Dernières études sur les sécheresses à l'échelle continentale

Recent studies of droughts on a continental scale

Chef du Service Hydraulique de l'ORSTOM Conseiller Scientifique à Electricité de France

Abstract

It is extremely difficult to make a synthesis of drought conditions on a regional scale. Drought must first be defined in accurate terms, but unfortunately, such definitions vary among different water consumers. Farmers and water power engineers have very different ideas on the subject, except in cases of very acute water shortage. L Serra defines drought as an abnormal decrease in water supplies at certain times of the year, or in specific cases during the whole year. Precise definition of the type of drought is essential before undertaking a general study of the subject. In addition, droughts lack homogeneity in both time and space, even when considered on a small scale. A considerable number of studies were made of the recent drought in tropical Africa (which includes the Sahel region), which were based on frequently unreliable rainfall records and river or lake gauging data which sometimes left to be desired. Nevertheless, this information provided a reasonably clear picture of the calamity which struck not only a major part of Africa, but also Brazil, Australia and the Indian sub-continent. A first report on the subject was produced by E.G. Davy, a World Meteorological Organization expert, followed in 1974 by a joint WMO/IAHS report on the hydrological aspects of the drought. A series of studies were undertaken in France by B.R.G.M., S.C.ET. Internationale and O.R.S.T.O.M., which were financed by the French Directorate-General for Scientific and Technical Research (D.G.R.S.T.) and the Ministry of Cooperation. All these studies were intended to provide practical, if possible quantitative data for use in planning counter-measures against the after-effects of the drought. Comprehensive research programmes have been undertaken in Great Britain and the United States on the subject of the Sahel drought, and in France, the hydrological and meteorological aspects of droughts on a continental scale were discussed at a Symposium organized by various international and local bodies in Grenoble in September 1975. The results of this meeting were sowewhat disappointing, as only few reports related to temperate regions or made reference to the causes of drought. From the purely scientific angle, therefore, much remains to be done before the factors involved can be really understood. On the practical side, a realistic report by the "Académie des Sciences d'Outre-Mer" outlining a practical water management policy for the Sahel and neighbouring regions of West Africa will no doubt be of interest.