Annual Water Availability (Precipitation minus Evapotranspiration)

Available water is calculated by subtracting evapotranspiration from precipitation. This water can be stored in lakes, soil moisture, and underground aquifers, or else it will flow into a river channel and eventually reach the ocean. Our map was built using precipitation data from WorldClim and evapotranspiration data from the MOD16 Global Evapotranspiration Product. Both datasets have one kilometer resolution, but the latter is not valid over urban or barren land, so available water was not calculated for these areas. In order to highlight the central roll topography plays in directing the flow of water, we used the No Alteration of Grayscale or Intensity (NAGI) method to combine this map with an elevation hillshade.