More Distinct Dry and Humid Heat in a Warming World

Abstract

The impacts of extreme heat events depend on the concurrent humidity level. Hot and dry conditions harm crops and vegetation, while hot and humid conditions are particularly dangerous for human health. Whether a place tends to experience heat waves that are hot and dry, hot and wet, or both, depends on the local correlation between temperature and humidity. This paper uses reanalysis, observational data, and climate models to show that the global temperature-humidity correlation has steadily declined since 1981 at a somewhat faster rate than climate models simulate. This decline in the temperature-humidity correlation has occurred because humidity is increasing less quickly (or decreasing) on days with high dry-bulb temperatures as compared to days with high wet-bulb temperatures. The relative drying of hot and dry days is associated with those days warming faster than hot and humid days. Overall, the decline in the temperature-humidity correlation has exacerbated the risk from hot and dry conditions while slightly slowing increases in hot and humid conditions.