Probing the Precipitationshed : A quantification of the biophysical dimensions of terrestrial moisture recycling

Abstract: Terrestrial moisture recycling is the phenomena whereby water evaporates from the land surface, travels through the atmosphere, and fall as precipitation downwind. The interaction of societies with this branch of the hydrological cycle, though critical to the productive functioning of ecosystems around the planet, remains poorly understood. With this thesis, I aim to improve our understanding of terrestrial moisture recycling by exploring two dimensions of the phenomena. First, I build on earlier work that quantified terrestrial moisture recycling relationships using precipitationsheds, defined as the upwind land surface and atmosphere that contributes evaporation to downwind precipitation. In other words, the precipitationshed can be thought of as a watershed of the sky. In this thesis, I quantify the variability of the spatial pattern of the precipitationshed in order to understand whether the same or different regions recycle moisture every year (Paper 1). The key finding from this analysis is that there is high overall stability in the regions that provide evaporation to the downwind precipitationshed, such that there is a core area of evaporation contribution that provides a significant volume of moisture to downwind areas, every year. Second, I synthesize terrestrial moisture recycling insights using an ecosystem services framework, by defining and quantifying the biophysical structure, function, and ecosystem service of terrestrial moisture recycling (Paper II). I define terrestrial moisture recycling as a regulating ecosystem service, with the vegetation in upwind areas providing the critical role of regulating the amount of evaporation that enters the atmosphere, and that is available downwind for precipitation. My key findings are that vegetation provides important regulation of terrestrial moisture recycling in certain areas globally, but less so in others, as well as there being a clear and well-defined decreasing importance of terrestrial moisture recycling with distance from the evaporation source region. Since we know from Paper 1 that terrestrial moisture recycling relationships are persistent in time, it implies that there is a relatively stable set of upwind social-ecological systems that provide terrestrial moisture regulation to downwind social-ecological systems. Thus, using the classification of terrestrial moisture recycling as an ecosystem service, we can begin to unpack the social dimensions of the robust biophysical relationships between these upwind and downwind systems. The key next steps in this research will be to further characterize the providers and beneficiaries of terrestrial moisture recycling, the value of these services, and how, if at all, terrestrial moisture recycling may be governed.