Land use change influences continental water cycle

Jun 28, 2011

Forests, and tropical forests in particular, play an important role in the global water cycle. Delft University of Technology PhD researcher Ruud van der Ent (TU Delft, The Netherlands) has recently shown that evaporation from the Amazon forest is for more than 50% responsible for the rainfall in Peru, Bolivia, Argentina, Uruguay, Paraguay and southern Brazil, where it feeds crops and rivers. Similarly in Africa, the Congo forest exports tons of water through the atmosphere to the West-African countries. Van der Ent also shows that land use changes such as irrigation, dams, and deforestation can alter evaporation patterns in a region, potentially affecting water resources in distant regions. With his research, Van der Ent has won the 2011 WMO (World Meteorological Organization) Research Award for Young Scientists.

Van der Ent won the WMO prize for his Water Resources Research paper 'Origin and fate of atmospheric moisture over continents', co-authored by Prof. Huub Savenije, Bettina Schaefli en Susan Steele-Dunne (all TU Delft). The paper shows that water falling as precipitation in one region may have originated in a distant region, or that it may be recycled moisture that originated as evaporation within the region. Global wind patterns, topography, and land cover all play a role in moisture recycling patterns and the distribution of global water resources. Land use changes such as irrigation, dams, and deforestation can alter evaporation patterns in a region, potentially affecting water resources in distant regions.

Many studies of moisture recycling have had a regional focus up until now. To provide a global perspective, van der Ent et al. created showing the sources of atmospheric moisture for various regions. The researchers estimate that on average 40% of terrestrial precipitation originates from land evaporation, and 57% of all terrestrial evaporation returns as precipitation over land. They found that some regions rely on from within the region, while others get moisture from different regions. For instance, water evaporating from Eurasia is responsible for 80% of China's water resources, and the Rio de la Plata basin in South America gets 70% of its water from evaporation from the Amazon.

Related research by recent TU Delft PhD graduate Miriam Gerrits looked into the way forests evaporate their water to the atmosphere. Gerrits found that forest floors are for a large part responsible for evaporation in forests. Removal of forests will thus not only reduce the evaporation from the trees, but will also reduce the evaporation from the forest floor. The resulting local decrease of is very likely to have global consequences for rainfall, and food security.

Explore further: Five anthropogenic factors that will radically alter northern forests in 50 years

More information: 'Origin and fate of atmospheric moisture over continents' in Water Resources Research, Vol. 46, W09525, 2010 www.agu.org/journals/wr/wr1009/2010WR009127/

add to favorites email to friend print save as pdf

Related Stories

Study finds wind speeds rose over world's oceans

Mar 24, 2011

During the last quarter-century, average wind speeds have increased over the world's oceans, as have wave heights, generating rougher seas, researchers reported in a study published online Thursday.

Moist Soil 'Hot Spots' May Affect Rainfall

Aug 22, 2004

While the Earth is moistened by rainfall, scientists believe that the water in soil can, in turn, influence rainfall both regionally and globally. Forecasters, water resource managers and farmers may benefit ...

How trees manage water in arid environments

Jan 03, 2007

Water scarcity is slowly becoming a fact of life in increasingly large areas. The summer of 2006 was the second warmest in the continental United States since records began in 1895, according to the National ...

The forest paradox during heatwaves

Sep 06, 2010

Comparatively speaking, forests initially have a weaker cooling effect during heatwaves than open grassland. This is revealed in a study that could help refine models for weather and climate forecasts. Moreover, ...

Recommended for you

More, bigger wildfires burning western US, study shows

9 hours ago

Wildfires across the western United States have been getting bigger and more frequent over the last 30 years – a trend that could continue as climate change causes temperatures to rise and drought to become ...

User comments : 0

More news stories

There's something ancient in the icebox

Glaciers are commonly thought to work like a belt sander. As they move over the land they scrape off everything—vegetation, soil, and even the top layer of bedrock. So scientists were greatly surprised ...

Clean air: Fewer sources for self-cleaning

Up to now, HONO, also known as nitrous acid, was considered one of the most important sources of hydroxyl radicals (OH), which are regarded as the detergent of the atmosphere, allowing the air to clean itself. ...

China says massive area of its soil polluted

A huge area of China's soil covering more than twice the size of Spain is estimated to be polluted, the government said Thursday, announcing findings of a survey previously kept secret.

Hackathon team's GoogolPlex gives Siri extra powers

(Phys.org) —Four freshmen at the University of Pennsylvania have taken Apple's personal assistant Siri to behave as a graduate-level executive assistant which, when asked, is capable of adjusting the temperature ...

Better thermal-imaging lens from waste sulfur

Sulfur left over from refining fossil fuels can be transformed into cheap, lightweight, plastic lenses for infrared devices, including night-vision goggles, a University of Arizona-led international team ...