UC Santa Barbara

The relationship amongst climate, root zone storage capacity, and plant physiology has long been a foundational question of hydrology, and later eco-hydrology. Plants access to water affects their ability to photosynthesize, accumulate biomass, access resources, and survive periods of drought. However, determining the amount of precipitation plants receive is challenging because a) the amount of water that can be stored in the rooting zone, termed plant accessible water storage capacity (PAWSC), is exceedingly difficult to observe, and b) the relationship between precipitation, PAWSC, and evapotranspiration, a direct corollary for photosynthesis, is highly non-linear. While the estimation of PAWSC, or a similar storage capacity parameter, is integral to most hydrological and climatological modeling, we still lack a general conceptual model to describe how does uncertainty and variability in PAWSC affect evapotranspiration. Our current conceptual model, which is as PAWSC increases—evapotranspiration increases, has little description as to how much does evapotranspiration increase when PAWSC increases, what is the range of PAWSC that affect evapotranspiration, and how does this relationship between PAWSC and evapotranspiration vary for different climates? In this thesis, we develop a novel and efficient method that allows us to update our current conceptual model on relationship amongst climate, PAWSC, and evapotranspiration, in a way that can efficiently describe the effect of variability and uncertainty in PAWSC across a range of climates. We apply this model across 9 Critical Zone Observatories to develop the conceptual theory, we then describe the effects of PAWSC across elevational gradients in climate, and finally we show how PAWSC affects the change in evapotranspiration under a warmer climate.