Meltwaters dominate groundwater recharge in cold arid desert of Upper Indus River Basin (UIRB), western Himalayas

Abstract Groundwater resources play a key role in sustaining irrigated agriculture and providing domestic water supplies in the trans-boundary Upper Indus River Basin. Understanding groundwater recharge and flow pathways in Upper Indus Basin is critical to good groundwater management, yet groundwater recharge sources remain poorly quantified. Here new dataset of stable oxygen and hydrogen isotope compositions and geochemical tracers of rain (n = 110), groundwater (n = 140), glacier melt (n = 56) and snowmelt (n = 46) collected during 2015–2018 has been analysed to investigate the spatio-temporal variation of δ18O and δ2H in source waters and groundwater and to quantify and estimate the sources of recharging water. We found microclimate in sub-basins is dominantly controlling stable water isotopic composition of source waters and groundwater. It is shown that meltwaters supply up to 83% of groundwater recharge, emphasizing the importance of the cryosphere in sustaining groundwater resources in the Upper Indus River Basin. Meltwater-derived recharge is split evenly among glacial meltwaters (44% of annual recharge) and snowmelt (39%); by contrast, rainfall contributes only 17% of annual recharge. Our data highlight the dependence of groundwater recharge on meltwaters derived from glaciers and snowpacks, suggesting that changes to the pattern, form, timing and amount of precipitation as well as glacial retreat may have disproportionate impacts on groundwater recharge, with potential to alter water supplies and affect local and regional economies.