Friday, 6 May 2016

The Fort McMurray fires and climate change

Historic Wildfires Burn Through Canada As Sub-Arctic Forests Heat Up
BY JEFF SPROSS 

CREDIT: SHUTTERSTOCK
Wildfires are taking off in Canada as the country goes through one of its hottest and driest summers in decades.

Wildfire activity in the Northwest Territories is more than six times higher than its 25-year average, and as of August 23 a total of 162 wildfires were burning in British Columbia. The latter province has seen 1,269 wildfires so far this year, along with 314,895 hectares of land burned — almost equivalent to 2010, when the province lost 337,149 hectares to various blazes.

The fires have cut through the boreal forests that lie just outside the Arctic Circle throughout Canada, aided by the hottest and driest summer the Northwest Territories have seen in 50 years.

According to Canada’s National Post, the fires can kick smoke up to 10 or even 15 kilometers into the atmosphere, leaving massive plumes that can be spotted by satellite and seen as far away as Portugal.

It’s a major event in the life of the earth system to have a huge set of fires like what you are seeing in Western Canada,” Douglas Morton, an earth scientist at NASA, told the Post.

A recent study of the nearby Yukon Flats in Alaska concluded that the boreal forests in the area are experiencing wildfires at a frequency that outstrips any prior period in the last 10,000 years — and that’s twice as high as it was 500 to 1,000 years ago.

Covering 10 percent of the Earth’s land surface, the boreal forests around the globe account for nearly a third of all the carbon stored in soils and biomass. A large part of this is the fact that, being sub-Arctic, the forests sit atop permafrost which can release huge amounts of carbon into the atmosphere when warmed.

In other words, wildfires in the boreal forest could be one example of a climactic feedback loop: changes wrought by global warming that physically alter the Earth’s ecosystem in such a way that even more carbon is released to begin moving through the planet’s natural cycles, thus increasing global warming even further beyond what’s being caused by human emissions.

Meanwhile, climate change has also assisted the spread of the Mountain Pine beetle in Canada, allowing it to eat through an unprecedented amount of the boreal forests in Canada’s western half. This again introduces the possibility of a feedback loop: as the trees are killed off, fewer of them are available to store carbon from the atmosphere, while the dead trees release the carbon they’ve stored up.

Heat waves and wildfires this year have also extended farther south along the West Coast, into Oregon and Washington State.

As of Saturday, August 23, 360 firefighters from outside British Columbia had been sent to the province to help contain the blazes, including 75 from Australia. 
An additional 90 firefighters from Ontario and Alberta reportedly joined them over the weekend.


For Peat’s Sake: Drying And Burning Wetlands Amplify Global Warming

BY JOE ROMM JAN 13, 2015 11:46 AM

CREDIT: AP PHOTO/RONY MUHARRMAN
13 January, 2013

A firemen sprays water to try to put out peatland fire in Indonesia, Sept 16, 2014.

Smouldering peat fires already are the largest fires on Earth in terms of their carbon footprint,”explained mega-fire expert Prof. Guillermo Rein last week. He is coauthor of a new study called “Global vulnerability of peatlands to fire and carbon loss,” which warns that massive, difficult-to-stop peatland fires are likely to become even larger in the future, as human activity keeps drying out the formerly wet peatlands.

Since a key reason many peatlands will become drier is global warming, and since peatland fires can release staggering amounts of carbon dioxide, this process is a vicious circle, a dangerous amplifying carbon cycle feedback.
Most of the world’s wetlands are peat, which are better known as bogs, moors, mires, and swamp forests. Wikipedia notes, ”Under the proper conditions, peat is the earliest stage in the formation of coal.”

The study explains why the loss of peatlands is of such great concern to scientists: “Globally, the amount of carbon stored in peats exceeds that stored in vegetation and is similar in size to the current atmospheric carbon pool.”

Massive Indonesia peatland fires of 1997 and 1998, when it was especially dry from El Niño, burned almost 25 million acres, among the largest set of forest fires in the past two hundred years. A 2002 Nature analysis estimated the CO2 released by those fires was “equivalent to 13–40% of the mean annual global carbon emissions from fossil fuels, and contributed greatly to the largest annual increase in atmospheric CO2 concentration detected since records began in 1957.”

Why do such fires release so much carbon? As one soil scientist explained in November, it is typical in Indonesia that “even after the forest fires end, the peat continues to smolder underground until all organic matter has completely burned into ashes.”

A 2008 Nature Geoscience study — “High sensitivity of peat decomposition to climate change through water-table feedback” — projected that “a warming of 4°C causes a 40% loss of soil organic carbon from the shallow peat and 86% from the deep peat” of Northern peatlands. On our current emissions path, the world is set to warm well beyond 4°C (7°F). According to the 2008 study, “We conclude that peatlands will quickly respond to the expected warming in this century by losing labile soil organic carbon during dry periods.”

20100225-rehabA 2011 study led by University of Guelph professor Merritt Turetsky found that “drying of northern wetlands has led to much more severe peatland wildfires and nine times as much carbon released into the atmosphere.” Turetsky noted at the time, “Our study shows that when disturbance lowers the water table, that resistance disappears and peat becomes very flammable and vulnerable to deep burning.” And that’s when peatlands turn from a CO2 sink to a CO2 source.

The latest peatlands study was also led by Turetsky. It explains that “drying as a result of climate change and human activity lowers the water table in peatlands and increases the frequency and extent of peat fires.” Tragically, Indonesia has drained a great deal of its peatlands (and even burned forested areas) to createpalm oil plantations, a key reason there are so many forest fires and smoldering peat fires — fires that often ruin the air quality in the region.

The scary thing is future climate change may actually do the same thing: dry out peatlands,” explained another co-author, climatologist Guido van der Werf. “If peatlands become more vulnerable to fire worldwide, this will exacerbate climate change in an unending loop.” As several 2014 studies made clear, climate change will dry out and Dust-Bowlify large parts of the planet’s arable landmass.

The new study concludes that “almost all peat-rich regions will become more susceptible to drying and burning with a changing climate.” It’s time for humanity to try harder to slash carbon pollution and avoid triggering yet another amplifying carbon cycle feedback



The long slow burn of smouldering peat mega-fires
From Indonesia to Botswana, from Scotland to North Carolina, peat mega-fires burn for months, destroy habitat, clog the air with haze, and self-accelerate climate change impacts

By Guillermo Rein


7 May, 2014


Smouldering combustion is the slow, low temperature, flameless burning of porous fuels. It is especially common in wildland fuels which are thermally thick and form a char on heating. In the natural environment, smouldering fires burn two types of biomass: thick fuels like tree branches or logs, and organic soils like the duff layer or peat. These are characterized by having a significantly greater thermal time compared to fine fuels like foliage. The persistent smouldering of thick fuels is typically observed for a few days after a flaming wildfire has passed, and it is often referred to as residual combustion. This can make residual smouldering be responsible for the majority of the biomass burned during a wildfires.

Peat soils are made by the natural accumulation of partially decayed biomass and are the largest reserves of terrestrial organic carbon. Because of this vast accumulation of fuel, once ignited, smouldering peat fires burn for very long periods of time (e.g. months, years) despite extensive rains, weather changes or fire-fighting attempts. Indeed, smouldering is the dominant combustion phenomena in mega-fires of peatlands which are the largest fires on Earth

in terms of fuel consumption. Smouldering fires contribute considerably to global greenhouse gas emissions, and result in widespread ecosystem destruction. Moreover, because peat is ancient carbon, and smouldering is enhanced under warmer and drier climates, it creates a positive feedback mechanism in the climate system, a self-accelerating global process [Rein, 2013].

Reports of peat fires lasting for several months are not unusual, like the 1997 Borneo fires in Indonesia, 2000 Okavango delta fires in Botswana or 2008 Evans Road fire in North Carolina, USA. Peat fires occur with some frequency worldwide in tropical, temperate and boreal regions. Droughts, drainage and changes in land use are thought to be main causes leading to the high flammability conditions of dry peatlands. Possible ignition events can be natural (e.g. lightning, self-heating, volcanic eruption) or anthropogenic (land management, accidental ignition, arson).

The most studied peat mega-fire took place in Indonesia in 1997 and led to an extreme haze event (see Figure 1). The smoke covered large parts of South-East Asia, even reaching Australia and China, and induced a surge of respiratory emergencies in the population and disruption of shipping and aviation routes for weeks. It was estimated that these fires released the equivalent to 13-40% of global man-made emissions of the year 1997 [Page et al, 2002]. This mega-fire was not an isolated case in the region, haze episodes have drifted to South East Asia once every three years on average. Rough figures at the global scale estimate that the average greenhouse gas emissions from peat fire is equivalent to >15% of manmade emissions.

Due to its complexity and coupling of heat and mass transport with chemical processes inside a reactive porous media, and despite its broad implications to the environment, current understanding of smouldering combustion is limited, and considerably less advanced than flaming combustion [Rein, 2013].

The characteristic temperature and intensity of smouldering combustion are low compared to flaming combustion. Because of these characteristics, smouldering spreads in a creeping fashion, typically around 1 mm/min, which is two orders of magnitude slower than flame spread. A smouldering front can be initiated with weaker ignition sources and is more difficult to suppress than flaming combustion. This makes it the most persistent combustion phenomena.

Because the water content of wildland fuels like peat can vary naturally over a wide range of values (from dry to flooded), and because water represents a significant energy sink, moisture content is the single most important property governing the ignition and spread of smouldering wildfires. The critical moisture content for ignition (related to the moisture of extinction) of boreal peat has been measured around 120% in dry basis [Frandsen, 1997], although exact value depends on mineral content and density. Peat drier than this is susceptible to smouldering. The prominent

role of moisture is such that natural or anthropogenic-induced droughts are the leading cause of smouldering mega-fires.

The second most important property that affects ignition is the mineral content. As experimentally found by Frandsen [1997], there is a decreasing linear relationship between the mineral content and the critical moisture content: higher mineral loads mean soil can only ignite at lower moistures. This is because the inert content is a heat sink to the fire. This rule can be applied to most organic soils or fuel beds to determine if they are susceptible to smouldering. Any soil which has a composition that is more than 80% mineral, cannot sustain a smouldering fire. After moisture and mineral contents, other important properties are bulk density, porosity, flow permeability and composition.

Organic material located close to the surface of the soil burns in shallow fires (roughly <1 m under the surface). They propagate laterally and downwards along the organic layers of the ground and leave voids or holes in the soil. This pattern allows fuel consumption to be using the depth of burn to calculate the volume of the void. Depth of burn is the vertical distance between the original soil location and the post-fire soil location. A typical value for the depth of burn reported in several field studies is around 0.5 m, which means that the average fuel consumptions per unit area is around 75 kg/m2 [Rein, 2013]. The depth of burn and amount of fuel consumption, along with the resulting impacts of peat fires, support their classification as mega-fires.

The prominent role of moisture is such that natural or anthropogenic-induced droughts are the leading cause of smouldering mega-fires.

Smouldering fires have detrimental effects on the forest soil, its microflora and microfauna. This is because it consumes the soil itself and also because the long residence time of smouldering means that heat penetrates deep into the soil layers. On the contrary, flames produce high temperatures above the ground for short periods of time (in the order of 15 min). This results in minimal heating of the soil below depths of a few cm and can leave the soil system relatively unharmed. However, smouldering fires lead to enhanced heat transfer into the soil for much longer durations (i.e. in the order of 1 h). As a comparison, the thermal conditions in smouldering are more severe than medical sterilization treatments, and mean that the soil is exposed to conditions that are lethal to biological agents [Rein, 2013].

Flaming wildfires may attract more attention than smouldering fires, but the study of flameless fires will contribute forward-looking ideas to understanding and managing a form of combustion that demands our focus.

References

Frandsen, W.H. (1997) Ignition probability of organic soils. Canadian Journal of Forest Research 27: 1471–7. http://dx.doi.org/10.1139/x97-106

Page, S.E., Siegert, F., Rieley, J.O., Boehm, H.D.V., Jaya, A. & Limin, S. (2002) The amount of carbon released from peat and forest fires in Indonesia during 1997. Nature 420: 61–65. http://dx.doi.org/10.1038/nature01131

G Rein, Smouldering Fires and Natural Fuels, Chapter 2 in: Fire Phenomena in the Earth System – An Interdisciplinary Approach to Fire Science, C Belcher (editor). Wiley and Sons, 2013. http://onlinelibrary.wiley.com/doi/10.1002/9781118529539.ch2

About the author

Dr. Guillermo Rein (g.rein@imperial.ac.uk) is Senior Lecturer in Mechanical Engineering at Imperial College London, and Editor-in-Chief of Fire Technology. His professional activities focus on research in fire and combustion, and teaching of thermofluid sciences toengineers. He has studied a wide range of fire dynamics topics in the built and natural environments, including pyrolysis, fire modeling, wildfires, structures and fire, and forecasting techniques. Over the course of the last 15 years he has also specialized in smouldering combustion, conducting both computational and experimental studies on a variety of fuels like polyurethane foam, cellulose, peat and coal.




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