ESTIMATION OF CONTINENTAL PRECIPITATION RECYCLING

The total amount of water that precipitates on large continental regio ns is supplied by two mechanisms: 1) advection from the surrounding ar eas external to the region and 2) evaporation and transpiration from t he land surface within the region. The latter supply mechanism is tant amount to the recycling of precipitation over the continental area. Th e degree to which regional precipitation is supplied by recycled moist ure is a potentially significant climate feedback mechanism and land s urface-atmosphere interaction, which may contribute to the persistence and intensification of droughts. Gridded data on observed wind and hu midity in the global atmosphere are used to determine the convergence of atmospheric water vapor over continental regions. A simplified mode l of the atmospheric moisture over continents and simultaneous estimat es of regional precipitation are employed to estimate, for several lar ge continental regions, the fraction of precipitation that is locally derived. The results indicate that the contribution of regional evapor ation to regional precipitation varies substantially with location and season. For the regions studied, the ratio of locally contributed to total monthly precipitation generally lies between 0. 10 and 0.30 but is as high as 0.40 in several cases.