River Lan discharge: current state and forecast

The results of the study of the water regime of the Lan River, a typical small river of the Belarusian Polesye, are presented. The Lan River is represented by three monitoring sites (Lognovichi, Loktyshi and Mokrovo) with drainage areas A = 480 km2, A = 909 km2 and A = 2550 km2, respectively, with different observation periods and the degree of anthropogenic impact. In addition to large-scale reclamation in the river basin, carried out in the middle of the last century, in 1977, a reservoir was built in the river bed for fish farming and agricultural use. Using the method of analogies, the series of observations of annual, maximum, minimum summer-autumn and winter water discharges are reduced to a single calculated period of 68 years from 1948 to 2015. Assessment of the influence of anthropogenic impacts and natural factors on the runoff, the initial time series, the averaging intervals were analyzed: from 1948 to 2015. (the entire observation period length is 68 years); from 1948 to 1977 (29 years period before the commissioning of the Loktyshi reservoir); from 1978 to 2015 (38 years of reservoir operation period); from 1978 to 1987 (10 years period of the reservoir functioning before the beginning of the modern climate warming,); from 1988 to 2015 (27 years period of the reservoir functioning under the current climate warming). Statistical heterogeneity was found as a result of intensive economic activity, which significantly disrupts the natural hydrological regime. It was revealed that for the average annual runoff there is a decrease along the Lognovichi site and an increase along the Loktyshi site; for the maximum runoff, a decrease is observed along all the stations under consideration; for the minimum summer-autumn discharge, an increase is observed along the Loktyshi site; for the minimum winter runoff, an increase is observed along all stations. Based on the hydrological and climatic hypothesis, predictive estimates of the average discharge values for the period of 2050 are given, which are expressed in a certain decrease in it and a shift in the peak of spring flood to earlier dates.