RETRIEVAL OF LAND SURFACE RESISTANCE TO WATER VAPOUR TRANSFER USING COMPLEMENTARY RELATIONSHIP AND REMOTE SENSING

摘要

In this study, we propose an alternative way to derive the surface-to-air gradient of vapour pressure (Δθ_s), the land surface resistance (r_s), and a derived aridity index by coupling a simple prognostic model (based on the complementary relationship) to evapotranspiration (E) estimates provided by the triangle/trapezoidal method (Jiang & Islam, 1999). This method requires a combination of remotely sensed data and few ground measurements, and is based on the use of the ratio E to potential evaporation (E_p) to derive the surface humidity prevailing at a given pixel. The method was applied to four sites in Western Africa, and the study of the temporal evolution of Δθ_s and r_s showed seasonal variations which are consistent with the wet and dry seasons that characterises the climate at these sites. We then propose a new dryness index, the surface aridity index (SAI) derived from the Δθ_s – rs space, which proved to be a useful tool to assess the aridity state over a region.