Hydrological Changes of the Ili River in Kazakhstan and the Possible Causes

Abstract

Hydrological changes of the Ili River were analyzed concerning the changes of annual runoff and its distribution features within a year measured by coefficient of variation and concentration degree. Abrupt changes were detected by the heuristic segmentation method. Possible causes of the hydrological changes were investigated considering climate changes and human activities (especially the reservoir operation and irrigation extension). The Mann-Kendall method was applied to estimate whether the temperature and precipitation were changed. The increased temperature and the decreased precipitation in the flood season may decrease the runoff. At the middle reaches, the impact of the reservoir is significant and may be the main factor leading to the abrupt decreases in annual runoff and its intra-annual variability and concentration. The increased water surface area of the reservoir aggravates the evaporation and leads to annual runoff reduction. The reservoir regulates runoff by storing water in the flood season and releasing water in the dry season.