 - Annual heating degree days for Scottish regions, 1961 to 2003, with smoothed curve

3500

3400

3300

3200

3100 N Scotland 3000 E Scotland W Scotland 2900

Heating degree days degree Heating 2800

2700

2600

2500

9 5 7 9 6 7 7 9 961 983 985 991 1 1963 1965 1967 19 1971 1973 19 19 1979 1981 1 1 1987 1989 1 1993 1995 1997 19 2001 2003

16 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

Figure 11 - Annual growing degree days for Scottish regions, 1961 to 2003, with smoothed curve

1500

1400

1300

1200 N Scotland E Scotland 1100 W Scotland

Growing degree days degree Growing 1000

900

800

65 75 85 95 961 963 9 969 971 973 9 977 979 981 983 9 987 989 991 993 9 997 999 001 003 1 1 1 1967 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2

Figure 12 - Annual growing season length (days) for Scottish regions, 1961 to 2004, with smoothed curve

310

290

270

E Scotland 250 N Scotland W Scotland

230 Growing season length (days) length season Growing

210

190

1 3 5 9 1 5 7 9 89 196 196 196 1967 1969 1971 1973 1975 1977 197 198 1983 1985 1987 19 1991 1993 199 199 199 2001 2003

17 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

Figure 13 - Growing season start dates (days from 1st January) for Scottish region from 1961 to 2004, with smoothed curve.

130

120

110

100

80 East Scotland North Scotland 70 West Scotland

Start of the growing season (days from 1st January) 1st from season(days growing the of Start 20

3 5 7 3 9 5 7 1 3 7 8 9 9 0 971 9 9 991 9 9 0 1961 196 1965 1967 1969 1 1973 197 1 1979 1981 198 1985 1987 1 1 1993 1 1 1999 200 2

Figure 14 - Growing season end date (days from 1st January) for Scottish regions from 1961 to 2004 with smoothed curve.

360

350

340

330 E Scotland N Scotland W Scotland 320

310

300 End of the growing season (days from 1st January) 1st from season (days growing End the of 290

3 65 71 5 1 93 7 99 96 98 99 99 1961 1 19 1967 1969 19 1973 1975 1977 1979 1981 1983 1 1987 1989 1 19 1995 1 19 2001 2003

18 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

Figure 15 - Annual extreme temperature range (°C) for Scottish regions, 1961 to 2003, with smoothed curve

37 N Scotland 35 E Scotland W Scotland 33

29 Extreme temperature range (deg C) (deg range temperature Extreme 27

1 1 9 7 5 7 3 96 967 969 97 977 97 985 98 993 99 99 001 00 1 1963 1965 1 1 1 1973 1975 1 1 1981 1983 1 1 1989 1991 1 1 1 1999 2 2

The patterns of change in heating degree days (HDD, Figure 16) mimic the temperature grids to some extent, with the southerly, coastal and lower lying areas exhibiting the greatest change. Areas of large decrease are also evident in the Shetlands and the Outer Hebrides. Growing degree day patterns of change (GDD, Figure 16) appear to be more uniform, although localised areas of large increase are evident within the highland areas of the north of Scotland, the Outer Hebrides, Orkney and Shetland Islands.

Figure 16 - Gridded change for a) growing degree days (percentage) and b) heating degree days (percentage) based on a linear trend from 1961 to 2003

19 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

The Extreme Temperature Range (ETR, Figure 17), on the other hand, exhibits a complex pattern with strong increases exhibited for some of the Western Isles and the Orkneys as well as the more mountainous areas surrounding Fort William and Inverness and the Great Glen joining these two areas. The Outer Hebrides and Shetland Islands display the opposite trend, as does much of the rest of the country. It must be remembered however that regional trends in ETR were small and not significant. The percentage changes shown here are also modest, typically less than five percent. It is not clear what confidence, if any, can be placed in the significance of this pattern of change.

Figure 17 - Gridded change for extreme temperature range (°C) based on a linear trend from 1961 to 2003.

In this study, the spatial analysis of growing season length, start and end dates is slightly different to that of the other derived variables, in that it is based directly upon the baseline observed climate of the UK dataset provided by the Met Office for UKCIP with the UKCIP02 scenarios. The dataset, based upon observed rather model data, provides monthly mean temperatures rather than the daily values required to calculate growing season, so a sine curve interpolation has been used to estimate daily values based on the method of Brooks (1943). These daily data were then used within the calculations for growing season length, start and end dates. Additionally, the standard UKCIP02 observed climate dataset is for 1961-2000, but for this application it has been updated to 2004.

The presentation style of the three growing season maps (Figures 18 and 19) is intentionally slightly different to the others in this technical report. This has been done in order to visually separate them from the other figures, as they have been derived using an estimation technique, thereby introducing additional uncertainty. A gridded dataset of growing season start and end could be constructed from existing data, however this is not a trivial task and no such dataset exists at this time, hence the use of the method employed here.

20 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

It has already been shown that the increasing growing season length is occurring as a result of both an earlier start and a later end to the season. This is seen in the mapped patterns of change presented in Figures 18 and 19. The greatest increases in growing season length are in coastal areas and the Shetland Islands where the season has extended by two months, or more. The regional averages discussed previously mask the fact that the length of the growing season has changed very little since 1961 in many areas, particularly in more mountainous areas. Further investigation would be required to investigate whether there has been a change in growing season at increasing altitude in these areas. The pattern of change for growing season start and end is similar to that for growing season length. Again, coastal areas show a greater tendency towards an earlier start and later end to the growing season than central Scotland. The longer growing season, and in particular the earlier start, has already been observed through a change in flowering dates of plants particularly those flowering in early spring (Roberts et al., 2004).

Figure 18 - Gridded change for growing season length (days) based on a linear trend from 1961 to 2004 calculated from the extended UKCIP02 dataset.

21 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

Figure 19 - Gridded change for the (a) start and (b) end of the growing season (days), based on a linear trend from 1961 to 2004. Negative values indicate an earlier start/end to the season.

Changes in heat wave and cold wave duration are shown (in number of days) in Table 7. The only trends identified that are statistically significant are the decreases in cold wave duration during the winter half year (October to March) in East and West Scotland. Although an increase in heat wave duration is seen in all regions throughout the year the change is not significant and therefore it may be a result of natural variability, but is likely to result from the increase in mean temperature.

Table 7 - Change in half-year heat wave10 and cold wave duration11 (days), 1961 to 2003. Statistically significant trends are shown in bold (significant at the 1% level) or italic (significant at the 5% level) type.

North East West Scotland Scotland Scotland Scotland CWDs 1.5 1.2 2.4 1.7 CWDw -5.8 -8.4 -8.9 -7.5 HWDs 6.3 6.3 4.3 5.7 HWDw 6.0 6.6 7.1 6.5

Time-series of winter half-year cold wave duration and summer half-year heat wave duration are shown in Figures 20 and 21. As with many of the other variables derived from temperature records it is clear that inter-annual variability is very similar in each of the

10 Heat Wave Duration = ∑ days with daily T_max – 1961-1990 daily normal > 3 °C for ≥ 6 consecutive days. 11 Cold Wave Duration = ∑ days with 1961-1990 daily normal - daily T_min > 3 °C for ≥ 6 consecutive days.

22 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006 regions. The patterns of change are shown in Figure 22. Winter cold wave duration has decreased most in southern Scotland and the Shetlands, a pattern that is well correlated with the pattern of winter temperature change. The duration of summer heat waves has increased most in inland and north eastern areas.

Figure 20 - Winter half-year cold wave duration (days) for Scottish regions, 1961/62 to 2003/04, with smoothed curve

16 N Scotland 14 E Scotland

12 W Scotland

6 Winter cold wave duration (days) duration wave cold Winter 4

3 1 7 3 5 9 1 5 7 9 3 6 7 7 8 8 8 9 9 9 9 0 9 9 9 9 1961 19 1965 1967 1969 19 1973 1975 19 1979 1981 19 1 1987 19 1 1993 19 1 1 2001 20

Figure 21 - Summer half-year heat wave duration (days) for Scottish regions, 1961 to 2003, with smoothed curve

20 N Scotland E Scotland

15 W Scotland

10 Summer heat wave duration (days) duration wave heat Summer 5

1 5 7 9 7 5 3 7 1 3 6 196 1963 19 196 196 1971 1973 1975 197 1979 1981 1983 198 1987 1989 1991 199 1995 199 1999 200 200

23 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

Figure 22 - Gridded change for a) winter half-year cold-wave duration (days) and b) summer half-year heat-wave duration (days), based on a linear trend from 1961 to 2003.

2.3. Rainfall

As with the temperature records presented in section 2.2 there is a long record of rainfall observations for Scotland. Where longer-term data records are available, the changes are presented alongside those for the 1961 to 2004 period. This is the case in Table 8. Here trends in total precipitation amount (i.e. rain and snow) over each period are expressed as a percentage change since the start of each period. What is most striking is the statistically significant increase in winter precipitation over the 1961 to 2004 period. In each region, and nationally, the winter change is statistically significant at the 1% level, based on the Mann Kendall test. In this analysis, over this specific period, an increase of almost seventy percent in winter precipitation since 1961 has been identified in North Scotland. This is equivalent to an average increase of approximately three millimetres a day throughout the winter season (December to February). Annually averaged precipitation has also increased significantly over the same period. As a whole, Scotland has become twenty percent wetter during the period 1961 to 2004, equivalent to an average increase of approximately 240 millimetres of rainfall a year. Conversely, there has been little or no change in regionally averaged summer rainfall totals, although a slight decrease (seven percent) can be identified in the northern region. Over the same period summer rainfall has increased by a similar amount in West Scotland. Changes in summer rainfall are not however significant for the 1961 to 2004 period.

24 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

Table 8 - Changes in total precipitation amount (percentage), 1961 to 2004 and 1914 to 2004. Statistically significant trends are shown in bold (significant at the 1% level) or italic (significant at the 5% level) type.

1961-2004 1914-2004 North East West North East West Scotland Scotland Scotland Scotland ScotlandScotland Scotland Scotland Spring 16.2 9.4 17.3 14.8 13.9 6.1 22.0 14.3 Summer -7.0 0.2 7.3 -0.6 -12.7 -18.9 -7.5 -12.7 Autumn 5.3 22.2 5.9 9.1 13.6 0.7 15.6 11.1 Winter 68.9 36.5 61.3 58.3 20.9 -0.8 9.0 11.6 Annual 21.0 18.4 23.3 21.1 9.6 -3.5 9.5 6.2

When the time-series is extended to consider the full period 1914 to 2004 the trend is less well established. Over the longer period the statistically significant trends identified are significant are at the five, rather than one, percent level. However, there is a statistically significant reduction in summer rainfall in all regions. East Scotland has experienced a significant nineteen percent decrease in summer rainfall since 1914. Precipitation has increased in North and West Scotland in all other seasons although the only trend that is statistically significant is the more than twenty percent increase in West Scotland in spring. Annual mean precipitation has increased across most of Scotland since 1914, and, with the exception of the summer season, rainfall has increased in all regions. The exception to this is the slight reduction of both annual mean and winter precipitation in East Scotland. This is the opposite of the trend calculated over more recent decades. These changes are not however significant, with the exception of the summer drying. Therefore, it is not possible to say definitively at this time whether there is a trend of long term drying in East Scotland and wetting over the rest of Scotland.

The apparent contradiction between the two periods of data can be explained by looking at a time-series of annual mean total precipitation since 1914 (Figure 23). The full sequence of data from 1914 is shown. It can be seen that during the 1960s and 1970s the inter-annual variation in rainfall (particularly in the North and West regions) is quite low and the totals are also lower than in the earlier record. This is then followed by an increasingly wet period. This is why the analysis over the shorter period produces such large percentage changes in annual, and possibly winter, averages. The wet period in the 1980s may also account for why the drying trend in East Scotland over the 1914 to 2004 period is not seen in the shorter time period from 1961. It is apparent from the time-series data that East Scotland has a much drier climate than the other two regions. The high correlation between the North and West Scotland time-series indicate the two regions are likely to have a very similar rainfall climatology. This can be seen in Figure 24 which shows the 1961 to 1990 rainfall annual rainfall climatology for Scotland12. North and West Scotland have a wetter climate than eastern regions. This is to be expected given the presence of the Highlands, which provide a rain shadow effect for eastern areas, due to the prevailing westerly winds over Scotland.

12 The 1971 to 2000 climatology is very similar and can be viewed on the Met Office website (http://www.metoffice.gov.uk/climate/uk/averages/index.html).

25 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

Figure 23 - Annual precipitation amount (mm) for Scottish regions, 1914 to 2004, with smoothed curve

2200

2000 ) 1800

1600

N Scotland 1400 E Scotland W Scotland

1200

1000 Annual precipitation amount (mm

800

600

2 0 0 1914 1918 1922 1926 1930 1934 1938 1942 1946 1950 1954 1958 1962 1966 1970 1974 1978 1982 1986 1990 1994 1998 2

Figure 24 - Climatology of annual rainfall amount (mm) for Scotland, 1961 to 1990. Source: www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html

The maps of spatial trends for each season are given in Figure 25. These trends have been calculated for the 1961 to 2004 period and therefore it must be remembered therefore that, in terms of long-term behaviour, they may be slightly misleading. It is however clear that the largest changes have occurred in winter months across all but the most eastern areas of Scotland. In some areas of the west Highlands and the Hebrides winter rainfall has more than doubled since 1961. The pattern of change is completely reversed in autumn with

26 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006 eastern areas being the only widespread region to become wetter, with increases in excess of twenty percent. In summer the east-west contrast of the changes shifts to produce pattern with more north-south variation. Northern areas of Scotland have become drier since 1961, particularly the north-west. This reduction in summer rainfall exceeds twenty percent in some locations. This is enhancing the strong seasonal cycle present in Scottish rainfall. Jones and Conway (1997) found no overall long-term trend in area-averaged annual precipitation for England & Wales or Scotland from 1766 to 1995, but did note a significant increase in winter precipitation, especially in Scotland since 1986, which agrees with these findings.

Figure 25 - Gridded change for precipitation (%), based on a linear trend from 1961 to 2004: a) spring, b) summer, c) autumn, d) winter.

27 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

Days of intense or heavy rainfall, in this case defined as days of rainfall in excess of ten millimetres, have also changed. Table 9 shows the change calculated from a linear trend analysis. Due to availability of data for derived fields such as this, only the 1961 to 2004 period has been analysed. As with total precipitation there is a significant trend of increasing heavy rainfall in winter months. North and West Scotland have seen an increase of more than eight days of heavy rainfall in a winter season. In all other seasons the changes are small and not significant.

Table 9 - Changes in days of heavy rain ≥ 10 mm (days), 1961 to 2004. Statistically significant trends are shown in bold (significant at the 1% level) or italic (significant at the 5% level) type.

North East West Scotland Scotland Scotland Scotland Spring 1.8 1.0 1.6 1.5 Summer -1.4 -0.5 0.9 -0.4 Autumn -0.2 2.3 0.1 0.7 Winter 8.3 3.5 8.2 6.7 Annual 8.2 6.2 10.6 8.3

A visual comparison with the time-series of annual mean total precipitation shows a high level of correlation (Figure 26). This implies that the years with highest total rainfall are also the years with the most days of heavy rainfall, and vice versa.

Figure 26 - Annual days of heavy rain ≥ 10 mm for Scottish regions, 1961 to 2004, with smoothed curve

Scotland N 50 Scotland E W Scotland

Days heavy rain of 40

7 9 7 9 1 9 1 9 1 8 96 98 99 1961 1963 1965 196 1 1971 1973 1975 197 197 19 1983 1985 1987 1 1 1993 1995 1997 199 200 2003

It must also be remembered that although significant trends are identified for change in winter and annual mean number of days of heavy rainfall, the apparent high correlation with total precipitation implies that it may be reasonable to assume a similar behaviour before 1961. This would imply that although recent winters have seen significantly more days of heavy rainfall that in a longer time-series of data the change may not be significant, given that the longer record also shows no significant increase in winter rainfall since 1914. This speculation shows that interpreting trends in relatively short records must be done with caution.

28 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

The spatial pattern of seasonal change in the number of heavy rainfall days (1961 to 2004) can be seen in Figure 27. The patterns of change are broadly similar to those for total precipitation with a strong east-west gradient in winter months. Although there has been little or no change in eastern Scottish regions, most of the west has seen a winter increase of more than five days of heavy rainfall. Changes in summer months are small and typically not significant. This is consistent with the findings of Osborn et al. (2000). They found, for the UK during 1961-1995, an increasing contribution of heavy rainfall events in winter compared to light and medium events, while the opposite occurred in the summer. The area in north-west Scotland, around Achnashellach has the largest change, with a reduction of up to ten days in spring, summer and autumn seasons. There are several stations in this region with different record periods that have been used in the data gridding process. This localised feature of decreasing number of heavy rains days is likely to be robust as more than one station’s data is being used.

29 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

Figure 27 - Gridded change for days of heavy rain ≥ 10 mm, based on a linear trend from 1961 to 2004: a) spring, (b) summer, (c) autumn, (d) winter.

A number of precipitation indices can be derived from observed data. These typically describe some aspect of the nature of precipitation within a year. A number of these indices have been calculated, and analysed for this report. Table 10 shows the results of analysis of the 1961 to 2004 precipitation dataset for three indices:

• The maximum number of consecutive dry days (CDD)13, where a dry day is defined as a day with no more than 0.2 millimetres of rainfall. It should be noted that this is not an indicator of drought. Even in drought conditions an occasional day of rain may occur.

13 Consecutive Dry Days = Maximum number of consecutive days with rainfall ≤ 0.2 mm

30 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

• Rainfall intensity14. This is the average amount of rainfall which falls on a rainfall day. This only includes days when rainfall is greater than or equal to one millimetre and represents the average rainfall on such a day.

• Maximum 5-day precipitation amount. This is a measure of the heaviest rainfall in a 5-day period for a year.

Table 10 - Changes in annual precipitation indices, 1961 to 2004: a) maximum consecutive dry days (days), b) mean rainfall intensity on days with rain ≥ 1mm (%), c) maximum 5-day precipitation amount (%). Statistically significant trends are shown in bold (significant at the 1% level) or italic (significant at the 5% level) type.

North East West Scotland Scotland Scotland Scotland Consecutive Dry Days (days) -0.2 1.1 0.1 0.3 Rainfall Intensity (%) 7.4 7.6 7.8 7.6 Maximum 5-day precipitation amount (%) 16.8 25.2 24.5 21.3

Over the period 1961 to 2004 there has been very little change in the maximum number of consecutive dry days (CDD) in a year. Figure 28 shows a time-series of this index and it is clear that inter-annual variability is high. It is also clear that there is no discernable long-term trend in this index for this period. Years with the highest values of CDD in each region often coincide indicating a period of widespread dry weather. However, there are also many examples in the time-series when correlation between the regions is not high.

Figure 28 - Annual maximum consecutive dry days for Scottish regions, 1961 to 2004, with smoothed curve

16 N Scotland E Scotland 14 W Scotland

12 Consecutive dry days dry (days) Consecutive 10

71 963 977 985 999 1961 1 1965 1967 1969 19 1973 1975 1 1979 1981 1983 1 1987 1989 1991 1993 1995 1997 1 2001 2003

There is a significant increasing trend in rainfall intensity in both East and West Scotland. There is a similar size of increase in North Scotland but the change is not significant as

14 Rainfall Intensity = Total rainfall on raindays ≥ 1 mm divided by the number of raindays ≥ 1 mm.

31 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006 natural variability in rainfall is higher in this region. This can be seen in the annual mean time-series shown Figure 29. There does not appear to be a high correlation between year- to-year rainfall intensity over the three regions, although the long-term trend (smoothed curve) is very similar.

Figure 29 - Annual mean rainfall intensity (mm/day) for Scottish regions, 1961 to 2004, with smooth filter

9.5

9.0

8.5

8.0 N Scotland 7.5 E Scotland W Scotland 7.0

Rainfall intensity (mm/day) 6.5

6.0

5.5

1 65 71 73 79 85 9 93 99 963 9 969 9 9 977 9 983 9 9 9 997 9 003 1961 1 1 1967 1 1 1 1975 1 1 1981 1 1 1987 1989 1 1 1995 1 1 2001 2

The most significant increases are in the maximum 5-day rainfall precipitation (see Table 10). The average increase since 1961 is over twenty percent. All increases are statistically significant at the one percent level. The year-to-year variation in this index for the period 1961 to 2004 can be seen in Figure 30. Inter-annual variability is high and, with the exception of a few years, there is little correlation between regions. Values of the index are very similar in North and West Scotland, although a steadily increasing trend is clearly apparent in all regions. The lower rainfall totals of East Scotland are reflected in lower maximum 5-day averages.

32 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

Figure 30 - Annual maximum 5-day precipitation amount (mm) for Scottish regions, 1961 to 2004, with smoothed curve

140

130

120

110

100 N Scotland E Scotland 90 W Scotland

70 Maximum five-day rainfall (mm) 60

1 3 5 7 9 9 1 5 7 9 6 6 7 9 96 96 96 971 973 98 983 985 989 99 99 001 19 1 1 19 1 1 1 1975 1977 19 1 1 1 1987 1 1991 1993 19 1 1 2 2003

Spatial patterns of change for these three derived indices are shown in Figures 31 and 32. There is a clear east-west contrast in the change in number of consecutive dry days (Figure 31). This pattern does not correlate well with any of the rainfall change patterns already presented, possibly indicating that the change is unlikely to occur predominantly in one particular season. Mapped trends of rainfall intensity and maximum five-day precipitation are shown in Figure 32. Both quantities increase for most of Scotland although there is a reduction for some northern and coastal location, including the Outer Hebrides, Orkney and Shetland Islands.

Figure 31 - Gridded change for annual maximum consecutive dry days (days), based on a linear trend from 1961 to 2004

33 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

Figure 32 - Gridded change (percentage) for a) annual rainfall intensity on days with ≥ 1 mm rainfall, and b) annual maximum 5-day precipitation amount, based on a linear trend from 1961 to 2004

2.4. Snow and frost

Some aspects of snow variability and change are captured in precipitation variables discussed previously. For example, the liquid equivalent of any snow that falls in a day is added to any rainfall measured to provide a total precipitation figure in millimetres per day. The length of the snow season is another measure that is often used. Meteorological observing stations record the state of the ground at 0900 hrs, i.e. 9 o’clock GMT, and from this a measure of the number of days with snow lying on the ground can be derived. It is recorded that snow is lying if more than fifty percent of the ground is covered with snow. This index does not equate to the length of the snow season but it is a good indictor of it. Table 11 shows the percentage change in the number of days of snow cover for Scotland and the three regions since 1961. The analysis covers the three seasons when snow cover is likely to occur, i.e. summer is excluded.

Table 11 - Changes in days of snow cover (percentage), 1961/62 to 2004/05. Statistically significant trends are shown in bold (significant at the 1% level) or italic (significant at the 5% level) type.

North East West Scotland Scotland Scotland Scotland Spring -28.0 -27.5 -44.6 -31.0 Autumn -70.9 -66.8 -82.6 -71.7 Winter -25.9 -31.8 -36.9 -30.2 Annual -28.8 -31.6 -40.7 -32.1

Over the last forty years, the number of days of snow cover has decreased in each region and in all seasons. In winter the decreases are greater than twenty five percent, and are the largest absolute changes, a decrease of 7 days. The largest percentage changes have occurred in spring and autumn, indicative of a shortening of the snow season. In autumn the

34 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006 decreases in each region are large, greater than seventy percent in North and West Scotland, and statistically significant. Climatology shows that the average number of days of snow cover in autumn is low (see Figure 33, lower panel) so even a large percentage change results in a relatively modest reduction of days. It is likely that the autumn reduction is due to the snow season beginning later in the year. In spring there are also large percentage decreases. The average number of days of snow cover in spring is however greater than in autumn (see Figure 33, upper panel). This springtime reduction again indicates that the season is likely to come to a close earlier in the year than previously. This reduction in the length of the snow season is probably due to the temperature increases discussed in Section 2.2.

Figure 33 - Climatology of number of days of snow cover for Scotland, 1961 to 1990. Spring (March, April and May) is shown in the upper panel, autumn (September, October and November) in the lower panel. Source: www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html

35 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

As noted above, for a day to be recorded as having snow cover more than fifty percent of the ground must be covered in snow. This is calculated for each year from August to July so that the snow season is not split. Time-series of number of days of snow cover in a year is shown in Figure 34. Inter-annual variability in the three regions is highly correlated. The decreasing trend is apparent in all regions, with North and East Scotland seeing a reduction from a typical thirty-five days of snow cover a year in the 1960s to an average twenty-six days per year in present climate. Over the same period, the number of days of snow cover in West Scotland has reduced from an average twenty per year to just thirteen. The time-series also highlight a number of years with a particularly long season of snow, such as the winter of 1962/63 and 1978/79.

Figure 34 - Annual days of snow cover for Scottish regions, 1961/62 to 2004/05, with smoothed curve

N Scotland 40 E Scotland W Scotland

30 Annual days of snow cover snow Annualdays of 20

0 Jul-62 Jul-64 Jul-66 Jul-68 Jul-70 Jul-72 Jul-74 Jul-76 Jul-78 Jul-80 Jul-82 Jul-84 Jul-86 Jul-88 Jul-90 Jul-92 Jul-94 Jul-96 Jul-98 Jul-00 Jul-02 Jul-04

A day of air frost is defined to be a day with minimum air temperature of less than 0°C. As with snow cover, the analysis of air frost is restricted to the seasons where air frost is likely to occur, i.e. summer is excluded. Analysis of change, based upon linear trends over the period 1961 to 2004, is presented in Table 12. A substantial reduction in the number of days of air frost in all seasons and in each of the three regions is clearly apparent. Since 1961 there has been more than a twenty-five percent reduction in the number of days of air frost annually, a change that is statistically significant in all three regions and nationally. As with snowfall, although changes in winter are the largest in absolute terms (decrease of 10 days), it is the spring and autumn seasons that show the largest percentage changes and most significant trends. This is consistent with the warming trend discussed earlier and the lengthening of the growing season.

Table 12 - Change in days of air frost (percentage), for 1961/62 to 2004/05. Statistically significant trends are shown in bold (significant at the 1% level) or italic (significant at the 5% level) type.

North Scotland East Scotland West Scotland Scotland Spring -30.5 -29.0 -29.2 -29.7 Autumn -33.5 -31.3 -33.7 -32.8 Winter -20.1 -21.3 -24.7 -21.7

36 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

Annual -25.7 -25.1 -27.7 -26.0

Time-series of annual days of air frost (Figure 35) provide further evidence in support of this as the peaks in years with higher number of days of air frost coincide with years having later start in the growing season (Figure 13). As the calculation of annual days of air frost is offset, i.e. calculated from August to July rather than January to December, it is not possible to directly compare the years of low occurrence of days of air frost with those of high annual temperatures. However, a visual comparison of Figures 3 and 35 indicates that there is a level of consistency between the two time-series.

Figure 35 - Annual days of air frost for Scottish regions, 1961/62 to 2004/05, with smoothed curve

120

110

100

80 N Scotland E Scotland 70 W Scotland

60 Annual days of air frost Annual air days of

30 Jul-62 Jul-64 Jul-66 Jul-68 Jul-70 Jul-72 Jul-74 Jul-76 Jul-78 Jul-80 Jul-82 Jul-84 Jul-86 Jul-88 Jul-90 Jul-92 Jul-94 Jul-96 Jul-98 Jul-00 Jul-02 Jul-04

Ground frost, which occurs when the grass minimum temperature reaches 0°C or below, is a common occurrence in Scotland, even in the summer. Since 1961 there has been a decreasing trend in the number of days of ground frost in all seasons, and each of the three Scottish regions (see Table 13). The decreasing trend is significant in the spring, especially for North and East Scotland. When the seasons are combined and the trends recalculated for each year the decrease in number of ground frost days in an average year is significant at the one percent level. Figure 36 shows that a steady decline in the number of days of ground frost each year began in the 1980's.

Table 13 - Changes in days of ground frost (percentage), 1961/62 to 2004/05. Statistically significant trends are shown in bold (significant at the 1% level) or italic (significant at the 5% level) type.

North East West Scotland Scotland Scotland Scotland Spring -11.4 -8.7 -7.5 -9.4 Summer -3.0 -1.8 -1.4 -2.2 Autumn -7.8 -4.1 -4.3 -5.6 Winter -8.2 -8.4 -9.8 -8.7 Annual -31.8 -25.2 -25.2 -27.8

37 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

Figure 36 - Annual days of ground frost for Scottish regions, 1961/61 to 2004/05, with smoothed curve.

180

170

160

150

140 N Scotland 130 E Scotland W Scotland 120

110 Annual days of ground frost ground of days Annual 100

8 0 2 1962 1964 1966 1968 1970 1972 1974 1976 197 198 198 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004

The number of days of air frost and snow cover are typically calculated as annual values. The trends in the gridded datasets of these quantities are mapped for 1961 to 2004 in Figure 37. The percentage changes in both quantities are typically greatest for the Scottish islands or in areas close to the coast. The proximity of the sea has a moderating effect on temperatures in these regions so days of frost or snow cover are less common than for areas further inland. This means that a relatively small increase in temperature, resulting in a small reduction in these cold weather phenomena, will have a larger proportional impact. For this reason the spatial patterns of change in Figure 37 are presented in terms of numbers of days rather than as a percentage. Although the overall changes described in this section are largely reductions it should be noted that in some localised areas there has been an increase in the number of days of snow cover, particularly in northern mainland Scotland.

38 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

Figure 37 - Gridded change for annual days of air frost and days of snow cover (days), based on a linear trend from 1961 to 2004.

For this study, the analysis of ground frost has been extended to look at seasonal rather than annual patterns of change. Figure 38 shows the spatial detail of these trends. While there has been a trend of decreasing occurrence of ground frost for most areas in all season, there has been little change on the Orkney and Shetland Islands. In fact, the number of days of ground frost have actually increased in winter on both the Shetland and Orkney Islands. The decreasing frequency of occurrence of ground frost has been especially marked over the western Highlands and Hebrides in spring.

39 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

Figure 38 - Gridded change for days of ground frost (days) based on a linear trend from 1961 to 2005; a) spring, b) summer, c) autumn, d) winter.

As with growing season gridded datasets of the start and end of the frost free season do not, as yet, exist. An analysis can however be completed on the records from individual observing sites. Analysis of the dates of occurrence of the first ground frost from August 1st and the last ground frost before the end of July at four Scottish stations15 has revealed that the length of

15 Threave near Castle Douglas in Dumfries and Galloway, Blythe Bridge near Peebles in the Scottish Borders, Wick in the Highlands and Kinloss in Moray. Threave and Blythe Bridge are inland stations at altitudes of 70m and 250m respectively, while Wick and Kinloss are low-lying coastal stations.

40 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006 the frost-free season has extended, by between 20-40 days (Table 14). At each of the stations, the first frost is occurring later, but the more significant and rapid change is seen in the date of the last frost, which has become between 12-24 days earlier since 1961. However, as can be seen in Figures 39 and 40, there is very high inter-annual variability in the first and last frost occurrence dates, and summer frosts are still common at each of the four sites.

Table 14 - Changes in the dates of the first and last ground frost, in days starting from 1st August, and changes (days) in the length of the frost-free season spanning 31st July – 1st August, for four Scottish stations over the period 1961 to 2005.

Blythe Threave Bridge Kinloss Wick First ground frost 3.4 10.2 7.3 11.8 Last ground frost -22.5 -15.0 -12.1 -24.0 Frost-free season 29.1 24.5 20.0 38.8

Figure 39 - Date of the first ground frost in days from the 1st August, 1960 to 2005, at four Scottish stations, with smoothed curve.

100

60 Threave Blythe Bridge 50 Kinloss Wick 40

20 First ground frost (days from 1st August) 1st from (days frost ground First 10

2 6 2 8 4 0 1960 196 1964 1966 1968 1970 1972 1974 197 1978 1980 198 1984 1986 198 1990 1992 199 1996 1998 200 2002 2004

41 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

Figure 40 - Date of the last ground frost before the end of July, in days from the 1st August, 1961 to 2005, at four Scottish stations, with smoothed curve

370

360

350

340

330

Threave 320 Blythe Bridge Kinloss 310 Wick

300

290

280 Last ground frost (days from 1st August) 1st from (days frost ground Last

270

260

61 7 71 73 83 9 93 95 05 963 96 969 975 979 981 985 98 991 997 001 003 19 1 1965 1 1 19 19 1 1977 1 1 19 1 1987 1 1 19 19 1 1999 2 2 20

2.5. Sunshine

Sunshine records are some of the longest duration meteorological kept in the UK. A dataset has been created, and analysed, which includes data from 1929. As previously, the analysis of these data is presented alongside the shorter 1961 to 2004 period that is being used as the benchmark for this study. The average number of sunshine hours in a day has increased by a small percentage annually in all three regions however there is no clear overall pattern of change with some seasons and regions seeing more sunshine and others less (Table 15). One signal though is clear: since 1961 the autumn months have been sunnier. This is true in all three regions. Although the changes are greater than ten percent they are not statistically significant and may therefore be due to natural variability. East Scotland has become sunnier in all seasons since 1961 but again the change is not statistically significant. Over the longer period, i.e. since 1929, patterns of change are different but there are some significant trends. These occur in North Scotland in winter and the annual mean. Although these changes are modest, less than a six percent reduction in the annual mean, they are statistically significant and therefore beyond the range expected from natural variability. The number of hours of sunshine have decreased, to varying degrees, in all seasons in North Scotland since 1929.

Table 15 - Changes in total sunshine hours (%), 1961-2004 and 1929-2004. Statistically significant trends are shown in bold (significant at the 1% level) or italic (significant at the 5% level) type.

1961-2004 1929-2004 North East West North East West Scotland Scotland Scotland Scotland ScotlandScotland Scotland Scotland Spring 4.5 6.9 2.7 4.7 -5.6 0.5 -4.4 -3.3 Summer -2.1 0.2 -1.4 -1.1 -3.1 1.1 1.9 -0.2 Autumn 17.9 12.1 11.0 13.8 -3.0 4.5 8.3 2.8 Winter -4.6 12.8 -0.6 2.6 -13.8 -0.4 -0.3 -5.1 Annual 2.7 5.5 1.6 3.3 -5.6 1.2 0.2 -1.6

42 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

The average number of hours of sunshine recorded each day is lowest in North Scotland but this is also the region that has seen some of the largest changes. This is demonstrated by the regional time-series since 1929, shown in Figure 41. The time-series and seasonal trends indicate a complex pattern of changing sunshine hours. There is a high level of correlation between inter-annual variability of annual means for the regions but this masks differences between the regions at a seasonal timescale. The wide spatial variation is apparent in Figure 42, which shows the patterns of change in sunshine for each season for the 1961 to 2004 period. The same colour scale is used for each season. This means that is it easy to see that there has been only slight change over this period in either spring or summer and that the main changes have occurred in the second half of the year. It must be noted that the maps show change in sunshine hours as a percentage, and, as daylight hours are lowest in winter it requires a smaller absolute change to result in a relatively large percentage change. However, in some areas the changes are large, e.g. up to a forty percent reduction in sunshine hours in winter (December-February) in parts of North and West Scotland. In many cases these areas are also the ones seeing the largest percentage increases in autumn months (September-November). As the patterns are highly localised these changes are not apparent in the regional and national averages.

Figure 41 - Annual sunshine hours for Scottish regions, 1929 to 2004, with smoothed curve. The vertical dashed line marks the position of 1961.

1600

1500

1400

1300

N Scotland 1200 E Scotland W Scotland

1100 Annual sunshine hours sunshine Annual

1000

900

800

968 992 1929 1932 1935 1938 1941 1944 1947 1950 1953 1956 1959 1962 1965 1 1971 1974 1977 1980 1983 1986 1989 1 1995 1998 2001 2004

43 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

Figure 42 - Gridded change for sunshine, based on a linear trend from 1961 to 2004: a) spring, b) summer, c) autumn, d) winter.

The east-west contrast in the winter change pattern is reminiscent of some of the patterns already seen. As would be expected, there is a strong similarity with patterns of change in rainfall. It would be logical to assume a similar pattern of change for cloud cover. This is discussed below in section 2.6

44 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

2.6. Cloud

Although the dataset employed in this study includes cloud cover, there is a point of caution to be made when the data are analysed. The records of cloud cover cannot be considered homogeneous. In particular, there has been a large scale move to automated observing methods over recent years, which has resulted in possible inconsistencies between records. Table 16 shows seasonal trends in cloud cover for each of the regions, calculated for the 1961 to 2004 period. None of the trends identified are statistically significant.

Table 16 - Changes in percentage cloud cover, 1961 to 2004. Statistically significant trends are shown in bold (significant at the 1% level) or italic (significant at the 5% level) type.

North East West Scotland Scotland Scotland Scotland Spring -0.73 -0.69 -0.56 -0.67 Summer -0.02 0.06 -0.64 -0.17 Autumn -0.57 0.55 1.00 0.24 Winter -1.98 -2.15 0.02 -1.45 Annual -0.90 -0.43 0.26 -0.42

Recording methods for hours of sunshine and cloud cover mean that there is no direct relationship between the two. However, it is reasonable to assume some degree of correlation. Visual comparison of the change in sunshine hours presented in Table 15 with cloud cover change in Table 16 shows that this is not the case. It is also possible that a level of correlation exists between changes in cloud cover and precipitation or diurnal temperature range, but the cloud cover changes presented here appear uncorrelated with these variables. It may be that the changes in cloud cover are not statistically significant and natural variability is dominating any underlying trend but it is much more likely to be indicative of the difficulties in comparing records based upon differing observing methods. The time-series of cloud cover for each region is shown in Figure 43. The large decrease in recent years is likely to be due to the change in observing methods.

Figure 43 - Annual percentage cloud cover for Scottish regions, 1961 to 2004, with smoothed curve

74 Scotland N Scotland E 72 Scotland W Cloud(%) cover

3 7 3 7 1 3 7 1 5 9 6 9 9 96 965 969 97 97 98 98 98 99 993 997 001 1961 1 1 19 1 1971 1 1975 1 1979 1 1 1985 1 1989 1 1 19 1 19 2 2003

45 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

It is clear from the time-series that identifying a trend in existing data using the current method is not possible due to the inconsistencies in the data records. Given the possible problems with the dataset any spatial patterns of change are likely to be misleading and hence, mapping of any trends in cloud cover has not been included in the analysis presented here.

2.7. Mean sea level pressure

Large-scale pressure patterns dictate the many aspects of Scottish weather. Low pressure systems pass across the country bringing weather that is predominantly wet and windy while high pressure is associated with less changeable and often drier conditions. The positioning of centres of high and low pressure determines the flow of air across Scotland and the type of weather experienced. The difference, or gradient, of pressure between the north and south of the country is related to mean wind speeds. The long-term average of this gradient, particularly in winter, is also linked with the North Atlantic Oscillation (NAO).

The change in seasonal and annual average mean sea level pressure since 1961 is shown in Table 17. Change is presented in terms of hectopascals (hPa), where one hectopascal is equivalent to one millibar. Given that the average mean sea level pressure for Scotland is approximately 1012 hPa it is clear that observed changes are low, much less that one percent. Year to year variation is high, as can be seen by the time-series presented in Figure 44. Correlation between the three regions is also high, consistent with the large-scale natural of pressure patterns.

Table 17 - Changes in mean sea level pressure (hPa), 1961 to 2004. No trends are statistically significant trends at either the 1% or 5% level.

North East West Scotland Scotland Scotland Scotland Spring 0.2 0.5 0.5 0.3 Summer -0.4 -0.4 -0.6 -0.4 Autumn -0.5 -0.6 -0.9 -0.6 Winter -2.6 -1.7 -1.3 -1.9 Annual -0.8 -0.5 -0.5 -0.7

46 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

Figure 44 - Annual mean sea level pressure (hPa) for Scottish regions, 1961 to 2004, with smoothed curve

1016

1015

1014

1013

N Scotland 1012 E Scotland W Scotland

1011

Mean sea level pressure (hPa) pressure level sea Mean 1010

1009

1008

63 67 75 77 85 89 97 99 01 961 969 971 979 981 983 991 993 995 003 1 19 1965 19 1 1 1973 19 19 1 1 1 19 1987 19 1 1 1 19 19 20 2

Table 17 and Figure 44 show that although mean sea level pressure is a large-scale variable, analysis of seasonal and regional averages is not necessarily the most informative analysis technique. Figure 45 shows mapped trends since 1961 calculated from the gridded dataset for the summer and winter season. The summer map indicates that there is no consistent pattern of change but in winter months a pattern is clearly discernable. Average winter pressures have been falling in northern Scotland, particularly over the Outer Hebrides, Orkney and Shetland Islands, over the period 1961 to 2004. At the same time, there has been little change to average winter mean sea level pressure in southern Scotland. Given that the area north of Scotland is predominantly one of low pressure (i.e. the so-called Icelandic low) this implies that low pressures have become lower and that that the average winter pressure gradient across Scotland has increased since 1961, although it has to be noted that the change is small and unlikely to be significant.

47 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

Figure 45 - Gridded change for annual average mean sea level pressure (hPa), based on a linear trend from 1961 to 2004: a) summer quarter, b) winter quarter

An increasing north-south pressure gradient is consistent with trends in the North Atlantic Oscillation (NAO) over the same period. In the early 1960’s the NAO index was at a record low meaning that the pressure gradient over Scotland and the UK was reduced. Since that time it has, on average, risen thereby increasing the pressure gradients again. When the NAO index is high, winter storm tracks are shifted south with storms potentially tracking across England and Wales with more frequency than Scotland. Analysis of pressure observations from across the UK and Iceland (1957 to 2003), undertaken by Alexander et al 2005, has shown evidence of a southwards move of the North Atlantic storm track. It is not possible to say whether the winter trend patterns mapped in Figure 45 are a direct result of recent trends in the NAO but they are consistent with it.

2.8. Wind

Observations of wind speed and direction can be very site dependent. For instance, there will be a marked difference between an observation in a mountain valley compared to one taken on flat arable land at the same moment in time. If the measuring instrument is moved on the observing site, buildings are erected in the vicinity or a site is relocated there will be an impact on the characteristics of wind observations at that location and the record will not be homogeneous. Although a gridded dataset of mean wind speed exists there are concerns about its use. Analysis has identified significant decreasing trends in the gridded dataset. It is thought that these trends are likely to be a result of inhomogenities in the station data rather than evidence of changes in the variable. For this reason the gridded dataset is not mapped here, instead records taken directly from three observing sites, where records are known to be reliable, are analysed.

Time-series of annual mean wind speeds since 1957 are shown in Figure 46. One observing site from each of the three regions is used. Data are shown for Lerwick, Tiree and Leuchars. It is noted that all three sites are in coastal locations but the variation in wind at each site should be indicative of any long term trends. It must also be noted that prior to 1969 values for Leuchars are estimated from Turnhouse. It is apparent that inter-annual variability is low

48 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006 at each location and that no large scale trend influences all three. There are similarities between the time-series for Tiree and Leuchars, both of which show a trend of decreasing mean wind speeds in recent decades, however Lerwick has seen a trend of increasing wind speeds over the same period.

Figure 46 - Annual mean wind speed (knots) for three Scottish stations; Lerwick, Tiree, and Leuchars (values estimated from Turnhouse prior to 1969), 1957 to 2004, with smoothed curve

13 Lerwick 12 Tiree Leuchars 11

10 Mean wind speed (knots) wind Mean 9

7 3 4 0 6 2 5 6 69 75 81 8 87 9 9 0 9 9 9 9 9 9 1 1960 1 1966 1 1972 1 1978 1 19 1 19 1993 19 1999 20

For comparison, Figure 47 shows time-series of the same quantity, annual mean wind speed, calculated from the gridded dataset. The three regions are shown as before. The anticipated decreasing trend is clear however the trend is very similar in all three regions and produces a larger decrease than is seen in the individual station records (Figure 46 above). This is not to say that the trends shown in Figure 47 are incorrect but that the gridded wind dataset requires further investigation before these possible inconsistencies can be explained.

Figure 47 - Annual mean wind speed (knots) for Scottish regions, 1969 to 2004, with smoothed curve

13 Scotland N Scotland E 12 Scotland W

11 Mean wind speed (knots) speed wind Mean

9 3 5 9 1 3 7 9 1 5 7 9 3 196 1971 197 197 1977 197 198 198 1985 198 198 199 1993 199 199 199 2001 200

49 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

One of the variables that can be derived from observed wind data is a measure of the number of days in a year that can be considered a day of strong wind. In this report, the measure used is that of a gale day, defined to be a day with mean wind speed of 34 knots or more over any 10-minute period. The exposed island locations of Lerwick and Tiree experience a higher number of gale days in a year than Leuchars (Figure 48). Inter-annual variability is also higher for the island locations but there is no clear trend in any of three records.

Figure 48 - Annual days of gale for three Scottish stations; Lerwick, Tiree, and Leuchars, 1957 to 2004, with smoothed curve

40 Lerwick Leuchars 30 Tiree Annual days of gale Annual days of 20

3 6 4 75 78 81 960 993 996 1957 1 196 196 1969 1972 19 19 19 198 1987 1990 1 1 1999 2002

50 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

3. FUTURE CHANGE IN SCOTTISH CLIMATE

Global climate models (GCMs) are currently the only scientific tool available for predicting realistic patterns of current and future changes in climate and, in particular, the large scale patterns of change. These models require a large computing resource and hence are run at relatively coarse resolution. For example, the current global climate model at the Met Office’s Hadley Centre, called HadCM3, represents the British Isles with a horizontal resolution of approximately 300km which means that only two grid squares cover Scotland. For greater detail, and for impact studies, higher resolution regional models can be ‘embedded’ within the GCM grid. The version of the Hadley Centre regional model used to produce the UKCIP02 scenarios, HadRM3, has a horizontal resolution of 50km. The regional model projections show much more detail than the global model and is able to better represent extremes. Regional models are better able to capture extreme weather because not only can they represent smaller scale weather features but they also have a much better representation of orography. For example, the mountains of Scotland cannot be represented in the global model at all but the 50km RCM permits the mountains of Scotland to be partially resolved which results in increased spatial variation of rainfall.

Every climate model, global or regional, produces a wealth of data. To achieve maximum value this data must be used in the context of the uncertainties (outlined in Appendix 2), and it must also be remembered that not all climate model data have been validated against observed climate. However, the large array of modelling studies which have been completed, and published, increase confidence and our understanding of model predictions and areas of uncertainty.

In 2002 the UK Climate Impacts Programme published the latest set of Climate Change Scenarios for the United Kingdom (UKCIP02, Hulme et al, 2002). The climate model results contained within this report were from the Met Office’s Hadley Centre, based upon findings from the latest regional climate model, HadRM3. Following the approach used by the Intergovernmental Panel on Climate Change (IPCC) the UKCIP02 report presents a range of scenarios of change, based upon a range of possible emissions scenarios (termed ‘low’, ‘medium-low’, ’medium-high’ and ’high’), all of which can be considered equally likely to occur. Results were presented for three ‘time-slices’ or thirty year periods centred about the 2020s, 2050s and 2080s.

It has to be recognised that UKCIP02 scenarios are based upon the projections of one regional climate model. While the UKCIP02 report presented the latest scientific understanding and modelling results for Scotland there are a number of sources of uncertainty (due to emissions scenarios, scientific uncertainties and natural variability), which should be borne in mind when interpreting the projected future Scottish climate. These uncertainties, discussed in Chapter 7 of UKCIP02, are summarised briefly in Appendix 2. Some of these uncertainties account for the differences between the 1998 and 2002 UKCIP reports and the Regional Climate Change Scenarios for Scotland report (Hulme et al, 2001).

3.1. Observed trends in Scottish climate: the UKCIP02 context

3.1.1. Temperature

Irrespective of emissions scenarios or time-slice, temperatures are expected to rise over Scotland, with increases being greatest during summer and autumn months when a warming of up to 4.0°C (with the medium-high emissions scenario of forcing) is expected over parts of Scotland by the end of the century. Southern Scotland is projected to warm at a faster rate than the north. The patterns of change identified in observed temperatures broadly agree with this, particularly the geographical variation in rates of warming, seen clearly in winter months (Figures 4, 7 and 8). The projected warming in autumn months is not seen in the mapped trends for the 1961 to 1990 period. However, the longer 1914 to 2004 period, shown in Table 2, does indicate some of the largest temperature trends in the last ninety years are

51 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006 during the autumn season. During the longer period the warming is least in the North, again consistent with the expected patterns of future warming.

In the UKCIP02 scenarios diurnal temperature range is expected the increase the most in summer with a complex pattern of smaller increases and decreases in other seasons. This pattern of change is not seen in the analysis of observed temperatures. Over recent decades there has been little change to the diurnal temperature range in summer and it has actually increased in all other seasons, particularly winter.

By the 2080s heating degree days are projected to decrease by fifteen to forty percent. The changes are likely to be greatest in southern and eastern Scotland. The pattern of change from the analysis of observed variables is consistent with this. By the same time, growing season length is expected to have increased by thirty to ninety days. An extended growing season is also identified in the observed dataset although the geographical pattern of change is different to that projected. However, the degree of change seen over the last century is comparable with that projected for this century.

3.1.2. Precipitation

Projected changes in precipitation across Scotland are more complex than those for temperature. Although there is expected to be relatively little change to annual rainfall amounts it is expected that winter months will become wetter, while summers months will be drier than at present. The pattern of change is not uniform, with eastern Scotland experiencing the most extreme percentage changes in precipitation, with a winter increase and a summer decrease. Changes are projected to be relatively small for all regions during the other seasons. Section 2.3 described the observed trends in Scottish rainfall. Since 1961 there has been a significant increase in winter rainfall, which is consistent with climate model projections. However, there has also been an increase in the annual mean and little change during summer. As with the trends of temperature change, there are similarities between the precipitation trends over the longer 1914 to 2004 period and the projected future trends. Over the longer period, the summer months have become drier and there has been relatively little change to the annual mean values.

The one aspect of the observed patterns of change in precipitation that is not consistent with the UKCIP02 scenarios is the spatial detail. East Scotland has seen the smallest increases in winter precipitation and some areas within this region have even become drier in winter since 1961. This is contrary to the pattern expected from the climate change projections. However, the summer drying is consistent with observed trends since 1914. It is possible that recent changes are a result of natural variability and masking any underlying impact of climate change. It is interesting to note that one of the major differences between UKCIP02 and its predecessor UKCIP98 was the projected change to seasonal precipitation over Scotland. This analysis highlights that there are many uncertainties in the predictions of climate change for Scotland and that both observed and projected trends required care in their interpretation.

Within the context of the UKCIP02 scenarios, it is likely that the intensity of rainfall will increase in winter months. An east-west contrast in change is expected, with the most extreme changes occurring in eastern Scotland. This geographical contrast is apparent in each of the scenarios presented in UKCIP02. However, the pattern has not been seen in the analysis of measures intense of heavy rainfall within the observed dataset, although the measures are not directly comparable with those used in UKCIP02. It is clear that since 1961 heavy rainfall has increased across Scotland during winter months and that both rainfall intensity and maximum five-day rainfall have increased significantly.

52 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

3.1.3. Snowfall

Projections of future climate indicate that it is also likely that snowfall will decrease significantly. Winter snowfall may be reduced by fifty percent or more across Scotland by the 2080s (UKCIP02, medium high scenario). The most pronounced projected changes are over eastern Scotland, with a potential decrease of over ninety percent. Again, it is not possible to compare the UKCIP scenarios directly with the variable analysed here but it is clear that the decreasing trend in observed snow cover is consistent with the climate change prediction although it is currently West Scotland that has experienced the greatest reduction in snow cover.

3.1.4. Sunshine

A measure of sunshine hours was not included in the UKCIP02 scenarios, so it is not possible to compare observed trends with those projected for the future. Cloud cover was considered although problems with the gridded dataset, as described in section 2.6, make the results of analysis uncertain. By the 2080s cloud amounts are expected to increase slightly in winter, particularly in the northern half of Scotland, and to decrease in all other season, with the greatest changes occurring in summer months in southern and eastern areas. The observed reduction of winter sunshine hours is, to some extent, consistent with this.

3.1.5. Mean sea level pressure

Maps of change in mean sea level pressure were also not given in the UKCIP02 scientific report although it is commented upon in the text. Changes in spring and autumn are small. In winter the north-south pressure gradient increases resulting in stronger winds in southern and central Britain but little change in Scotland. Mean sea level pressure was used to investigate possible change in both North Atlantic storm tracks and the North Atlantic Oscillation (NAO). In the scenarios it was found that the storm track shifted southwards of their current position which resulted in strengthening winter winds across southern England. The NAO index was also expected to become predominantly positive indicating an increased north-south winter pressure gradient across Britain, consistent with more winters which are more ‘westerly”, i.e. milder, wetter and windier. The observed change in mean sea level pressure is broadly consistent with these projected future changes.

3.1.6. Wind

Future change in average mean wind-speed is highly uncertain. In the High emissions scenario, by the 2080s, a change of plus or minus five percent is typical. The values should be treated with caution given the uncertainties in modelling wind speeds.

53 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

54 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

4. CONCLUSIONS

A wide range of observed quantities have been analysed in this study and a complex picture of a changing Scottish climate has emerged. Some variables, such as temperature and precipitation, have a long record, which has enabled the more rapid changes of the last four decades to be put into the context of longer-term variation. It has also been shown that presenting a nationally averaged figure of change masks the fact that patterns of change are not uniform across Scotland or throughout the seasons. Difficulties in obtaining homogeneous datasets that can be gridded for mapping have also been highlighted, underlining the caution that should be exercised when interpreting some types of data.

Significant increases in temperature have occurred in recent decades. These increases in temperature have been at a faster rate than at any other time in the ninety-year period considered in this study. Since 1961 spring and winter temperatures have increased at a faster rate in southern and eastern Scotland than in the northwest. In contrast when considering the longer ninety-year period it was found that average winter temperatures in northern Scotland are currently very similar to those recorded toward the start of the 1900s. This is even though annual mean temperatures have risen, fallen and then increased again over the same period of time. Since 1961 24-hour minimum temperatures (effectively night- time minimum), have been increasing at a rate that is slower than day-time maximum temperatures, i.e. the diurnal temperature range has increased. This is contrary to the global trend for the period 1950 to 1993. When the Scottish data are considered over the longer 1914 to 2004 period the relationship is reversed, and minimum temperatures increase at the faster rate, implying a decreasing diurnal temperature range. Given the different periods of time being compared it is not possible to say whether long term national, and local, diurnal temperatures ranges are changing in a different manner to the global average or not.

The rate of change of both annual and winter mean precipitation has also been faster since 1961 than at any other time in the 1914 to 2004 record. As with temperature records some aspects of the changes projected by climate models are only seen in the longer record. There are aspects of the spatial pattern of observed change, such as the wetter autumns and drier winters of Aberdeenshire, which are absent from the UKCIP02 future climate scenarios. The differences between future changes to seasonal rainfall patterns given by the UKCIP02 scenarios and those of their predecessors are well known. Although the UKCIP scenarios are derived from models that are more scientifically complex than those of the earlier scenarios, none of the scenarios can be discounted. All are scientifically valid. The complexity of patterns of observed change and the variation in scenarios underlines the uncertainties associated with future regional precipitation changes.

This study has shown that the use of a consistent dataset over a standard period of time, permits the interaction between certain variables to be seen clearly. For instance, the rises in temperature are linked to an increase in the length of the growing season. It has also been possible to use changes in one variable as supporting evidence for trends in another. For example, the fact that the last frost day of a year typically occurs earlier in spring now than previously supports the finding of an earlier start to the growing season. This consistency gives confidence in the identified trends. When trends appear to be inconsistent it may be that the relationship between variables is more complex than can be represented using this subset of data, which is based on one set of observing methods. It may also indicate a problem with the dataset, as is perhaps the case with cloud cover data.

This study has focused upon the identification of trends in Scottish climate and, where possible, mapping the geographical patterns of these trends. The study does not seek to explain or attribute a cause to any of the changes. Many interesting features are identified that warrant further investigation but to do so is outside the scope of this study. However,

55 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006 what this study does is provide an up-to-data assessment of the changing climate in Scotland and a firm foundation for any party undertaking climate related work in Scotland.

Many of the changes identified are consistent with the nature of change presented in the UKCIP02 scenarios. This is not to say that the changes identified can be attributed to anthropogenic climate change or that they are early indications of human impact on Scottish climate. In recent years it has become possible to discern changes in climate that cannot be attributed to natural causes but only at a spatial scale much larger than Scotland. While the similarities between observed and projected change are compelling, it is at this present time, not possible to tell whether local changes in Scottish climate are early indications of future climate change. What can be said with confidence is that the climate of Scotland has changed in recent decades. Where observed changes are comparable with those expected for Scotland it is now possible to point to the evidence that shows that Scotland has experience of what such changes mean and may therefore be better placed to plan adaptation measures for future climate change.

56 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

5. REFERENCES

Alexander, L.V., S.F.B. Tett and T. Jonsson (2005) Recent observed changes in severe storms over the United Kingdom and Iceland. Geophysical Research Letters, 32, no 13.

Begert M., T. Schlegel and W. Kirchhofer (2005) Homogeneous temperature and precipitation series of Switzerland from 1864 to 2000. International Journal of Climatology 25: 65-80.

Brooks (1943) Interpolation tables for daily values of meteorological elements. Q. J. Roy. Meteor. Soc., vol 69, no 300, 160-162

Domroes M. and A. El-Tantawi (2005) Recent temporal and spatial temperature changes in Egypt. International Journal of Climatology 25: 51-63.

Gregory J.M., P.D. Jones and T.M.L. Wigley (1991) Precipitation in Britain: an analysis of area-average data updated to 1989. International Journal of Climatology 11:.331-345

Hanna E., T. Jonsson and J.E. Box (2004) An analysis of Icelandic climate since the nineteenth century. International Journal of Climatology 24: 1193-1210.

Hulme, M., G.J. Jenkins, X. Lu, J.R. Turnpenny, T.D. Mitchell, R.G. Jones, J. Lowe, J.M. Murphy, D. Hassell, P. Boorman, R. McDonald and S. Hill (2002) Climate Change Scenarios for the United Kingdom: The UKCIP02 Scientific Report. Published by the Tyndall Centre, UEA Norwich, April 2002.

Hulme, M., J. Crossley and X. Lu (2001) An Exploration of Regional Climate Change Scenarios for Scotland. Published by the Scottish Executive Central Research Unit, 2001

IPCC (2001) Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change. [J.T.Houghton, J.T., Y. Ding, D.J. Griggs, M. Noguer, P.J. van der Linden, X. Dai, K. Maskell and C.A. Johnson (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 881pp.

Jenkins, G.J., J. Lowe (2003) Handling uncertainties in the UKCIP02 scenarios of climate change. Hadley Centre Technical Note 44, November 2003.

Jenkins, G.J., C Cooper, D Hassell and R Jones (2003) Scenarios of climate change for islands within the BIC region. Published by the Met Office, Bracknell, July 2003.

Jones P.D. and D. Conway (1997) Precipitation in the British Isles: an analysis of area- average data updated to 1995. International Journal of Climatology 17: 427-438.

Jones P.D. and D. Lister (2004) The development of monthly temperature series for Scotland and Northern Ireland. International Journal of Climatology 24: 569-590.

Kerr, A., S. Shackley, R. Milne and S. Allen (1999) Climate Change: Scottish Implications scoping study. Scottish Executive Central Research Unit, Saughton House, Broomhouse Drive, Edinburgh, EH11 3XA.

Lee, M.J., D.M. Hollis, E. Spackman (2000) From raw data to the internet – producing quality climatological services. Proceedings of the 3rd European Conference on Applied Climatology, Pisa.

57 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006

Mayes, J. (1996) Spatial and temporal fluctuations of monthly rainfall in the British Isles and variations in the mid-latitude westerly circulation. International Journal of Climatology 16: 585-596.

Nakicenovic, N, et al (2000) Special Report on Emission Scenarios. Cambridge University Press, Cambridge, 2000.

Osborn, T.J., M Hulme, P.D. Jones and T.A. Basnett (2000) Observed trends in the daily intensity of United Kingdom precipitation. International Journal of Climatology 20: 347-364.

Perry, M.C. and D.M. Hollis (2005a) The development of a new set of long-term climate averages for the UK. International Journal of Climatology 20: 1023-1039.

Perry, M.C. and D.M. Hollis (2005b) The generation of monthly gridded datasets for a range of climatic variables over the UK. International Journal of Climatology 20: 1041-1054.

Shen, S.S.P., H. Yin, K. Cannon, A. Howard, S. Chetner, T.R. Karl (2005) Temporal and spatial changes of the agroclimate in Alberta, Canada, from 1901 to 2002. Journal of Applied Meteorology 44: 1090-1105.

Smith, K. (1995) Precipitation over Scotland, 1757-1992: some aspects of temporal variability. International Journal of Climatology 15: 543-556.

Sneyers, R. (1990) On the statistical analysis of series of observations. WMO Technical Note No. 143.

Roberts, A.M.I., F.T. Last, and E. Kempton (2004) Preliminary analyses of changes in the first flowering dates of a range of plants between 1978 and 2001. Scottish Natural Heritage Commissioned Report No. 035 (ROAME No. F01NA04). . Stott, P.A., (2003) Attribution of regional scale temperature changes to natural and anthropogenic causes. Geophys. Res. Lett., doi:10.1029/2003GL017324, 21, 493-500.

Stott, P.A., D.A. Stone, M.R. Allen (2003) Human contribution to the European heatwave of 2003 . Nature, 432, 610-614.

58 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006 (Appendices)

APPENDIX 1: SCOPING STUDY

59 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006 (Appendices)

1. INTRODUCTION

There is an increasing body of evidence, which shows that the climate of our planet is changing. Long records of observed data exist for specific locations however combining these separate records into gridded data sets is a relatively new innovation exploiting advanced spatial averaging techniques. Using such datasets to validate climate model simulations of observed climate has enabled scientists to say, with some level of confidence, that the changes which have been observed cannot be due to natural forcing alone and that man’s actions are contributing to global warming (IPCC, 2001). More recently it has become possible to say that regional patterns of change are also being influenced by man’s actions (Stott et al, 2003).

In 2002 the UK Climate Impacts Programme published the latest set of Climate Change Scenarios for the United Kingdom (UKCIP02, Hulme et al, 2002). The climate model results contained within this report were from the Met Office’s Hadley Centre, based upon findings from the latest regional climate model HadRM3. his model was run for a ‘baseline’ period in order to represent present day climate, where present day climate was taken to be an average over the thirty-year period 1961 to 1990. In addition to the model representation of present day climate and the scenarios of future change, a database of gridded observed variables was constructed (See Hulme et al, Appendix 7).

In recent years there have been a number of weather related events that have been linked in the media to climate change. While it is not possible to say whether any individual event is due to climate change it is possible to draw comparisons between current weather and how weather may be expected to change in the future. For example, the heat wave that impacted much of Europe in 2003 cannot, as a single event, be attributed to climate change. The temperatures reached are however comparable with the scenarios of an average summer by the middle of this century.

There now exists a sometimes bewildering array of information relating to both the changes already observed in our climate and those which may be expected in the future. Figures of temperature change, either observed or projected, are often presented as average values on a global or national scale. There is no simple way for an individual in Scotland to find out what global warming and climate change mean in their region. The aim of this project is to address this need and to set a marker in time against which future changes may be examined. Therefore, we seek to collate readily available data in order to identify trends in the observed weather of Scotland and then to compare these with expected changes in future climate.

60 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006 (Appendices)

2. DATA SOURCES

There are four key sources for climate related data within the UK. Each provides access to readily available data, typically with a licence agreement and is either free of charge or will be supplied for a nominal fee to cover extraction and shipping. A licence is granted based upon certain criteria. The primary restriction is often that data is only provided for non- commercial applications or for academic research. A short description of each organisation and the data they supply is given below. Full conditions of data licensing are given on each organisation’s website.

2.1 The Met Office

The Met Office is a world-leading provider of environmental and weather-related services in the UK and around the world. In addition to providing the public with daily forecasts and warnings of high-impact weather the Met Office has a mandate to maintain an up-to-date climatological record of the UK, the National Meteorological Library and Archive. Historically weather observations have been recorded and stored on paper but increasingly these records are being transferred to digital media thus improving accessibility.

The Met Office’s network of UK weather stations report a mixture of snapshot hourly observations of the weather known as synoptic observations, and daily summaries of the weather known as climate observations. Observations from around 200 UK synoptic stations, approximately 50 of which are sited in Scotland, are collected in real time; climate data from synoptic stations also comes in straight after readings are taken. This is supplemented by climate observations from several hundred co-operating observers which are submitted as collectives at the end of the month. All climate stations record daily maximum and minimum air temperature and rainfall amount, recorded over the period 0900-0900 period (1000-1000 in summer). Many observe additional elements with synoptic stations recording a wide range of quantities. In addition there are around 5,000 rainfall stations in the rainfall network, approximately 1,000 being in Scotland. Maps of the locations of current synoptic, climate and rainfall recording sites in Scotland are available on the Met Office website (http://www.metoffice.gov.uk/climate/uk/networks/index.html).

The station network provides a long record of weather observed at a series of individual locations. A sample of these (see Annex 1) are available from the Met Office website and can be downloaded free of charge. The Scottish locations available are Lerwick, Stornoway airport, Braemar, Tiree, Leuchars and Paisley. The data given are monthly means of

Mean maximum temperature Mean minimum temperature Mean grass minimum temperature Total rainfall Total sunshine duration

The World Meteorological Organization (WMO) requires the calculation of averages for consecutive periods of 30 years, with the latest covering the 1961-1990 period. However, many WMO members, including the UK, update their averages at the completion of each decade, i.e. 1971 to 2000. Thirty years was chosen as a period long enough to eliminate year-to-year variations distorting the mean. These averages help to describe the climate and are used as a base to which current conditions can be compared. A selection of station, district and regional averages, or contoured maps, for a wide range of weather elements is available on the Met Office website (see Annex 1). The website also provides more information on the methods used to create the long-term averages and maps.

61 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006 (Appendices)

In association with the UK Climate Impacts programme a number of gridded datasets have been developed by the Met Office. These data sets have been created for 26 weather parameters, based on the archive of UK weather observations held at the Met Office. For most parameters approximately 500 stations are used to create each grid; for rainfall approximately 3,500 stations are used. The regression and interpolation process used to obtain the 5 km grids alleviates the impacts of station openings and closures on homogeneity but the impacts of a changing station network cannot be removed entirely, especially in topographically variable areas. Full details of the techniques used to create the datasets are available on the Met Office website (http://www.metoffice.gov.uk). Available parameters are listed in Annex 1.

2.2 British Atmospheric Data Centre

The British Atmospheric Data Centre (BADC) is the Natural Environment Research Council's (NERC) Designated Data Centre for the Atmospheric Sciences. The role of the BADC is to assist UK atmospheric researchers to locate, access and interpret atmospheric data and to ensure the long-term integrity of atmospheric data produced by NERC projects.

The BADC has substantial data holdings of its own but also provides information and links to data held by other data centres. The data held at the BADC are of two types:

• Datasets produced by NERC-funded projects. • Third party datasets that are required by a large section of the UK atmospheric research community and are most efficiently made available through one location (e.g. Met Office and the European Centre for Medium Range Weather Forecasting (ECMWF) datasets).

All BADC data are available on-line through a World Wide Web interface (http://www.badc.rl.ac.uk/) or via an ftp service. Software is provided to assist in the manipulation of the data and extensive information is provided on the data collection procedures, formats, data quality, contact names and references to journal papers.

Since its establishment the BADC has become the main point of contact for UK researchers needing access to the meteorological products of both the Met Office and ECMWF.

2.3 British Oceanographic Data Centre

The British Oceanographic Data Centre (BODC), as a national facility for looking after and distributing data concerning the marine environment, has a range of roles and responsibilities which include:

• The National Oceanographic Database. BODC maintains and develops the National Oceanographic Database (NODB). The NODB is a collection of marine data sets originating mainly from UK research establishments. • UK Tide Gauge Network. BODC manages the data for the UK Tide Gauge Network. The network records tidal elevations at 45 locations around the UK coast. It is part of the National Tide & Sea Level Facility (NTSLF). • The designated marine data centre for the Natural Environment Research Council (NERC). BODC is one of seven designated data centres that manage NERC's environmental data.

The BODC holds a wealth of marine publicly accessible data collected using a variety of instruments and samplers and collated from many sources. It handles biological, chemical,

62 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006 (Appendices) physical and geophysical data and has databanks containing measurements of nearly 10,000 different oceanographic variables.

BODC encourages the use of its data holdings for science, education and industry, as well as the wider public and makes data available under a licence agreement. In the case of NERC data the conditions are in line with the NERC Data Policy that formally lays down the conditions under which the data may be used. For data from non-NERC organisations the conditions are broadly similar. Full details on data holdings and access are available on the BODC website (http://www.bodc.ac.uk/).

2.4 UK Climate Impact Programme

The UK Climate Impacts Programme (UKCIP) provides scenarios that show how our climate may change in coming decades and co-ordinates research on dealing with our future climate. UKCIP shares this information, free of charge, with organisations in the commercial and public sectors to help them prepare for the impacts of climate change. The UKCIP02 climate change scenarios datasets were produced by the Hadley Centre (Met Office) and Tyndall Centre, with funding from DEFRA, as a key component in UK national and regional climate impact assessments. It is strongly recommended that all potential users of the scenarios datasets read the accompanying UKCIP02 Scientific Report (Hulme et al, 2002) before proceeding with data analysis.

UKCIP have constructed a Scenarios Gateway, a structured walk-through intended to be read in sequential order. Firstly, the "Maps" pages provide a visual representation of the results from the scenarios including additional material that could not be included in the report due to lack of space. They provide a reference to the range of data that has been extracted from the climate model. Further pages provide the essential information on how the scenarios were produced and thereafter on the different datasets that are available. Instructions on how to obtain a licence to become a registered user of the datasets can also be found on the website (http://www.ukcip.org.uk).

Although the UKCIP scenarios are primarily associated with future change a baseline current climate dataset (1961 to 1990) is also available, based upon the regional model simulation of present day climate by the Hadley Centre regional climate model (HadRM3). The future climate fields are presented as changes relative to this baseline. All of the data is available at the 50km (HadRM3) grid-box scale in the form of monthly averages for the 2020s, 2050s and 2080s time slices, where each time slice refers to a thirty year period, i.e. the '2020s' period refers to 2011-2040, the '2050s' period to 2041-2070, and the '2080s' period to 2071-2100. Further interpolation of some of the climate variables down to 5km has also been developed both for the time slices and the full time sequence from 2011 to 2100. Baseline data is available either as model simulated (50km) or based upon observations (5km) - in the latter case from the Met Office website. Full details are available on the UKCIP website (http://www.ukcip.org.uk).

2.5 Climate change indicators

A list of 34 Indicators of Climate Change in the UK was published in 1999 by Defra. More recently an expert meeting in March 2003 reviewed the set of indicators, see http://www.edinburgh.ceh.ac.uk/iccuk/. Only a limited number of the indicators include Scottish data. These include

• Precipitation gradient across the UK, based upon the difference between a Scottish winter precipitation series and a SE England summer precipitation series. • The predominance of westerly weather, based upon a North Atlantic Oscillation index • River flows in northwest and southeast Britain

63 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006 (Appendices)

• Frequency of low and high river flows in northwest and southeast Britain • Scottish skiing industry

These indicators are based upon either point or aggregated data, rather than gridded datasets. Hence their ability to capture the spatial variation across Scotland is limited. Only if information from them is particularly relevant to this study will they be included.

The usefulness of indicators should also be assessed in terms of other global changes that have accompanied climatic change, for example, land-use change. This makes disentangling the climate change signature for river-flow data difficult, as changes in stream-flow patterns will reflect a whole host of changes in land-use and catchment management practices as well. Future predictions of stream-flow will require rainfall-runoff modelling that is well beyond the scope of this project.

64 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006 (Appendices)

3. ACCESS TO DATA

Each of the data centres listed in section 2 holds archives of data which is both readily available and potentially relevant to this project. A summary of the parameters available is presented in tabular form in Annex 1. The datasets have been categorised as either gridded or point. Although this study is to focus upon gridded datasets it is considered beneficial to include data records for point locations. Similarly, although data used in the analysis of Scottish climate will be restricted to that which is readily available to the public or the project team, the listings in Annex 1 include some datasets that require a licence and are not free. This additional data has been included to benefit the reader, as these may prove useful supplementary information at a later date.

It is recognised that the data lists presented in Annex 1 are not exhaustive but they do represent sufficient fields to describe Scotland’s climate and any trends in key parameters. Further datasets exist which are based upon model results, such as the UKCIP02 baseline climatology or ECMWF reanalyses. The tables in Annex 1 present only sources which have been derived from observed data and not that derived from models. There are also datasets which present climatologies which may be useful to the reader, such as the Flood Studies report (NERC, 1975) however these have also been excluded from the tables at this time.

65 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006 (Appendices)

4. STAKEHOLDER VIEWS ON ADDITIONAL VARIABLES

A brief email and telephone survey was undertaken of stakeholders in key sectors across Scotland. The survey provided a proposed list of derived variables to be included within the handbook and asked respondents which they would be interested in seeing and what aspects of those variables were most important to them. Initially 21 organisations/contacts were emailed and 11 responses by phone or email were received. Eight of these specifically indicated variables of interest and these include representatives from 8 of the 9 sectors contacted (tourism is absent). The full list of respondents is provided in Table 1 below. The list of organisations contacted is included in Annex 2.

The number of respondents who selected each variable from the original list is shown in Table 2. Rainfall return periods was identified as being a key variable set to include in the handbook, with every respondent recognising the value of this to them. Cooling degree days and crop temperature sums were the least favoured variables, possibly reflecting a lack of familiarity in some sectors with these variables as well as no direct agricultural industry involvement. One respondent also emphasised the need to recognise the importance of micro-climate for agriculture and biodiversity.

Table 1 – List of Respondents

ORGANISATION NAME of RESPONDENT

Scottish Executive Duncan Beamish Jennifer Hamilton Forestry Commission Steve Gregory SEPA Tim Jolley June Graham Rail track Scotland Andy Scobie NFU Scotland Craig Campbell COSLA Kathy Cameron Scottish Power Jane Telfer Scottish Water Annette Wilkinson RSPB Clifton Bain Stirling City Council Alan Speedie Dundee City Council Bryan Harris STEERING GROUP MEMBERS (CONTACTED FOR INFORMATION) SNIFFER Vanessa Kind SEPA Peter Singleton June Graham Scottish Executive Guy Winter Forestry Commission Helen McKay Scottish Natural Heritage Noranne Ellis

Follow-up telephone calls were made to clarify what aspects of the variables and what threshold levels were important to them. However, it became apparent that most of those contacted could not readily provide further information on the importance of changes in the seasonality or threshold levels of the variables. This is not unexpected since the respondents are generally not scientists and their approach to this work is based more on anecdotal evidence of variable value rather than knowledge of significant thresholds. However, many respondents expressed interest in the handbook, even if they were unable to comment in

66 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006 (Appendices) detail on the variables relevant to them. The need to make the handbook readily accessible to non-scientists was stressed by several respondents.

A number of additional variables were suggested by the respondents, since several of these were from the water sector, these include a number of water resource related datasets rather than pure climate variables:

• Snow cover/ski season/snow patch records • Storm index/convective activity – i.e. measure of storm frequency/intensity • Runoff rates or river flow – Peak over threshold (POT) records, monthly means etc. • Groundwater level data • Spring flow records • Dates of first and last frosts of season • First flowering dates and other phenological information • Snow cover days • Wind speed

Table 2 – number of respondents who selected each variable

Variable Response rate Growing season lengths, + start and end dates 10/11 Growing season intensity 10/11 Other temp sums for key/indicative crops 8/11 Soil moisture content or deficit /10/11 PET (potential evapo-transpiration) 9/11 Rainfall return periods 11/11 Derived rainfall variables 10/11 Frost days 10/118 Heat wave duration 9/11 Heating degree days 9/11 Cooling degree days 8/11 NAO index 10/11 Sea level rise 10/11

67 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006 (Appendices)

5. FUTURE CLIMATE CHANGE

As stated earlier the aim of this project is to collate available observed data which describes the climate of Scotland and how it has changed over recent decades. Following the analysis of this data it is important to consider any identified trends within the context of the UKCIP02 climate change scenarios. It is useful to be aware of other data which relates to scenarios of the future climate of Scotland.

Global climate models are currently the only scientific tool available for predicting changes in climate and, in particular, the large scale patterns of change. These models require a large computing resource and hence are run at relatively coarse resolution. For example, the current Hadley Centre global model, HadCM3 represents the British Isles with a horizontal resolution of approximately 300km which means that only two grid squares cover Scotland. For greater detail, and for impact studies, higher resolution regional models can be ‘embedded’. This means that a regional model, which represents a limited area of the globe at higher resolution, takes all information for the surrounding area from a global climate model. The version of the Hadley Centre regional model used to produce the UKCIP02 scenarios, HadRM3, has a horizontal resolution of 50km. The regional model prediction shows much more detail than the global model and is able to better represent extremes.

Regional models are able to better capture extreme weather because not only can they represent smaller scale weather features but they also have a much better representation of orography. For example, the mountains of Scotland cannot be represented in the global model at all; the entire country is represented by two grid boxes. In the UKCIP02 scenarios, the 50km regional climate model (RCM) permits the mountains of Scotland to be partially resolved which results in increased spatial variation of rainfall. The model used for the British Irish Council report (Jenkins et al, 2003) was a single run of a 25 km RCM, the finer resolution resulting in an ability to represent the varied topography of Scotland more accurately. The increased resolution also permitted some of the Scottish islands to be resolved, and included in climate modelling studies, for the first time.

Every climate model, global or regional, produces a wealth of data. To achieve maximum value this data must be used in the context of the uncertainties (to be discussed later in the technical handbook), and it must also be remembered that not all climate model data have been validated against observed climate. The observational datasets listed in this study can all be used to validate the performance of models.

All modelled data from the global model, HadCM3, are available from present day to 2100 (and beyond in some cases) under a number of emissions scenarios, however as Scotland is represented by two grid boxes in the global model this is likely to be of limited practical use in studies of Scottish climate. The RCM (both 50km and 25km) has been run for two thirty year periods, a present day time-slice (1961 to 1990) and a future time-slice (2071 to 2100). These represent the current and projected future climates. Daily data are available throughout both of these periods. Many physical parameters are available, such as precipitation, snowfall, humidity, temperature, etc, with a representative list being given in Table A.1 of the UKCIP02 report (Hulme et al, 2002). Although this list is for monthly mean data, and is by no means exhaustive, it is indicative of the parameters available from the Hadley Centre model integrations.

Aggregation of data to larger geographical areas will diminish the impact of extreme events. However, understanding the regional impact of climate change can be usefully achieved by assigning sub-regions which exhibit similar impacts. In the case of Scotland it may be useful to consider three such sub-regions. Taking average changes over the mountainous west coast, south-eastern Scotland, and northern Scotland may prove a valuable descriptor of changes such as summertime precipitation under different emissions scenarios. Such regions, defined by their climatological characteristics, are used in the Met Office’s datasets (listed in Appendix 1). Other definitions of regions exists, such as the four Scottish regions

68 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006 (Appendices) defined by Gregory et al (1991) however, for consistency with the available data, this project will be restricted to the Met Office’s three.

The full range of marker scenarios must also be considered, where possible, as each is considered to be of equal likelihood. Consideration of all of the marker scenarios provides a useful guide as to the range of plausible possible futures as climate changes.

69 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006 (Appendices)

6. RECOMMENDATIONS

The selection of variables for inclusion in the handbook is dependent upon a number of factors. The selection will be based upon

• Realised and future changes • Data availability – past, present and future • Applicability to a broad audience • Ease of calculation • Budgetary and time constraints

The selection of variables also needs to take cognisance of the sample size of Scottish representatives surveyed and the industry biases that they may have. While the survey should be used as a guide it should not dictate the content of the handbook. For example, the eagerness to see the compilation of rainfall returns periods may be impractical owing to computational demand, budgetary constraints and their suitability for representing climatic change. It must also be recognised that the analysis of realised changes is limited by data availability. The same could, of course, be said of the variables in future datasets.

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7. REFERENCES

Gregory, J. M., P. D. Jones and T. M. L. Wigley (1991) Precipitation in Britain: an analysis of area-average data updated to 1989. Int. J. Climatol., v.11, n.3 pp.331-345

Jenkins, G.J., C Cooper, D Hassell and R Jones (2003) Scenarios of climate change for islands within the BIC region. Published by the Met Office, Bracknell, July 2003.

NERC (1975) Flood Studies Report, Institute of Hydrology, Wallingford, Oxford

Stott, P.A.(2003) Attribution of regional-scale temperature changes to anthropogenic and natural causes, Geophys. Res. Lett., v. 30, n.14, p.1728

71 SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006 (Appendices)

Appendix 1, Annex 1 : Datasets of observed current climate.

See source websites for full details of each dataset, licensing, etc

Point datasets

Table A1.1 Temperature Table A1.2 Rainfall Table A1.3 Sunshine Table A1.4 Marine

Gridded data

Table A1.5 Temperature Table A1.6 Rainfall Table A1.7 Snow Table A1.8 Sunshine Table A1.9 Marine Table A1.10 Other elements

Table A1.11 Other datasets

Key

M = monthly average S = seasonal average A = annual average V = various recording periods

* stored as an image ** dependent upon licensing conditions.

72 SNIFFER Project CC03: Patterns of climate change across Scotland (appendices) April 2006

Table A1.1 Temperature

Dataset Start End Mean Location Source Web address Licence? Cost? Date Date period Maximum temperature 1930 2004 M Lerwick Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No

Maximum temperature 1873 2004 M Stornoway Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No Airport Maximum temperature 1931 2004 M Tiree Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No

Maximum temperature 1959 2004 M Braemar Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No

Maximum temperature 1957 2004 M Leuchars Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No

Maximum temperature 1959 2004 M Paisley Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No

Minimum temperature 1930 2004 M Lerwick Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No

Minimum temperature 1873 2004 M Stornoway Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No Airport Minimum temperature 1931 2004 M Tiree Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No

Minimum temperature 1959 2004 M Braemar Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No

Minimum temperature 1957 2004 M Leuchars Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No

Minimum temperature 1959 2004 M Paisley Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No

Grass minimum temp 1930 2004 M Lerwick Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No

Grass minimum temp 1942 2004 M Stornoway Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No Airport Grass minimum temp 1931 2004 M Tiree Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No

Grass minimum temp 1959 2004 M Braemar Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No

Grass minimum temp 1957 2004 M Leuchars Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No

73 SNIFFER Project CC03: Patterns of climate change across Scotland (appendices) April 2006

Maximum temperature 1959 2004 M Paisley Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No

Maximum temperature 1961 1990 30-year Various Met Office http://www.metoffice.gov.uk/climate/uk/averages/19611990/index.html No No (M/A) (16 stations) mean minimum 1961 1990 30-year Various Met Office http://www.metoffice.gov.uk/climate/uk/averages/19611990/index.html No No temperature (M/A) (16 stations) days of air frost 1961 1990 30-year Various Met Office http://www.metoffice.gov.uk/climate/uk/averages/19611990/index.html No No (M/A) (16 stations) mean maximum 1971 2000 30-year Various Met Office http://www.metoffice.gov.uk/climate/uk/averages/19712000/index.html No No temperature (M/A) (16 stations) mean minimum 1971 2000 30-year Various Met Office http://www.metoffice.gov.uk/climate/uk/averages/19712000/index.html No No temperature (M/A) (16 stations) days of air frost 1971 2000 30-year Various Met Office http://www.metoffice.gov.uk/climate/uk/averages/19712000/index.html No No (M/A) (16 stations)

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Table A1.2 Rainfall

Dataset Start End Mean Location Source Web address Licence? Cost? Date Date period Total rainfall 1930 2004 M Lerwick Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No

Total rainfall 1873 2004 M Stornoway Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No Airport Total rainfall 1931 2004 M Tiree Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No

Total rainfall 1961 2004 M Braemar Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No

Total rainfall 1957 2004 M Leuchars Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No

Total rainfall 1959 2004 M Paisley Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No

Total rainfall 1961 1990 30-year Various Met Office http://www.metoffice.gov.uk/climate/uk/averages/19611990/index.html No No (M/A) (16 stations) Days of rain >1mm 1961 1990 30-year Various Met Office http://www.metoffice.gov.uk/climate/uk/averages/19611990/index.html No No (M/A) (16 stations) Total rainfall 1971 2000 30-year Various Met Office http://www.metoffice.gov.uk/climate/uk/averages/19712000/index.html No No (M/A) (16 stations) Days of rain >1mm 1971 2000 30-year Various Met Office http://www.metoffice.gov.uk/climate/uk/averages/19712000/index.html No No (M/A) (16 stations)

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Table A1.3 Sunshine

Dataset Start End Mean Location Source Web address Licence? Cost? Date Date period Total sunshine duration 1930 2004 M Lerwick Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No

Total sunshine duration 1929 2004 M Stornoway Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No Airport Total sunshine duration 1928 2004 M Tiree Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No

Total sunshine duration 1961 2004 M Braemar Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No

Total sunshine duration 1957 2004 M Leuchars Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No

Total sunshine duration 1959 2004 M Paisley Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No

Total sunshine duration 1961 1990 30-year Various Met Office http://www.metoffice.gov.uk/climate/uk/averages/19611990/index.html No No (M/A) (16 stations) Total sunshine duration 1971 2000 30-year Various Met Office http://www.metoffice.gov.uk/climate/uk/averages/19712000/index.html No No (M/A) (16 stations)

76 SNIFFER Project CC03: Patterns of climate change across Scotland (appendices) April 2006

Table A1.4 Marine

Dataset Start End Mean Location Source Web address Licence? Cost? Date Date period Sea surface temperature 1949 2004 D Keppel Pier, BODC http://www.bodc.ac.uk Yes Yes Clyde 16 Moored current meters 1968 - - various CEFAS http://www.cefas.co.uk

North Sea Groundfish survey 1982 1991 A North Sea CEFAS http://www.cefas.co.uk (various) Western European Shelf 1982 - A W. European CEFAS http://www.cefas.co.uk Groundfish survey Shelf

MLA moored self-recording 1967 - V Various FRS, Marine Lab., www.bodc.ac.uk/services/current_meter_search/ Yes Yes instrument data17 Aberdeen current_meter_search.html

18 MLA hydrographic data 1893 - V Various FRS, Marine Lab, http://www.ices.co.uk No Aberdeen MLA Thermosalinograph 1970 - V Various FRS, Marine Lab., http://www.ices.co.uk No 19 Data Aberdeen

UK National Databank of 1842 - V Scottish coasts BODC http://www.bodc.ac.uk Yes Yes Coastal Tide gauge data

UK National Databank of 1967 - V NE Atlantic and BODC http://www.bodc.ac.uk Yes Yes Moored Current Meter Data continental shelf

UK National Databank of 1975 - V NE Atlantic and BODC http://www.bodc.ac.uk Yes Yes CTD/STD profiles20 continental shelf

UK classical hydrographic 1893 - V UK Shelf seas BODC or ICES http://www.bodc.ac.uk or http:// www.ices.dk/ocean Yes Yes station data set21

16 Current speed and direction, also temperatures, pressure and conductivity recorded 17 Dataset updated annually. Ocean currents, ocean temperature, ocean circulation, current speed and direction, temperature, conductivity (salinity), pressure. 18 Dataset updated annually. Pressure, temperature, salinity, oxygen, phosphate, nitrate, silicate, ammonia, chlorophyll-a, phaeopigments, particulate organic carbon and particulate organic nitrogen. 19 Updated 6-8 times a year. Temperature, salinity, fluorescence and occasionally soundings logged with data, time and position (as latitude and longitude). 20 Conductivity/salinity, temperature, depth/pressure, occasionally oxygen, transmittance, chlorophyll fluorescence 21 Temperature, salinity, nutrients, oxygen, pH, alkalinity, and chlorophyll-a.

77 SNIFFER Project CC03: Patterns of climate change across Scotland (appendices) April 2006

UK National Databank of 1955 1985 V Various BODC http://www.bodc.ac.uk Yes Yes Wave Data

UK World Ocean Circulation 1991 - V North Atlantic BODC http://www.bodc.ac.uk Yes Yes Experiment (WOCE) data set22 Mean Sea Level 1933 - M/A Various23 Permanent Service http://www.pol.ac.uk/psmsl No No for mean Sea Level

22 Temperature, salinity, dissolved oxygen, nutrients, tracers, carbonic system, bathymetry, surface meteorology, current profiles 23 Scottish locations included Lerwick, Sullom Voe, Wick, Invergordon, Moray Firth, Buckie, Aberdeen, Dundee, Rosyth, Leith, Dunbar

78 SNIFFER Project CC03: Patterns of climate change across Scotland (appendices) April 2006

Table A1.5 Temperature

Dataset Start End Mean Spatial Source Web address Licence? Cost? Date Date period scale Maximum temperature * 1961 1990 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No (m/s/a) Office Minimum temperature * 1961 1990 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No (m/s/a) Office Mean temperature * 1961 1990 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No (m/s/a) Office 30cm soil temperature * 1961 1990 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No (m/s/a) Office Grass minimum 1961 1990 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No temperature * (m/s/a) Office Days of ground frost * 1961 1990 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No (m/s/a) Office Days of air frost * 1961 1990 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No (m/s/a) Office Maximum temperature * 1971 2000 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19712000/mapped.html No No (m/s/a) Office Minimum temperature * 1971 2000 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19712000/mapped.html No No (m/s/a) Office Mean temperature * 1971 2000 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19712000/mapped.html No No (m/s/a) Office 30cm soil temperature * 1971 2000 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19712000/mapped.html No No (m/s/a) Office Grass minimum 1971 2000 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19712000/mapped.html No No temperature * (m/s/a) Office Days of ground frost * 1971 2000 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19712000/mapped.html No No (m/s/a) Office Days of air frost * 1971 2000 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19712000/mapped.html No No (m/s/a) Office Maximum temperature 1914 2000 M 5km Met www.metoffice.gov.uk/research/hadleycentre/obsdata/ukcip/index.html Yes Yes/ Office No** Minimum temperature 1914 2000 M 5km Met www.metoffice.gov.uk/research/hadleycentre/obsdata/ukcip/index.html Yes Yes/ Office No**

79 SNIFFER Project CC03: Patterns of climate change across Scotland (appendices) April 2006

Mean temperature 1914 2000 M 5km Met www.metoffice.gov.uk/research/hadleycentre/obsdata/ukcip/index.html Yes Yes/ Office No** No. of days of air frost 1961 2000 M 5km Met www.metoffice.gov.uk/research/hadleycentre/obsdata/ukcip/index.html Yes Yes/ Office No** No of days of ground 1961 2000 M 5km Met www.metoffice.gov.uk/research/hadleycentre/obsdata/ukcip/index.html Yes Yes/ frost Office No** Annual extreme 1961 2000 A 5km Met www.metoffice.gov.uk/research/hadleycentre/obsdata/ukcip/index.html Yes Yes/ temperature range Office No** Heating degree days 1961 2000 A 5km Met www.metoffice.gov.uk/research/hadleycentre/obsdata/ukcip/index.html Yes Yes/ Office No** Growing degree days 1961 2000 A 5km Met www.metoffice.gov.uk/research/hadleycentre/obsdata/ukcip/index.html Yes Yes/ Office No** Growing season length 1961 2000 A 5km Met www.metoffice.gov.uk/research/hadleycentre/obsdata/ukcip/index.html Yes Yes/ Office No** Summer heat wave 1961 2000 A 5km Met www.metoffice.gov.uk/research/hadleycentre/obsdata/ukcip/index.html Yes Yes/ duration Office No** Winter heat wave 1961 2000 A 5km Met www.metoffice.gov.uk/research/hadleycentre/obsdata/ukcip/index.html Yes Yes/ duration Office No** Summer cold wave 1961 2000 A 5km Met www.metoffice.gov.uk/research/hadleycentre/obsdata/ukcip/index.html Yes Yes/ duration Office No** Winter cold wave 1961 2000 A 5km Met www.metoffice.gov.uk/research/hadleycentre/obsdata/ukcip/index.html Yes Yes/ duration Office No** Mean temperature area 1914 2000 M Scotland Met http://www.metoffice.gov.uk/climate/uk/seriesstatistics/scottemp.txt No No series Office Highest maximum 1961 1990 Jan/Jul 5km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No temperature * Office Lowest maximum 1961 1990 Jan/Jul 5km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No temperature * Office Highest minimum 1961 1990 Jan/Jul 5km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No temperature * Office Lowest minimum 1961 1990 Jan/Jul 5km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No temperature * Office

80 SNIFFER Project CC03: Patterns of climate change across Scotland (appendices) April 2006

Table A1.6 Rainfall

Dataset Start End Mean Spatial Source Web address Licence? Cost? Date Date period scale Total Precipitation * 1961 1990 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No (m/s/a) Office Days of rain > 0.2mm * 1961 1990 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No (m/s/a) Office Days of rain > 1mm * 1961 1990 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No (m/s/a) Office Total Precipitation * 1971 2000 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19712000/mapped.html No No (m/s/a) Office Days of rain > 0.2mm * 1971 2000 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19712000/mapped.html No No (m/s/a) Office Days of rain > 1mm * 1971 2000 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19712000/mapped.html No No (m/s/a) Office Days of rain > 1mm 1961 2000 M 5km Met www.metoffice.gov.uk/research/hadleycentre/obsdata/ukcip/index.html Yes Yes/ Office No** Days of heavy rain 1961 2000 M 5km Met www.metoffice.gov.uk/research/hadleycentre/obsdata/ukcip/index.html Yes Yes/ >10mm Office No** Total precipitation 1914 2000 M 5km Met www.metoffice.gov.uk/research/hadleycentre/obsdata/ukcip/index.html Yes Yes/ Office No** Max no of consecutive 1961 2000 A 5km Met www.metoffice.gov.uk/research/hadleycentre/obsdata/ukcip/index.html Yes Yes/ dry days Office No** Greatest 5-day 1961 2000 A 5km Met www.metoffice.gov.uk/research/hadleycentre/obsdata/ukcip/index.html Yes Yes/ precipitation total Office No** Rainfall intensity 1961 2000 A 5km Met www.metoffice.gov.uk/research/hadleycentre/obsdata/ukcip/index.html Yes Yes/ Office No** Precipitation area 1914 2000 M Scotland Met http://www.metoffice.gov.uk/climate/uk/seriesstatistics/scottemp.txt No No series Office Days of heavy rain > 1961 1990 Jan/Jul/ 5km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No 10mm* A Office

81 SNIFFER Project CC03: Patterns of climate change across Scotland (appendices) April 2006

Table A1.7 Snow

Dataset Start End Mean Spatial Source Web address Licence? Cost? Date Date period scale Days of snow cover 1961 1990 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No >50% * (m/s/a) Office Days of snow lying * 1971 2000 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19712000/mapped.html No No (m/s/a) Office No of days with snow 1961 2000 M 5km Met www.metoffice.gov.uk/research/hadleycentre/obsdata/ukcip/index.html Yes Yes/ falling Office No** No of days with snow 1961 2000 M 5km Met www.metoffice.gov.uk/research/hadleycentre/obsdata/ukcip/index.html Yes Yes/ cover Office No** Days of heavy rain > 1961 1990 Dec/Jan/ 5km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No 10mm* Feb/S Office

Table A1.8 Sunshine

Dataset Start End Mean Spatial Source Web address Licence? Cost? Date Date period scale Sunshine hours * 1961 1990 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No (m/s/a) Office Sunshine hours * 1971 2000 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19712000/mapped.html No No (m/s/a) Office Cloud cover 1961 2000 M 5km Met www.metoffice.gov.uk/research/hadleycentre/obsdata/ukcip/index.html Yes Yes/ Office No** Mean hours of bright 1929 2000 M 5km Met www.metoffice.gov.uk/research/hadleycentre/obsdata/ukcip/index.html Yes Yes/ sunshine Office No** Sunshine hours areal 1929 2000 M Scotland Met http://www.metoffice.gov.uk/climate/uk/seriesstatistics/scotsun.txt No No series Office

Table A1.9 Marine

Dataset Start End Mean Location Source Web address Licence? Cost? Date Date period HadISST1, sea ice and 1870 2004 M 1 degree Met Office http://www.metoffice.gov.uk Yes Yes/ sea surface temperature No**

82 SNIFFER Project CC03: Patterns of climate change across Scotland (appendices) April 2006

Table A1.10 Other elements

Dataset Start End Mean Spatial Source Web address Licence? Cost? Date Date period scale Days of thunder * 1961 1990 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No (m/s/a) Office Days of thunder * 1971 2000 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19712000/mapped.html No No (m/s/a) Office Mean sea level 1961 2000 M 5km Met www.metoffice.gov.uk/research/hadleycentre/obsdata/ukcip/index.html Yes Yes/ pressure Office No** Vapour pressure 1961 2000 M 5km Met www.metoffice.gov.uk/research/hadleycentre/obsdata/ukcip/index.html Yes Yes/ Office No** Mean wind speed 1969 2000 M 5km Met www.metoffice.gov.uk/research/hadleycentre/obsdata/ukcip/index.html Yes Yes/ Office No** Maximum relative 1961 1990 Jan/Jul 5km Met www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No humidity * Office Minimum relative 1961 1990 Jan/Jul 5km Met www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No humidity * Office Windspeed at 10m * 1961 1990 Jan/Jul/ 5km Met www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No A Office Days of hail * 1961 1990 S/A 5km Met www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No Office

Table A1.11 Other data sources

Dataset Web address Description Integrated Coastal Hydrography http://www.coastalhydrography.com Integrated Coastal Hydrography (ICH) is a practical partnership between the United Project Kingdom Hydrographic Office (UKHO), the Environment Agency, Ordnance Survey and the Maritime and Coastguard Agency (MCA). It aims to produce an on-line database of hydrographic metadata Summary of the climate of http://www.metoffice.gov.uk/climate/uk/location/ Scotland, including extremes scotland/index.html Bathing water data http://www.sepa.org.uk/data/bathingwaters/bw2005/ SEPA's Annual Bathing Water reports and regularly-updated monitoring results for index.htm identified and non-identified waters around the coast of Scotland. 1988 to present. Harmonised monitoring data http://www.sepa.org.uk/data/hm/index.htm The Harmonised Monitoring Scheme for river water quality commenced in 1974. The (water quality) Harmonised Monitoring Scheme is a national archive of water quality data aimed at

83 SNIFFER Project CC03: Patterns of climate change across Scotland (appendices) April 2006

providing information throughout the United Kingdom, including the estimation of river borne input of selected contaminants to the sea. The sampling network including 230 sites, mainly located on major rivers at, or near, the tidal limit. In Scotland there are 58 sites. The National Groundwater Level http://www.nwl.ac.uk/ih/nrfa/groundwater/index.htm The National Groundwater Level Archive (NGLA) is maintained by the British Geological Archive Survey at Wallingford and holds water level data for around 170 wells and boreholes throughout the United Kingdom National Marine Monitoring http://www.cefas.co.uk/monitoring/page-b3.htm The National Monitoring Plan (now called the National Marine Monitoring Programme) Programme (NMMP) was initiated in the late 1980s to co-ordinate marine monitoring in the United Kingdom between a number of organisations. The NMMP aims to detect long-term trends in the quality of the marine environment, to ensure consistent standards in monitoring, to establish appropriate protective regulatory measures, to co-ordinate and optimise marine monitoring in the UK, and to provide a high quality key dataset for key variables. The Department for Environment, Food and Rural Affairs, is a major funder of the NMMP. National River Flow archive http://www.nwl.ac.uk/ih/nrfa/index.htm To service a very broadly-based need for river flow data the UK maintains a network of over 1300 gauging stations. Responsibility for these stations in Scotland rests principally with the Scottish Environment Protection Agency. Data from the UK based measuring authorities now constitute a database of around 50,000 station years of daily and monthly flow data. In addition, monthly catchment rainfall data (mostly derived from data provided by The Met Office) are routinely archived. UK atmospheric deposition data ITE Edinburgh; Contact: Prof. D. Fowler / Mr. R.I. Spatial estimates of pollutant wet and dry deposition, including NO3-, NH4+, NO2, NH3, Smith; [email protected]; O3, total N deposition. Estimates available on a grid scale basis and for different receptor ecosystems within each grid square. Available for 1992 - present for 20km grid squares.

84 SNIFFER Project CC03: Patterns of climate change across Scotland April 2006 (Appendices)

Appendix 1, Annex 2: Stakeholder organisations surveyed

Table A.2.1 Stakeholder organisations contacted

ORGANISATION RESPONSE RECEIVED? Scottish Exec Y Forestry Commission Y SEPA Y Rail track Scotland Y SCOTS (Society of Chief Officers for Transportation in N Scotland) Visit Scotland N Scottish and Southern Electric N Scottish Power Y Scottish Water Y Scottish Enterprise N NFU Scotland Y SAC N RSPB Scotland Y COSLA (Convention of Scottish Local Authorities) Y Highland council N Dundee City Council Y Edinburgh City Council N Perth and Kinross C. N Stirling C Y Aberdeen C N Sustainable Scotland Network N

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86 SNIFFER Project CC03: Patterns of climate change across Scotland April 2006 (Appendices)

APPENDIX 2: A BRIEF DISCUSSION OF UNCERTAINTY IN CLIMATE MODELLING

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A BRIEF DISCUSSION OF UNCERTAINTY IN CLIMATE MODELLING

There are three key areas of uncertainty in climate modelling. These relate to emissions scenarios, scientific uncertainties and the impact of natural variability. i.) Emissions scenarios

Future anthropogenic emissions of gases that alter climate will depend upon the way in which society evolves. There is no way of knowing how population, technology, economic growth, etc., will develop and thus ‘scenarios’ of future development have to be constructed. The IPCC Special Report on Emission Scenarios (SRES, IPCC, 2000) considered four plausible narrative storylines and from these, produced details of a wide range of possible future emissions scenarios, where each scenario associated with a particular storyline is considered a member of that ‘family’. This is illustrated in Figure A1 that shows the CO2 emissions associated with the ‘marker scenario’ for each family, where marker scenarios are considered representative of a storyline.

It is this set of marker scenario which were used in the UKCIP02 report (A1FI, A2, B2 and B1) although they were relabelled as ‘high’, ‘medium-high’, ‘medium-low’, and ‘low’ respectively. As a rough guide, the ’medium-high’ emissions scenario can be considered to approximate to a ‘business as usual’ evolution. It must be noted however that no likelihood of occurrence can be placed upon any of the storylines of emissions scenarios. Although the scenarios diverge very quickly, all are plausible and while they may not be equally probable they are possible, therefore none can be discounted. This is why predictions should always be qualified by saying which scenario of forcing was used when the result was produced.

As predicted climate changes depend upon the scenario of forcing used it is not surprising that a range of possible futures results. When considering the global mean temperature change predicted by a single global model the choice of forcing scenario actually has very little impact over the next fifty years (not shown). It is only in the second half of this century that predictions begin to diverge. This is because of the large thermal inertia of the climate system and the long lifetime of CO2. This means that the changes global climate will experience over the next few decades are already programmed into the climate system because of the emissions of recent decades.

Figure A1. Emissions of carbon dioxide in four of the SRES emissions scenarios. (Source, Hadley Centre Technical Note 44)

88 SNIFFER Project CC03: Patterns of climate change across Scotland April 2006 (Appendices) ii.) Scientific uncertainties

The IPCC Third Assessment Report (IPCC TAR, 2001) included predictions from over thirty models of varying complexity. Each model was run using the same SRES scenarios but each model predicts a different future, and some of the differences are large, much greater than the range introduced by the choice of emissions scenario. These differences are due to the way the models each represent the globe, the processes that are included and the manner in which they are parameterised. Some models have a finer resolution than others and include more complex physical processes. It was not possible, at this time, to say how credible each model was because evaluation is not simple and until recently included some level of subjectivity. It was therefore not possible to discount any of the models. Even the more extreme predictions could be underestimating what will occur because a vital feedback process could be as yet undiscovered and therefore is not represented in the models.

The range of futures predicted by the different models is one of the largest uncertainties in prediction of climate change, however when model predictions are consistent, increased confidence can be placed in the result. For example, all models predict global warming under all scenarios of forcing. Difficulties arise when there is a low level of consistency between model results. Figure 26 of the UKCIP02 report (not shown) illustrates this, comparing changes in winter precipitation over the UK as predicted by nine different global climate models. The models presented in the figure all predict an increase in winter precipitation over Scotland but the range of predicted change is quite large, from just greater than zero to over fifty percent. Given the nature of weather patterns across the UK it is perhaps unsurprising that it is a challenging area to model, a slight shift in the location of a pressure system over the Atlantic can mean that storms may track to the north or south rather than travelling across Scotland. Work is continually being done to validate the representation of current climate by the models and to find plausible reasons for the different climate predictions of models.

The impact of scientific uncertainties can be easily demonstrated by comparing the results of the UKCIP98 report, the 2001 report by Hulme et al and the UKCIP02 report. Each of these publications was based upon Hadley Centre modelling results but in each case a different model was used. UKCIP98 was based upon the Hadley Centre’s HadCM2 global model. Winter precipitation was predicted to increase over Scotland and indeed the increase was seen to persist throughout the year with the summer months also experiencing more rainfall under most of the emissions scenarios by the 2080s. It must be noted however that these results came from a global climate model in which Scotland was represented by only two model grid points.

The UKCIP98 report was followed in 2001 by ‘An exploration of regional climate scenarios for Scotland’ (Hulme et al 2001) presenting results from HadRM2, the Hadley Centre’s regional version of the model used in UKCIP98. Although this model was scientifically the same as the model used in UKCIP98 it had a much greater horizontal resolution of fifty kilometres, so spatial detail of the predicted climate changes over Scotland became possible. In this case only one scenario of emissions forcing (Medium-High, 2080s) was available so a normalising technique was employed to allow the regional model predictions to be compared more easily with those from the global model. It must be remembered that values presented in this report are normalised and so represent the changes that may be expected over Scotland for each degree Celsius increase in global mean temperature. Hence, the size of a predicted change is not directly comparable with either UKCIP98 or the later UKCIP02.

It was found that results were broadly similar to those found in the UKCIP98 report although the spatial resolution permitted identification of an east-west contrast in precipitation changes. In particular, the greatest predicted increase in precipitation occurs over the Western Highlands with increased precipitation throughout the year. However the model also predicted decreased rainfall over eastern Scotland during summer months, a result not seen in the UKCIP98 report. The study also found relatively little difference in the predicted change to precipitation return

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periods between the regional and global models, although the intensity of rainfall is greater in HadRM2.

The results contained within the UKCIP02 report came from the Hadley Centre’s latest regional climate model, HadRM3, based upon the global model HadCM3, the successor to the model used in UKCIP98. Although HadCM3 is scientifically more complex than its predecessor, it cannot be argued that it is scientifically more valid than HadCM2. The models include different parameterisations and thus predict slightly different regional patterns of climate change. This is to be expected. The reports also use slightly different periods (2081 to 2100 in HadRM2 versus 2071 to 2100 in HadRM3) and different emissions scenarios. All of the differences are discussed in Section 7.5 of the UKCIP02 report but the major difference is in summertime rainfall across Scotland with the latest model predicting a widespread drying when HadRM2 predicted generally wetter summers. While some of the differences can be explained by natural variability the major contributing factor is the different large scale circulation patterns established in each model. While many general features of the simulated climate are similar between the models, each predicted climate is modulated (locally and seasonally) by changing patterns of large scale air flow. iii.) Natural variability

The Earth’s climate varies naturally, with the climate system’s internal variability providing year to year and decade to decade change. It is highly likely that at some time in the future there will be periods when this natural variability combines with anthropogenic climate change to produce a period of extreme warming or summer drying while it is equally likely that the two will combine at another time to produce a relatively cold or dry winter. For this reason is it important to consider natural variability when looking at predicted mean climate change.

One technique to address the uncertainty due to natural variability as simulated within climate models is to run an ensemble of integrations. The starting conditions of a model can be ‘perturbed’ slightly which sets a model off on a slightly different, but equally plausible, predictive pathway. This technique effectively introduces new ‘weather’ to the starting conditions, introducing a small but feasible alteration of starting conditions. The difference which results from predictions by members of such an ensemble, in which each member has identical physics, is the modelled representation of natural variability.

The majority of mapped results presented in the UKCIP02 report are for an ensemble mean. Three integrations with slightly perturbed starting conditions where completed for the control period (1961 to 1990) and for the 2080s time-slice with the Medium-High emissions scenario. This means that three sets of thirty year integrations are available for each period. In this way the simulated variability of the modelled present day climate can be more fully assessed and the impact of climate change on variability more fully captured than could be achieved with a single ensemble member.

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APPENDIX 3: GLOSSARY

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GLOSSARY

5DR maximum five-day precipitation amount CDD consecutive dry days (also used in other text to refer to cooling degree-days) CWD(s/w) cold-wave duration (summer/winter half-year). Cold Wave duration = ∑ days with 1961-1990 daily normal - daily T_min > 3 °C for ≥ 6 consecutive days DTR diurnal (or daily) temperature range ENSO El Niño Southern Oscillation ETR extreme temperature range GCM global climate model or general circulation model GDD growing degree days. Growing Degree Days = ∑ daily T_mean – 5 for T_mean > 5 °C. GIS Geographical information system GMT Greenwich mean time GSL growing season length. Growing season length = period (days) bounded by daily T_mean > 5 °C and < 5 °C (after 1st July) for ≥ 6 days HadCM3 A global climate model developed by the Hadley Centre at the Met Office HDD heating degree days. Heating Degree Days = ∑ 15.5 – daily T_mean for T_mean < 15.5 °C hPa hectopascal, a unit of pressure equivalent to a millibar HWD(s/w) heat-wave duration (summer/winter half-year). Heat Wave duration = ∑ days with daily T_max – 1961-1990 daily normal > 3 °C for ≥ 6 consecutive days. IPCC Intergovernmental Panel on Climate Change NAO North Atlantic Oscillation NAO index A measure of the pressure gradient between the Icelandic low and Azores high pressure systems. The index indicates the phase of the NAO. RCM regional climate model RI rainfall intensity SRES Special report on emissions scenarios UKCIP United Kingdom climate impacts programme UKCIP02 Scenarios created in 2002 as part of UKCIP output, using HadRM3, a Hadley regional climate model UKCIP98 Scenarios created in 1998 as part of UKCIP output, using HadCM2, a global climate model WMO World Meteorological Organisation