HR: 1340h
AN: A43B-0048    [Abstracts]
TI: Evaluations of West African Surface Water and Energy Balances from 1982 to 1990 Based on Ground & Satellite Observations and SSIB Vegetation Model
AU: * Poccard, I
EM: ipoccard@geog.ucla.edu
AF: Department of Georgaphy, University of California, 1255 Bunche Hall, Department of Georgaphy, UCLA, Los Angeles, CA 90095-1524 United States
AU: Xue, Y
EM: yxue@geog.ucla.edu
AF: Department of Georgaphy, University of California, 1255 Bunche Hall, Department of Georgaphy, UCLA, Los Angeles, CA 90095-1524 United States
AB: The Sahel is a key area for studying the climate change because of a unique severe drought and a marked land cover changes. However, the studies of surface hydrology at continental scale over this area are spare, mainly due to the lack of data. Here, a comprehensive study of seasonal and inter-annual variability of surface hydrology has been conducted in order to highlight the specific characteristics of different sub-regions in the Sahel. Total 217 rain gauge stations have been selected from the Institut de Recherche pour le Developpement (IRD-France) daily rainfall database and other sources. The choice of the stations is based on three different criteria: the maximization of the spatial coverage within 2øN-20øN and 18øW-25øE, the maximum period length without any gap (1982-90), and the maximum variation of different associated vegetation types (7 types are included). The stations data have been interpolated into 1øx1ø grid boxes. Leaf Area Index (LAI) and vegetation cover parameters were derived from AVHRR NDVI satellite data (Los et al., 2001). We also obtain the near surface temperature, humity, wind, and radiation from the NCEP/NCAR Reanalysis data (Kalnay, 1996). The above forcing data are used to drive an offline version of the model SSiB (Xue et al., 1991) to produce surface meteorological and hydrological variables. The spatial and temporal patters of the SSIB's outputs (such as latent and sensible heat fluxes, surface temperature, and runoff are analyzed. Some of them (such as surface temperature) are compared with observations. The results show important roles played by the vegetation properties and/or the soil moisture in different regions of West Africa. In the studied regions, the relationship between soil moisture and evaporation is systematically higher than the relationship between LAI and latent heat flux. In Sahel, the soil moisture is very dominant. The Sudanian region has the lowest relationship among these regions. The soil moisture hence contributes significantly in all the regions than LAI in the water and energy balances, even if in the west part of Central Africa despite the presence of tall vegetation and more precipitation. A study has been conducted to investigate the characteristics in 3 sub-regions' water and energy balances between the 3 driest and the 3 wettest years. The first one, located in the Sahel region, has a regional response to the inter-annual rainfall variability. The anomaly surface variables, such as evaporation, are highly correlated to precipitation and net radiation, which indicates a dominant regional surface-atmosphere feedback. The second one corresponds of the area along the Guinean coast and the west Central Africa. This large area is controlled by large scale circulation. There is absence in coherent signal between major variables, such as net radiation, precipitation, sensible heat flux, and evaporation. In between these two areas, the Sudanian region show different atmosphere-surface feedback. It can be considered as a transition area, with a mixed signal partly due to the cloud feedback.
DE: 3322 Land/atmosphere interactions
DE: 3360 Remote sensing
DE: 3309 Climatology (1620)
DE: 1836 Hydrologic budget (1655)
DE: 1878 Water/energy interactions
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting