We frequently hear that climate change is increasing the frequency and severity of droughts in Africa. There is, of course, no evidence that current droughts are any worse than historical ones.

However, there is evidence that deforestation can have an effect on droughts, both on a local and regional basis.

1) First, let’s look at a paper by Zheng & Eltahir, called “The response to deforestation and desertification in a model of West African monsoons”.


ABSTRACT

Since Charney proposed his theory on the dynamics of deserts and droughts in the Sahel [Charney, 1975], there has been significant scientific interest in the interaction between vegetation and climate in this region. The essence of this interaction is that the atmospheric circulation, and therefore rainfall, over this region may be sensitive to changes in vegetation cover near the desert border. Here we describe simulations of the West African monsoons with a simple zonally-symmetric model. The results suggest that the potential impact of human induced change of land cover on regional climate depends critically on the location of the change in vegetation cover. That is, desertification along the border with the Sahara (e.g., in Chad, Niger, Mali and Mauritania) leaves a relatively minor impact on monsoon circulation and regional rainfall; deforestation along the southern coast of West Africa (e.g., in Nigeria, Ghana and Ivory Coast) may result in complete collapse of monsoon circulation, and a significant reduction of regional rainfall.




2) A report from the UN in 2006, also went into detail about the effects of deforestation, making the following points:-

Frequent droughts and floods in eastern Africa can partly be blamed on widespread deforestation in the region.
Contrary to conventional wisdom, an estimated 62 percent of precipitation occurs over land as a result of evapotranspiration from lakes and wetlands and dense vegetation, particularly forests, which pump ground water into the sky. The moisture then condenses and falls as rain.
Only about 38 percent of the precipitation is generated over oceans and seas.
Kenya, one of the countries in East Africa that has been affected by severe droughts in recent decades, has had a high rate of deforestation.
The findings of a study carried out by UNEP following the 1999-2000 drought estimated that between 2000 and 2003 the country’s main water catchment areas – Mt Kenya Forest, Mau Forest, Mt Elgon Forest, Cherangani Forest – were deforested by between 0.2 and 2 percent over a two-year period.
As well as the climatic impact of deforestation, the local environmental effects can also be devastating, as Nick Nuttal of the United Nations Environmental Programme explains.

“Trees actually do two processes. They drill water into the ground. They funnel water into underground aquifers where it is stored to supply rivers during drought.
They also hold soil. Where there are no trees, the soil is washed away into rivers causing siltation into the oceans choking coral reefs.

The link between deforestation and drought is very significant.Forests are needed to build in resilience in the natural ecosystem. They are a buffer against extreme floods and droughts. It is crucial that Kenya invests in vegetation as one way of storing and returning moisture to the air so as to increase the chances of regular rainfall throughout the year."



Beneah Odhiambo, a professor of geography at Moi University adds that

“The loss of ground cover due to deforestation resulted in flash floods during heavy rainfall, leading to soil erosion. That is the start of desertification."


It’s all common sense really, but worth bearing in mind next time someone says droughts are caused by global warming.