The islands of Hawaii are world renowned for their generally pleasant and tranquil weather. However, the Aug. 8, 2023, wildfire tragedy on Maui was a stark reminder that Hawaii also can experience drought and hot, dry, windy weather, providing the conditions for destructive fires.
Our results suggest that as the planet warms, Hawaii’s dry regions will get drier, heightening the fire risk. At the same time, its wet areas will become wetter. The very steep mountains on each of the main Hawaiian islands block the prevailing northeast trade winds. This results in abundant rain on the slopes facing the windward direction and dry “rain shadows” in the leeward areas. Maui’s west coast tourist communities, including Lahaina, are in one of those rain shadows.
Computer models used to project the future climate approximate the atmospheric wind, temperature and humidity at discrete points on a regular grid. The horizontal spacing between grid points in global climate models is typically 20 miles or larger. To put that in perspective, Maui is only 26 miles by 48 miles at its widest.
We found that in the wet windward areas of Hawaii, rainfall is projected to increase substantially. That includes increasingly frequent extreme downpours. On the other hand, rainfall is predicted to decrease substantially over much of the rain shadow regions.