The variations of climate and water resources in the Buqtyrma River Basin (BRB), which is located at the cross-section of the Altai Mountains, Eurasian Steppe and Tian Shan Mountains, have a great significance for agriculture and ecosystems in the region. Changing climatic conditions will change the hydrological cycle in the whole basin. In this study, we examined the historical trends and change points of the climate and hydrological variables, the contributions of climate change and human activities to runoff changes, and the relative changes in the runoff to the precipitation and potential evapotranspiration from 1950 to 2015 by using the Mann–Kendall trend test, Pettitt test, double cumulative curve and elasticities methods. In addition, a multi-model ensemble (MME) of the six general circulation models (GCMs) for two future periods (2036–2065 and 2071–2100) was assessed to estimate the spatio-temporal variations in precipitation and temperature under two representative concentration pathways (RCPs 4.5 and 8.5) scenarios. Our study detected that the runoff change-point occurred in 1982. The impacts induced by climate change on runoff change were as follows—70% in the upstream, 62.11% in the midstream and 15.34% in the downstream area. The impacts of human activity on runoff change were greater in the downstream area (84.66%) than in the upstream and midstream areas. A continuously increasing trend was indicated regarding average annual temperature under RCP 4.5 (from 0.37 to 0.33 °C/decade) and under RCP 8.5 (from 0.50 to 0.61 °C/decade) during two future periods. Additionally, an increasing trend in predicted precipitation was exhibited under RCP 4.5 (13.6% and 19.9%) and under RCP 8.5 (10.5% and 18.1%) during both future periods. The results of the relative runoff changes to the predicted precipitation and potential evapotranspiration were expected to increase during two future time periods under RCP 4.5 (18.53% and 25.40%) and under RCP 8.5 (8.91% and 13.38%) relative to the base period. The present work can provide a reference for the utilization and management of regional water resources and for ecological environment protection.

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.