With Climate Change Comes Floods

by Anna Vigran, NPR

Climate change is disturbing the delicate balancing act that people have with water. Water is critical to life — for drinking and irrigation, and as a source of food, transportation and recreation. But too much water — or water that comes at an unexpected time, or in unexpected places — can be a big problem.

As global temperatures rise, many places are threatened by flooding. A recent study looking at who is at risk shows many coastal cities could be hit hard, particularly heavily populated cities in Asia. But in terms of economic loss, the Organization for Economic Co-operation and Development found that the top 10 cities at risk are all in three industrialized countries: the United States, Japan and the Netherlands.

Warming water can cause rises in sea levels and strong storms, with the potential to impact people around the globe. As global temperatures rise, oceans get warmer. And when water heats up, it expands and sea levels rise.

The United Nations' Intergovernmental Panel on Climate Change (IPCC) reports that from 1993 to 2003, global sea level rose about 3 millimeters each year, and approximately half of that increase is attributed to the ocean expanding as it warms.

About one-quarter of this rise is attributed to melting glaciers and ice caps. Melting from the Greenland ice sheet and the Antarctic ice sheet combined is estimated to account for about 14 percent of observed sea level rise. If the Greenland ice sheet melted entirely, sea level would rise 20 feet around the world. But such a catastrophic melt isn't projected for thousands of years, if it happens at all. Currently there is no scientific consensus on how much of these giant ice sheets will melt, or when that might happen.

"Scientists do not understand the ice process enough for accurate predictions of Greenland and Antarctica," says Carol Auer, an oceanographer with the National Ocean and Atmospheric Administration.

It is also not known exactly how much warmer the planet will get. "We can change this around, at least to a degree," Auer says. "It's not a disaster yet."

A sea level rise of just a few millimeters a year may seem insignificant, but Auer says that on flat land, it adds up. She says that a half-inch of vertical sea level rise translates to about three feet of land lost on a sandy open coast, due to long-term erosion. And even a slightly higher sea level can cause more dramatic tides in deltas and estuaries.

Rising sea levels also make coastal areas more vulnerable to storm surges and, in turn, to flooding.

"Basically the story is because sea level rises have made everything a little higher, when a storm hits that makes for more vulnerability," Auer says. The higher sea level gives a storm surge a boost to reach further inland.

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A warming planet also means snowy regions become rainy. People who live near rivers could see more flash floods: Melting snow slowly trickles into rivers, but rain can dump large amounts of water all at once.
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