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IWRA World Water Congress 2008 Montpellier France
3. Climate Change and Disasters
Author(s): S. Valet
Ph. Le Coustumer
M. Motélica -Heino
P.S. Sarr
1Consultant. PASSERELLES, 9, rue du Bât d’Argent, 69001, Lyon France ; valet.serge2@wanadoo.fr ; 2 Université de BordeauxI, av. France.; 3 Unité : UMR6113 Institut des Sciences de la Terre d'Orléans (ISTO), France ; stefan.motelica-heino@univ- orleans.fr.;

Keyword(s): run-on, simulated hydrological budget, simulated yield, millet, morphopedologic units, Sudano- Sahelian zone.

AbstractIn Sudan-Sahelian zone, the yield and quality of cultures are essential to the human well-being and the stability of societies. Climatic change, rain losses and the accentuation of its spatio-temporal variability generate an increase of the hydrological stress on traditional food crops. At the hillslope and the field scale, the accumulation of water by the crops is modified by the run-off. A part of this run-off, even during a year of high hydrological deficit, forms the runon of the same importance on the field than on the hillslope. This runon is defined as “a natural, complementary and simultaneous irrigation to the rainfall that has generated it in according to natural (topographical, morphological, permeability) anthropogenic (soil work) conditions”. It can explain the yield variability that does not correspond to the potential fertility of the different morphopedological units. Cultivated areas are only partially represented in global models. Now the elaboration of new patrimonial management modes of the Soudano-Sahelian zone must rely on the analysis of the spatio-temporal dimension of the climatic factors. They regulate the land and environmental dynamics and this suggest that their co-evolution must be integrated in an evolutionary and flexible scheme of such as the cultivators use empirically. The study investigated the hydrological balance of the mil for 90 days duration, cultivated traditionally, including the impact of climatic change (three contrasted rain years, one normal, one year showing a deficit and one very rainy) and the variability of the morphopedological units on the slope. The runon was taken as a complementary irrigation. On the slope, the actual evaporo-transpiration (AET) expected varies from 126 to 289 mm during a year showing a rain deficit, from 275 to 314 mm during a normal year and from 296 to 351 mm during a very rainy year. To these commotions in real water simulated correspond to extreme yields of 0 to 1083 kg.ha-1, of 1128 to 1599 kg.ha-1 and from 1382 to 2047 kg.ha-1 for the three years respectively. Results demonstrate that face to the climatic change, the integration of the multi-scale variability of the productivity of the media and of the spatial distribution of hydrological resources to adapt to environmental fluctuations allows to foreseen this change and attenuate its violence. The mastery and control of the hydrological fluxes on the slope and on the field to eradicate the erosion could be realised through bocage planning.
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