We all know that manmade dams change water availability in the areas surrounding their construction, but could they also alter the weather patterns and climate in these areas? Wired reports on new research suggesting they might. According to the article, dams' "reservoirs could be increasing the intensity of extreme rainstorms in their immediate vicinities."
Hydrologist Fasial Hossain of Tennessee Tech University studies whether dams and their reservoirs accelerate or intensify heavy rainfall patterns, worrying that the dams themselves might cause storms that will "exceed [their] capacity" and make them potentially unsafe. The changes to weather patterns could occur because the large bodies of water change the evaporation/condensation cycles for the area, not to mention changes in irrigation which "transform the land in the area, possibly leading to local climactic impacts."
Currently, the research shows a large variance among areas around the world where mandmade dams have been built. Wired mentions that some areas on Africa or Europe have noticed 20 percent increases in "extreme precipitation events" whereas some American dams have only shown one percent increase. Even this small change can be catastrophic, however, since dams lose storage capacity with time as silt builds up and leaves less room for water. Hossain notes this could pose a danger for the dams overflowing and suggests perhaps keeping the water level of the reservoirs lower to make room for rainwater.