ANALYSIS OF DROUGHTS IN FRANCE FROM 1988 TO 1990 USING NOAA-AVHRR DATA AND AN AGROMETEOROLOGICAL MODEL

The study reported here aimed at proposing an operational methodology to estimate actual evaporation on a large scale, using AVHRR images of the NOAA satellite and an agrometeorological model. The method was ap plied to detect drought effects for 3 yr (1988-1989-1990) over all of France. For each year, 48 cloud-free images were selected on a 5-d bas is. Surface temperatures obtained from AVHRR images were combined with the output data of an agrometeorological model using ground data from 20 stations. The simplified relationship, based on an energy budget r elating midday surface-air temperature difference to daily evaporation and net radiation was used for this study. A new local split-window m ethod was applied to the images in order to get a better accuracy of s urface temperature. Analysis of the cumulative surface-air temperature difference revealed a regional climatic effect. Evaporation maps prov ided a global evaluation of droughts in all of France for the 3 yr stu died.