Investigating the nexus of groundwater levels, rainfall and land-use in the Kathmandu Valley, Nepal

Abstract Globally, groundwater resources play a crucial role in supporting livelihoods and sustaining human health. Groundwater recharge is mainly influenced by the spatial distribution of rainfall patterns across groundwater basins and the heterogeneous distribution of geology, soil, and topographical characteristics. This study evaluates the implications of variations in rainfall and land-use on groundwater level fluctuations in the Kathmandu Valley, Nepal. We selected and analyzed data from thirty-five monitoring wells observed by citizen scientists from July 2017 to June 2019. Over two years, groundwater levels varied spatially from -0.11m (negative sign denotes a groundwater level higher than the ground surface) to 11.5m, with a mean of 4.24m and a standard deviation of 2.29m. Our results indicated a strong positive correlation between rainfall and groundwater levels, as the fluctuation was influenced by the rainfall of that area. The seasonal fluctuations in groundwater level showed the direct influence of monsoonal rainfall. In areas with agricultural land use, 80% of the analysed wells showed a strong and statistically significant correlation between rainfall and groundwater levels. In contrast, higher groundwater extraction rates and surface sealing limited groundwater recharge in built land uses; therefore wells across non-agricultural land-uses showed a weak correlation in most of the cases. In the northern groundwater district, we found areas with highly permeable sand and gravel have nearly constant groundwater levels (shallow in agricultural land-use and deep in built land-use) year-round and act as potential recharge zones for the aquifer. The areas with less permeable but highly porous clay and silt in agricultural land use, and show greater seasonal groundwater fluctuations. Our study highlights the ability of citizens to generate meaningful hydrogeologic datasets, and the importance of rainfall and land use planning to groundwater recharge. Understanding these complex relationships must form the basis for the sustainable management of the rapidly declining groundwater resources of the Kathmandu Valley.