Abstract
Annual and monthly water loss data, namely precipitation minus runoff, from experimental watersheds of all over the world, are collected and stored in the database. The data are released to public through WWW. Annual water loss is regarded as annual actual evapotranspiration, Et. By combining the database to Geographic Information System, GIS, the world distribution of Et is obtained. The important point is that the database is based on the observational results. The map of Et is consistent with empirical evidences. It can be used as verification data of the models that calculates the fluxes or as ground truth for the products of satellite remote sensing. Annual Et is plotted against annual precipitation, Pa. Et increases with Pa almost along 1:1 line, however, the relationship departs at certain Pa. This value is different among the region, and is an important parameter which governs the regional hydrological environment. The maximum annual Et in wet tropics is around 1800mm. It is estimated that Et slightly decrease with Pa after Et reaches maximum because energy available for evapotranspiration decreases with precipitation.
