Variation in Runoff of the Arys River and Keles River Watersheds (Kazakhstan), as Influenced by Climate Variation and Human Activity

Runoff formation is a complex meteorological-hydrological process impacted by many factors, especially in the inland river basin. In this study, long-term (1960–2015) river runoff and climate data in the Arys and Keles River watersheds (Kazakhstan) were gathered to analyze the impacts of climate variation and human activity on runoff. The non-parametric Kendall test and the Pettitt test were used to identify trends and change points in the time data series. It was found that both watersheds had significant upward trends in temperature and potential evapotranspiration data, and insignificant upward trends in the runoff. Change points in annual runoff were identified around the year 1973. The hydrological sensitivity method was employed to evaluate the impacts of climate variation and human activity on mean annual runoff based on precipitation and potential evapotranspiration. It was found that the decline in annual runoff over both catchments can be mainly attributed to human activity, the reduction percentages due to human activities range from 59% to 99%. The results of this study can provide a reference for the development and water management of the regional water resources.