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Analysis of past weather data shows three distinct types of circulation patterns for the region, classified as W, E and C. The zonal type W is associated with increased precipitation, warm winters and moderately hot summer conditions. Type E is characterised by stable high pressure over the European Territory of Russia (ETR). In winter this is accompanied by cold conditions, and in summer by very hot and cloudless conditions. Type C is characterised by a trough over the ETR, resulting in cyclonic fields over the Volga drainage basin, and bringing precipi-tation and lower air temperatures.
These graphs show the seasonal and inter-annual variations in the frequency of these three basic weather types. Type E is most common and – since the mid-70s when higher precipitation has been observed over the Volga basin – the frequency of this type has been above average. The frequency of types W and C, with which most precipitation is associated, has been below average. Seasonal plots show that type C occurs most frequently in summer, which is when the highest rainfall falls over most of the basin.
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