China's massive Three Gorges Dam project across the Yangtze River will take another two years to complete, but the world's largest dam is already changing the local weather, claim scientists.
Both modeling and actual meteorological data suggest that the reservoir is cooling the Yangtze Valley, which is causing changes in rainfall patterns.
Climate modeler Liguang Wu of NASA's Goddard Space Flight Center and the University of Maryland in College Park have collaborated with Chinese scientists to study the changing climate around what will soon be a 401-square-mile reservoir of more than five trillion gallons of water and a hydroelectric power plant 20 times more powerful than the Hoover Dam.
The researchers combined satellite data and ground weather stations to create a computer climate simulation, which they then compared to what has already happened in recent years.
More recently, other NASA satellites have been watching the weather changes, said Wu. The Tropical Rainfall Measuring Mission (TRMM) provided some data to estimate changes in rainfall, while the Terra and Aqua satellites kept track of surface temperatures.
Among the surprise weather changes has been the increase in rainfall between the Daba and Oinling mountains, said Wu.
The rains come from a "lake effect" intensification of precipitation, like that seen around the Great Lakes of North America. The lake effect happens when already moist air picks up more moisture as it crosses over a warm body of water, then rains or snows it out quickly upon reaching the shore.
In a way, he said, Three Gorges is a great laboratory for studying how well local climate changes caused by very local land-use changes can be detected and distinguished from larger-scale global climate change.
At almost 4,000 miles, the Yangtze is the fourth longest river in the world, discharging into the sea about twice the water of the Mississippi. For as long as people have kept records, the Yangtze has been in the habit of periodically overflowing its banks and flooding vast areas. Controlling that ancient threat, along with producing electricity, are the main goals of the Three Gorges Dam.