Regional variability of the mean and extreme characteristics of the present meteorological regime of the eastern part of the Baltic Sea catchment

Abstract

The features of the regional heterogeneity of the modern meteorological regime are assessed, as a refinement of existing estimates of large-scale climate changes – for the eastern part of the Baltic Sea catchment on the example of the Leningrad Region and nearby territories of neighbouring subjects of the Russian Federation (northern part of the region), as well as the Zapadnaya Dvina catchment within the Republic of Belarus (southern part of the region). Significant differences in surface air temperature and snow water equivalent (hereinafter referred to as snow storage) were revealed for the winter period, with similar precipitation, more intense interannual and long-term changes in the southern part of the region. The common feature for the region is the presence of a significant correlation of the long-term January – March atmospheric circulation indices variability only with the variability of surface air temperature, as well as minor differences in the number of anomalous years with similar anomaly amplitudes. Surface air temperature has the greatest contribution to the long-term variability of snow storage everywhere, which is most pronounced in the south of the region. The turning points in the long-term variability of surface air temperature coincide in the north and south of the region, the turning points in the course of total precipitation do not coincide. The number of anomalies (exceeding the standard deviation) in the long-term series of characteristics in the northern and southern parts of the region differ little (9–12 cases in the positive and negative ranges of values) in the absence of coincidences and the similarity of the amplitude of the anomalies. The range of values of extreme threshold values (extreme percentiles) of surface air temperature in the north of the region is lower than the range of values in the south, the variability of small percentiles exceeds the variability of large ones; the rate of long-term increase in average temperatures is accompanied by a significant increase in small percentiles in the north and large percentiles in the south of the region. The values of extreme threshold values of precipitation and their standard deviation vary little across the territory; positive trends in maximums and negative trends in minimum thresholds are small, consistent with a slight increase in mean total precipitation. According to the spatial distribution of average values of snow storage, the values of their extremely small and large threshold values in the north of the region are higher than in the south; in the north of the region, the values of percentiles in the interval 1985–2002 stand out as the lowest.