ИСТИНА

The main purpose of the work is establishing linear trend and study of spatial-temporal variation of the monthly mean river discharge of the Belaya River basin of Bashkiria based on correlation analysis. As the basis for analysis, the data measured in the following hydrological stations of the Federal Service for Hydrometeorology and Environmental Monitoring (Bashkir Department, “BashUGMS”) used are 1) Nugush river (Novoseitovo village, 1936-1999); 2) Nugush river (Andreevskii, 1971-1999); 3) Ashkadar river (Novofedorovka, 1971-1999); 4) Inzer river (Azovo, 1958-1999); 5) Urshak river (Lyakhovo, 1949-1999); 6) Chekmagush river (Chekmagush, 1967-1999); 7) Chermasan (Novoyumranovo, 1957-1999); 8) Sterlya river (Otradovka, 1942-1999); 9) Yuruzan river (Chulpan, 1957-1999); 10) Yuruzan river (Atnyash, 1963-1999). The establishment of the low-frequency (long-term) component of the discharge oscillation of the main inflows of the Belaya basin was carried out using a method of differential-integral curves (DIC). By means of the method, the discharge cycles of the 11 and 22 year longitudes (the Schwab and Hale cycles), presumably associated with the solar activity cycles, have been established. The lowest frequency determined by the method was associated with the 87-90 years cycle (the Glayshberg cycle). Evaluation of the linear trend was performed with the least-squares method. Significance level of the corresponding coefficients of the trend equations was also established. Results of the river discharge analysis showed positive trend from years 1970-1999. The analysis of the discharge data observed for more than 50 years pointed on the initial negative trend up to the 1970s that later on changed to positive trend. In general, the positive trend for the river discharge was determined taking all period of measurements at the stations under study. Correlation analysis of the river discharge clearly showed a good correlation between the data measured on hydrological stations located on the same river/inflow (R is 0.5 - 0.9). However, the data from the stations that were close to each other but located on different inflows showed rather poor correlation (R was 0.1-0.4). The authors are grateful to Federal Service for Hydrometeorology and Environmental Monitoring (Bashkir Department, “BashUGMS”) for the provided data for the analysis.