Investigating groundwater recharge using hydrogen and oxygen stable isotopes in Kabul city, a semi-arid region

[Display omitted] •Stable isotope analysis has been carried out on surface and groundwater across Kabul city.•Significant groundwater depletion is observed in the Central Kabul sub-basin and western parts of the city.•Isotopic data variability is influenced by local recharge and groundwater-surface water mixing.•River water contribution to groundwater recharge declined from 60% in 2007 to less than 50% in 2020. There are significant concerns about the sustainability of groundwater, and the inhabitants that depend on it, due to rapid groundwater depletion from the alluvium aquifers in Kabul city. Sustainable groundwater management in Kabul requires an understanding of the sources and rates of groundwater recharge, however, both these parameters are poorly quantified. In this study, we examined the stable isotopic composition (δ18O and δ2H) of groundwater and surface water from the Upper Kabul River and Logar River. Utilizing the hydrograph separation approach, we assessed the percentage contribution of river water to groundwater, including the uncertainty analysis of its estimation. Our results, based on isotopic analysis, demonstrated that precipitation was the primary source of groundwater recharge in the Central Kabul sub-basin. Mixed recharge from the river, precipitation and irrigation return flow governed groundwater recharge in the Logar sub-basin. In Paghman and Lower Kabul, and Upper Kabul sub-basins, more rainfall input was observed besides the river contribution to groundwater recharge. We have noted substantial spatial and depth-related variation in the contribution of the river water to groundwater recharge. In the study area, the river water contribution (fraction contribution) to groundwater recharge has changed from over 60 ± 5 % (on average) in 2007 to less than 50 ± 5 % (on average) in 2020. We documented significant groundwater level depletion in the Central Kabul sub-basin and western parts of Kabul city (Paghman and Upper Kabul sub-basins). The present study provides important insights into the local water cycle in Kabul City, which is critical for developing sustainable management strategies for groundwater sources in this semi-arid region.