Vegetation Indices to Aid Areal Evapotranspiration Estimations

Multiyear (1982-1990) monthly areal evapotranspiration (AET) was modeled with the Morton approach at the Solar and Meteorological Surface Observation Network stations within the conterminous United States. The AET values were correlated with satellite-derived, monthly maximum-value-composited Normalized Difference Vegetation Indices (NDVI) at half-degree resolution over the growing season (April-October). Generally, the strongest monthly correlation was obtained when the NDVI values were related to the AET estimates of the previous month. Geographically, both the monthly and growing-season averaged NDVI-AET relationships were best over the prairie (with an r=0.66±0.21 and 0.55±0.22, and a RMSE=26.75±12.62 and 6.24±1.67 mm month-1, respectively) and worst along the coastline and in the most humid, southeast region of the conterminous United States, where the Morton approach may function improperly.