Student - May 14, 2009


Since the extreme droughts of 1983 and 1984, rainfall in the Sahel has gradually increased, and farming has gone better. This trend will not continue in the coming decades, however – according to the predictions of Dr. Lars Hein of the Environmental systems management chair group.

In a recent publication in Climatic Change, Hein and his colleagues Professor Rik Leemans and Dr. Marc Metzger point to the big drop in rainfall in the Sahel predicted for the next fifty years by most climate models. The IPCC climate panel’s scenarios range from nine to fifty two percent less rainfall. A drier climate will mean less grassland. Various drought scenarios show how this will lead to a reduction in herd sizes and in the productivity of livestock in northern Senegal.

The publication makes use of other recent research by Hein and others, including Dr Nico Ridder of Plant production systems, analyzing how the vegetation dynamics in the Sahel are influenced by rainfall. The two scientists are involved in an academic dispute with remote sensing experts on the question of whether the increased rainfall of recent years has led to increased vegetation, or whether there has been overgrazing. Interpretations of satellite images suggest that there is no large-scale degradation in the Sahel, but De Ridder and Hein claim that these interpretations are based on an over-optimistic rain use efficiency, a measurement of how efficiently plants turn water into biomass. It appears that the minimal soil fertility in the Sahel limits the growth of plants when there is more rain. They think the satellite images must be reinterpreted in order to determine the level of degradation in the Sahel.

Together with Dr. Hans-Peter Weikard of Environmental Economics, Hein developed a model with ecological and economic data, to calculate livestock keepers’ maximum incomes with more and with less rain. It appeared that the current livestock population and grazing pressure leads to lower incomes for livestock keepers. To make optimal use of the available grassland, they would do best to sell off part of their herd at the market, says Hein. If rainfall drops in the coming decades, he predicts increased migration from the rural areas to the cities of the Sahel. That will take us full circle, says Hein. ‘Ten years ago I worked in the Sahel for the FAO. I saw that there was too little understanding of how the Sahel responds to the management of the pastoralists. Development projects sank wells and vaccinated livestock without stopping to ask whether there was enough grass for all the cattle. I have an answer to that question now.’