Researchers evaluate connection between California wildfires and human-caused climate change

A group of seven scientists published a paper last month that looks at the connection between California wildfires and human-caused climate change, titled Observed Impacts of Anthropogenic Climate Change on Wildfire in California. One of their main conclusions was that climate warming dries the atmosphere which in turn dries fuels, promoting forest fires in the summer.

Here is the abstract:

“Recent fire seasons have fueled intense speculation regarding the effect of anthropogenic climate change on wildfire in western North America and especially in California. During 1972–2018, California experienced a fivefold increase in annual burned area, mainly due to more than an eightfold increase in summer forest‐fire extent. Increased summer forest‐fire area very likely occurred due to increased atmospheric aridity caused by warming. Since the early 1970s, warm‐season days warmed by approximately 1.4 °C as part of a centennial warming trend, significantly increasing the atmospheric vapor pressure deficit (VPD). These trends are consistent with anthropogenic trends simulated by climate models. The response of summer forest‐fire area to VPD is exponential, meaning that warming has grown increasingly impactful.

“Robust interannual relationships between VPD and summer forest‐fire area strongly suggest that nearly all of the increase in summer forest‐fire area during 1972–2018 was driven by increased VPD. Climate change effects on summer wildfire were less evident in nonforested lands. In fall, wind events and delayed onset of winter precipitation are the dominant promoters of wildfire. While these variables did not change much over the past century, background warming and consequent fuel drying is increasingly enhancing the potential for large fall wildfires. Among the many processes important to California’s diverse fire regimes, warming‐driven fuel drying is the clearest link between anthropogenic climate change and increased California wildfire activity to date.”

An illustration from the paper:

Climate change California wildfires
Seasonal and annual burned areas in California for 1972–2018. (a) Total burned area in the four regions of focus: (b) North Coast, (c) Sierra Nevada, (d) Central Coast, and (e) South Coast. Annual burned area is decomposed into that which occurred in January–April (green), May–September (red), and October–December (orange). Significant (p < 0.05) trends are shown as bold black curves.

Below is an excerpt from the paper:

“In this study we evaluated the various possible links between anthropogenic climate change and observed changes in California wildfire activity across seasons, regions, and land cover types since the early 1970s. The clearest link between California wildfire and anthropogenic climate change thus far has been via warming‐driven increases in atmospheric aridity, which works to dry fuels and promote summer forest fire, particularly in the North Coast and Sierra Nevada regions. Warming has been far less influential on summer wildfire in nonforest areas. In fall, the drivers of wildfire are particularly complex, but warming does appear to enhance the probability of large fall wildfires such as those in 2017 and 2018, and this effect is likely to grow in the coming decades.

“Importantly, the effects of anthropogenic warming on California wildfire thus far have arisen from what may someday be viewed as a relatively small amount of warming. According to climate models, anthropogenic warming since the late 1800s has increased the atmospheric vapor‐pressure deficit by approximately 10%, and this increase is projected to double by the 2060s. Given the exponential response of California burned area to aridity, the influence of anthropogenic warming on wildfire activity over the next few decades will likely be larger than the observed influence thus far where fuel abundance is not limiting.”

Citation:
Observed Impacts of Anthropogenic Climate Change on Wildfire in California.
A. Park Williams John T. Abatzoglou Alexander Gershunov Janin Guzman‐Morales Daniel A. Bishop Jennifer K. Balch Dennis P. Lettenmaier
First published: 15 July 2019 https://doi.org/10.1029/2019EF001210

Former fire chiefs warn Australians about increasing climate threat

Pilliga Fire New South Wales
Pilliga Fire 60km southwest of Narrabri, New South Wales, Australia, January 2018.

An article in The Guardian says 20 former fire chiefs in Australia are warning that the country and the emergency services are not prepared for the escalating threat from bushfires caused by climate change.

Below is an excerpt:

In a statement issued before a federal election date is announced, 23 former emergency services leaders and senior personnel have called on both major parties to recognise the need for “national firefighting assets”, including large aircraft, to deal with the scale of the threat.

The document calls on the next prime minister to meet former emergency service leaders “who will outline, unconstrained by their former employers, how climate change risks are rapidly escalating”.

The group also wants the next government to commit to an inquiry into whether Australia’s emergency services are adequately resourced to deal with increased risks from natural disasters caused by climate change.

Last year, in Australia alone, the NSW fire season began in early August, a heatwave led to fires in rainforest areas of Queensland in early December, and forest in Tasmania’s world heritage area caught fire in January, Australia’s hottest month on record.

Fires Queensland satellite photo
Satellite photo of smoke from the fires in Queensland, Australia, November 26, 2018.

Climate change brings less rain with more dry lightning and wildfires to Tasmania

wildfires in Tasmania satellite photo
Satellite photo of smoke from wildfires in Tasmania, January 21, 2019. The red dots represent heat detected by the satellite. NASA & Wildfire Today.

Climate change has already brought alarming change to Tasmania, the huge island south of the Australian mainland. Until recently it was assumed that the climate differences would not be massive since it was thought by some that the ocean surrounding the island would not be heating as quickly as it was in other areas.

Now the southwest area of the state, the heart of its world heritage area, is being described as dying — the rainforest and heathlands are beginning to disappear. The nearby seas, it turns out, are warming at two to three times the global rate.

Richard Flanagan writes about this issue in an opinion article at The Guardian. Below is an excerpt:

…Then there was the startlingly new phenomenon of widespread dry lightning storms. Almost unknown in Tasmania until this century they had increased exponentially since 2000, leading to a greatly increased rate of fire in a rapidly drying south-west. Compounding all this, winds were also growing in duration, further drying the environment and fuelling the fires’ spread and ferocity.

Such a future would see these fires destroy Tasmania’s globally unique rainforests and mesmerizing alpine heathlands. Unlike mainland eucalyptus forest these ecosystems do not regenerate after fire: they would vanish forever. Tasmania’s world heritage area was our Great Barrier Reef, and, like the Great Barrier Reef, it seemed doomed by climate change.

Later [Prof Peter] Davies [an eminent water scientist] took me on a research trip into a remote part of the south-west to show me the deeply upsetting sight of an area that was once peatland and forest and was now, after repeated burning, wet gravel. The news was hard to comprehend – the enemies of Tasmania’s wild lands had always had local addresses: the Hydro Electricity Commission, Gunns, various tourism ventures. They could be named and they could be fought, and, in some cases, beaten.

Six weeks ago, the future that Davies and others had been predicting arrived in Tasmania. Lightning strikes ignited what would become known as the Gell River fire in the island’s south-west. In later weeks more lightning strikes led to more fires, every major one of which is still burning.

Climate assessment predicts increasing wildfires

By mid-century western wildfires could increase 200% to 600%

At 2 p.m. Friday on the day after Thanksgiving President Trump’s administration released an important document about our climate. Required every four years by a 1990 act of Congress, the Fourth National Climate Assessment focuses on the human welfare, societal, and environmental elements of climate change.

Surprising in its bluntness, it lays out the devastating effects on the economy, health, environment, and wildfires. Within the 1,656-page document wildfires are covered rather extensively and photos of fires are used several times in the headers of sections, like the one below for Chapter 1 (which may have been taken at the Howe Ridge Fire in Glacier National Park in Montana in August).

The scientists concluded that by the middle of this century, the annual area burned in the western United States could increase 2–6 times from the present, depending on the geographic area, ecosystem, and local climate. The area burned by lightning-ignited wildfires could increase 30 percent by 2060.

In the Southeast rising temperatures and increases in the duration and intensity of drought are expected to increase wildfire occurrence and also reduce the effectiveness of prescribed fire. Intra-annual droughts, like the one in 2016, are expected to become more frequent in the future. Thus, drought and greater fire activity are expected to continue to transform forest ecosystems in the region.

In the Southwest, recent wildfires have made California ecosystems and Southwest forests net carbon emitters (they are releasing more carbon to the atmosphere than they are storing). With continued greenhouse gas emissions, models project more wildfire across the area. Under higher emissions, fire frequency could increase 25%, and the frequency of very large fires (greater than 5,000 hectares) could triple.

The Northwest is likely to continue to warm during all seasons under all future scenarios, although the rate of warming depends on current and future emissions. The warming trend is projected to be accentuated in certain mountain areas in late winter and spring, further exacerbating snowpack loss and increasing the risk for insect infestations and wildfires. In central Idaho and eastern Oregon and Washington, vast mountain areas have already been transformed by mountain pine beetle infestations, wildfires, or both, but the western Cascades and coastal mountain ranges have less experience with these growing threats. Forests in the interior Northwest are changing rapidly because of increasing wildfire and insect and disease damage, attributed largely to a changing climate. These changes are expected to increase as temperatures increase and as summer droughts deepen.

Below are wildfire-related excerpts from the report.


Climate assessment overview

Chapter 1: Overview

The impacts of climate change and extreme weather on natural and built systems are often considered from the perspective of individual sectors: how does a changing climate impact water resources, the electric grid, or the food system? None of these sectors, however, exists in isolation. The natural, built, and social systems we rely on are all interconnected, and impacts and management choices within one sector may have cascading effects on the others.

Continue reading “Climate assessment predicts increasing wildfires”

Wildfires can be part of a series of cascading events

Maximum Wildfire Elevation
Maximum Wildfire Elevation. MBTS & Nature.

In the natural world one environmental event or disturbance can initiate or be part of a series of cascading events that intensify the impacts of natural hazards, possibly turning them into disasters.

An article at The Conversation explores how these effects can be enhanced by a warming climate. Below is an excerpt from an article written by Amir AghaKouchak (UC Irvine) and Farshid Vahedifard (Mississippi State University).


“Multiple hazardous events are considered cascading when they act as a series of toppling dominoes, such as flooding and landslides that occur after rain over wildfires. Cascading events may begin in small areas but can intensify and spread to influence larger areas.

[…]

“Also, the severity of these cascading weather events worsens in a warming world. Drought-stricken areas become more vulnerable to wildfires. And snow and ice are melting earlier, altering the timing of runoff. This has a direct relationship with the fact that the fire season across the globe has extended by 20 percent since the 1980s. Earlier snowmelt increases the chance of low flows in the dry season and can make forests and vegetation more vulnerable to fires.

“These links spread further as wildfires occur at elevations never imagined before. As fires destroy the forest canopy on high mountain ranges, the way snow accumulates is altered. Snow melts faster because soot deposited on the snow absorbs heat. Similarly, as drought dust is released, snow melts at a higher rate, as has been seen in the Upper Colorado River Basin.

[…]

“When landscapes are charred during wildfires, they become more vulnerable to landslides and flooding. In January, a debris flow event in Montecito, California killed 21 people and injured more than 160. Just one month before the landslide, the soil on the town’s steep slopes were destabilized in [the Thomas Fire]. After a storm brought torrential downpours, a 5-meter high wave of mud, tree branches and boulders swept down the slopes and into people’s homes.”


More Information

Researchers look at how warming will exacerbate the occurrence of wildfires in Mediterranean Europe

wildfire portugal
Wildfire south of Porto, Portugal, September 2, 2012. Photo by Bill Gabbert.

The climate warming that we have been seeing is expected to continue along with the increased risk of larger, more suppression-resistant wildfires. Scientists have examined how this will affect fires in Europe up to a 1.5°C  rise, which is the not-to-exceed target in the Paris climate agreement. Now a study is complete that examines increases of 1.5, 2, and 3°C warming scenarios. Not surprisingly, it found that the higher the warming level, the larger is the increase of burned area, ranging from ~40% to ~100% across the scenarios. Their results indicate that significant benefits would be obtained if warming were limited to well below 2 °C.

wildfires Climate Change Southern Europe
Ensemble mean burned area changes. Burned area changes (%) for a the +1.5 °C case with the stationary model SM (i.e., using Eq. 3), (b) the +1.5 °C case with non-stationary model NSM (i.e., NSM). using Eq. (4), (c) the +2 °C case with SM, (d) the +2 °C case with NSM, (e) the +3 °C case with SM, and f the +3 °C case with NSM. Dots indicate areas where at least 50% of the simulations (1000 bootstrap replications × the ensemble of RCMs) show a statistically significant change and more than 66% agree on the direction of the change. Coloured areas (without dots) indicate that changes are small compared to natural variations, and white regions (if any) indicate that no agreement between the simulations is found. Click to enlarge.

The paper, published in Nature, was written by Marco Turco, Juan José Rosa-Cánovas, Joaquín Bedia, Sonia Jerez, Juan Pedro Montávez, Maria Carmen Llasat, and Antonello Provenzale.