Projections of Summertime Hot and Dry Compound Extremes in North America Using Large Ensemble Simulations

Hot-dry compound extremes, defined as the co-occurrence of unusually hot and dry conditions, bring more severe impacts compared to either unusual heat or drought in isolation. Observations show that the frequency of such extremes has increased in recent years, and such trends are projected to continue with additional global warming. Here, using large-ensemble simulations from a climate model, we compute the frequency, duration, and intensity of hot-dry extremes across North America during the summer (June—August), for individual months and for the entire summer season. Relative to model simulations in the 1980–2014 period, the frequency, duration, and intensity of hot-dry compound extremes show an increase nearly everywhere across North America, under a high-emissions scenario (SSP5-8.5) in the 2065–2099 period. We find varying subseasonal and regional trends in future characteristics of hot-dry extremes. The greatest increases in hot-dry compound extremes are projected in July and August rather than June. Increases in absolute frequency are most pronounced over the Pacific Northwest and west-central Canada, and parts of Texas and Mexico. The highest increase in duration is shown over a broad swath of Alaska and western Canada as well as the south-central United States and Mexico. Increases in intensity are relatively uniform across the continent. Results from additional simulations for different emissions scenarios and the mid-century time period (2030–2064) will be shown. The results from this study have important implications for the future vulnerability and impacts from hot-dry compound extremes, as well as for adaptation and mitigation of such extremes.