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Water ponds and sanitary risk in the Ferlo area: Contribution of remote sensing in studying Rift Valley Fever between August 2003 and January 2004 Volume 20, issue 1, janvier-février-mars 2009

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Authors
Centre de suivi écologique (CSE) BP 15532 Dakar-Fann Sénégal, Laboratoire de physique de l’atmosphère et de l’océan Siméon-Fongang/ESP-UCAD ESP-UCAD BP 5085 Dakar-Fann Sénégal, Médias-France Centre national d’études spatiales (CNES) 18, avenue Édouard-Belin BPI 2102 31401 Toulouse cedex 04 France, Bâtiment C 1 er étage 10, rue Hermès 31526 Ramonville Saint-Agne France

The abundance of mosquitoes around ponds is essentially linked to the intra-seasonal 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).