Unraveling the Distinct Roles of Snowmelt and Glacier-Melt on Agricultural Water Availability: A Novel Indicator and Its Application in a Glacierized Basin of China’s Arid Region

Mountain runoff is a vital water source for irrigation in global arid regions. Investigating the roles of major mountain runoff components such as snowmelt and glacier-melt, on downstream irrigation water availability is important for understanding water resource security. Snowmelt and glacier-melt have different timing and availability. However, their potentially distinct impacts on water supplies for downstream irrigation have been seldom investigated previously. This study proposes a novel indicator, Irrigation Dependence on runoff Component (IDC), to assess the individual impact of different runoff components on irrigation water availability, considering water supply, water demand and their relationship. Applying IDC to the Yarkant River basin (YRB) in China’s arid region, mainly fed by mountain runoff from the northern Tibetan Plateau, reveals that, despite glacier-melt runoff being the primary contributor to total runoff in the YRB, irrigation water availability is generally more reliant on snowmelt runoff due to seasonal variations in the water supply/demand relationship. Further sensitivity tests under 48 climate scenarios indicate that IDC of glacier-melt runoff significantly increases under drier climates, while that of snowmelt runoff decreases as the climate warms, implying potentially increased importance of glacier-melt in future, especially under drier conditions and during the transition season. Additionally, the crucial role of anthropogenic factors, including changes in planting area and irrigation water use efficiency, in influencing irrigation water demand is highlighted for improved estimation. This study provides important implications on how cryosphere changes impact water resources management and an efficient indicator for further studies in glacierized arid basins globally.