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Eungul Lee, 608-890-2516
elee43@wisc.edu
Thomas Chase, 303-492-1274
tchase@cires.colorado.edu
Adriana Bailey (CIRES News), 303-492-6289
adriana.bailey@colorado.edu
Nov. 3, 2008
New Study Shows Greenness Of Landscape Affects Strength Of Monsoon Rains
In Asia, how green your garden grows may affect the strength of the summer monsoon, reports a new study appearing in the journal Water Resources Research.
Scientists at the University of Colorado at Boulder’s Cooperative Institute for Research in Environmental Sciences (CIRES) have found that the abundance of vegetation during winter and spring months is an important indicator of how much summer precipitation will fall.
The East Asian Summer Monsoon, which was the focus of the study, affects a quarter of the world’s population and is critical for the cultivation and production of rice, East Asia’s staple food. Forecasts of monsoon intensity and duration largely affect yearly agricultural planning.
“By including the land cover in our monsoon forecast models, we were able to explain about 80% of the variation in monsoonal rainfall. That’s a huge improvement in how well models successfully predict the strength of the monsoon several months out,” said lead author Eungul Lee, now with the Center for Sustainability and the Global Environment (SAGE) at the University of Wisconsin-Madison, who conducted the work as a Ph.D. student at CU and CIRES.
Earlier monsoon models, which based their predictions on ocean factors like sea surface temperature, typically explained just 25-40% of variations in East Asian summer rainfall. Such low predictive skill made it impossible to accurately forecast droughts or floods, said Lee.
The CIRES research team was able to double the predictive capability of these models by including both ocean factors and estimates of the greenness of the landscape. They found that land cover in certain regions of Asia correlates particularly well with the strength of the monsoon.
Specifically, Lee and colleagues found that strong northern East Asian Summer Monsoons tend to follow verdant springs in southern Asia but are weaker when northern and central Asia are more green. Southern East Asian Summer Monsoons are strongest following springs with abundant vegetative growth in Mongolia and western Asia.
The researchers believe vegetation is an indicator of high soil moisture.
“In northern Asia, high soil moisture is probably cooling the land as it evaporates, in the same way that sweating cools the body. This cooling decreases the temperature difference between the land and ocean, inhibiting the formation of a strong monsoon system,” said study author Thomas Chase, a CIRES Fellow and professor of engineering at CU.
In contrast, higher soil moisture in southern Asia, near the ocean, appears to provide an additional moisture source to fuel monsoonal rains.
Earlier this year, the researchers found similar links between land cover and the Indian Monsoon.
“Findings from both regions enhance our hopes of identifying land-atmosphere relationships that will allow us to better predict the North American Monsoon, which serves as an important source of moisture for the US Southwest,” said CIRES Fellow and CU professor Balaji Rajagopalan, who also participated in both studies.
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