One year after the deadly Lahaina fires, where winds whipped up flames across both the islands of Maui and the Big Island of Hawaii in Hawaii on August 8, 2024, people are getting ready for more drought conditions and the potential for more fires. While Thursday marks the anniversary of the 2024 historic fire disaster, it wasn’t the first nor will it be the last fire to impact the Aloha State.
While Hawaii may be best known for its tropical breezes, sun-drenched beaches, and tropical rain forests, a federal analysis of wildfire risk to communities shows that of all 50 states, Hawaii has by far the highest risk of “fire consequence” — the likelihood of high-intensity fires near homes.
According to the National Weather Service, “fire weather” is the use of meteorological parameters such as relative humidity, wind speed and direction, mixing heights, and soil moisture to determine whether conditions are favorable for fire growth and smoke dispersion. Over the last 16 years, Hawaii has seen such fire weather conditions develop in every month but February, with August being the primary month for fire weather conditions.
When it appears a combination of strong winds, low relative humidity levels, and dry fuels contribute to extreme fire behavior, the Honolulu office of the National Weather Service will issue a Fire Weather Watch for the entire state. When key criteria is met in the short-term, the Fire Weather Watch is upgraded to a Red Flag Warning, generally within 24 hours of when the fire weather conditions are expected.
One key metric looked at by meteorologists studying fire weather is the Keetch-Byran Drought Index (KBDI). According to the Honolulu office of the National Weather Service, the usual KBDI index reaches the 600 mark in late July or early August, showing the threat of possible red flag warning conditions. The KBDI is a number representing the net effect of evapotranspiration and precipitation in producing cumulative moisture deficiency in deep duff and upper soil layers. It is a continuous index, relating to the flammability of organic material in the ground. When the KBDI is 0-200, soil moisture and large class fuel moistures are high and don’t contribute much to the intensity of fire. With a KBDI of 200-400, lower litter and duff layers are drying and begin to contribute to fire intensity. When the index reaches 400-600, lower litter and duff layers actively contribute to fire intensity and will burn actively. The 600-800 score represents conditions typical of severe drought with increased wildfire occurrence. With a KBDI over 600, intense, deep burning fires are possible while live fuels can be expected to burn actively too.
In Hawaii, a Red Flag Warning is triggered when the KBDI is over 600, minimum relative humidity is less than or equal to 45% for 2 or more hours, and the wind is sustained at 20 mph or more for 2 hours or more.
Since 2012, the National Weather Service has issued Red Flag Warnings 50 times for Hawaii.
In 2023, Red Flag Warnings were issued four times, with some valid for several days. On August 7, a Red Flag Warning was issued for 3 days, with the warning up during the tragic August 8 fires. On August 31, another Red Flag Warning was issued for 1 day. On November 5, a Red Flag Warning was issued for 2 days. On November 14, a Red Flag Warning was issued for one day. In all events except for the November 14 event, a Fire Weather Watch had been posted earlier.
In 2022, there were also 4 Red Flag Warnings issued, most only lasting 1-2 days.
In 2021, 5 Red Flag Warnings were issued including one, on October 6, that lasted for 5 days. The others lasted 1-3 days.
In 2020, there were 3 Red Flag Warnings issued, all lasting a day or two long.
Over the years of 2014-2019, Hawaii had a temporary break from fire weather conditions and no Red Flag Warnings were issued at all over those six years. But that pause came on the heels of two active years: 2012 saw 7 Red Flag Warnings while 2013 saw 6.
These Red Flag Warning days now have greater awareness in Hawaii; the primary electrical utility in the state, Hawaiian Electric, rolled out a Public Safety Power Shutoff or PSPS program for the entire state on July 1. The utility has announced that they will proactively shut down portions of their electrical grid in high fire danger zones around the state when Red Flag Warning and/or other key criteria is met. Hawaiian Electric has said since this is their first year of the program, the criteria to determine which zones are disconnected could change.
A well forecasted drought by the National Weather Service and NOAA’s Climate Prediction Center has taken root over much of the state. In the latest Drought Monitor update, southern portions of Kauai, all of Oahu and Maui, and large parts of Hawaii islands are experiencing at least Moderate Drought. But for much of southern Maui, including Lahaina, and for portions of northwest Hawaii, including South Kohala, a Severe Drought exists. With a lack of recent rain, it’s possible the next Drought Monitor update due out this week could increase the intensity metrics of the drought across the Aloha State.
Hawaii Division of Land and Natural Resources (DLNR) Division of Forestry and Wildlife State Protection (DOFAW) Forester Mike Walker said, “Forecasters continue to predict things will get worse before they get better, with an expectation that more severe drought conditions will plague larger areas of the state into late summer, early fall, and even through next winter.”
Beyond the larger major islands of the Hawaiian Island chain, some of the smaller islands are also experiencing dry conditions. The entire island of Kaho‘olawe is in a Moderate Drought, as is all of Lana‘i and western Moloka‘i.
National Weather Service (NWS) Forecaster Derek Wroe explained, “Dryer conditions are predicted over the next few months, and drought is expected to redevelop over all islands. As drought expands you will notice vegetation drying out, and the NWS urges everyone to be aware of forecasts for windy and dry conditions that lead to high fire danger.”
Maui Fire Assistant Chief Jeffrey Giesea added, “Wildfires have occurred or have the potential to occur on every one of the inhabited Hawaiian Islands, in both windward and leeward areas. Drought conditions, like the ones forecast over the coming months, make this more likely and potentially dangerous.” He said wildfires are different than other natural hazard events, in that they can be prevented and lessened with proactive actions by government, landowners, and individual residents.
According to the Hawaii Wildfire Management Organization, about 0.5% of Hawaii’s total land area burns each year, equal to or greater than the proportion burned of any other US state. Over 98% of wildfires are human caused. Human ignitions coupled with an increasing amount of nonnative, fire-prone grasses and shrubs has made the threat of wildfire worse throughout Hawaii.
