A satellite image of a swirling hurricane Men with gas masks and protective suits on The planetary rover Sojourner A large group of refugees huddled together

 HUMAN
 IMPACT

Floods and
 Dams

Ozone and
 Pollution

Deforestation
 and
 Desertification

Overpopulation





Humans have contended with floods since ancient times. According to the Old Testament, Noah built an ark. So did Utnapishtim in the even earlier story of Gilgamesh.

Another ancient response is to build levees to keep rivers in their channels—and to make them more navigable in the bargain. People around the world still rely on levees, for example along the Mississippi. But as the 1993 Midwest deluge demonstrated, levees can be overwhelmed.

The threat of flooding is exacerbated by excessive land-clearing and cultivation, which reduces the ability of soil to retain water and encourages runoff. Restoration of trees and other vegetation—as well as soil management techniques such as crop rotation and contour plowing—helps control flooding. Another method is to artificially widen rivers at certain points to prevent overflow in other areas.

An obvious way to try to avoid floods is to live somewhere other than a floodplain. But for a variety of reasons, many people choose to live near water. The inconvenience or catastrophe of a flood is the price they sometimes pay.

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VIDEO:

Residents of a town along the Mississippi River methodically try to holdback a massive flood.


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VIDEO:

A virtual flyover provides dramatic side-by-side comparisons of the Mississippi River at normal levels and during a flood.


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FAST FACT:

Removing trees and other plant cover, along with farming, can worsen runoff by decreasing the ability of soil to absorb water.

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