Evolution trends and drivers of glacier and snowmelt induced floods in Upper Yarkant River Basin, Karakoram (1954–2020)

The Upper Yarkant River Basin (UYRB), located in the Karakoram Mountains of Northwest China. Climate warming has intensified both the frequency and severity of flood disasters in alpine regions. Classifying flood events and investigating their complex causes is essential for improved prediction and management. This study developed a multi-temporal scale framework for the extraction and classification of multi-source floods, with a specific focus on the hydrological evolution and driving mechanisms of Glacier and Snowmelt Floods (GSMFs) over the past 70 years. (1) GSMFs are the predominant flood type in the UYRB, accounting for 93% of the total flood volume, with an average event duration of 17 days and a volume of approximately 1.5 × 10⁹ m³ . The evolutionary trend is characterized by increased peak discharge, reduced duration, earlier peak timing, and greater variability. Notably, the frequency of GSMFs with return periods exceeding 10 years has increased since the 1990s. (2) The diurnal variation intensity of GSMFs has increased. Since the 1980s, daily peaks have shifted to occur predominantly during the day. The daily hydrograph reveals distinct patterns, with daytime peaks occurring in the early-to-mid flood period and nighttime peaks in the mid-to-late period. (3) Driving mechanisms exhibit distinct characteristics across time scales. Higher summer temperatures primarily drive the earlier occurrence of floods rather than significantly increasing total volume. On the daily scale, GSMF discharge shows a linear correlation with the zero-degree isotherm height with a notable time lag; a 100-meter rise in the isotherm corresponds to a runoff increase of 56 m³ /s at the mountain outlet on the third day. On the diurnal scale, elevated nighttime temperatures play a crucial role in generating flood runoff. These findings provide a scientific basis for watershed-scale flood forecasting and defense strategies in arid inland basins under a warming climate. • GSMFs exhibit increasing peak discharge, shortened duration, earlier peak timing in yarkant river basin. • The driving factors of GSMFs exhibit different characteristics across various time scales. • Increasing of nighttime temperatures play a crucial role in generating flood runoff.