- The last rainy season in eastern Africa has recorded a decline of about 15 percent of rainfall experienced in the region since the 1980's records, from round stations and satellites.
According to a new study, co-funded by NASA, a link between a warming Indian Ocean and less rainfall in eastern and southern Africa has been identified.
Observations along with computer models have revealed a decline in rainfall, with implications for the region's food security.
Statistical studies show that the decline is due to irregularities in transport of moisture between the ocean and land, brought about by rising Indian Ocean temperatures, according to research published today in Proceedings of National Academy of Sciences.
This inter-disciplinary research was organised to support United States Agency for International Development's Famine Early Warning Systems Network.
"The last 10 to 15 years have seen particularly dangerous declines in rainfall in sensitive ecosystems in East Africa, such as Somalia and eastern Ethiopia. We wanted to know if the trend would continue or if it would start getting wetter," said co-author of study, Molly Brown from NASA's Goddard Space Flight Center, Greenbelt, Md.
To find out, the team analysed historical seasonal rainfall data over Indian Ocean and eastern seaboard of Africa from 1950 to 2005.
NASA Global Precipitation Climatology Project's rainfall dataset has supplied a series of data covering both land and oceans.
They discovered that declines in rainfall in Ethiopia, Kenya, Tanzania, Zambia, Malawi and Zimbabwe were related to increases in rainfall over the ocean.
The team used computer models that describe atmosphere and historical climate data to identify and validate source of this link. Chief author, Chris Funk, of University of California, Santa Barbara, and colleagues showed that on-shore movement of moisture was disrupted by increased rainfall over ocean.
Mr Funk and colleagues used a computer model from National Center for Atmospheric Research to confirm their findings.
A combination of evidence from models and historical data suggest that human-caused warming of Indian Ocean leads to an increase of rainfall over the ocean, which in turn adds energy to the atmosphere.
Models and data indicate that it goes without saying that added energy could create a weather pattern that reduces flow of moisture on-shore and bring dry air down over African continent, reducing rainfall.
Furthermore, team established as to whether or not decline in rainfall over eastern Africa would continue. Under guidance from researchers at USGS, which co-funded study, team looked at 11 climate models to simulate rainfall changes in future.
Ten of the 11 models agreed that through 2050, rainfall over the Indian Ocean would continue to increase, depriving Africa's eastern seaboard of rainfall.
"We can be quite certain that the decline in rainfall has been substantial and will continue to be. This 15 percent decrease every 20-25 years is likely to continue," Mr Funk said.
Trend toward dryer rainy seasons in eastern and southern Africa directly impacts agricultural productivity. To evaluate how potential future rainfall scenarios and shifts in agriculture could affect undernourishment, the team came up with a "food-balance indicator" model.
The model considers factors such as growing-season rainfall, fertiliser, seed use, crop area and population to estimate the number of undernourished people a region can anticipate.
"A strong commitment to agricultural development by both African nations and the international community could lead fairly quickly to a more food-secure Africa," Mr Funk concluded.
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