A new study in Nature Geoscience examines how the movement of dry air drives moist heatwaves, which pose serious risks to human health through the combination of humidity and high temperatures. Scientists supported by the Climate Program Office’s Modeling, Analysis, Predictions, and Projections (MAPP) program discovered that contrary to prior assumptions, dry air entrainment, the mixing of dry air from higher altitudes into the moist air below, plays a key role in the formation of moist heatwaves. Using reanalysis data, climate models, and experiments, they found that dry air in the lower-free troposphere (the layer of the atmosphere about 1-3 kilometers above the surface) can limit the upward movement of warm, moist air that usually cools the surface. The suppression of this movement leads to higher temperatures and humidity near the ground. As the climate warms, the increasing dryness of the lower-free troposphere could lead to more frequent and intense moist heatwaves, exacerbating health risks and economic impacts, particularly in densely populated tropical and subtropical areas.
This work shows that our previous understanding of moist heatwave drivers was incomplete, highlighting the critical role of dry air entrainment in amplifying these conditions. The results are particularly concerning for regions near hot, arid lands and even for typically wet areas like Southeast Asia and the northern Indian Plain. Through developing better heatwave dynamics simulations to predict and prepare for future extreme heat events, the paper’s authors are contributing to a growing body of MAPP-funded research aimed at improving climate models. These findings will help inform and emphasize the importance of heat health services like those provided by the National Integrated Heat Health Information System (NIHHIS), which works with communities to plan for heat and build heat resilience.
For more information, contact Clara Deck.