The challenge of closing the climate adaptation gap for water supply utilities

Many drinking water utilities face immense challenges in supplying sustainable, drought-resilient services to households. Here we propose a quantified framework to perform drought risk analysis on similar to 5600 potable water supply utilities and evaluate the benefit of adaptation actions. We identify global hotspots of present-day and mid-century drought risk under future scenarios of climate change and demand growth (namely, SSP1-2.6, SSP3-7.0, SSP5-8.5). We estimate the mean rate of unsustainable or disrupted utility supply at 15% (interquartile range, 0-26%) and project a global increase in risk of between 30-45% under future scenarios. Implementing the most cost-effective adaptation action identified per utility would mitigate additional future risk by 75-80%. However, implementing the subset of cost-effective options that generate sufficient tariff revenue to provide a benefit-cost ratio that is greater than 1 would only achieve 5-20% of this benefit. The results underline the challenge of attracting the financing required to close the climate adaptation gap for water supply utilities.