Adapting to extremes, managing the shallow - pathways to climate-resilient water supplies in tropical drylands

<p dir="ltr">Tropical drylands are home to some of the world’s poorest and most marginalized communities. Progress toward the UN Sustainable Development Goals (SDGs) including SDG6 (Ensure access to water and sanitation for all) in these environments is vital yet also challenging in the context of increasing freshwater demand. Groundwater plays a central role in sustaining water supplies and livelihoods that include smallholder irrigation due to its resilience to seasonal and inter-annual climate variability; groundwater is often the only perennial source of freshwater in drylands. As our planet warms, rising evapotranspiration, the amplification of rainfall extremes, and the heightened unpredictability in the timing of rainfall, magnify the importance of groundwater’s climate-resilient properties yet also expose its vulnerability to contamination. Drawing upon transdisciplinary research under the CLARITY consortium addressing acute and complex water-supply challenges in peninsular India, the central Sahel of Niger and Nigeria, and central Tanzania, we identify emerging lessons to support pathways towards more sustainable and climate-resilient water supplies in tropical drylands. <i>Adapting to Extremes</i> reflects evidence from CLARITY observatories and beyond that shows how episodically heavy, extreme rainfall is associated with major groundwater recharge events and can create opportunities for freshwater capture from enhanced surface runoff. <i>Managing the Shallow</i> was inspired by the scale of groundwater depletion observed most pronouncedly in weathered hard rock aquifer systems of peninsular India, whereby small-scale irrigators of paddy rice drill progressively deeper wells (i.e. 300 to 500 m) to tap increasingly precarious and dwindling groundwater storage. This ‘race to the bottom’ undermines the equity and sustainability of groundwater withdrawals. More sustainable and equitable groundwater use in tropical drylands needs to consider both demand-side and supply-side interventions and be reconciled to water budgets generated from increasingly variable monsoonal surpluses over decadal scales rather than deplete speculative and highly uncertain deep groundwater storage.</p>