Topographically corrected land surface temperatures reveal a 2005 regime shift and prolonged thawing in the Yellow River Source Region (1981–2020)

The source area of the Yellow River (SAYR) is a critically important cryospheric region highly sensitive to climate warming. However, capturing fine-scale thawing–freezing dynamics remains challenging due to the region's rugged topography and sparse observational networks. In this study, we developed a 1-km, 40-year (1981–2020) dataset of surface temperatures and thawing–freezing indices by applying month-specific topographic corrections to ERA5-Land reanalysis data. Validation against independent station observations yielded a root mean square error (RMSE) of 1.49℃, and uncertainty assessments demonstrate that the monthly-derived indices capture interannual trends with high consistency (R² > 0.97). Over the past four decades, regional freezing indices have significantly decreased, while thawing indices have increased, resulting in an extension of the average thawing duration by 1.17 days per decade. Furthermore, a regime shift detected in 2005 prolonged the annual thawing duration by 14.8 days, extending the unfrozen soil period and potentially enhancing moisture infiltration into the subsurface. Spatially, this thawing intensification is most pronounced in the southeastern valleys, whereas changes in the thermal regime over the northwestern and central highlands indicate intensified ground warming, which is likely associated with permafrost degradation and active-layer deepening. Overall, this high-resolution dataset offers an improved representation of surface thermal processes compared to traditional air-temperature-based proxies, providing valuable support for climate adaptation and infrastructure planning in this critical headwater region.