Abstract
Though springs are the primary source of water for communities in the mid-hills of Nepal, an in-depth scientific understanding of spring systems is missing, preventing the design of effective climate-resilient interventions for long-term sustainability of springs. This study marks the first attempt to combine environmental isotopes analysis with hydrometric and hydrogeological measurements to identify dominant recharge zones for springs in two mountainous catchments—Banlek and Shikarpur—in Far-Western Nepal. In total, 422 water samples collected from rainfall, springs and streams between March 2016 and March 2017 were analyzed for their isotopic composition (δ18O and δD). Isotopic composition of rainwater shows seasonality, suggesting that different sources of water vapor cause rains in monsoon and in dry season. Rainfall responses of individual springs were used to identify connections to unconfined and deeper groundwater strata. The isotopic composition of springs in the two catchments ranges from −9.55 to −8.06‰ for δ18O and −67.58 to −53.51‰ for δD. The isotopic signature of the spring sources falls close to the local meteoric water line for the corresponding season, indicating strong rainfall contribution to springs. Altitudinal isotopic gradients suggest mean recharge elevation of 2,600–2,700 m asl for springs in Shikarpur, which lies beyond the surface-water catchment, and a recharge elevation of 1,000–1,100 m asl for Banlek, which partially extends beyond the surface-water catchment. The demarcated recharge zones will be used by government agencies to implement recharge interventions to increase the resiliency and reliability of springs in Far-Western Nepal.
Highlights
Two-thirds of the global population are experiencing severe water scarcity at least 1 month of each year (Mekonnen and Hoekstra 2016), which is expected to be further aggravated by increasing demands and impacts of climate change (Palmer et al 2008; Oki et al 2014)
These recharge zones, transcending the local village boundary in which the spring system is located, pose practical challenges in implementation and maintenance of the recharge interventions. Such practical considerations imply that recharge interventions are better suited in Banlek. Other proposed interventions such as piped diversions and focus on increasing water-use efficiency is recommended for Shikarpur
The spring recharge areas in two mountainous catchments located in Far-Western Nepal, Shikarpur and Banlek, were delineated by comparing the isotopic ratios of δ18O and δD in precipitation with springs
Summary
Two-thirds of the global population are experiencing severe water scarcity at least 1 month of each year (Mekonnen and Hoekstra 2016), which is expected to be further aggravated by increasing demands and impacts of climate change (Palmer et al 2008; Oki et al 2014). Climate-change induced increase in temperature and uncertainties in precipitation are expected to have a direct bearing on water availability for agriculture and livelihood through changes in evapotranspiration, recharge. Water security is an imperative driver to achieve sustainable development, ensure economic sustenance and increase the climate resilience of rural vulnerable communities in Nepal, in which utilization of spring sources play a vital part (WECS 2011). For 80% of rural communities perched on hilltops far from river sources, springs are the primary source of water for sustaining domestic, agriculture and livestock water demands (Tambe et al 2012; Sharma et al 2016)
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