What is Flash Drought that caused wildfires in Hawaii?

In just a few short weeks, a dramatic transformation occurred in Hawaii, changing its once lush state to an arid environment, significantly increasing the risk of fire. This rapid change played a crucial role in creating a dangerous combination of factors that intensified the destructive impact of the ongoing wildfires in Hawaii.

Climate experts assert that the growing influence of flash droughts and various other extreme weather incidents stems directly from climate change. The island of Maui serves as a vivid illustration of this scenario, with the loss of numerous lives and extensive devastation befalling a historically important resort town due to the ongoing wildfire crisis.

"It's leading to these unpredictable or unforeseen combinations that we're seeing right now and that are fueling this extreme fire weather," said Kelsey Copes-Gerbitz, a postdoctoral researcher at the University of British Columbia's faculty of forestry. "What these ... catastrophic wildfire disasters are revealing is that nowhere is immune to the issue."

According to Hawaii emergency management records, there is no evidence that warning sirens were activated before people fled the Maui wildfires, a disaster that tragically claimed the lives of at least 55 people and eradicated a city of great historical importance. Instead, authorities issued notifications to mobile phones, televisions, and radio stations. However, extensive power and cellular outages could have restricted the effectiveness of these alerts.

Let's examine the Maui fires and the factors that contributed to their occurrence:

What is Flash Drought?

Flash drought occurs when drought rapidly begins or intensifies. It originates from precipitation rates dropping below normal levels while experiencing unusually high temperatures, winds, and radiation. These alterations in weather can swiftly modify the local climate.

Elevated temperatures heighten evapotranspiration—an interaction where water moves from land to the atmosphere through soil evaporation and plant transpiration—leading to reduced soil moisture, which declines rapidly throughout the persistence of drought conditions.

If meteorologists fail to predict and detect these shifts in soil moisture promptly, the accompanying effects of flash drought can inflict substantial harm on agriculture, economies, and the benefits provided by ecosystems.

What are the causes of flash drought?

The main triggers for flash droughts are inadequate rainfall and increased evaporative requirements, which measure the evaporation of water from the environment.

• The main driver of flash droughts is the depletion of soil moisture.
• Flash droughts do not progress slowly; come from reduced rainfall. They coincide with high temperatures and strong winds. They amplify evapotranspiration rates within the atmosphere.
• Weather patterns and geographic distinctions also influence the occurrence of flash droughts.
• Mainly, flash droughts arise in the warmer seasons.

Maui's drought escalation and fire risk

As of May 23, Maui showed no unusual dryness; however, the following week, more than half of the region experienced abnormal dryness. By June 13, about two-thirds of the area had entered abnormally dry or moderately dry conditions. Currently, about 83% of the island is in abnormal drought or moderate to severe drought conditions, according to the US Drought Monitor.

In the span of just three weeks, from May to June, Maui experienced a two-category escalation in drought severity: an abrupt intensification that aligns with the definition of a flash drought, explained Jason Otkin, an atmospheric scientist at the University of Wisconsin, Madison.

Otkin, co-author of an April study, showed that flash droughts are becoming more frequent due to human-induced climate change as the Earth warms. He pointed to a link between an unusual outbreak of wildfires in Gatlinburg, Tennessee, in 2016 and a flash drought.

Even in the last week, there has been a rapid acceleration of the drought, said Venkat Lakshmi, a hydrologist at the University of Virginia. Flash droughts arise when the rain stops, and increasing heat causes the atmosphere to draw moisture directly from the soil and plants, increasing their susceptibility to ignition.

Lakshmi noted: "Plants get too dry. Everything is intertwined with water, in various ways."

"Droughts often precede the most devastating fires. If an area quickly plunges into drought, a longer time frame emerges for fire outbreaks," Otkin explained, stressing: "The potential for severe fires could increase in the future if flash droughts become more frequent, as indicated by certain studies."

Climate change dries out plants

Hawaii's state climatologist, Pao-Shin Chu, found Dora's impact surprising at roughly 500 miles (800 kilometers) away.

"Hurricane Dora remains distant from Hawaii, yet triggers fires. This is an unexpected occurrence," he said.

"When all conditions coincide, it's often 'red flag conditions,' per Erica Fleishman, Oregon State University's Oregon Climate Change Research Institute director.

"Climate change globally heightens vegetation dryness, mainly due to hotter temperatures," Fleishman noted. "Even with unchanged precipitation, higher temperatures accelerate drying."

University of Hawaii's fire scientist, Clay Trauernicht, pointed out that the wet season accelerates Guinea grass growth—nonnative and invasive on Maui—up to 6 inches (15 centimeters) daily, reaching 10 feet (3 meters). Dryness turns it into a fire-ready tinderbox.

"These grasslands amass fuel swiftly," Trauernicht stated. "Hotter, drier conditions with uneven rainfall will worsen the issue."

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