Enhanced Risk of Concurrent Regional Droughts with Increased ENSO Variability and Warming

Spatially compounding extremes pose substantial threats to globally interconnected socio-economic systems. Here we use multiple large ensemble simulations of the high-emissions scenario to show increased risk of compound droughts during the boreal summer over ten global regions. Relative to the late twentieth century, the probability of compound droughts increases by ~40% and ~60% by the middle and late twenty-first century, respectively, with a disproportionate increase in risk across North America and the Amazon. These changes contribute to an approximately ninefold increase in agricultural area and population exposure to severe compound droughts with continued fossil-fuel dependence. ENSO is the predominant large-scale driver of compound droughts with 68% of historical events occurring during El Niño or La Niña conditions. With ENSO teleconnections remaining largely stationary in the future, a ~22% increase in frequency of ENSO events combined with projected warming drives the elevated risk of compound droughts. The co-occurrence of drought across different regions will have far-reaching effects on global agriculture and food supply. Model projections show an increased likelihood of these compound droughts under a high-emissions scenario, with a ninefold increase of farm land and population exposure.