Mapping Hope for Africa

Winter/Spring 2006

With the devastation wrought by Hurricanes Katrina and Rita in 2005, it's easy to forget that drought has long been a cause of widespread human misery.

One of the most insidious effects of drought has been famine, which may occur when hot, dry winds reduce soil moisture and water below the point where plants (and animals) can survive.

While droughts occur on all continents, the most severe ones in recent decades have been in Africa. Although you might have heard of long and devastating droughts in countries such as Ethiopia in the mid-1980s (which helped cause widespread famine and contributed to the deaths of more than a million people), even a relatively short dry spell of two to three weeks can significantly reduce crop yield.

This is especially problematic in sub-Saharan Africa because food security is often tied to the small farmer, and subsistence farming relies heavily on rain-fed agriculture. The bitter irony is that many of these regions in Africa also face intense rainfall, which likewise reduces crop productivity because topsoil is lost. (Plants generally concentrate their roots in, and obtain most of their nutrients from topsoil.)

However, excess rainfall — called runoff — may be used to irrigate crops if it's caught in ponds. In his Engineering, Science, and Technology Council (ESTC) Award-winning article, SAIC's Gabriel Senay (and co-author) presents a way to help assess runoff potential between regions for use as a water-management tool.

In fact, the authors developed water harvest index maps of Africa to aid regional planners in pond feasibility studies. The maps range from a simple indicator of runoff distribution across Africa to the number of potential ponds per family — a small pond filled by runoff can provide about half the water of a half-hectare plot (enough water to turn potential catastrophe into a modest success.)

"These maps are believed to be the first of their kind for continental Africa," according Senay. "Comparable maps have been produced for the contiguous United States by the NRCS [Natural Resources Conservation Service]."

In addition, the maps include average runoff depth by catchment area (a place set aside for collecting water which runs off the surface of the land), recommended watershed area for a small pond, and recommended pond depth.

"This study shows that a large part of food-insecure regions in Africa have sufficient amount of runoff that can be stored in small ponds for smoothing out the erratic patterns," according to Senay. "It is hoped that these maps will encourage regional planners to conduct further feasibility studies to pursue economically feasible pond-based, small-scale supplemental irrigation schemes."

The article by Senay and (co-author), "Developing Index Maps of Water-harvest Potential in Africa," appeared in Applied Engineering in Agriculture. (The study was conducted with financial contributions from the Famine Early Warning System Project of the U.S. Agency for International Development and a grant from the U.S. Department of Agriculture Foreign Agriculture Service Scientific Cooperation Research Program.)

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