Import and export of atmospheric water vapor between nations

We have applied a methodology for estimating the source regions of evaporation supplying precipitation over specific regions to the areas of most of the nations of the world. The methodology has been used in the past to estimate recycling ratios and the surface sources of moisture supplying rainfall over specific river basins. Extension to nations is straightforward, and we have incorporated other demographic information to gain a new viewpoint on the linkages between nations through the atmospheric branch of the hydrologic cycle. We find that nations with the highest recycling ratio, when scaled to a common area, have a combination of mountainous terrain, humid climate, or are at high latitudes. Nations with the lowest scaled recycling ratio are usually and or semi-arid and on the coast. Small landlocked nations are most likely to receive most of their precipitation from the evaporation of the territories of other nations. "Moisture independence" is greatest for large isolated nations. Nations that import a majority of their precipitating moisture from other countries who rank lower in terms per capita precipitation, i.e., more "water-poor" nations, tend not to be economically rich themselves, but are often also poor nations possessing lower population densities than their neighbors. (C) 2008 Elsevier B.V. All rights reserved.