Groundwater may be a bigger player in predicting rainforest fires than previously thought

Indonesian military personnel fight a large peat fire in Central Kalimantan, Borneo, Indonesia, in 2015. Photo credi: David Gaveau/Centre for International Forestry Research

Tropical rainforests are called so because they are geographically located in areas that experience high rainfall, but also close to the equator. But in Southeast Asia (SEA), they are instead drying up, causing calamitous fires over the past twenty years. In 1997 and 2015, forest fires in Indonesia choked surrounding countries in SEA in haze and were behind more than 400,000 pollution-related deaths.

Frequently, blame for rainforest fires fall squarely on climate change and deforestation, and studies have shown that if the current trends we are experiencing now continue, droughts and fire risk will increase in severity and regularity.

In this case, research scientists say that predicting fires and forecasting areas that may catch fire will become significantly vital for better management. According to Eco-Business, present prediction models for fire use meteorological parameters like the wind, rainfall, air temperature, and atmospheric humidity, all of which affect the levels of moisture content in the air and how combustible a forest is.

But a recent study published in Nature Climate Change puts a new factor forward: Groundwater. Conducted by group of researcher from Wageningen University, Gelderland, The Netherlands, looked at available fire data for Borneo and found that integrating groundwater dynamics into predictive models improves the accuracy of fire predictions.

 

The three elements: Fire, water, wind
As it often rains in the tropics, what lies on the forest floor and upper layers of the soil is usually damp and hardly considered fuel for forest fire.

During the intermittent dry spells, leaf litter continually draws groundwater up, maintaining its moistness. But during longer and more frequent dry spells, groundwater levels can drop so low, leaf litter cannot draw it up, thus creating a condition known as “hydrological drought”.

To combat the effects of drought, trees may also shed their leaves, which has the potential to further aggravate the situation as it increases the amount of dry potential fuel on the ground while also reducing shade, which allows the surface fuel to dry up even more. As David Bowman from the University of Tasmania, Tasmania, Australia, put in writing for a Nature Climate Change: News and Views piece that accompanied the paper, “rainforests become highly flammable.”

As Bowman explained in his writing, when hydrological drought sets in, peat, deep organic soils formed over thousands of years, become incendiary, “Importantly, even without fire, the drying out of peat during hydrological drought causes carbon losses due to rapid aerobic decomposition of organic matter.”

Underlying peat is sprawled over vast areas in places with tropical forests like the Congo Basin and SEA, where the organic matter acts like a sponge and keeps soil sodden. But, if drained, the peat instead becomes tinder, giving fuel to fires that are difficult or even impossible to control.

It was last seen on a devastating scale in 2015, when peat in a forest was drained for agriculture, but caught fire, burning an area the size of Vermont, in the United States (U.S.), leaving around half a million people sickened, and stifling surrounding countries like Singapore in haze and more carbon dioxide than Germany releases in a year.

Additionally, shifts attributed to climate change like the El Niño-Southern Oscillation (ENSO) shift are some of the factors behind rainforest droughts. Periodic and irregular weather deviations in the tropics, ENSO emerges from the variation in winds and sea surface temperatures over the Pacific Ocean, and can lead to alterations in precipitation order much like heavy rainfall in northwest South America and droughts in SEA.

Data from Global Forest Watch Fires proved that the number of fires Indonesia witnessed between 2013 and 2016 climaxed in 2015 and also corresponded with an ENSO event, which altogether, created the length and asperity of the 2015 wildfire crisis with delayed seasonal rains that would have largely helped in putting out the fires.

 

Drying land and less groundwater
Researchers also looked at rainfall, evapotranspiration – the amount of water trees and water bodies release into the air – and data of soil moisture from the Climatic Research Unit (CRU), United Kingdom (U.K.).

There, they found Borneo’s “drying trend” of groundwater, which had been occurring since the early 20th century. When the research scientists compared it with the groundwater data with fire occurrence reports, the results showed an interrelationship between low groundwater levels – hydrological drought – and increased fires. While fires occur almost annually, according to the research scientists, “the amplification of wildfires occurs during drought years.”

They discovered that in areas where fires occur, around ten times more land is burned in a year stricken with hydrological drought than otherwise. Years where more than 10,000 hectares of land were ablaze were also higher during years with drought. In short, larger areas are flammable when larger areas are experiencing hydrological drought.

Predictive models that integrated hydrological drought managed to more effectively predict both fire occurrence and area burned, especially during ENSO events, as compared to predictive models that rely only on the climate, which also considerably underestimated the area burned under conditions of an ENSO event.

The research scientists also noted that while groundwater plays a vital role in susceptibility of flammable areas, few prediction models subscribe to them.

“We investigated hundreds of statistical models,” Henny Van Lanen, a hydrology professor at Wageningen University, stated to Eco-Business. “So far, only models that use weather data are used to predict wildfire probability. We have proven that if you include hydrological information in the models, that is, groundwater recharge, the prediction improves.”

Professionals outside the industry commend the research study, stating that the inclusion of hydrological drought offered a perspective many present methods of prediction do not consider.

“The authors did a great job at exploring aspects of droughts that are not normally considered such as water availability in the soils. This is in part due to the lack of observational data, which the authors overcame by modelling groundwater recharge,” Katia Fernandes, from the International Research for Climate and Society at Columbia University, said. “This is a novel approach that can potentially be used for more accurate estimates for burned area, which is an essential parameter for fire prevention and mitigation measures ahead of the fire season.”

“Hydrological drought has never been considered, so far, as an indicator for strategic policy formulation, and the results indicate that the approach offers a powerful tool to improve planning and strategies to adapt to climate change,” the research scientists wrote. “Most practically, such a tool may be adopted in the ambitious government effort in Indonesia to restore two million hectares of degraded peatland by 2020, among others by rewetting drained peatlands.”

 

Source: Eco-Business