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Human activities in arid urban environments can affect rainfall and water cycle

EurekAlert (19-Jun-2006)

Human activities in arid urban environments can affect rainfall and water cycle

EurekAlert (19-Jun-2006)

In the past half-century, cities have begun to expand in some of the Earth’s most arid areas. While scientists have known for some time that the so-called "heat-island" effect of large cities such as Atlanta and Houston can affect their weather, they knew less about this effect and other processes in arid cities, such as Phoenix, which have experienced explosive population growth. Now, a study by a climatologist in the department of geography at the University of Georgia has shown, using a unique 108-year-old data record and NASA’s Tropical Rainfall Measuring Mission (TRMM) satellite, that arid cities such as Riyadh in Saudi Arabia and Phoenix have an effect on rainfall patterns around them. As important, it appears that human activities such as land use, aerosols and irrigation in these arid urban environments affect the entire water cycle as well.

One of the most interesting findings in the new study was a 12-14 percent increase (which scientists call an anomaly) in rainfall in the northeast suburbs of Phoenix from the pre-urban (1895-1949) to post-urban (1950-2003) periods. A previous study first noted the possible anomaly but focused only on the post-urban period, so it was not clear whether the change was tied to post-1950 urbanization around Phoenix. It is hypothesized that this anomaly is related to urban-topographic interactions and possibly irrigation moisture. Indeed, the role of irrigation in changing the weather of cities in arid areas is one of the more intriguing findings, and one that will bear more study.

Riyadh has also shown significant grown in the past few decades, and its weather also has been affected by the heat-island affect. (The large surface of pavement and buildings actually increases the heat of a city area, and when that heat rises, it can change weather patterns in and near cities.) Precipitation patterns have changed in Riyadh as well, though the causes are less clear than in Phoenix. Ground data confirm a recent significant increase in rainfall around Riyadh.

Story Source : University of Georgia

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Page publiée le 16 mars 2016