Drought is an important natural hazard in southwestern North America, and there is strong evidence that climate change is already increasing the severity of droughts in the region. Using the latest, state-of-the-art climate change projections, we find that warming in the future will increase the risk of both extreme single-year and 21-year soil moisture droughts that are similar to major events of the last two decades.

Furthermore, we show that while the magnitude of warming has a strong influence on single-year droughts, even modest warming is likely to lock in an approximately 50% chance of a 21-year drought similar to 2000–2020 by the end of the 21st century.

The high levels of 21-year drought risk are driven by large precipitation declines in half the models, which shift the region to a drier mean state under even the lowest warming scenario. Despite the apparent insensitivity of 21-year drought risk to mitigation measures, our results still demonstrate the value of climate change mitigation for reducing future drought severity and single-year extreme drought risk in the region.

Our study also highlights the importance of precipitation responses in the models as major uncertainties that must be resolved to increase our confidence in these projections.