Abstract: Snowmelt runoff and its timing are expected to undergo significant changes in cold mountainous basins, where the formation of water resources is vulnerable to climate change. Fluctuations in the magnitude and timing of snowmelt runoff present challenges for flood control and downstream irrigation. Consequently, an analysis of snowmelt run-off variations and timing in the UIB and its sub-basins was conducted using methodologies such as the ‘Center Time (CT)’, ‘Spring Pulse Onset (SPO)’ and comprehensive analysis of monthly fractional streamflow (MFS). This analysis revealed the response of shifts in snowmelt runoff timing to various climatic variables and the spatial heterogeneity of changes across different basins. Consequently, spring and winter runoff in the UIB has significantly increased over recent decades, suggesting a reduction in water storage for subsequent melt runoff. The timing of snowmelt runoff, as indicated by the CT and SPO indicators, was significantly advanced in the UIB, exhibiting notable spatial heterogeneity among sub-basins. The shift of snowmelt runoff timing is more closely related to temperature and snowpack coverage than to precipitation. In the glaciated Karakoram and the snow-covered Gilgit and Astore sub-basins, temperature significantly influences snow-pack meltwater regulation, resulting in a more pronounced advancement of snowmelt runoff timing. In the Kharmong basin, reduced snowpack cover results in a more significant response of snowmelt runoff to variations in precipitation. While the indices may not fully capture the changes in snowmelt runoff timing and uncertainties remain, the magnitude and timing of snowmelt runoff identified in this study are essential for regional water resources management.