ИСТИНА

In the conditions of arid climate, which is typical for the Republic of Uzbekistan, water is of paramount importance in the life of a person and his economic activity. Of particular importance is the change in runoff during dry years, causing a shortage of water resources and enormous damage to various sectors of the economy. Runoff in the Amudarya and Syrdarya river basins in dry years can decrease by 25-40%. The main objective of the work is to assess the characteristics and causes of low-water flows in the mountain rivers of Central Asia, within the Republic of Uzbekistan, to determine the relative number and frequency of low-water years depending on the power sources causing the variability of annual and seasonal runoff. To solve the tasks, we used data on the average annual and monthly water consumption of the 38 mountain rivers of the Republic of Uzbekistan and the adjacent territories with a natural hydrological regime. The calculations used materials from 9 meteorological stations on air temperature and precipitation until 2016 inclusive. To study the dry years on the rivers, the features of the spatial-temporal variability of annual and seasonal runoff were investigated. If the modular coefficients of water discharge for the year Кi are less than 0.92, the years are considered to be dry. Another possible indicator characterizing the overall water deficit is the volume of runoff above the threshold value — water consumption of 90% of water availability. Depending on the types of river feeding, the deficit manifests itself at different times of the year and with different durations. In high-mountain rivers with glacier-snow feeding, the low-water months with the greatest water deficiency are January-March, and in other rivers August-October. In most cases, there is a shortage of 2-3 months a year. In the fluctuations of the flow of the mountain rivers of Uzbekistan, there are also some low-water years and their groups (series). The low-water period of 1980–1986, including 7 low-water years in a row, was especially long. Characteristics of low water, including the frequency of low water, indicators of water deficiency and severity of low water, depend on the type of feeding of the studied mountain rivers. Recurrence of dry years increases from 30% (glacier-snow feeding rivers) to 70% (snow-rain feeding rivers). The relative number of low-water years for the glacier and snow-glacier-type rivers was on average 43.8%, for the rivers of the snow and snow-rain type of feed, this figure was 49.0% on average. The average duration of the “low water period” on the mountain rivers of Central Asia is 3 years. As an indicator of hydrological drought for the mountainous rivers of Uzbekistan, one can use the amount of water in snow cover in the mountains at the end of February and March or the total amount of precipitation during the cold period. The latter indicator is used to predict the flow of the growing season, which constitutes the bulk of the flow for the year, and water content for the hydrological year.