Tropical Rainfall

One often ignored consequence of global climate change is that the Northern Hemisphere is becoming warmer than the Southern Hemisphere, which could significantly alter tropical precipitation patterns, according to a new study by climatologists from the University of California, Berkeley, and the University of Washington, Seattle. Such a shift could increase or decrease seasonal rainfall in areas such as the Amazon, sub-Saharan Africa or East Asia, leaving some areas wetter and some drier than today. "A key finding is a tendency to shift tropical rainfall northward, which could mean increases in monsoon weather systems in Asia or shifts of the wet season from south to north in Africa and South America," said UC Berkeley graduate student Andrew R. Friedman, who led the analysis.

"Tropical rainfall likes the warmer hemisphere," summed up John Chiang, UC Berkeley associate professor of geography. "As a result, tropical rainfall cares a lot about the temperature difference between the two hemispheres." Generally, rainfall patterns fall into bands at specific latitudes, such as the Intertropical Convergence Zone. The researchers say that a warmer northern hemisphere causes atmospheric overturning to weaken in the north and strengthen in the south, shifting rain bands northward. The regions most affected by this shift are likely to be on the bands' north and south edges. Chiang and his colleagues argue that climate scientists should not only focus on the rising global mean temperature, but also the regional patterns of global warming.

 

As their study shows, the interhemispheric temperature difference has an apparent impact on atmospheric circulation and rainfall in the tropics.


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