Executive Summary
In August 2023, a series of wildfires on the Hawaiian island of Maui caused widespread damage and loss of life (Figure 1). The most destructive wildfire struck the historic city of Lahaina, where approximately 81% of the city’s structures were destroyed (FEMA 2023). With a total insured loss of $3.4 billion, the wildfire ranks as Hawaii’s second costliest natural disaster on record behind only Hurricane Iniki in 1992. At least 100 fatalities have been confirmed, making the wildfire the deadliest in the United States in over a century (Insurance Business 2023).
Figure 1 – 2023 Maui Wildfires and impact to Lahain
Several factors contributed to the event’s unprecedented loss of life and property. These loss drivers include:
⦁ Drought conditions dried out vegetation and increased the chance of ignition.
⦁ Flammable surface fuels from invasive grass species provided ample fuel.
⦁ Strong trade winds strengthened by Hurricane Dora sustained the wildfire’s development.
⦁ Downslope winds due to Maui’s mountainous terrain produced strong wind gusts.
⦁ Water shortage limited firefighting efforts to contain and suppress the fire.
⦁ Building stock features typical of Lahaina’s single-family homes helped spread of the fire.
⦁ Changing weather patterns has made Hawaii warmer and drier over recent decades.
Rebuilding Lahaina will likely take years to complete given the scale of destruction. Several obstacles include removal of toxic debris, rezoning to ensure housing affordability, determination of shoreline setbacks, and reconstruction of destroyed infrastructure.
Loss Drivers
Drought Conditions
The rapid drying known as a flash drought (AP 2023) at the start of the summer led to strong drought conditions in August. Nearly a quarter of the island was in a severe drought by the time of the wildfires on August 8 (Figure 2).
Figure 2 – U.S. Drought Monitor from May 23 to August 8, 2023
Flammable Surface Fuels
As the once dominant sugarcane industry has been replaced by tourism, land previously used for plantations has become overwhelmed by invasive grasses (Hawaii Public Radio, 2023). These species tend to spread aggressively during the wet season and dry out rapidly during droughts. These vegetation types common in the outskirts of Lahaina accelerated the spread of the wildfire once ignited (Figure 3).
Figure 3 - Surface fuels surrounding Lahaina, Maui
Strong Trade Winds
Strong Trade Winds
Strong wind is the driver behind many catastrophic wildfires and was critical to the rapid development of the Maui fire (CBS, 2023). The pressure difference between the high-pressure North Pacific High and low-pressure Hurricane Dora passing south of Hawaii intensified trade winds just as the wildfire broke out (Figure 4).
Downslope Winds
Maui’s mountainous terrain helped produce wind gusts up to 70 miles per hour (NBC, 2023). Wind passing over the West Maui Mountains and descending towards Lahaina became warmer, drier, and more intense (Figure 5). This downslope wind phenomenon is equivalent to the Santa Ana winds in California.
Figure 5 – Downslope winds due to Maui’s mountainous topography
Building Stock
Lahaina’s building stock was dominated by single-family residential construction built between 1960 and 1980 (Figure 6). Several design features typical of these buildings made them susceptible to wildfire (IBHS, 2023):
⦁ Architectural features: Carports and balconies acted as traps that could catch burning embers.
⦁ Open eaves: Roof openings used for ventilation in the warm climate gave embers access to a building’s interior.
⦁ Flammable materials: Wooden decks provided an ample fuel source to sustain new ignitions.
⦁ Building density: The close proximately of buildings (typically less than 20 feet) facilitated fire spread.
Figure 6 – Comparison of destroyed (red) and unaffected (green) building in Lahaina
Changing Weather Patterns
Rising temperatures and declining rainfall has made Hawaii more vulnerable to wildfires (Figure 7). In Maui, the average annual temperature has increased by approximately a degree over the last 50 years. The island’s average annual rainfall has decreased by about 25% over the same period. These trends are projected to continue in the future even under low greenhouse gas emission scenarios (NOAA, 2022).
