As water moves through the terrestrial hydrologic cycle it may take many different pathways as it returns from the land surface to the atmosphere. These pathways include, transpiration from plants, evaporation from soils and surface waters, and evaporation of water intercepted by vegetation. Though each of these processes is controlled by different biogeochemical factors, only the sum of these processes, evapotranspiration, is readily observable though current measurement techniques. Because water movement through these different pathways occurs at different spatial and temporal scales, quantifying the separate amounts of water passing through each of these distinct pathways is critical to improving our understanding of the entire hydrologic cycle. The objective of this project is to use space-based observations of geochemical tracers of water cycle pathways to develop estimates of the hydrologic flux sub-components.