Современная пространственно-временная структура поля экстремальных осадков на территории Западной Сибири

At the present time, one of the most critical issues in the climate change problem is to assess variability of climatic parameters against variation in their average values. Many researchers note that, in the context of the global warming over the recent decades, extreme events of the climatic regime have become more frequent in most regions. The significant growth of extreme characteristics in the atmospheric precipitation regime against a small increase in average values may aggravate the risks of difficult-to-predict rainfall floods in rivers, flooding of urban areas and agricultural lands, washouts of roads. The following characteristics are used in this study: - number of days with precipitation > 15 mm - Q ; - number of days with precipitation > 5 mm at the negative daily mean temperature - Q . For the study were used: daily meteorological data from the Russian Research Institute of Hydrometeorological Information - the World Data Center (meteo.ru) for 1951-2010, based on 45 stations of Western Siberia. The characteristics mean of the number of days with precipitation, frequency of days with precipitation for a month and a year; maximum continuous periods with extreme precipitation were calculated. The difference between mean values for 1951-1980 and 1981-2010 was calculated at the station for each indicator. The choice of the 30-year period is explained by the fact that 1951-1980 can be taken as the reference period in which there were no significant climate changes in Russia on average. The statistical significance was determined on the basis of t-test. The sequence of data was confirmed to belong to Gauss-Laplace distribution on the basis of the test for concordance. The criteria of the per annum frequency of occurrence do not exceed 3.3 % for Q and 1.5 % for Q (13 and 5 days per year, respectively) in the total number of days in the annual frequency for the 60-year period. The maximum continuity of the number of days with precipitation > 5 mm at the negative daily mean temperature does not exceed 5 days. The average value for the most stations reaches 3-4 days. The maximum continuous period for the criterion Q does not exceed 5 days as well, at the average value of 2-3 days. The distribution for Q in 1981-2010 against 1951-1980 shows that the number of days with precipitation of this level increased by 1-2 days per year over the major part of the territory. The distribution of changes in Q for 1981-2010 as compared with 1951-1980 demonstrates the opposite trends: the zone where the indicator grows (eastern part of the territory) and the zone where the indicator decreases (around the Gulf of Ob and in the Far North of the area). The differences reach 1.5 days per year. The method of principal components (factor analysis) and cluster analysis were used for assessing the synchronism in time and space. The component analysis of the precipitation regime for extremes in the study area shows that this regime is unevenly distributed. This can be associated with the significant effect of the local station conditions on the precipitation regime, the prevalence of different forms of atmospheric circulation and the specifics of the cyclonic activity over the different parts of the selected area. The first two components of precipitation variability make up about 35%. It can be concluded that changes in the precipitation regime of Western Siberia are determined by global climatic events only to the extent of one-third. The information technologies which enable to account for local conditions should be involved for constructing models of the atmospheric precipitation field in this area. Thus, the total share of the interpreted dispersion for fields of criteria Q and Q does not exceed 28-35 % for the whole territory of Western Siberia. Where the results of classification are taken into account, the share of the interpreted dispersion increase up to 40-60 %. The performed classification reflects the increase of synchronism with decreasing the scale of the area.

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