Degradation of Seasonally Frozen Ground in the Three–River Source Region and Its Correlation Impact Within Precipitation–Runoff Process

Seasonally frozen ground (SFG), known as ‘solid groundwater’ in the Three–River Source Region (TRSR), exerts a critical impact on regional water availability and distribution. Under the warming‐wetting conditions on the Tibetan Plateau (TP), it is necessary to explore how frozen ground, precipitation and runoff change and interact with each other to understand the natural water cycle characteristics. This study analyses hydrological data from the past 60 years, derived from ground stations and satellite observations. The findings reveal clear SFG changes over the past decades: the annual maximum freezing depth (MFD) decreases with warmer winters and is also influenced by monsoon precipitation. An interdecadal response exists between runoff and SFG across the TRSR. However, this coupling has weakened over time, while the response of runoff to precipitation has enhanced. Quantitative analysis shows that the contribution of SFG to spring–summer runoff declined from 16.2% before 1997 to 5.8% thereafter. These results show that runoff relies increasingly on precipitation. Under climate warming, the associated decline in freezing depth thereby heightens the vulnerability of TRSR water resources to climate variability.