GEOGRAPHICAL, BIOLOGICAL AND REMOTE-SENSING ASPECTS OF THE HYDROLOGIC ATMOSPHERIC PILOT EXPERIMENT IN THE SAHEL (HAPEX-SAHEL)

HAPEX Sahel (Hydrologic Atmospheric Pilot Experiment in the Sahel) was an international program focused on the soil-plant-atmosphere energy, water and carbon balance in the west African Sahel. It was intended to improve our understanding of the interaction between the Sahel and the general atmospheric circulation, both at present and in the future, providing a base line for studies of climate change. It was carried out in a 1 degrees X 1 degrees area of west Niger over a 3-4 year period with an 8-week intensive observation period from August to October 1992. HAPEX-Sahel was funded by a wide range of agencies in seven participating countries. Over 170 scientists visited and worked in the field. An interdisciplinary approach was adopted with contributed studies in hydrology and soil moisture surface fluxes and vegetation, remote sensing science, and meteorology and mesoscale modeling Detailed field measurements were concentrated at 3 ''supersites'' and 3 ancillary sites. Four aircraft were used for remote sensing and flux measurement. Observations from space were acquired from nine sensors on seven different satellite platforms. Conditions in 1992 turned out to be average far the last decade with good gradients of precipitation and a variety of vegetation productivities between the study sites. An information system has been established to provide a data base to disseminate the measurements. An active program of meetings, workshops, and interdisciplinary studies is now in progress.