The interaction of water and climate has a major impact on human life and health. The hydrologic cycle, for example, provides precipitation that fills reservoirs and lakes, thus providing drinking water. Climate patterns influenced by the ocean determine where people live and have major effects on economic activity, quality of life, and every other aspect of human behavior.
The interaction between water, climate, and people is complicated. On one hand, changes in water and climate can affect people. On the other hand, people can in turn affect water and climate. One example of this interrelationship can be seen in connections between human development and the hydrologic cycle. When human beings build cities, they pave large areas of land. Water that used to soak into soil and grass cannot soak through pavement. As a result the growth of cities, or urbanization, "generates more stormwater runoff and higher peak stream discharge."8 Peak stream discharge is the amount of water passing through any part of a stream at a given time. When storm water runoff and peak stream discharge are high, it means that more water is running faster into and down a stream, which can
result in more flooding. Thus, human development can have a strong effect on the hydrologic cycle, and those changes in the water cycle can in turn have a large, and sometimes negative, effect on human quality of life. Building cities in some areas can cause floods that damage those cities and the people who live in them.
Another larger and more complicated example of the interconnection of people, water, and climate is El Niño. El Niño is a periodic warming of the ocean. This warming appears to be natural, and it can have major effects on weather. Traditionally, El Niño events have occurred in the Pacific, close to the South American coast. Such El Niño events usually mean a quieter storm season. Recently, however, El Niño events have been occurring farther west in the central Pacific. These new El Niños have been "resulting in a greater number of hurricanes with greater frequency and more potential to make landfall," accord-
One of the most important and striking climate phenomena in the world is the monsoon. A monsoon is a seasonal prevailing wind that lasts for several months. In India and surrounding countries, a monsoon blowing from the Indian Ocean results in torrential rains between June and September. In India, around 35 inches (89cm) of rain usually fall in that period.
A study led by Noah Diffenbaugh at Purdue University's Climate Change Research Center suggests that global warming may push back the start of the monsoon season in India by 5 to 15 days. At first, a delay in the monsoons may seem like a good thing: The downpour causes flooding and even landslides. India relies on the rainfall, however, to provide water for drinking, for agriculture, and for hydroelectric power. If the monsoons are delayed, it could have serious negative consequences for huge numbers of people.
A reduction in monsoon winds where they are expected can be bad. But the appearance of monsoon winds where they are not anticipated could also cause problems. University of Oregon Geology Professor Greg Retallack has studied historical changes in climate patterns, and he believes that if world temperatures warm, the Pacific Northwest may begin to experience monsoon storms. In one global warming event 55 million years ago, rainfall increased by 50 percent.
If warming again triggered monsoons on that scale, the climate and perhaps the landscape of Seattle and the surrounding region would be significantly changed, resulting in major adjustments for people living there.
Changes in monsoon patterns demonstrate again that water and climate can be connected in complicated ways. Thus, global warming may change weather patterns around the globe in ways that are hard to predict but may have major consequences for millions of people.
ing to Peter Webster of Georgia Tech's School of Earth and Atmospheric Sciences.9
The changes in El Niño may be in part a result of global warming. Or they might not be. Webster, who was co-author of a study investigating the El Niño effect, was not sure. However, the possibility that global warming may change water temperatures, which could in turn affect the frequency and power of storms, has led to both concern and debate among scientists. University of Chicago ocean chemist David Archer notes that "Tropical storms tend to intensify as the sea surface warms, everything else being equal. Hurricane intensities reconstructed from satellite images seem to show strengthening as sea surface temperature warms over the past decades." Archer also notes that "though there is a clear danger that hurricanes could intensify. . . . Scientists don't understand the working of hurricanes in the climate system well enough to be able to predict how strong they will get."10
Thus, scientists know there is a link between water temperature and storm systems, but how those links work exactly, and how they may affect people, are difficult to determine. Scientists do know, however, that as the earth's temperature increases, the changes may affect the earth's water in many different, surprising, and possibly dangerous ways. In turn, the changes in the oceans, in precipitation, in the icecaps, and in lakes and rivers may have powerful effects on climate and on human beings.
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