Peculiarities of climate characteristics behavior on the West SiPeculiarities of climate characteristics behavior on the West Siberia territory in the second half of the 20th century: Reanalysberia territory in the second half of the 20th century: Reanalysis and inis and in--situ datasitu dataT.M. Shulgina (T.M. Shulgina (stm@scert.rustm@scert.ru), E.Yu. Genina, E.P. Gordov), E.Yu. Genina, E.P. Gordov

Institute of Monitoring of Climatic and Ecological Systems SB RAInstitute of Monitoring of Climatic and Ecological Systems SB RAS, S, Siberian Center for Environmental Research and Training, Tomsk, Siberian Center for Environmental Research and Training, Tomsk, RussiaRussia

ID 946835ID 946835

ABSTRACTIn recent decades studying of climate changes on the globe became one of the most important reserach. Fromthis point of view, Siberian terrotiry is of particular interest because Siberia is climatically significant regionin Eurasia, it is notable for variety of climate forming factors and contributes substantially into regional andglobal climate processes. This report presents results of analysis of surface air temperature and precipitationbehavior in Siberia in the second half of the 20th century. The analysis was made using ECMWF ERA-40, ERA INTERIM and APHRODITE JMA reanalyses. Presented climatic characteristics are the following: mean values, extremes and characteristics that influence forest ecosystem evolution. Calculations were made using computational unit of information-computational web-GIS system which is developed to analyze and process archives of spatially-distributed environmental data. To reveal dynamics of climatic characteristics, we calculated their trends, assessed statistical significance, as well as compared results obtained from different datasets. We found that ECMWF ERA-40, ERA INTERIM and APHRODITE JMA reanalyses present different patterns for climatic characteristics behavior that poses a problem of correction of existing climate models and adaptation them for Siberian territory in order to take into account regional peculiarities.

DESCRIPTION OF THE WORKAt present there are a large number of papers devoted to studying of temperature regimes in both Eurasia as a whole [1], and in separated regions [2, 3]. These papers present general pattern of air temperature behavior on the territory under study. Also general behavior of precipitation means in the second half of the 20th century was analyzed [ 4-6].However, to understand climatic changes occurring in Siberia, further detailing is needed, which is a subject of the present study.Purpose: Studying temperature and precipitation behavior on the West Siberia territory in the second half of the 20th century based on model data.

Climatic characteristics:• Annual, seasonal and month means of air temperature;• Diurnal and annual air temperature amplitude;• Cold season duration (daily mean air temperature below 0 °С);• Growing season length (daily mean temperature is higher than 5°С, 10 °С and 15°С, respectively);• Annual sum of daily mean temperatures which is higher 5°С and 10 °С, respectively;• Annual, cold and warm season precipitation;• Annual precipitation for days with daily mean temperature higher than 5°С and 10 °С.

Data:• ECMWF ERA-40 Reanalysis: spatial resolution of 2.5°х2.5°, period from 1958 to 2002;• ECMWF ERA INTERIM Reanalysis: spatial resolution of 0.25°х0.25°, period from 1989 to 2009;• APHRODITE JME Project: spatial resolution of 0.25°х0.25°, period from 1958 to 2002.

TEMPERATURE DYNAMICSComparison of main Reanalysis temperature data and data obtained from Siberian weather stations [7] has shown that for the period 1958–2002 only ECMWF ERA-40 data and in-situ data are in a good agreement (Figs.1.a. and 1.b) Therefore we used ERA-40 as the most reliable dataset for analysis. However, processing ECMWF ERA INTERIM Reanalyses reveals some peculiarities in air temperature dynamics which are absent in ECMWF ERA-40 Reanalysis.Mean air temperatures: Trends of annual mean air temperature, calculated on ECMWF ERA-40 Reanalysis for the second half of the 20th century (1958 - 2002), are positive for all West Siberia territory and equal to 0.2-0.53 °С/10 years.

a b cFig.1. Trend of annual mean temperature. a) Weather stations in West Siberia; b) ECMWF ERA-40 Reanalysis. 1958 – 2002; c) ECMWF ERA INTERIM Reanalysis. 1989 – 2009.

Results obtained for the later period (ECMWF ERA INTERIM Reanalysis, 1989 – 2009) are more inhomogeneous. Thus, air temperature increase (0.2-0.5 °С/10 years) is observed in northern and western parts of West Siberia, while in south-eastern part trends are negative (up to – 0.4°С/10 years). Analysis of seasonal and monthly mean temperatures, made on the basis of ECMWF ERA-40 Reanalysis, revealed peculiarities in forming annual dynamicsof this meteorological characteristics. The main contribution is due to winter (0.7-0.9 °С/10 years) and spring (0.5-0.6°С/10 years) warming, while temperature changes in summer and fall are statistically insignificant. In particular, maximum winter warming is observed in the north and east of West Siberia, where trend is 0.5 – 0.75 °С/10 years, whereas in the west cooling is observed (– 0.14 °С/10 years). The pattern is opposite for the period from 1989 to 2009, namely, warming is in the north-west and cooling is in the south-east.

Air temperature extremesExtreme values behavior, namely, daily maximum and minimum air temperatures, were considered in terms of daily and annual temperature amplitude. The results obtained did not present statistically significant changes in temperature extremes’ dynamics.

Fig.6. a) Trend of annual mean of daily temperature range. ECMWF ERA-40 Reanalysis. 1958 – 2002; b) Trend of intra-annual extreme temperature range ECMWF ERA-40 Reanalysis. 1958 – 2002.

a b

It should be noted that climate changes influence biological processes, in particular, forest capability which plays important role in global carbon balance. A number of climatic indicators has been calculated which determine forest ecosystem evolution: warm and growing season length, number of thaw days in winter and frost days in warm season, etc. The main characteristics influencing vegetation are cold season, frostless and growing season length. Cold season length was calculated as follows. Day, when daily mean temperature was below 0 °С and the same temperature was for the next 5 days, was considered as the cold season beginning. Day, when daily mean temperature was above 0 °С and the same temperature was for the next 5 days, was considered as the cold season end. This characteristic was calculated from ECMWF ERA-40 Reanalysis data, its trend was determined as well. This trend shows that cold season length decreases by 1-3 дня/10 years over most part of West Siberia. The exception is the northern part of West Siberia, where insignificant increase of cold season length (1 day/10 years) is observed. Calculation of growing season length was done following the same technique: day, when daily mean temperature was above 5 °С (10 °С) and the same temperature was for the next 5 days, was considered as the growing season beginning. Day, when daily mean temperature was below 5 °С (10 °С) and the same temperature was for the next 5 days, was considered as the growing season end. Trends obtained are presented in Figs. 8.a. and 8.b., respectively. Calculation results have shown significant increase of growing season length for both cases, which is 2-4 days for every 10 years. We also analyzed dynamics of sum of degree day temperature, when daily mean temperatures are higher than 5 °С and 10 °С. Results have shown increase of sum of degree day temperature by 40-70 °С /10 years.

Fig.2. a) Trend of cold season length. ECMWF ERA-40 Reanalysis data. 1958 – 2002. b) Trend of growing season length with daily mean temperature > 5 °С. ECMWF ERA-40 Reanalysis data. 1958 – 2002. c) Trend of growing season length with daily mean temperature > 10 °С. ECMWF ERA-40 Reanalysis data. 1958 – 2002.

a b c

Air temperature characteristics influencing forest ecosystem evolution

PRECIPITATION DYNAMICSAnalysis of annual total precipitation made on the basis of APHRODITE JMA dataset, which is interpolation of weather stations’ measurements, has shown its small decrease in the central part of Siberia. Total precipitation increase by 10-30 mm/10 years is observed in the north and south-east of Siberia. But calculations made on the basis of ECMWF ERA INTERIM for the period from 1989 to 2009 present absolutely opposite pattern for the northern part of Siberia, where total precipitation decreases by 20 mm/10 years.

Fig.4. Trend of annual total precipitation. a) APHRODITE JMA data. 1958 – 2002. b) ECMWF ERA INTERIM Reanalysis. 1989 – 2009.

Trends of total precipitation for cold and warm seasons are inhomogeneous over Siberian territory. Thus, annual total precipitation in south-east part of West Siberia is formed mostly due to total precipitation for warm season that reaches 25 mm / 10 years.It should be noted that APHRODITE JMA precipitation data are measurements interpolated over territory, ERA INTERIM precipitation data are model results. Since time periods for these data are different, we did not compare them directly. We only calculated annual total precipitation from both datasets for common time period and estimated their difference. This difference is significant and reaches 200 mm per year in the south of West Siberia. Such an inconsistence obtained necessitates careful use of, first of all, ECMWF ERA INTERIM precipitation data, comparison of results with observational data, as well as modeling of meteorological fields taking into account regional peculiarities of the region under study.

CONCLUSIONThe study of air temperature and total precipitation dynamics in the second half of the 20th and the beginning of the 21st century has shown that they have inhomogeneous structure. Results obtained from different datasets are different which poses the problem on both inter comparison of these datasets and comparison them with weather stations data for West Siberia territory. Comparison of total precipitation presented by datasets ECMWF ERA INTERIM and APHRODITE JMA for common time period has shown essential data distinctions reaching 200 mm per year. Such an inconsistence obtained necessitates careful use of, first of all, ECMWF ERA INTERIM precipitation data, comparison of results with observational data, as well as modeling of meteorological fields taking into account regional peculiarities of the region under study. Dynamics of climatic characteristics influencing ecosystem evolution revealed decrease of cold season length over most part of West Siberia territory by 1-3 days/10 years and increase of growing season length by 2-4 days per 10 years. All above facts indicate that for this territory it is necessary to develop a new regional high-resolution climate model and using this model to obtain reliable archive of meteofields. Such an archive should be a basis for detailed analysis of contemporary climatic changes in Siberia. AcknowledgementsThe work was partially supported by RFBR (grant No.10-07-00547), SB RAS Program (projects 4.31.1.5 and 4.31.2.7) and Integration projects Nos. 4, 50 and 66.References:1. Groisman P. and Soja A. Ongoing climatic change in Northern Eurasia: justification for expedient research. Environ. Res. Lett. 2009.

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