Decreased river runoff on the Mongolian Plateau since around 2000

Abstract Context Mongolian Plateau is one of the largest contingent arid and semi-arid regions of the world. Rivers on the plateau provide vital water for millions of indigenous Mongolian people and numerous endangered wildlife, but are increasingly disturbed by climate change and human activities. Yet, long-term changes in river runoff across the plateau remain poorly studied due to data unavailability. Objectives This study aimed to analyze the temporal trends in gauged river runoff on the Mongolian Plateau, identify drivers of the observed changes, and evaluate CMIP6 models' performance in simulating historical runoff changes across the plateau. Methods We compiled possibly the largest database of long-term (20 - 71 years) river runoff for the plateau comprising measurements over 30 major rivers. Statistical analyses were conducted to assess trends in river runoff and correlations between runoff and climatic variables. Additionally, we applied the Budyko curve framework to identify the influence of human activities on river runoff in specific basins. Furthermore, we compared ground-measured runoff data with simulations from CMIP6 models to evaluate the ability of CMIP6 models to replicate runoff dynamics in typical arid and semi-arid regions. Results We observed pervasive and abrupt reduction in runoff in 21 out of the 30 rivers within 5 years before or after the year of 2000. Variations in river runoff were most significantly caused by changes in total precipitation (TP). In particular, 27 rivers experienced abrupt TP changes around 2000, and there was a significant positive correlation between annual fluctuations in TP and river runoff for 18 rivers. In addition to climate factors, the influence of human activities was identified in certain basins. The CMIP6 simulations failed to capture the abrupt changes in runoff occurred pervasively across the plateau around 2000. Conclusions Around 2000, major rivers on the Mongolian Plateau, especially in Inner Mongolia, experienced runoff declines, primarily due to TP changes. Human activities like dam construction and water diversion further influenced local runoff. CMIP6 historical runoff simulations were inaccurate across the plateau, highlighting the difficulty of simulating river runoff in this critical region. Our study could contribute to a more comprehensive understanding of the water resource changes on the Mongolian Plateau, with direct implications for enhancing ecological conservation and management practice.