No. 12/2016 ISSN 2387- 4201 Climate MET report *150 years Homogenization of daily precipitation in Norway Elin Lundstad Meteorologisk institutt Oslo Bergen Tromsø Meteorological Institute P.O. Box 43 Blindern Allégaten 70 P.O. Box 6314, Langnes Org.no 971274042 0313 Oslo, Norway 5007 Bergen, Norway 9293 Tromsø, Norway [email protected] T. +47 22 96 30 00 T. +47 55 23 66 00 T. +47 77 62 13 00 www.met.no Abstract Title Date Homogenisation of daily precipitation in Norway 2016-05-31 Section Report no. Climate data and spatial analysis section No. 12/2016 Author(s) Classification Elin Lundstad ● Free ○ Restricted Client(s) Client's reference Statkraft Gastón Santisteban-Martinez Abstract When assessing trends and variability of climatic time series it is necessary to ensure that these only represent a climate signal, and that the series not are influenced by external factors such as station relocations, instrumentation changes and changes in the surroundings. To check this, the series should undergo a homogenization analysis, where such inhomogeneities are identified and adjusted. This report presents such an analysis for five Norwegian precipitation series applying three different homogenization software’s with different time resolution; HOMER, MASH and RHtests_dlyPrcp. HOMER is applied to detect homogeneity breaks for annually series, while MASH 3.03 is applied to adjust these breaks in monthly time series, and RHtests_dlyPrcp is applied to adjust these breaks in daily time series. Five precipitation series representing different energy consumption regions in Norway are successfully homogenized; Fokstua, Sauda, Takle, Mo i Rana and Bardufoss. The study show that HOMER, MASH 3.03 and RHtests_dlyPrcp are strong tools and well suited for such analyses. The three different methods show both agreements and differences in the results. Much of the differences lay in challenges with raw data, E.g. Mo i Rana. Keywords Daily Homogenization, Homer, MASH 3.03, RHtests_dlyPrcp, homogeneity 2 Disiplinary signature Responsible signature Table of contents Innhold 1 - Introduction ........................................................................................................................... 5 2 - Background .......................................................................................................................... 10 3 - Methods and approach ....................................................................................................... 12 HomeR ............................................................................................................................... 13 MASH v3.03 ....................................................................................................................... 13 RHtests_dlyPrcp ................................................................................................................ 14 4 - Locations and networks ..................................................................................................... 16 I. Fokstua ............................................................................................................................... 18 16610 Fokstua ................................................................................................................... 18 Fokstua network ............................................................................................................... 20 II. Sauda ................................................................................................................................ 22 46610 Sauda ...................................................................................................................... 22 Sauda network .................................................................................................................. 24 III. Takle ................................................................................................................................. 26 52860 Takle ....................................................................................................................... 26 Takle network ................................................................................................................... 28 IV. Mo i Rana ......................................................................................................................... 31 79480 Mo i Rana III ........................................................................................................... 31 Mo i Rana network ............................................................................................................ 33 V. Bardufoss .......................................................................................................................... 36 89350 Bardufoss ............................................................................................................... 37 Bardufoss network ............................................................................................................ 37 5 - Results ................................................................................................................................. 40 I. Fokstua ............................................................................................................................... 40 Annual homogeneity analysis ........................................................................................... 42 Seasonal homogeneity analysis ........................................................................................ 42 Homogenization of daily Precipitation ............................................................................. 44 II. Sauda ................................................................................................................................ 47 3 Annual homogeneity analysis ........................................................................................... 48 Seasonal homogeneity analysis ........................................................................................ 49 Homogenization of daily Precipitation ............................................................................. 51 III. Takle ................................................................................................................................. 53 Annual homogeneity analysis ........................................................................................... 54 Seasonal homogeneity analysis ........................................................................................ 55 Homogenization of daily Precipitation ............................................................................. 57 IV. Mo i Rana ......................................................................................................................... 60 Annual homogeneity analysis ........................................................................................... 61 Seasonal homogeneity analysis ........................................................................................ 62 Homogenization of daily Precipitation ............................................................................. 64 V. Bardufoss .......................................................................................................................... 66 Annual homogeneity analysis ........................................................................................... 66 Seasonal homogeneity analysis ........................................................................................ 67 Homogenization of daily Precipitation ............................................................................. 69 6 - Conclusions .......................................................................................................................... 73 Acknowledgements .................................................................................................................. 76 References ................................................................................................................................ 77 4 1 - Introduction Homogeneous time series of weather elements are essential for studies of climatic fluctuations and changes. When analysing trends and variability of climatic time series will the accuracy and consistency of the underlying observations be of extreme importance. A homogenous representation of climate only exists when variations in the time series are only results of variations in weather and climate (Easterling et al, 1996). Changes in the technical and/or environmental conditions such as relocations, change in instruments and sensors, change of observers, change of observing practices, new buildings etc. at observation stations might seriously affect the measurements in such a way that sudden shifts (homogeneity breaks) in the time series will be introduced. Other conditions such as land use changes, urban development and changes in vegetation and built environment introduce trends in the time series that might deviate from the regional climate characteristics. Analysing and correcting for such external influences to achieve homogeneous climatic time series is therefore necessary before making an assessment of climatic change. This report presents the results for homogeneity analyses of daily precipitation series for five locations in Norway having different measurement challenges: This study is a part of the MIST-2 project, which is collaboration between Statkraft and MET. The aim of this study is to develop adjustment/homogenization