Percolation theory combined with ecological optimality (the ecosystem that best converts atmospheric carbon to biomass is the one that we actually find) explains a large number of phenomena in nature, including the response of streamflow to climate changes and the ability of ecosystems to actually produce biomass across the world's biomes. The latter also can be used to predict the number of tree species present as a function of principal climate variables, precipitation and solar energy available. Now we show that it is possible to use the associated predictions of evapotranspiration to generate the interaction of shallow subsurface storage and precipitation recycling, including how the evapotranspiration depends on the scale of its measurement.