Precipitation trends determine future occurrences of compound hot-dry events

Co-occurring hot and dry extremes are predicted to increase with global warming. Changes in precipitation will modulate the extent of these changes, highlighting the importance of understanding regional precipitation trends to prepare society and minimize impacts. Compound hot-dry events-co-occurring hot and dry extremes-frequently cause damages to human and natural systems, often exceeding separate impacts from heatwaves and droughts. Strong increases in the occurrence of these events are projected with warming, but associated uncertainties remain large and poorly understood. Here, using climate model large ensembles, we show that mean precipitation trends exclusively modulate the future occurrence of compound hot-dry events over land. This occurs because local warming will be large enough that future droughts will always coincide with at least moderately hot extremes, even in a 2 degrees C warmer world. By contrast, precipitation trends are often weak and equivocal in sign, depending on the model, region and internal climate variability. Therefore, constraining regional precipitation trends will also constrain future compound hot-dry events. These results help to assess future frequencies of other compound extremes characterized by strongly different trends in the drivers.