Observation and Simulation of Runoff During an Extreme Heatwave in a Glacial Basin on the Central Tibetan Plateau

Abstract

Glacier meltwater runoff during extreme heat waves is crucial for overall runoff replenishment; however, studies on the characteristics and mechanisms of extreme meltwater runoff on the Tibetan Plateau (TP) are relatively scarce. In this study, we combine field observations (hydrological, meteorological, and glaciological) with a precipitation runoff modelling system and glacier model (PRMSglacier) to investigate the characteristics of extreme glacier meltwater runoff and the associated energy balance and hydrological processes from October 2018 to September 2022 in the Sangqu Basin on the central TP. Good agreement was shown between observed and modelled total runoff and glacier-wide mass balance, with a mean Nash–Sutcliffe efficiency (NSE) of 0.74 and root-mean-square error (RMSE) of 22 mm w.e. The mean glacial meltwater runoff contributed 14% of the total runoff and snowmelt runoff 72.5% during the study period. Contributions of 21.3% and 59% for glacier meltwater and snowmelt runoff, respectively, during a heatwave from June to September 2022 thus indicated anomalously high glacial meltwater and snowmelt runoff in association with hot and dry meteorological conditions. Basin-scale energy balance results suggest that extremely low albedo and extremely high surface temperatures control the net shortwave and longwave radiation, leading to anomalously high melting of glaciers and snow. The hot and dry meteorological conditions from June to September 2022 primarily affected the source regions of the Yangtze River and Selincuo in Geladandong. This study highlights the importance of extreme glacial meltwater runoff to terrestrial water resources in association with frequent extreme heat waves.