Projected drought risk in 1.5°C and 2°C warmer climates

The large socioeconomic costs of droughts make them a crucial target for impact assessments of climate change scenarios. Using multiple drought metrics and a set of simulations with the Community Earth System Model targeting 1.5 degrees C and 2 degrees C above preindustrial global mean temperatures, we investigate changes in aridity and the risk of consecutive drought years. If warming is limited to 2 degrees C, these simulations suggest little change in drought risk for the U.S. Southwest and Central Plains compared to present day. In the Mediterranean and central Europe, however, drought risk increases significantly for both 1.5 degrees C and 2 degrees C warming targets, and the additional 0.5 degrees C of the 2 degrees C climate leads to significantly higher drought risk. Our study suggests that limiting anthropogenic warming to 1.5 degrees C rather than 2 degrees C, as aspired to by the Paris Climate Agreement, may have benefits for future drought risk but that such benefits may be regional and in some cases highly uncertain. Plain Language Summary Droughts are among the costliest natural disasters. It is therefore crucial to understand how drought risk will change in the future and whether climate mitigation might help reduce exposure to drought. We use a set of simulations with a climate model targeted at climates that are 1.5 degrees C and 2 degrees C warmer than the era before industrial development-the warming target in the Paris Climate Agreement -to investigate potential future drought risk. We find that drought risk increases across many regions of the world in both of these scenarios, by two different measures: general drying, as well as an increased frequency of consecutive dry years. In Europe, the Mediterranean, Amazon, and southern Africa, the 1.5 degrees C warmer scenario has significantly lower drought risk than the 2 degrees C scenario. In contrast to other simulations with much more warming, drought risk does not change significantly over the U.S. Central Plains and Southwest for these low warming scenarios. This study highlights that aggressive climate change mitigation might reduce future drought risk, but more research with other climate models is necessary to make sure these results are robust.