Every drop counts: What part of rainfall drives ecosystem function?

Decades of research in drylands have focused on ecological responses to precipitation including productivity, gas fluxes, and remotely-sensed greenness. However, not all precipitation is available to ecosystems because of losses to runoff, drainage, and evaporation. Future ecosystem function therefore depends not only on precipitation, but on the fate of that precipitation upon the land. This ecohydrologic partitioning involves complex interactions among weather, land cover and soils. Here we present our efforts to conceptualize, measure and predict ecosystem-available water. We outline novel methods to quantify ecosystem-available water at plot, stand, catchment and regional scales across dryland ecosystems of the Southwest.