Current trends in the annual flow of the Ile (Ili) River and its large tributaries under climate warming

Changes in climatic conditions significantly adjust the regime of surface runoff. In particular, current trends in climatic indicators over the zone of runoff formation within the Kazakhstan part of the Ili River basin, located in the mountain systems, change the flow characteristics of rivers. Analysis of the dynamics of average air temperatures and annual precipitation totals using the data of meteorological stations at different heights above sea level, generally allows identifying patterns and trends in surface runoff within the drainage-forming catchment areas. The paper presents conclusions about significant changes in meteorological indicators and identified periods of relatively stable state of their average long-term values, i.e. norms. The considered space-time fluctuations of the average annual air temperatures and the amount of annual precipitation made it possible to reveal that since the 1970s the average annual air temperature in the region has increased by an average of 0,74°C. And the rate of annual precipitation has increased since the early 1990s by an average of 34 mm over most of the basin. The annual runoff is unclearly related to the amount of precipitation in arid zones; however, it depends on the temporal and spatial distribution of moisturizing and results from the influence of heat balance and water balance factors. Parameters of the annual river flow for Ili, Sharyn and Shelek rivers are calculated for the identified climatic periods and with due account of the cyclic water regime of rivers in the region. The choice of calculation periods is confirmed by the analysis of homogeneity of the series of average annual water flow rates under consideration. It was found that since the beginning of the 1990s there was a fairly significant increase in annual precipitation in the region, which caused an intensive increase of the average annual water discharge of the rivers in question. So, the rate of the annual runoff of the Ili River increased by 40 m³/s (9%), and its values for the Sharyn and Shelek rivers increased by 21 and 18%, respectively. Possible consequences and prospects of solving water problems and water security issues within the Ili River basin are indicated.

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