Responses of seasonal baseflow to climate warming in an alpine mountain basin: Insights from GAMLSS modeling

Study region The Kaidu River is a cryosphere-fed inland river in the central Tianshan Mountains of arid northwest China, sustaining downstream oases, irrigated agriculture, and Bosten Lake. Study focus We examined seasonal baseflow responses to warming during 1961–2020 and an abrupt regime shift. Daily streamflow for 2009–2020 was reconstructed with a Long Short-Term Memory model, baseflow was separated using nine methods centered on the Eckhardt filter, and monthly controls were quantified with Generalized Additive Models for Location, Scale and Shape. New hydrological insights for the region Baseflow averaged 77.6 m 3 /s (68% of streamflow), indicating strong groundwater buffering by the Quaternary aquifer. Around 1996, annual streamflow and baseflow increased by 24% and 22%, respectively, and the shift was reproduced by all nine methods. Antecedent wetness was significant from April to November, revealing persistent groundwater memory. Climate–baseflow coupling followed four seasonal phases: storage-dominated spring, climate-sensitive summer, storage-controlled autumn recession, and an early-winter transition. Over 1961–2020, a 1°C increase in temperature was associated with 8.6% higher July baseflow; stratified analyses further showed that temperature emerged as a significant July driver only after 1996. These findings reveal strong groundwater memory and an increasing influence of warming on warm-season baseflow, with implications for downstream water supply in the Yanqi Basin.