Declining Runoff Sensitivity to Precipitation Following Permafrost Degradation: Insights From Event‐Scale Runoff Response in the Yellow River Source Region

Abstract Frozen ground, including permafrost and seasonally frozen ground (SFG), is a critical element of the cryosphere that strongly regulates hydrological processes in cold regions. It has been debated whether frozen ground degradation will make landscapes more, or less, sensitive to precipitation inputs; either outcome has profound implications for water resources and climate resilience. Using a data‐driven approach based solely on observations, we quantify four decades of changes in event‐scale runoff responses to daily precipitation in the source region of the Yellow River on the northeastern Tibetan Plateau. We apply Ensemble Rainfall‐Runoff Analysis (ERRA), which infers hydrologic impulse responses directly from precipitation and streamflow time series without relying on model assumptions. This enables the assessment of nonlinear, nonstationary, and spatially heterogeneous hydrologic behavior across different frozen ground types and precipitation intensities. Results show that, relative to 1979–1998, the permafrost‐dominant zone experienced a 47% reduction in peak runoff response per unit precipitation during 1999–2018 and a 32% decrease in the 25‐day runoff coefficient, while the SFG‐dominant region showed no substantial changes. The weakened runoff response in the permafrost‐dominant zone, particularly under high‐intensity precipitation (>10 mm d −1 ), likely reflects enhanced infiltration and subsurface storage driven by active‐layer deepening and weakened near‐surface seasonal freezing. These findings highlight the power of data‐driven approaches in detecting hydrological regime shifts and provide critical insights for drought mitigation and flood risk assessment in permafrost‐affected regions.