How Soil Water Storage Moderates Climate Change's Effects on Transpiration Across the Critical Zone Observatories

While the atmospheric water demand is predicted to increase under a warmer climate, actual evapotranspiration (AET) will be moderated by the supply of water available to vegetation. A key question is how will plant accessible water storage capacity (PAWSC) effect the partitioning of precipitation between AET and runoff. Our results indicate that whether and by how much AET increases or decreases with moderate warming is significantly based upon interactions between PAWSC and characteristics of precipitation such as the amount, frequency, and skew as well the partitioning between rain and snow. In snow dominated climates, if PAWSC cannot make up for the loss of storage as snowpack then AET may decrease despite warming temperatures. Even in rain dominated climates, PAWSC could significantly limit the increase in AET associated with higher atmospheric demand. Changes in AET will have significant impacts for forests vulnerability to drought, insect out breaks, and fire as well as for the amount of runoff that flows downstream for our use and management. Due to the highly heterogeneous nature of PAWSC and the difficulty of measuring it across large scales, we use a well-tested hydrologic model to estimate the impacts from a range of PAWSC on the partitioning of precipitation between runoff and AET. We completed this analysis for the range of precipitation and vegetation characteristics found across the 9 Critical Zone Observatories of the United States.