Less rain, more water in ponds: a remote sensing study of the dynamics of surface waters from 1950 to present in pastoral Sahel (Gourma region, Mali)

摘要: Changes in the flooded area of ponds Gourma region from 1950 to present are studied by remote sensing, general context current multi-decennial Sahel drought. The seasonal and interannual variations areas covered surface water assessed using multi-date multi-sensor satellite images (SPOT, FORMOSAT, LANDSAT-MSS, -TM, -ETM, CORONA, MODIS) aerial photographs (IGN). Water body classification is adapted each type spectral resolution, with or without a middle-infrared band, spatial linear unmixing for mixed pixels MODIS data. high-frequency data document cycle areas, an abrupt rise early wet season progressive decrease dry season. They also provide base study inter-annual variability sharp contrasts between years such as 2004 (low maximal area) wetter 2001 2002 (respectively high late area).The highest reached annually greatly depends on volume, intensity timing rain events. However, overall reduction 20% annual rains during last 40 concomitant apparently paradoxical large increase water, starting 1970's accelerating mid 1980's. Spectacular two cases Agoufou Ebang Mallam, which time series covering 1954 period exist, this diagnosed at regional scale LANDSAT spanning 1972-2007. It reaches 108% September 1975 91 identified central Gourma. Ponds turbid waters no aquatic vegetation mostly responsible increase, more pronounced centre north zone. Possible causes differential changes discussed relation specifics topography, soil texture cover over watersheds that feed ponds. pattern sedimentation ruled out, impact land use, limited area, found secondary, opposed what has often been advocated southern Sahel. Instead, major responsibility attributed increased runoff triggered lasting 1970-80's droughts system shallow soils prevailing third landscape.