One of the wettest places in the US is Mount Waialeale on the Hawaiian island of Kauai. The 5,148-foot peak receives an average of 374 inches of rain each year, but even with this annual flood after flood, the island nation as a whole is in a period of prolonged drought.
Almost all of Hawaii is currently experiencing some degree of drought, from “moderate” to “extreme,” according to federal monitoring data. Although this year is not as severe as the 7-year dry spell that ended in 2015, it is in line with a larger sample flood reductions in Hawaii over the past 30 years. To make matters worse, the drought also corresponded with a increasing average temperatureswhich accelerates evaporation.
“Globally, we’re seeing more new kinds of drought,” says Abby Frazier, an assistant professor of geography at Clark University in Worcester, Mass., who studies climate change and habitat in the Hawaiian Islands. “The concern is that we don’t know that drought can have a transformative effect on our ecosystems.” Since droughts become longer, more severe, and more frequent, researchers like Fraser worry about the possibility that ecosystems will be irreparably altered and unable to recover even if regular rains begin to fall again.
There are many scientists who still do not know how Hawaii’s unique ecosystems respond to the prolonged absence of rain, which is closely related to the general change in climatic conditions. But it’s clear that the dynamics of invasive species management and endangered species protection are changing with the ecosystem.
Despite the threat that droughts pose to forest health, biologists know that preserving them is one of the best ways to reduce the effects of drought and conserve as much water as possible in the ecosystem. The forests of the Hawaiian Islands have adapted to capture the moisture that is in the air in the form of fog or low-hanging clouds. “Harvesting cloud water is just as important as rainfall,” says Emma Ewen, program manager for the state’s Department of Land and Natural Resources. “But if you don’t have native vegetation to collect the moisture, you’re going to have a lot less water going into the groundwater.”
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But lack of water is not the only threat to forests: invasive animals, primarily ungulates such as deer and pigs, damage the local vegetation. Without natural predators, wild deer, pigs and goats can cause serious damage – especially during droughts when herds have been saw aggressively graze on whole native plants. When areas of land are left bare, it allows dry, invasive grasses to move into cleared land, serving as fuel and increasing the risk of wildfires.
“Hawaii doesn’t get the national press coverage of wildfires, but we’re on par with the western states in terms of land burned,” Ewen says. In 2021, the largest fire in history occurred in Hawaii almost 40 thousand hectares– which may seem small compared to the nearly 180,000 acres there are burned in California in the same year. But if you compare the size of the fires relative to the size of the states, a much larger portion of Hawaii’s total land mass has been burned. Weather conditions and invasive grasses on the islands have become reminiscent of the most fire-prone mainland states, Hawaii Public Radio informed in 2019.
Wildfires also feed a negative cycle, Yuen explains, as invasive grasses re-grow in the space created by the flames and become fuel for larger fires in the future. What’s more, wildfires can make drought worse—in addition to destroying vegetation that collects moisture in the cloud, the flames and heat make the burned land less permeable, so precipitation doesn’t sink into it and instead flows into streams and waterways. This means less water recharge in underground aquifers and a higher risk of more frequent and destructive floods.
Because fire is historically uncommon in Hawaii’s forests, wildfire mitigation approaches prescribed burns (a a commonly used tactic in the West) is not an option. Hawaii has had a burn ban since 2012, which restricts all burning practices and requires permits from agricultural pursuits or land management. And unlike California and other parts of the American West, where many species of trees and other plants are well-adapted to withstand flames and recover with healthy regeneration, native Hawaiian vegetation is not designed to burn. Prescribed burns will be destructive, not healthy and regenerative, as Hawaiian trees and plants may not come back stronger (if at all). Instead, the primary tool available for fighting wildfires is firebreaks—gaps in vegetation cut to contain the spread of flames.
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The drought, combined with Hawaii’s unique topography and geography, makes managing invasive species and protecting endangered species especially challenging. As an island nation, it is home to a number of endemic species – organisms that evolved on the islands and do not exist anywhere else. Some species may be hyper-specialized to live in a particular ecosystem. While this is true for many species around the world, in the limited islands of Hawaii, these particular ecosystems can be very small. There is a a disproportionate number of endangered species relative to the land available in the Hawaiian Islands, which has only been exacerbated by the pressures of climate change and invasive species.
“Within six miles, the average annual rainfall in Hawaii can vary from 15 inches to 366 inches per year,” Fraser says. Wide variability can leave many species stranded. Flora and fauna have nowhere to sensibly move to when habitable habitats disappear year after year due to wildfires, drought or invasive species – if they can move at all.
Local organizations are working to save local wildlife from recent dry spells. Fraser is part of the Pacific Drought Knowledge Exchange, a network of regional environmental researchers, natural resource managers and other experts who share information about the effects of drought and how to mitigate it. She says many conservation managers are looking for creative solutions, such as replacing lost native species with other native plants better suited to the region’s changing climate. However, she adds, there is a dearth of future climate information needed for good planning and a lack of awareness of Hawaii’s special challenges in the continental US.
The islands may be known for their waterfalls and lush rainforests, Fraser says, but “we need people to know that we also have drought.”