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.
Hawaii has seen a generally rising trend in the amount of land that burns each year as the local climate warms. Climate change was one of several contributors to Maui’s wildfire catastrophe, and rising temperatures and associated rainfall changes are expected to increase the islands’ fire risk. These changing weather patterns will also affect Hawaii’s ecosystems and freshwater resources.
You can listen to more articles from The Conversation, narrated by Noa, here.
While Hawaii is home to some of the wettest spots on earth, it also has regions that receive little rain.
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.
We created a model that zooms in on Hawaii and is able to capture those variations, including the rain shadow effect.
Using that model, we simulated the Hawaiian climate at the end of the 21st century under a scenario in which global greenhouse gas emissions from human activities continue at a rate that drives a global increase of temperature of about 4 degrees Fahrenheit (2.2 C). Such a scenario is quite plausible and even demands some significant reduction in current emission rates, but still pushes well beyond the internationally agreed goal of keeping global warming under 3.6 F (2 C) compared with preindustrial levels.
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.
The “dry gets drier” aspect is particularly important for formulating Hawaii’s plans to adapt to climate change. The soil in already dry regions may become even drier as rainfall decreases and warmer air promotes more evaporation from the surface. That includes Maui’s highly developed west coast and agricultural areas that until recently were home to large sugar cane farms.
Simulating rainfall in climate models still has many uncertainties, and there are particular challenges in representing the fine geographical details of the rain in Hawaii. Another study using a different approach produced results broadly consistent with ours but projects an overall stronger drying trend in the islands.
While further research should help reduce the uncertainties in climate projections, our results suggest that, in the long term, Hawaii needs to prepare for more extreme conditions, including a heightened risk of wildfires.
Kevin Hamilton has received funding from NASA, NOAA, US Department of Interior, Japan Agency for Marine-Earth Science and Technology.