Hurricanes can get supercharged when they hit river mouths, researchers now find.
Hurricanes keep alive by converting the warmth of tropical waters into motion. The strong winds they kick up in turn cause surface water heated by the sun to mix with deeper, cooler waters, and that drop in warmth causes hurricanes to weaken.
Rivers and rainfall alter this pattern by adding freshwater, which is less dense than saltwater. Therefore, this freshwater sits on top of cold seawater for much the same reason oil sits on top of water. The resulting “barrier layer” of freshwater keeps winds from mixing the warm surface layer with cooler, deeper water, giving hurricanes more heat to intensify with.
Although the chances that hurricanes will hit regions swamped by freshwater is small at only 10 to 23 percent, the effect can be startlingly large—hurricanes can become up to 50 percent more intense in regions where freshwater pours into the ocean, such as from river systems like the Ganges, or where tropical storms rain considerably, as in the western Pacific Ocean.
National Geographic has the full article
