A lesson to be learned from the Sahel is that humanitarian aid will not be enough if these societies subjected to drought are viewed as passive victims of external forces.
Strictly speaking, what is occurring is not drought but desertification, a process that leads to the extension of desert conditions at the edges of deserts. Desertification is part of a process where there is drought as well as stress on the land. Typically, stress on the land results from deforestation, overgrazing and overcultivation.
Deforestation results from a growing population's use of wood for fuel. Over-grazing results from four interrelated factors. Population growth has meant an increase in the number of nomadic desert herdspeople and thus more animals. Better veterinary care has resulted in lower animal mortality. Widespread drilling of wells has allowed more animals to be watered than can be fed in periods of drought. More and more animals on less and less land leads to stress on the land. During drought that stress strips the land bare.
As populations grow, people steadily encroach on the traditional grazing lands to farm soil that is too arid to be perpetually cropped, but would remain productive if left in permanent grass. Importantly, these things are not the sole cause of desertification; but they produce land that has lost the capacity to protect itself when drought strikes.
The other important cause of desertification is the way these changes to the land trigger climate processes in a cycle that feeds on itself, prolonging the effects of drought.
Rain is brought to the Sahel by the African summer monsoon characterised by the northward advance of warm, rain-bearing oceanic air over the land, affecting an area between the South Atlantic and the Sahel in the north. The Sahel experiences drought when the summer monsoon does not reach far enough north. Movement depends largely on solar energy available for driving the pressure systems and winds. Should the migration of the monsoon air advance northwards only a few degrees of latitude less than normal, large areas of the Sahel experience a great reduction in rain. In modern times the northward movement of the rain-bearing air has been less than normal and, in effect, the dry Sahara climate has been moving south. This has been linked to feedback processes between the atmosphere and the land surface as modified and used by the very population that is at risk.
Overgrazing of the land by livestock leads to loss of vegetation resulting in bare soil being exposed to wind erosion. Large quantities of windblown dust in the atmosphere reduce sunlight and heating of the land surface, which in turn leads to a reduction in rising warm air and rainfall caused as it cools. The dust may also directly affect rainfall by making available too many condensation nuclei which collectively compete for the water in clouds. The resulting water droplets are too small for coalescence and raindrop formation to occur.
There are other processes at work. Overgrazed land reflects more incoming energy from the sun than a vegetated surface, which results in cooling. This in turn leads to subsidence of air that expands as it descends, drying and warming in the process and inhibiting cloud formation. The dry conditions result in a further loss of vegetation causing increased reflectivity and subsidence of dry air even further to the south, and so on in a cycle of positive feedback. The result is an expansion of desert margins, conditions under which a natural drought prolongs itself.
Humanitarian aid to the people of the Sahel may not be enough, especially if the societies subjected to ongoing climatic stress are viewed as passive victims of external forces. The problem stems from a failure of societies to adapt to their specific circumstances and our failure to combine relief aid and disaster planning with appropriate adaptation strategies.
* Chris de Freitas is an associate professor in the School of Environment at the University of Auckland.
