Understanding the hydrological regime based on the runoff events in a mountainous catchment with seasonally frozen soil in the Qinghai‐Tibet plateau

Abstract

AbstractSeasonal thawing of frozen soil will significantly affect the hydrological regime, water storage capacity and ecosystem services in the future, which contributes to the uncertainty of regional water resources. However, based on the scale of runoff events, the mechanism of seasonal frozen soil thawing on the hydrological regime are still unclear. In this study, we systematically analysed the runoff characteristics and interactive effects of environmental factors and pre‐event catchment state on runoff processes based on the runoff event scale, using data sets of air temperature, precipitation, runoff, soil moisture, and soil temperature observed in a mountainous catchment with seasonally frozen soil distribution on the Qinghai‐Tibet Plateau from 2010 to 2019. It was found that the event runoff coefficient did not increase significantly with the increase of precipitation. Event runoff coefficients exhibited strong seasonality. The catchment exhibited a gradual increase in the event runoff coefficient with increasing pre‐event baseflow and antecedent soil moisture, especially during stable period (August to November). Event runoff generation through infiltration excess as the result of intensive rainfall seemed to be only possible in the stable period, while heavy precipitation events were common during this period. Normalized event peak discharge and event runoff coefficient showed positive trends with changes in pre‐event catchment state indicators, which were commonly observed phenomena in runoff events. For this catchment, the increased storage capacity pre‐event saturation may be the main mechanism of event runoff generation, as it was unlikely that a single precipitation event would lead to catchment saturation. Soil temperature affects runoff processes through both direct effects on runoff processes and indirect effects on pre‐event catchment state. Temperature indicators were the most important predictors of runoff changes in the Qinghai‐Tibet Plateau.