Forests make heatwaves ‘initially warmer’


During heatwaves forests reduce their evaporation, causing the atmosphere to warm up even more, say researchers.

During extremely long periods of heat, however, this reduction enables the forests to continue their evaporation for longer, so the net effect is ultimately one of cooling in relation to the surroundings, explained a team of scientists led by Ryan Teuling from Wageningen University in the Netherlands.

Writing in the journal Nature Geoscience, Dr Teuling worked on the investigation in collaboration with climate researchers from a number of European countries.

The study was prompted by recent heatwaves in Europe, which had raised interest in questions about the influence of land use on temperatures and climate.

Up to now, scientists had assumed that a lack of precipitation during heatwaves automatically led to a reduction in evaporation.

That reduction was thought to be less for forests, because trees, with their deeper root systems, have more water available to them. Examination of the precise role of land use, however, has been largely neglected up to now.

The study found large differences in evaporation strategies during heat waves. Grasslands evaporate more at higher temperatures and stop only when no more water is available.

Forests, in contrast, respond to higher temperatures by evaporating less, which leaves more water at their disposal.

During brief heatwaves, therefore, the greatest warming is found above forests, but during prolonged heat waves the increased evaporation of grasslands ends up causing a shortage of water.

This can lead to exceptionally high temperatures, such as those measured in France in the summer of 2003.

This mechanism might also offer an explanation for the unusually high temperatures near Moscow this summer, the researchers suggest.

In these types of extreme situations, forests in fact have a cooling effect on the climate.

The research was done on the basis of observations made above forests and grasslands in Europe by an extensive network of flux towers. For areas without towers, satellite data were used.

Source: Wageningen University press release

Date: 06/09/2010

Amazon forest fires ‘on the rise’


The number of fires destroying Amazon rainforests are increasing, a study has found.

Take Cover library pictureThe BBC’s Mark Kinver reports that a team of scientists said fires in the region could release similar amounts of carbon as deliberate deforestation.

Reporting on a paper published in the journal Science, Kinver says the researchers found that that fire occurrence rates had increased in 59% of areas with reduced deforestation.

As a result, the rise in fires could jeopardise the long-term success of schemes to reduce emissions from deforestation, they added.

The researchers – from the University of Exeter, UK, and Brazil’s National Institute for Space Research – based their findings on satellite-derived data on deforestation and forest fires.

“The results were a surprise because we expected that fires would have decreased with the decrease of deforestation,” said co-author Luiz Aragao from the University of Exeter.

“The implication for REDD is that we first need a system that can monitor fires,” he told the Science journal.

“There is also a need to shift land use in the Amazon to a system where fire is not used.”

‘Slash and burn’

REDD (Reducing Emissions from Deforestation and forest Degradation) schemes aim to create a financil value for the carbon stored in developing nations’ tropical forests.

It offers nations incentives to protect forest areas from a variety of impacts that release carbon into the atmosphere, including tree felling and logging, agricultural expansion, land degradation.

As deforestation accounts for about 20% of emissions resulting from human activity, the REDD programmes are considered to be a key component in the global effort to curb climate change.

“Fires following drought years are likely to release a similar amount of carbon as emissions from deliberate deforestation,” the researchers wrote.

“The higher probability of a drier Amazon in the 21st Century predicted by some global circulation models… may push Amazonia towards an amplified fire-prone system.”

They added that previous studies showed that fires in the region increased after large-scale droughts in 1998 and 2005.

“Forest landscapes in Amazonia are becoming more fragmented and, therefore, a growing proportion of forests is exposed to the leakage of accidental fires from adjacent farms,” they suggested.

The practice of “slash and burn” is widely used by farmers in the Amazon region to clear secondary forests and allow food and cash crops to be cultivated.

But Dr Aragao said: “We need to change the way people use and manage their land so that they can do this without fire.”

Commenting on the paper’s findings, Andrew Mitchell, director of the Global Canopy Programme, said: “These results have important implications for REDD negotiations.

“If we are to control deforestation, you have got to look at what local people are doing outside of the forests,” he told BBC News.

“The entire REDD regime need to encourage a better use of land without fire.

“But if they do not use fire, which is cheap, then what are they going to use – strimmers? Chainsaws? Tractors?

“That means that money from REDD programmes need to go to people that not only live within the forests, but also the farmers living outside them.”

Dr Aragao agreed, adding that switching to fire-free land management in already deforested area that lie next to forests could “drastically reduce fires and carbon emissions”.

“It would be expensive,” he observed, “but it would protect the stability of Amazonian carbon stocks and diversity.”

Pieter van Lierop, a forestry officer for the Food and Agriculture Organization (FA) – a member of the UN’s REDD programme, said the findings were relevant to policies aimed at reducing deforestation.

“The article clearly demonstrates that within REDD, specific attention should go to analyzing the role of fire and propose more responsible use of fire and/or alternatives for fire,” he told BBC News.

“However, we should also take into consideration that the article is mainly discussing fire incidence and occurence, meaning number of fires and not the size of emissions.”

Source: BBC News website

Date: 06/06/2010

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