The role of future aridification in multi-year drought persistence for global hydrologic basins

Increasing aridity is a growing concern for many regions across the globe, primarily driven by an alteration to the balance of evaporative loss and incoming precipitation. While this is likely to drive declines in the long-term mean of surface water, interannual and decadal variability of precipitation will still produce wet and dry periods. Yet, the potential increase in the occurrence of multiple sequential drought years is of particular concern especially for basins without substantive water shortage infrastructure. In this presentation, we evaluate the enhanced likelihood of multiple consecutive , i.e. years with below 20^th percentile annual runoff, occurring within large basins (25,000-150,000 km­²) across the globe that are projected to experience increasing aridity within an ensemble of 16 CMIP6 general circulation models. We use historical simulations (1950-2014) and future projections (2015-2100) from three emission scenarios to demonstrate how aridification, as measured by increases in the long-term ratio of potential evapotranspiration and precipitation, is expected to change. We examine the ways in which changes in aridity paired with projected changes to the interannual variability of precipitation can conspire to enhance the probability, magnitude, and persistence of multi-year drought.