ANALYSIS OF CORRECTED PRECIPITATION SERIES IN THE VOLGA-URAL BASIN FOR 1961-1990

摘要

For the Volga and Ural basin, monthly precipitation totals corrected by Golubev's method are analyzed for the period 1961-1990. Calculations are performed using daily precipitation at 22 stations averaged over three natural zones: overmoisten-ing and humid (zone Ⅰ), weakly arid and arid (zone Ⅱ), and very arid and dry (zone Ⅲ). The correction factors (K_0) for monthly precipitation show a significant annual cycle with a maximum in winter (40-50% of the long-term mean) and a minimum in summer (9-12% in zone Ⅰ). On average, the corrected annual precipitation is 22% greater than the measured value. Comparison of the annual cycle of corrected monthly precipitation totals from the climatic reference books for 1891-1964 with those corrected by Golubev's method for 1961-1990 has shown that they are rather close. Daily precipitation data are also used to calculate the number of precipitation days prior to precipitation correction and afterward. After the correction was applied, the number of days with precipitation above 0.1 mm increased by 26, 27, and 44% in zones Ⅰ, Ⅱ, and Ⅲ, respectively. This increase is due mainly to the transition of days with traces of precipitation into the category of days with precipitation above 1 mm. Linear trends of corrected and measured precipitation and wind speeds at individual stations and over natural zones for different periods of the annual cycle are estimated. On the whole for the Volga and Ural basin, the corrected precipitation for 1961-1990 decreased by 8% in the cold half of the year and increased by 17% in the warm half of the year and by 5% for the whole year. A statistically significant decrease in the annual mean wind speed is found at 20 out of 22 stations. During the 30-year period, the wind speed decreased by a factor of 1.6,1.2, and 1.3 in zone Ⅰ, Ⅱ, and Ⅲ, respectively.