Changes in intra-annual runoff and its response to climate variability and anthropogenic activity in the Lake Issyk-Kul Basin, Kyrgyzstan

An attribute study of the runoff changes due to climate change and anthropogenic activities is of great value to determining the best response to runoff changes. This study investigates the evolution of the intra-annual runoff and evaluates the effects of changes in climate and anthropogenic activities on runoff variations in the Lake Issyk-Kul Basin (LIKB). The monotonic trend test and wavelet transform analysis were used to characterize the trends and periods of the hydro-meteorological variables in the LIKB. In addition, the periodicity-trend superposition model and double-mass curves were used to assess the contributions of climate change and anthropogenic activities to runoff variations. The analyses were conducted using regional climate data combined with runoff data derived from 13 different river stations in the LIKB for the period between 1943 and 2012. The results indicate the following. (1) The monthly runoff trends in the three groups of tributaries (northern, southeastern, and southern tributaries) exhibit distinct differences, and the percentage of the data sets with no pattern gradually increased (from 26% to 38%) from north to south. There is a positive trend, with a similar decrease (from 50% to 24%) from north to south. (2) The air temperature, precipitation, and runoff in the LIKB increased throughout the low and high flow periods. The statistical index of the runoff concentration degree (RCD) decreased at most stations (Chong-Koi-Suu, Chong-Ak-Suu, Chong-Urykty, Pzhergalan, Ak-Sai, Tossor, Ton, Chong-Kyzyl-Suu, Tamga, and Karakol), except for the Cholpon-Ata, Ak-Suu, and Dzhuuku stations. (3) In addition, the periodic characteristics of the RCD show that the RCD has a 12-year significant period over the low flow period, which is similar to that for precipitation but varies from that for air temperature. (4) Climate variability and anthropogenic activities are two different contributors to runoff reduction in the LIKB. The respective contributions of anthropogenic activities to the runoff determined using the two methods were 35.3% and 18%, whereas the climate change contributions were 64.7% and 82%, respectively. Climate change was the main reason for the runoff variations. These results provide a basis for the scientific management and sustainable allocation of water resources in the LIKB.