700 years of monsoons mapped

By analysing tree-ring data from more than 300 sites in Asia, researchers could piece together a year-by-year history of the region’s monsoon rains as far back as 1300 AD.

The new database, called the Monsoon Asia Drought Atlas, is important because the summer monsoon, which affects half of the world’s population, is little understood by climate modellers.

In fact, the models are poor enough that they don’t even agree on whether global climate change will strengthen the Asian monsoon or weaken it, said tree-ring expert Edward Cook, who is director of the Tree-Ring Laboratory at Columbia University .

“That gives you an idea of just how difficult the problem is,” Nature quoted him as saying.

The problem is that the good weather records that are necessary for validating climate models don’t exist for much of Asia before about 1950, said Cook.

Filling this gap, is one of the reasons his team compiled the drought atlas, he said.

The data were compiled from tree-ring chronologies showing the year-to-year growth of ancient trees at 327 sites.

Although these sites are, by necessity, clustered in regions where there are old trees, the rest of the map can be filled in by statistical analyses, explained Cook.

These analyses used tree-ring data from recent years, comparing them to existing weather data to find correlations with the older data and so extrapolate to the regions for which no such records were available.

In addition to mapping annual rainfall across thousands of kilometres of Asia, encompassing the Indian, east Asian and Australian monsoon areas, the team also correlated rainfall patterns with nearly 150 years of sea-surface-temperature recordings throughout the Pacific and Atlantic oceans.

This reveals how distant ocean conditions might affect Asian weather – again, useful for refining climate models, said Eugene Wahl, a palaeoclimatologist.

Wahl noted that Cook’s data give climate modellers a wealth of new information.

“It gives you something to start with, and that”s really important,” he said.

And by extending climate records back in time, the Asian tree-ring data, like similar studies in North America, have revealed past droughts that were much longer and more severe than anything these regions have had to deal with in modern times.

This “opens the possibility of understanding what nature can throw at us. That”s a big deal,” said Wahl.

The first analysis of the monsoon atlas has been published in Science1.

700 years of monsoons mapped

By analysing tree-ring data from more than 300 sites in Asia, researchers could piece together a year-by-year history of the region’s monsoon rains as far back as 1300 AD.

The new database, called the Monsoon Asia Drought Atlas, is important because the summer monsoon, which affects half of the world’s population, is little understood by climate modellers.

In fact, the models are poor enough that they don’t even agree on whether global climate change will strengthen the Asian monsoon or weaken it, said tree-ring expert Edward Cook, who is director of the Tree-Ring Laboratory at Columbia University .

“That gives you an idea of just how difficult the problem is,” Nature quoted him as saying.

The problem is that the good weather records that are necessary for validating climate models don’t exist for much of Asia before about 1950, said Cook.

Filling this gap, is one of the reasons his team compiled the drought atlas, he said.

The data were compiled from tree-ring chronologies showing the year-to-year growth of ancient trees at 327 sites.

Although these sites are, by necessity, clustered in regions where there are old trees, the rest of the map can be filled in by statistical analyses, explained Cook.

These analyses used tree-ring data from recent years, comparing them to existing weather data to find correlations with the older data and so extrapolate to the regions for which no such records were available.

In addition to mapping annual rainfall across thousands of kilometres of Asia, encompassing the Indian, east Asian and Australian monsoon areas, the team also correlated rainfall patterns with nearly 150 years of sea-surface-temperature recordings throughout the Pacific and Atlantic oceans.

This reveals how distant ocean conditions might affect Asian weather – again, useful for refining climate models, said Eugene Wahl, a palaeoclimatologist.

Wahl noted that Cook’s data give climate modellers a wealth of new information.

“It gives you something to start with, and that”s really important,” he said.

And by extending climate records back in time, the Asian tree-ring data, like similar studies in North America, have revealed past droughts that were much longer and more severe than anything these regions have had to deal with in modern times.

This “opens the possibility of understanding what nature can throw at us. That”s a big deal,” said Wahl.

The first analysis of the monsoon atlas has been published in Science1.

Study finds human role in Indonesian forest fires

London, Feb 23 (ANI): A new study has revealed that severe fires in Indonesia, responsible for some of the worst air quality conditions worldwide, are not only associated with drought, but also with changes in land use and population density.

“During the late 1970s, Indonesian Borneo changed from being highly fire-resistant to highly fire-prone during drought years, marking the period when one of the world’s great tropical forests became one of the world’s largest sources of pollution,” said Robert Field of at University of Toronto.

“Ultimately, this abrupt transition can be attributed to rapid increases in deforestation and population growth. The resulting occurrences of haze currently rank among the world’s worst air pollution episodes, and are a singularly large source of greenhouse gas emissions,” he added.

Sumatra has suffered from large fires at least since the 1960s, but Indonesian Borneo seems to have been resistant to large fires – even in dry years – until population density and deforestation increased substantially and land use changed from small-scale subsistence agriculture to large-scale industrial agriculture and agro-forestry.

“We’ve had a good understanding of fire events since the mid 1990s, but little before this due to the absence of fire data from satellites,” said Field.

“However, one of the major impacts of large-scale fires is a reduction in visibility due to the smoke produced. Visibility is recorded several times a day at airports in the region, and these records proved to be an excellent indicator of severe fire activity. We were able to piece together visibility observations back to the 1960s, and hence develop a longer term record of the fires,” he added.

Having a long-term record of the fires allowed the scientists to better understand their causes.

“Using weather records, we were able to estimate the specific rainfall level below which large fires have occurred in the previous two decades. In turn, we found that the rainfall over Indonesia was influenced equally by the Indian Ocean Dipole and the El Nino Southern Oscillation phenomena. Hopefully, this information can be used to better anticipate and prevent future haze disasters in Indonesia,” Field

Field said that there is a direct association between the increased prevalence of severe fires and haze disasters and the man-made change in land use.

“The visibility record also showed, quite strikingly, the impact of human settlement on a previously pristine tropical forest. This should give pause to further agro-forestry expansion in Indonesia, particularly for oil palm as a source of biofuel,” he added.

For the study, Field collaborated with Guido van der Werf of VU University Amsterdam and Sam Shen of San Diego State University.

The study is published in Nature Geoscience. (ANI)