A DAILY RESOLUTION EVAPOCLIMATONOMY MODEL APPLIED TO SURFACE-WATER BALANCE CALCULATIONS AT THE HAPEX-SAHEL SUPERSITES

This paper describes the results of Lettau's evapoclimatonomy model at daily time scales as applied to the Central East and Southern supersi tes of the HAPEX-Sahel region in Niger, West Africa. A revised version of the evapoclimatonomy model has been applied to the millet and bush fallow (Guiera senegalensis) fields at both supersites during the int ensive observation period (IOP; 20 August-12 October, 1992), using dai ly means of precipitation, potential evapotranspiration, solar radiati on, normalized difference vegetation index (NDVI) from the HAPEX-Sahel observations, as well as vegetation and soil parameters for the regio n. Soil moisture and immediate and delayed evapotranspiration and runo ff are predicted, It has been found that the model predicts the soil m oisture at the Central Eastern supersite quite well. However, it overe stimates soil moisture at the Southern supersite even though its varia bility is captured by the model, Model results also indicate that soil moisture estimates are very sensitive to the NDVI-evaporivity relatio nship, which is robust at monthly scales but needs more revision for a pplication at the daily scale. Overall the model performance when appl ied to the IOP observations is sufficiently good to indicate the suita bility of the climatonomy for water balance studies on daily time scal es.