Water ponds and sanitary risk in the Ferlo area: Contribution of remote sensing in studying Rift Valley Fever between August 2003 and January 2004
J.A Ndione, J.P Lacaux, Y. Tourre, C. Vignolles, D.Fontanaz, M.Lafaye
Abstract
The abundance of mosquitoes around ponds is essentially linked to the intraseasonal variability of rainfall which can be modulated by a panoply of climate signals. Larvae sites for the Aedes vexans and Culex poicilipes can thus proliferate accordingly and contribute to the diffusion of RVF. The ponds’ small sizes and their spatio-temporal variability are monitored by high res. SPOT-5 (10 m) imagery. Two new normalized indices have been developed, the NDPI and NDTI, which make it possible to detect small ponds and associated turbidity. Indeed small ponds, less than 0.5 ha in size, dominate at all times and represent 65 to 90% of all ponds during the rainy season. Based on the measured average flying ranges of mosquitoes (500 to 600 m), risks/hazards maps have been developed that give the spatial extent to which mosquitoes can be found: the Zone Potentially Occupied by Mosquitoes or ZPOM. Between the dry- and the rainy-seasons the maximum difference in ZPOM spatial extent can be as large as 25%. All of the above is meant to contribute to the implementation of health early warning systems (HEWS).
Key words: remote sensing, Rift valley fever, Senegal, surface water.
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