Changes in Climate Extremes and Exploratory Reservoir Associations in the Jinsha River Basin, China

Climate extremes in the Jinsha River Basin have changed during a period of regional warming and cascade hydropower development, but the climatic contribution of reservoir impoundment remains uncertain. We analyzed 20 indices derived from daily observations at 15 meteorological stations during 1980–2022. Regional and station-level trends were assessed, and reservoir associations were explored using matched before–after–control–impact (BACI) contrasts, distance–trend analyses. The station aggregates showed a consistent warming pattern: summer days (SU) and warm-day frequency (TX90p) increased by 0.50 and 0.72 reference-period standard deviations per decade, respectively, whereas frost days (FDs) and cold-night frequency (TN10p) decreased by 0.24 and 0.33. The five compound dry–hot indices increased by 0.24–0.43 standard deviations per decade, while the joint warm–dry severity index (SCEI) declined by 0.34, indicating more severe monthly warm–dry conditions. Precipitation trends were less spatially coherent. Autocorrelation-aware tests retained the full-network trends, although station-level support for maximum event duration weakened. BACI contrasts were mixed and uncertain, and the full-period distance gradient was absent in the common pre-impoundment period. These analyses describe the sampled station network but do not establish a basin-wide causal effect of reservoir impoundment.