Global urban drought risk

This study aims to assess current and future global hydrological drought risk for 263 cities around the globe. Preliminary results among 98 cities show that around 73% of them will likely experience an increase in drought costs in the coming decades. Furthermore, they show that current drought costs are on average between USD 8,000 – 32,000 per 1000 citizens per year, which could increase to approximately USD 9,000 – 40,000 by 2050.  Not many studies have focussed on drought risk at the global scale before, and even fewer explicitly consider cities. However, drought events can have profound impacts on urban areas, as is illustrated by past events like those in Cape Town (2015-2018) and São Paolo (2014-2015). Although research has been done on such specific events, their individual results are often difficult to compare. Therefore, we try to enable that comparison by performing a global urban drought risk assessment, which reveals hotspots of urban drought risk and potentially even puts drought risk on the agenda for cities that are not yet aware of the risks they face. In our approach, we focus on hydrological drought, which is the drought type that most directly affects urban water resources. We link surface-water availability with urban-water withdrawals in the water-source locations of the cities, while taking into account water stress and environmental flow requirements. The hazard is dynamic in time, and future scenarios are based on a selection of RCPs. Exposure is represented as the total population in each city, and evolves over time as well, based on several SSPs. From the hazard and exposure, we use global estimates of freshwater replacement costs to calculate drought cost ranges for each city. We also qualitatively add vulnerability by overlaying the cost ranges with several vulnerability indicators to provide bivariate maps of risk for each city. In addition, attempts are made to verify the results with city practitioners as well as to identify several transformative adaptation options for cities.