June 22, 2007 — Two years before its completion, the world’s largest dam is already changing the local weather, say scientists studying the Three Gorges Dam on China’s Yangtze River. Both modeling and actual meteorological data suggest that the reservoir is cooling its valley, which is causing changes in rainfall.
"In China there are a lot of people who complain because of the construction of the dam" and specifically about changes in local weather, said climate modeler Liguang Wu of NASA’s Goddard Space Flight Center and the University of Maryland in College Park.
To find out if the dam was really to blame, Wu and his colleagues collaborated with Chinese scientists to study the changing climate around what will soon be a 401-square-mile reservoir of more than 5 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.
The construction of the dam and changes to the land and vegetation around it have been recorded for years by the NASA-US Geological Survey Landsat satellites. They show steady progress from 2000 to today, with the biggest changes in 2004, when the reservoir was partially filled and water backed up into many side canyons.
By last summer the main wall of the dam was done and the water in the reservoir was two miles across.
"Frequently people tend to use these (Landsat images) in a time series," said Jeff Masek a Landsat scientist at NASA. Because Landsat satellites have been operating since 1972, there are a lot of human changes to be seen, he said.
What’s more, since the data is available to the world, many countries, like China, can use them to get a different view of what’s happening on their own land.
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.
