Large Dams Can Affect Local Climate

New research has shown that large dams have the ability to affect the local climate, to the point of drastically altering the local rainfall in some regions.

This marks the first time that researchers have found a clear difference had on the surrounding environment by large reservoirs compared to natural lakes and wetlands.

The study showed that this phenomenon occurs most often in the Mediterranean and semi-arid climate such as ones in California and in the Southwestern United States.

The results should spur consideration of more robust management of dams and set the stage for further research on the regions and climates to focus on, says Faisal Hossain, Tennessee Tech University civil engineering professor.

“This research shows you the smoking gun,” said Hossain. “Logically and physically we knew it was possible that a having a large body of water and spreading it around would change the local climate. Now, our results give us a better idea of which dams are most likely to gradually change local climate and what that means for managing those reservoirs as time passes.”

The research team looked at 30 years’ worth climate data based on a technique known commonly as reanalysis, which aims to create the “gold standard record” of weather conditions everywhere in a certain location by using as much information in hindsight as possible. The data used by the researchers in this instance covered 1979 and 2009.

Roger Pielke Sr. of the University of Colorado’s Cooperative Institute for Research in Environmental Sciences says the work was a breakthrough study in scope and mission.

“it is a critically important, much needed study with multiple authors and institutions using diverse datasets in order to obtain information on how dams and their surroundings affect the region’s climate rather than a local snapshot that may not be representative for larger areas,” said Pielke.

The how and why of this research is relatively obvious. Whenever you introduce a large amount of water, spread across a large area, the water will be evaporated into the atmosphere and fall down as precipitation.

“Think of your typical backyard swimming pool,” said Hossain. “If you pumped all the water out of your swimming pool and spread it onto your lawn, it wouldn’t take long for all that water to evaporate.”

“We now know we need to do better building and managing dams and reservoirs in those arid and Mediterranean regions where water is really scarce,” Hossain added, who believes that the report reflects a changing mindset in this area of research.

“We know a lot about how climate change affects reservoirs, but what we didn’t know a lot about was what a reservoir could do to the local climate,” he said. “We just reversed our thinking by saying that a reservoir and the activities it supports are just as important a player for climate as the larger climate is for the reservoir. Basically, it’s a two-way street.”

Source: Tennessee Tech University
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