Flooding in Pakistan
This gallery is part of a special National Geographic News series on global water issues.
Mohammed Nawaz was rescued by the Pakistani Navy on August 10 in Sukkur, Pakistan, as floods swept through the country. At the peak of the flooding, the worst in decades, a third of the country sat underwater.
The deluge left at least 1,500 dead, tens of millions displaced, and millions of acres of agricultural land in ruin.
(See more photos: "Pakistan Flood Pictures: Millions Flee Rising Rivers.")
Ironically, some water engineers and environmental groups point to farming as a catalyst for the disaster. Pakistan has the world's largest contiguous irrigated landscape, with riverside agriculture and human-made canals replacing natural floodplains, wetlands, and river flows that would traditionally hold more water and ease flooding. (Read more in "Pakistan Flooding Because of Farms?")
A recent study points to another reason for increased flooding: the water cycle is speeding up. Using satellite observations, NASA and university researchers have found that rivers and melting ice sheets delivered 18 percent more water to the oceans in 2006 than in 1994. The findings, which National Geographic Freshwater Fellow Sandra Postel blogged about in October, suggest that the volume of water running off the land toward the sea is expanding by the equivalent of roughly one Mississippi River each year.
Why is the water cycle speeding up? "As the atmosphere warms from the addition of carbon dioxide and other greenhouse gases, it can hold more moisture," explains Postel. "As a result, more water evaporates from the oceans, leading to thicker clouds that then dump more rainfall over the land. That heavier-than-normal rain can then produce massive flooding as it runs back toward the sea, where the cycle begins all over again." (Read more about the relationship between climate change and flooding.)