August 10, 2023

expert reaction to Hawaii wildfires

Deaths have been reported following wildfires on the Hawaiian island of Maui.

Comments sent out 11/08/2023:

Prof Yadvinder Malhi, Professor of Ecosystem Science, University of Oxford, said:

“It may surprise many that Hawai’i can have wildfires, but the western sides of the islands sit in the shadow of extinct volcanoes which shelter those areas from rain and make them quite dry.  There is a long history of fire since Polynesian times, but a few factors may have amplified risk: the spread of non-native, flammable species, land abandonment and suppression of small fires that leads to wood fuel build up so fires are big when they burn (I don’t know which of these factors might have played a role in the Lahaina fire, but it is likely at least one did).  On top of these local factors, climate change is leading to warmer atmosphere everywhere, which has more drying power, so the same fire that would have been moderate a few decades ago will be more intense now.  Finally, intense winds seem to have fanned this particular fire and led to its devastating speed and tragic consequences.”

Dr Thomas Smith, Associate Professor in Environmental Geography, London School of Economics and Political Science, said:

“Land abandonment is a factor that played a role in the intensity and speed of the fire.  It’s clear from satellite imagery and from those who know the area well that the rural land to the east of Lahaina was once intensely managed plantations, with irrigation ditches and terracing.  The agricultural land would have been fire resistant, with a very low fuel load (flammable vegetation) and higher fuel moisture due to the irrigation.  Since most of this land has been abandoned, long grasses, shrubs and young trees had taken root, substantially increasing the amount of flammable vegetation surrounding the town.

“The high winds, driven by the hurricane to the SW and another strong low pressure system further to the NW, were driven over the island and then downslope towards the town.  Downslope (katabatic) winds are dry and warm, further reducing the moisture in the vegetation and driving more extreme fire behaviour.

“The combination of a sudden ignition and rapid spread by katabatic (warm and dry downslope) winds is a similar situation to the Camp Fire (Paradise) in 2018, which is (possibly was) the deadliest US wildfire since 1918.”

(See comment below also from Dr Thomas Smith, from Thursday 10 August.)

Comments sent out 10/08/2023:

Dr Douglas Kelley, a land surface modeller at the UK Centre for Ecology & Hydrology (UKCEH), said:

“Hawaii does get fires but the scale of these are larger, more intense and faster-spreading than usual.  The number of deaths and evacuations suggest it’s more than local emergency services normally cope with.  This would therefore be classed as an extreme and unusual wildfire event.

“These events are often exacerbated by high winds, so it is plausible that the hurricane is having an influence.  But ground conditions have to be dry enough for fires to spread, so that would suggest other factors than just the hurricane.”

Dr Thomas Smith, Associate Professor in Environmental Geography, London School of Economics and Political Science, said:

“Wildland fires are not unusual in Hawaii, there are occasional fires every year.  This year’s fires, however, are burning a greater area than usual, and the fire behaviour is extreme, with fast spread rates and large flames.

“Fire behaviour (spread rate and intensity) is driven by the fuel (vegetation), weather conditions, and the terrain.  The vegetation in the lowland areas of Maui is particularly parched this year, with below-average precipitation in the spring, and hardly any rainfall this summer.  Temperatures have been above average, particularly overnight temperatures.  This is important because low relative humidity drives more extreme fire behaviour, and if relative humidity remains low overnight, the fires become difficult to control and can spread for multiple days.

“A combination of the hurricane to the southwest and another strong low pressure system further to the west near Japan has contributed to sustained wind speeds of more than 35 km/hr or greater.  This is unusual for this time of year, and will have been responsible for the very fast moving wildfires that have led to severe impacts, including deaths and widespread loss of homes.”

Declared interests

Dr Thomas Smith: “I have no declaration of interests.”

For all other experts, no reply to our request for DOIs was received.