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Hydroelectric dams use river flow to turn a series of turbines to generate electricity. It is a source of renewable energy that doesn’t depend on fossil fuels. However, it disrupts the flow of rivers, and impact the wildlife habitat, agricultural land, and scenic lands there.

Not all wildlife impacts associated with dams can be directly attributed to hydroelectric power. However, hydroelectric facilities can still have a major impact on aquatic ecosystems.

However, large-scale hydroelectric dams continue to built in many parts of the world. In the United States, there are about 80,000 dams of which only 2,400 produce power. The other dams are for recreation, stock/farm ponds, flood control, water supply, and irrigation.

Installation and dismantling of hydroelectric power plants cause global warming.

Nonetheless, global warming emits during the installation and dismantling of hydroelectric power plants. However, current estimates suggest that life-cycle emissions of hydroelectric power plants can be over 0.5 pounds of carbon dioxide equivalent per kilowatt-hour.

Scientists are monitoring the environmental consequences of hydroelectric dams to know the effect on a river’s temperature.

Recently, a team of researchers at the University of Washington has published their study on how several hydroelectric dams affected the temperature of Southeast Asia’s three major rivers.

Use of satellite data to track changes in surface water temperature

The researchers used Landsat satellites to track changes in surface water temperature for the Sekong, Sesan and Srepok rivers. The satellites capture the heat, or infrared radiation, from the rivers.

The Sekong, Sesan and Srepok rivers combine into one river, which eventually enters the Mekong River, a central feature of the Southeast Asian ecosystem. People rely on these rivers for fish and irrigation mostly.

Using 30 years of satellite data, the team discovered that within one year of the opening of a major dam, downstream river temperatures during the dry season dropped by up to 2 degrees centigrade.

The cooling kept on where these three rivers meet the Mekong River, showed a 0.8 centigrade cooling most.

Researchers’ Opinion

“People are seeing a cooling effect after the installation of the hydroelectric dam 20 years ago. But what we see in the Mekong is really amazing’” said senior author Faisal Hossain. He is a civil and environmental engineering professor at the University of Washington.

“Lots of dams were just suddenly coming on, left and right. And now we can see this cooling effect that is no longer restricted but continuing into the river system. It is the best of our knowledge.”

The team investigated whether anything else might be driving these temperature drops, such as air temperature, precipitation or land use in the surrounding region.

Remarkably, the air temperature showed a slight warming trend. The land around the rivers causes deforestation during that period. But researchers said that is often linked to water warming, not cooling. That points to the role of these dams.

The team found that this infusion once warmed the Mekong so that the river was, at most, 0.4-degree centigrade warmer downstream of the confluence than it was upstream.

But after 2001, the trend reversed, with the rivers now slightly cooling the Mekong River. The river is now up to 0.8-degree centigrade cooler — not warmer — downstream of the confluence.

The cooler water could have an effect on the fish that live downstream, the researchers said.

Lead author Matthew Bonnema, a postdoctoral researcher at NASA’s Jet Propulsion Laboratory, said, “New dams are building closer to the Mekong. These are also big dams. It means the impacts on the Mekong will likely be more significant. These temperature changes are going to get more dramatic.”

Limitations of this study

Using satellite data to monitor river temperature has a caution: clouds block the satellites’ view of the Earth.

So, the team could only monitor changes during the region’s dry season. Still, the researchers were able to detect decreases in river temperature within a year after major dams on all three rivers came online.

The team has used the Reservoir Assessment Tool. This is the world’s first publicly available global reservoir-monitoring system that processes massive amounts of data from satellites for more than 1,500 dams around the world.