Terrestrial Moisture Recycling Estimates Derived from an Idealized Model Framework

In many parts of the world, water resources for human and natural systems are heavily dependent on precipitation. Precipitation over land derives from moisture evaporated from both the ocean and land surface; the fraction of land surface evaporation contributing to local precipitation is often quantified in terms of a value known as the continental precipitation recycling ratio. Similarly, evaporation from the land surface may rain out over both ocean or land; the fraction of rainout over land to total evaporation is known as the continental evaporation recycling ratio. Here we present an idealized approach based on a simple two-box model moisture balance applied to a land-ocean domain, from which we ultimately derive analytic expressions for the precipitation and evaporation recycling ratios. We explore the behavior of these analytic expressions under different conditions, e.g., by varying the rate of atmospheric mixing between the land and ocean. We then use these analytic solutions to inform interpretation of the ratios as obtained from application of a moisture tracking algorithm to simulations of the GFDL-ESM2G earth system model.