Tag Archives: Wildfires

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Thinning clouds increase California’s wildfires

Southern California’s wildfires are likely to increase as a protective layer of cloud is driven away by the warmer climate and urban growth.

LONDON, 4 June, 2018 – Southern California’s wildfires are posing a growing risk, as the Sunshine State threatens to become too sunny for its own good. In many southern coastal areas, rising summer temperatures caused by spreading urbanisation and the warming climate are driving off formerly common low-lying morning clouds and increasing the prospect of worse wildfires, US scientists say.

Park Williams, a bioclimatologist at Columbia University’s Lamont-Doherty Earth Observatory, is lead author of their study. He says: “Cloud cover is plummeting in southern coastal California. And as clouds decrease, that increases the chance of bigger and more intense fires.” This conclusion reinforces earlier research which found that low-level clouds could help to cause some cooling.

What is happening is a neat example of a process known by climate scientists as a positive feedback, a way in which climate change contrives to feed on itself to worsen the situation still further (negative feedbacks, by contrast, cool things down). Another example is Arctic melting.

“People in these areas are very good at putting out fires, so the area burned hasn’t gone up. But the dice are now loaded…the fires should be getting more intense and harder to contain”

Professor Williams says the decrease is driven mainly by urban sprawl, which increases near-surface temperatures, but that overall warming climate is contributing too. Increasing heat drives away clouds, admitting more sunlight to heat the ground further, leading to dryer vegetation and higher fire risk. The team’s research is published in the journal Geophysical Research Letters.

It follows a 2015 study in which Williams first documented a decrease in cloud cover around Los Angeles and San Diego. Urban road surfaces and buildings absorb more solar energy than open countryside does, and that heat is radiated back out into the air – a major part of the so-called heat-island effect.

At the same time, overall temperatures have been rising in California thanks to global warming driven by prodigal human combustion of fossil fuels, and this has boosted the effect. In the new study, Williams and his colleagues have found a 25 to 50% decrease in low-lying summer clouds since the 1970s in the greater Los Angeles area.

Normally stratus clouds form over coastal southern California during early morning within a thin layer of cool, moist ocean air sandwiched between the land and higher air masses that are too dry for cloud formation.

Burning off

The stratus zone’s altitude varies with weather, but sits at roughly 1,000 to 3,000 feet (305-915 metres). But heat causes clouds to dissipate, and decades of intense urban growth plus global warming have been damaging the stratus layer’s base, causing it to thin and clouds to burn off earlier in the day or disappear altogether.

Cloud bases have risen 150 to 300 feet since the 1970s, says the study. “Clouds that used to burn off by noon or one o’clock are now gone by 10 or 11 AM, if they form at all,” said Williams.

He and his colleagues have shown a strong link between a warming climate and an increase in wildfires in the western US. But in southern California the link is more subtle, and clouds are a rarely studied part of the system.

However, many of California’s airports have been collecting hourly cloud observations since the 1970s, not for research, but rather for navigational safety. Williams and his colleagues used this data to develop a fine-grained picture of changing cloud cover over the region.

Telling comparison

They then compared it to a separate large database kept by the US Wildland Fire Assessment System, whose researchers have for decades regularly measured vegetation moisture in the hills outside Los Angeles. By comparing the two data sets they found that periods of less cloud cover during the summer correlated neatly with lower vegetation moisture, and thus more danger of fire.

But the study has not found that the total area burned in summer has increased because of decreases in cloud shading. There are too many other factors at play, says Professor Williams, including yearly rainfall variations, winds, the places where fires start, and – perhaps most of all – decreases in burnable area as urban districts have grown, together with the increased effectiveness of fire-fighting.

“Even though the danger has increased, people in these areas are very good at putting out fires, so the area burned hasn’t gone up,” he said. “But the dice are now loaded, and in areas where clouds have decreased, the fires should be getting more intense and harder to contain. At some point, we’ll see if people can continue to keep up.”

The California-wide fires in the autumn of 2017 were probably not strongly affected by the reductions in summer cloud cover, he said. They were driven mainly by extreme winds and a late onset of the autumn rainy season. But he expects to see California’s overall fire danger increase, as long as there is adequate vegetation to burn. – Climate News Network

Southern California’s wildfires are likely to increase as a protective layer of cloud is driven away by the warmer climate and urban growth.

LONDON, 4 June, 2018 – Southern California’s wildfires are posing a growing risk, as the Sunshine State threatens to become too sunny for its own good. In many southern coastal areas, rising summer temperatures caused by spreading urbanisation and the warming climate are driving off formerly common low-lying morning clouds and increasing the prospect of worse wildfires, US scientists say.

Park Williams, a bioclimatologist at Columbia University’s Lamont-Doherty Earth Observatory, is lead author of their study. He says: “Cloud cover is plummeting in southern coastal California. And as clouds decrease, that increases the chance of bigger and more intense fires.” This conclusion reinforces earlier research which found that low-level clouds could help to cause some cooling.

What is happening is a neat example of a process known by climate scientists as a positive feedback, a way in which climate change contrives to feed on itself to worsen the situation still further (negative feedbacks, by contrast, cool things down). Another example is Arctic melting.

“People in these areas are very good at putting out fires, so the area burned hasn’t gone up. But the dice are now loaded…the fires should be getting more intense and harder to contain”

Professor Williams says the decrease is driven mainly by urban sprawl, which increases near-surface temperatures, but that overall warming climate is contributing too. Increasing heat drives away clouds, admitting more sunlight to heat the ground further, leading to dryer vegetation and higher fire risk. The team’s research is published in the journal Geophysical Research Letters.

It follows a 2015 study in which Williams first documented a decrease in cloud cover around Los Angeles and San Diego. Urban road surfaces and buildings absorb more solar energy than open countryside does, and that heat is radiated back out into the air – a major part of the so-called heat-island effect.

At the same time, overall temperatures have been rising in California thanks to global warming driven by prodigal human combustion of fossil fuels, and this has boosted the effect. In the new study, Williams and his colleagues have found a 25 to 50% decrease in low-lying summer clouds since the 1970s in the greater Los Angeles area.

Normally stratus clouds form over coastal southern California during early morning within a thin layer of cool, moist ocean air sandwiched between the land and higher air masses that are too dry for cloud formation.

Burning off

The stratus zone’s altitude varies with weather, but sits at roughly 1,000 to 3,000 feet (305-915 metres). But heat causes clouds to dissipate, and decades of intense urban growth plus global warming have been damaging the stratus layer’s base, causing it to thin and clouds to burn off earlier in the day or disappear altogether.

Cloud bases have risen 150 to 300 feet since the 1970s, says the study. “Clouds that used to burn off by noon or one o’clock are now gone by 10 or 11 AM, if they form at all,” said Williams.

He and his colleagues have shown a strong link between a warming climate and an increase in wildfires in the western US. But in southern California the link is more subtle, and clouds are a rarely studied part of the system.

However, many of California’s airports have been collecting hourly cloud observations since the 1970s, not for research, but rather for navigational safety. Williams and his colleagues used this data to develop a fine-grained picture of changing cloud cover over the region.

Telling comparison

They then compared it to a separate large database kept by the US Wildland Fire Assessment System, whose researchers have for decades regularly measured vegetation moisture in the hills outside Los Angeles. By comparing the two data sets they found that periods of less cloud cover during the summer correlated neatly with lower vegetation moisture, and thus more danger of fire.

But the study has not found that the total area burned in summer has increased because of decreases in cloud shading. There are too many other factors at play, says Professor Williams, including yearly rainfall variations, winds, the places where fires start, and – perhaps most of all – decreases in burnable area as urban districts have grown, together with the increased effectiveness of fire-fighting.

“Even though the danger has increased, people in these areas are very good at putting out fires, so the area burned hasn’t gone up,” he said. “But the dice are now loaded, and in areas where clouds have decreased, the fires should be getting more intense and harder to contain. At some point, we’ll see if people can continue to keep up.”

The California-wide fires in the autumn of 2017 were probably not strongly affected by the reductions in summer cloud cover, he said. They were driven mainly by extreme winds and a late onset of the autumn rainy season. But he expects to see California’s overall fire danger increase, as long as there is adequate vegetation to burn. – Climate News Network

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Temperature rise will fan forest flames

FOR IMMEDIATE RELEASE The forest fires raging through states in the western US are among the worst on record, but latest research indicates that they will get even worse in future as temperatures rise. LONDON, 2 September − As fire crews battle to control the forest fires that have been devastating areas of the western US, a bleak warning has been issued that such fires in future are likely to break out over longer periods and wider areas each year, and create up to twice as much smoke. Forest wildfires are a regular event in California and other states in the western US, but this year’s conflagrations are being described as some of the worst on record. One fire, which has threatened California’s Yosemite National Park, was at one stage spread over nearly 200,000 acres, or more than 300 square miles. Environmental scientists at Harvard School of Engineering and Applied Sciences (SEAS) fed data into a number of models to come up with predictions about how such fires will behave in future. The data included not only historical records of fires but also seasonal temperatures, relative humidity levels, and amounts of brush and dry fuel on the forest floor over six “ecoregions” in the western states. The models were matched with data from the fourth Intergovernmental Panel on Climate Change (IPCC) report on possible future atmospheric and climatological conditions for the year 2050. Based on this multi-model approach, the Harvard team was then able to calculate the likely extent of fires in mid-century, and to gauge areas that would be burned. “We weren’t altogether certain what we would find when we started this project,” says Loretta J Mickley, the study’s co-author and a senior research fellow in atmospheric chemistry at Harvard SEAS.

Conducive to fires

“In the future, we expect warmer temperatures, which are conducive to fires, but it’s not apparent what the rainfall and relative humidity will do. Warmer air can hold more water vapour, for instance, but what does this mean for fires? “It turns out that, for the western US, the biggest driver for fires in the future is temperature, and that result appears robust across models. When you get a large temperature increase over time, as we are seeing, and little rainfall, fires will increase in size.” Among the study’s forecasts for fires in the western US in 2050 are:

  • Areas burned in the month of August could increase by 65% in the Pacific Northwest, nearly double in the Eastern Rocky mountains, and quadruple in the Rocky Mountains Forest region.
  • Probability of large fires could increase by factors of two or three.
  • The start dates of the “fire season” could be earlier (late April instead of mid-May) and the end date could be later (mid-October instead of early October).

During the last 40 years, air quality has improved considerably over much of the US, mainly due to government efforts on regulating emissions. However, the study predicts that, due to more fires, smoke levels could increase by between 20% and 100% by 2050. “I think what people need to realise is that embedded in those curves showing the tiny temperature increases year after year are more extreme events that can be quite serious,” Mickley  says.  “It doesn’t bode well.” − Climate News Network

FOR IMMEDIATE RELEASE The forest fires raging through states in the western US are among the worst on record, but latest research indicates that they will get even worse in future as temperatures rise. LONDON, 2 September − As fire crews battle to control the forest fires that have been devastating areas of the western US, a bleak warning has been issued that such fires in future are likely to break out over longer periods and wider areas each year, and create up to twice as much smoke. Forest wildfires are a regular event in California and other states in the western US, but this year’s conflagrations are being described as some of the worst on record. One fire, which has threatened California’s Yosemite National Park, was at one stage spread over nearly 200,000 acres, or more than 300 square miles. Environmental scientists at Harvard School of Engineering and Applied Sciences (SEAS) fed data into a number of models to come up with predictions about how such fires will behave in future. The data included not only historical records of fires but also seasonal temperatures, relative humidity levels, and amounts of brush and dry fuel on the forest floor over six “ecoregions” in the western states. The models were matched with data from the fourth Intergovernmental Panel on Climate Change (IPCC) report on possible future atmospheric and climatological conditions for the year 2050. Based on this multi-model approach, the Harvard team was then able to calculate the likely extent of fires in mid-century, and to gauge areas that would be burned. “We weren’t altogether certain what we would find when we started this project,” says Loretta J Mickley, the study’s co-author and a senior research fellow in atmospheric chemistry at Harvard SEAS.

Conducive to fires

“In the future, we expect warmer temperatures, which are conducive to fires, but it’s not apparent what the rainfall and relative humidity will do. Warmer air can hold more water vapour, for instance, but what does this mean for fires? “It turns out that, for the western US, the biggest driver for fires in the future is temperature, and that result appears robust across models. When you get a large temperature increase over time, as we are seeing, and little rainfall, fires will increase in size.” Among the study’s forecasts for fires in the western US in 2050 are:

  • Areas burned in the month of August could increase by 65% in the Pacific Northwest, nearly double in the Eastern Rocky mountains, and quadruple in the Rocky Mountains Forest region.
  • Probability of large fires could increase by factors of two or three.
  • The start dates of the “fire season” could be earlier (late April instead of mid-May) and the end date could be later (mid-October instead of early October).

During the last 40 years, air quality has improved considerably over much of the US, mainly due to government efforts on regulating emissions. However, the study predicts that, due to more fires, smoke levels could increase by between 20% and 100% by 2050. “I think what people need to realise is that embedded in those curves showing the tiny temperature increases year after year are more extreme events that can be quite serious,” Mickley  says.  “It doesn’t bode well.” − Climate News Network

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Alaska's forest fires burn more fiercely

FOR IMMEDIATE RELEASE
Some recent fires in the forests of Alaska have been the worst for 10,000 years, researchers say – and they could happen elsewhere in this warming world.

LONDON, 26 July – There have always been fires in the cold forests of Alaska. Periods of burning are part of the ecological regime, and fires return to black spruce stands of the Yukon Flats at intervals of tens to hundreds of years.

But recent evidence suggests that fire is about to come back with a vengeance – or, in the language of science, “a transition to a unique regime of unprecedented fire activity”.

Ryan Kelly and Feng Sheng Hu, two biologists at the University of Illinois, Urbana, have examined charcoal records from 14 lakes in Yukon Flats to reconstruct the history of burning for the last 10,000 years.

They and colleagues report in the Proceedings of the National Academy of Sciences that during the Medieval Climate Anomaly – the warm period that brought monastery vineyards to Britain a thousand years ago – the dry conditions favoured what they call “peak biomass burning”.

But this apparent limit has, they report, been surpassed during recent decades, characterised by “exceptionally high fire frequency and biomass burning.”

Their warning came during a week in which, on just one day, the US space agency Nasa published satellite images of burning scrub and forest in the states of California and Idaho, in the Irkutsk region of south-eastern Siberia, and of illegal slash-and-burn fires to clear land in Indonesia.

This last led to unprecedented levels of air pollution in Malaysia and Singapore: schools were closed and aircraft grounded, and the Government of Malaysia issued gas masks.

Potential for ‘dramatic impacts’

The fires in the northern forests matter, because the boreal forests cover about a tenth of the planet’s land surface, and they store about 30% of the planet’s terrestrial carbon.

So they are vulnerable to global warming, climate change and wildfire: wetlands, too, are likely to dry up, and permafrost continues to melt, all of which makes the forests more vulnerable. When they burn, the stands of timber release huge amounts of carbon into the atmosphere.

The slow return to normal has its own knock-on effects, say the authors: it has an impact on biogeochemical cycles, on the energy balance and the hydrology of the region, all of which can in turn feed back into climate change.

So to understand the possible global consequences for the northern forests, the authors reasoned, it would pay dividends to make a case study of one sustained natural experiment in one easily accessible landscape.

The researchers found that, after bouts of burning in centuries past, the area was colonised by more fire-resistant species, and the same has begun to happen after the most recent fires. They report that Yukon Flats is now a fragmented mosaic of “lower flammability vegetation” which ought to keep the place safe for a while.

But the fires of recent years have been the worst for 10,000 years and, they warn, things are likely to get worse: what happened to the conifers of Alaska could happen in other places as the world warms and the sub-Arctic begins to dry, with a change to deciduous trees. “Such dynamics”, they say, “have potentially dramatic ecological impacts.” – Climate News Network

FOR IMMEDIATE RELEASE
Some recent fires in the forests of Alaska have been the worst for 10,000 years, researchers say – and they could happen elsewhere in this warming world.

LONDON, 26 July – There have always been fires in the cold forests of Alaska. Periods of burning are part of the ecological regime, and fires return to black spruce stands of the Yukon Flats at intervals of tens to hundreds of years.

But recent evidence suggests that fire is about to come back with a vengeance – or, in the language of science, “a transition to a unique regime of unprecedented fire activity”.

Ryan Kelly and Feng Sheng Hu, two biologists at the University of Illinois, Urbana, have examined charcoal records from 14 lakes in Yukon Flats to reconstruct the history of burning for the last 10,000 years.

They and colleagues report in the Proceedings of the National Academy of Sciences that during the Medieval Climate Anomaly – the warm period that brought monastery vineyards to Britain a thousand years ago – the dry conditions favoured what they call “peak biomass burning”.

But this apparent limit has, they report, been surpassed during recent decades, characterised by “exceptionally high fire frequency and biomass burning.”

Their warning came during a week in which, on just one day, the US space agency Nasa published satellite images of burning scrub and forest in the states of California and Idaho, in the Irkutsk region of south-eastern Siberia, and of illegal slash-and-burn fires to clear land in Indonesia.

This last led to unprecedented levels of air pollution in Malaysia and Singapore: schools were closed and aircraft grounded, and the Government of Malaysia issued gas masks.

Potential for ‘dramatic impacts’

The fires in the northern forests matter, because the boreal forests cover about a tenth of the planet’s land surface, and they store about 30% of the planet’s terrestrial carbon.

So they are vulnerable to global warming, climate change and wildfire: wetlands, too, are likely to dry up, and permafrost continues to melt, all of which makes the forests more vulnerable. When they burn, the stands of timber release huge amounts of carbon into the atmosphere.

The slow return to normal has its own knock-on effects, say the authors: it has an impact on biogeochemical cycles, on the energy balance and the hydrology of the region, all of which can in turn feed back into climate change.

So to understand the possible global consequences for the northern forests, the authors reasoned, it would pay dividends to make a case study of one sustained natural experiment in one easily accessible landscape.

The researchers found that, after bouts of burning in centuries past, the area was colonised by more fire-resistant species, and the same has begun to happen after the most recent fires. They report that Yukon Flats is now a fragmented mosaic of “lower flammability vegetation” which ought to keep the place safe for a while.

But the fires of recent years have been the worst for 10,000 years and, they warn, things are likely to get worse: what happened to the conifers of Alaska could happen in other places as the world warms and the sub-Arctic begins to dry, with a change to deciduous trees. “Such dynamics”, they say, “have potentially dramatic ecological impacts.” – Climate News Network