RURAL AFFAIRS AND ENVIRONMENT COMMITTEE

SUBMISSION FROM THE METEOROLOGICAL OFFICE

Introduction The is a Trading Fund Agency owned by MOD. It is a world leading organisation, both in the field of forecasting and climate prediction1, operating on a 24/7 basis with the highest standards of operational resilience. Responsible for providing forecasts on all timescales (from an hour ahead to 100+ yrs), the Met Office is uniquely positioned to support the Scottish Government’s response to changing incidence of events due to climate change. It is responsible - through its Public Weather Service - for providing the National Severe Service (NSWWS) for the whole of the UK.

Unlike many other nations in Europe where weather and forecasting and warning are integrated into a single meteorological and hydrological agency, the Met Office has no direct responsibility for river or coastal flood forecasting. In Scotland, river (fluvial) flood forecasting is provided by the Scottish Environment Protection Agency (SEPA), with whom the Met Office works closely, providing daily rainfall and general weather forecast inputs, together with rainfall data for the Flooding Early Warning System (FEWS).

The Met Office also provides tide and surge warnings for the service introduced by SEPA in 2007. The historical data required by SEPA to develop an effective coastal system is not available though it is understood that investment in this initiative would allow development of the modelling capability required. Currently no agency provides warnings of localised flash flooding (also known as pluvial flooding), although the Met Office will give an indication of such risks alongside its weather forecasts.

Current weather and flood forecasting capability The Met Office routinely utilises three atmospheric forecast models over land: a Global model at 40km resolution; a North Atlantic and European (NAE) model at 12km resolution, and a fine scale UK model at 4km resolution. The regional models are deployable and can be run for any location in the world in support of military and commercial customers. In addition, the Met Office can also run a model at 1.5km resolution (used to significant benefit during the summer 2007 in England) but usage is restricted by available supercomputer power. The Met Office has also introduced a probabilistic, or ensemble, system of forecasting using multiple model scenarios to simulate and quantify uncertainty. This system currently has a 24 km resolution.

Weather provide the ability to detect the areal coverage of in real time. Improvements are being made to the Scottish network as part of a commercial arrangement with Scottish Power. The first of

1 A recent independent review of the Met Office Hadley Centre, commissioned by Defra and MoD, concluded that the Hadley Centre was at the pinnacle of world climate science. The review is available at: http://www.defra.gov.uk/environment/climatechange/research two new radars recently became operational at Holehead, near Kilsyth and the second, at Munduff Hill, south of Perth, is expected to become operational in the next few months. The updated network will improve weather radar coverage over the main centres of population in Scotland and is sufficient for across the UK. However, gaps in coverage – notably Moray – is such that the resolution is less than optimal for the fine detail required in flood modelling.

Because weather radars have high running costs, the Met Office has always sought partners willing to share the expense; for example the Environment Agency meets half the running costs of 8 radars in England and Wales and the Royal Navy contributes towards the running costs for 2 radars. The Met Office is currently providing advice to Shetland Islands Council on the viability of a local radar installation ahead of their expected submission on the issue to the Scottish Government.

Climate change may mean we see more intense severe weather events. Although any specific individual event cannot, and should not, be attributed to climate change, we are able to make statements about the likelihood of such events altering as a result of climate change. Broadly speaking, climate change in Scotland is predicted to produce wetter winters and drier summers with the potential for increasing intensity of severe weather events.

It is likely that there will be an increase in the proportion of summertime precipitation falling as intense . Short period intense events tend to cause local flash floods. In all UK regions there is evidence of greater increases, or smaller decreases, in precipitation for those extremes that are rarest during summer (i.e. the most intense).

Confidence in climate model projections Although there is a general consensus on the broad features of expected climate change, there are still uncertainties, particularly when considering how the climate may change locally. Although climate models capture the key processes identified as important for climate change, it is not possible to represent the full complexity of the climate system. Generally we use the ability of a model to reproduce the climate of the recent past as an indicator of its likely skill in predicting the future.

Natural variability of the atmosphere is a further source of uncertainty. For example, the overall weather pattern that caused the flooding in the UK this summer was broadly consistent with conditions during previous La Nina events, although with the low pressure situated slightly further south. This weather pattern is not associated with climate change. Nevertheless, the amount of rainfall could have been larger because of climate change. In particular, warm sea surface temperatures in the vicinity of the UK this summer probably contributed to the high levels of atmospheric moisture. Future projections will in part reflect natural variability and it is important to distinguish this from an underlying shift in the climate caused by increased greenhouse gases. In addition, natural variability is a significant factor when considering extreme events on a local scale.

Although we are able to make confident statements about increases or decreases in extreme precipitation in some regions (greater risk of heavy rainfall across the UK in winter and relatively greater increases in rainfall in the most intense events), the magnitude of these changes remains uncertain, especially so in summer as central Europe and the UK lies within a transition zone between expected increased and decreased precipitation.

The past is no longer an adequate guide to the future. There is significant uncertainty over the impact of climate change on flooding events and the probability of them occurring over any given period. As climate research develops, and higher resolution models can be run, there will be increased certainty about regional scale impacts and its effect on flooding. This is important because, under a changing climate, the use of return periods2 (based on previous climatology) for deciding on national infrastructure may not be the most appropriate mechanism; decisions should draw heavily on the best available regional climate predictions.

Research developments in weather forecasting and their impact on flood forecasting Higher resolution forecasting High resolution modelling enables forecasts to become more precise about the weather expected in any locality. The results of our research are extremely promising. The graphic below, for example, shows the potential benefit of higher resolution models by retrospectively applying them to the major flooding event in Carlisle in January 2005. It shows how an increase in forecast model resolution from 12Km (b) to 1Km (c) provides a much increased improvement in accumulated precipitation when compared to observations (a).

(a) observed/measured rainfall (b) 12km resolution forecast (c) 1km resolution forecast

Probability forecasting Due to the chaotic nature of the atmosphere, the further in advance forecasts are made, the more small scale weather features become unpredictable. The severity of this unpredictability depends on the particular weather pattern and

2 A return period denotes a recurrence interval. It is a statistical measure of how often an event of a certain size is likely to happen. For many of the recent rainfall events return periods were greater than 200 years. location. Consequently, although we can provide a “best” forecast it is not possible to indicate how likely this really is. This is particularly important for severe events where the chosen response is likely to vary with the confidence associated with the forecast. In response to this problem we developed ‘ensemble’ forecasting techniques whereby our models are run a number of times with varying initial conditions. This provides a range of solutions and allows us to estimate the probability of an event occurring. Greater use of probabilistic forecasting techniques in principle allows more informed decision making – particularly for emergency response organisations. For example, a 25% chance of an event occurring may require a different response to a 75% chance. Normally, probability increases as an event gets closer, so the customer response process should be able to react to changing uncertainty.

Improved weather forecasts will lead to improved flood forecasts. Both of these research advances will lead to significant improvements in the information available from Met Office forecasts. We are now looking towards combining the ensemble approach with the high resolution model to look at forecasting the probability of intense local rainstorms. This combination of high resolution modelling and probabilistic ensemble forecasting is very important – neither approach alone will give both confidence in the predicted weather or the precision in the detailed location.

These research advances require substantial increases in computer power before they can be implemented in routine operational forecasting. In 2009 we expect to be able to purchase a new supercomputer with sufficient power to implement a UK scale 1.5km high resolution forecast model and a small ensemble model with a 12km resolution. Further funding would be needed to fully realise the benefits (better pinpointing of areas at risk) that can be delivered through operational use of a 1km ensemble.

Integrated models will increase the effectiveness of warnings The Met Office is developing its range of ensemble based forecasting techniques to provide a probabilistic framework within which to deliver enhanced decision support tools to government agencies. Development of these tools will require close cooperation between agencies. Integration of ensemble weather forecast and river models would provide more reliable river flood forecasts at extended lead times.

The Met Office currently provides 6hrly forecasts to SEPA for use in the FEWS model. The underlying model is capable of ingesting ensemble forecasts, which, in combination with higher resolution deterministic forecasts will increase the precision in flood forecasts in a locality as well highlight the confidence in the broad pattern. An operational system in Holland is already utilising both techniques. The Met Office is committed to working with SEPA and other agencies in Scotland and the rest of the UK to investigate the integration of ensemble weather forecast and river models to provide more reliable river flood forecasts at extended lead times.

Service Delivery The Met Office has very strong links with UK’s emergency response infrastructure, its customers (both government and private sector) and the general public, through its role as the National Weather Service and the body responsible for the NSWWS. It also has well established and trusted mechanisms for communicating severe weather warnings in particular through our offices in Exeter and Aberdeen, its website and its partnership with the BBC. The Met Office also has a number of Public Weather Service (PWS) Advisors -established in response to the Civil Contingencies Act (2004) - to provide advice and assistance to the resilience community on all weather- related issues. There are currently ten such Advisors covering the UK, two of whom are based in and cover Scotland.

Lessons learned from previous events A notable lesson to emerge from the flooding events experienced in England this summer, was that although the communication of warnings took place successfully, there was evidence that the underlying message was confused for a number of reasons:

a. individuals and agencies can confuse severe weather warnings and flood warnings; b. some organisations or individuals look to one organisation for warnings – on occasions customers expected flood briefings as well as weather warnings from the Met Office; c. although severe weather and flooding are linked they do not necessarily occur at the same time (for example the Met Office web site showed no weather warnings at a time when parts of the UK were experiencing severe flooding).

Although lessons learned exercises undertaken by regional authorities highlighted Met Office forecasts as being of high quality, it was generally acknowledged that the fragmented responsibilities for warnings hinder understanding and therefore response.

Improvements to the NSWWS The Met Office is improving its NSWWS for winter 2007-08. In short, the improved service will differentiate between severe3 and extreme4 weather events and provide advisory messages on the Met Office website where the risk of severe/ is between 20 and 60 per cent. There will also be a new web based “traffic light” type alert system.

Very High Very Low Low Moderate High Risk/ Confidence ≥80% <20% ≥20<40% ≥40<60% ≥60<80% Including

3 Severe weather – these events are not unusual and are experienced on a number of occasions throughout the year, but more commonly winter months. They will impact on individual areas, but often not significantly. 4 Extreme weather – these events are unusual and only happen around 3 or 4 times per year. They have a significant impact on infrastructure and may lead to casualties. Events this year include 18th Jan , 8th Feb and flooding in June/July.

flash messages

Severe Event GREEN GREEN YELLOW AMBER AMBER

Extreme Event GREEN YELLOW AMBER RED RED ‘unusual weather’

As a result of these improvements the risk of severe and extreme weather events will be highlighted earlier (up to 5 days ahead) and during normal working hours (currently the Met Office has to wait for 60% confidence before issuing warnings, which could take place outside of normal working hours). In addition, emergency planners should better be able to forward plan and increase (or decrease) mitigation actions as an event approaches.