The large fires that killed dozens of people in Maui, Hawaii’s second-largest island last week, were fueled by strong winds and dry vegetation, the two factors that are driving the expansion worldwide. of forest fires. But Maui has a specific problem that various experts are now associating with the devastation caused by the fire: the widespread spread of highly flammable non-native Hawaiian grasses on land once occupied by sugar cane and pineapple plantations.
Until the beginning of the twentieth century, Lahaina, the city of almost 13,000 inhabitants destroyed by fires, it was surrounded by swamps, therefore from marshes and a type of vegetation that thrives in very rainy climates, such as that of Hawaii: a type of environment that normally prevents the spread of fires. However, the swamps were reclaimed to make room for pineapple and above all sugar cane plantations, which for about a century were Hawaii’s main economic resource, until tourism overcame them.
The islands last sugar cane plantation closed in 2016, right on Maui. On the land once occupied by plantations, plants native to Africa and brought to Hawaii by US colonizers to produce fodder for livestock thrived. The scientific names of these plants are Megathyrsus maximus, Cenchrus ciliaris e Melinis minutiflora: essentially they are herbs that exceed one meter in height, grow very quickly when it rains, and for this reason they are very popular in Hawaii, where rainfall is abundant. They also resist the drought of the dry season, to which they are well accustomed in their native environment, central Africa.
Areas of burnt vegetation in the Upcountry region of Maui, essentially the center of the island, on Aug. 11, 2023 (Hawaii Department of Land and Natural Resources via AP, LaPresse)
They are also species that burn very easily and are favored by fires, because they grow back well on burnt soils and do so before other plants. After a fire on the island of Hawaii in 2018 burned 14 square kilometers of Hawaii Volcanoes National Park, these species expanded even on the lava fields where until then only the ʻōhiʻa trees grew, a local species (Hawaii are volcanic islands). It is a worrying phenomenon, also because the lava fields would be an excellent barrier for fires, if devoid of vegetation except for the scattered ʻōhiʻa. On the other hand, they lose this firebreak function if they are covered with grass.
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Elizabeth Pickett, executive officer of the Hawaii Wildfire Management Organization, a nonprofit that seeks to address wildfire risk through outreach and other initiatives, told to Wired that today the three species of plants are estimated to be present on 26 percent of the Hawaiian territory. Not only where there once were plantations, land outside the city that is now essentially abandoned, but also along the streets and in the city’s green areas, including the gardens of the houses. Fields of these grasses filled the slopes around Lahaina, the destroyed city, down to the residential areas.
According to Clay Trauernicht, a botanist expert in vegetation fire science and management at the University of Hawaii, it is evident that expanses of non-native grasses can make wildfires completely uncontrollable and widespread that in other contexts would be completely manageable.
Bruciation zone in Lahaina, Maui, August 11, 2023 (Hawaii Department of Land and Natural Resources via AP, LaPresse)
The fire investigations that have been opened in Maui concern fire warning and evacuation operations and what triggered the flames, almost surely intentional or unintentional human actions. However, they also concern the lack of prevention, because the Maui authorities were aware of the fact that the island was at high risk of fires this season, which is precisely the dry season and this year has been particularly affected by drought.
The 2018 fires also affected Maui and destroyed 21 homes right in the west of the island, where Lahaina is located. On that occasion Trauernicht himself, who is one of Hawaii’s leading fire experts, had written a letter to Maui News to warn inhabitants of fire risks and urge them to do something to prevent them: «Fuel (all that grass) is the single thing we can directly intervene on to reduce the risk of fires».
More generally, an increased risk of fire damage to Hawaii was observed due to reduced rainfall. At the same time, average temperatures have increased in line with global warming caused by human activities: this has made the dry season drier and therefore the vegetation more vulnerable to fires. As for Maui, the Lahaina area was known to be the most exposed to wildfire risk in the western part of the island, according to an official 2020 risk reduction plan.
Fire hazards could be contained by building fire barriers, growing plants more resistant to flames, and grazing livestock on abandoned grasslands. So far no major initiatives of this kind have been taken although it was known that they would be useful.
Aftermath of large #wildfire in #Lahaina, #Maui.
Images taken by @CopernicusEU #Sentinel2 on Aug. 8 and Aug. 13, 2023.
Data processed in @sentinel_hub @ai6yrham @WildlandFirefig #Hawaii #hawaiifires #MauiFires #LahainaFires #MauiFire #lahainafire pic.twitter.com/5EbeDfAsFP
— kosmi 🛰️🌍 (@kosmi64833127) August 14, 2023
Beyond the global increase in temperatures, which has also been seen in Hawaii, it is not known exactly what the possible contribution of climate change to the fires of recent years has been, but it is known that a warmer atmosphere leads to greater evapotranspiration , i.e. evaporation of water from the soil and transpiration from plants, and therefore drier vegetation.
We must also consider a social factor that could have influenced the triggering of the fires: Hawaii is affected by a housing crisis due to which many people are homeless and live in camps of campers and caravans. In this context, cooking is often outdoors, which increases the risk of unintentional fires in areas on the edge of urban centers and therefore closer to uncontrolled vegetation.
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