On the Importance of Roots to Eco-hydrology: The Effect of Plant Accessible Water Storage Capacity on Evapotranspiration

ABSTRACT

The relationship among 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. 

BIO

Christopher Heckman is currently a PhD Candidate at the Bren School of Environmental Science and Management. Christopher’s research interests lie in how hydrology shapes patterns of vegetation under both current and future climates. Specifically, he is interested in how the amount of water that can be stored in the soil mediates vegetation’s response to climate. Through using computer models, he explores the mechanisms that hydrologically link climate, soil, and vegetation. Christopher did his undergraduate degree in Environmental Studies and Geography, at Colorado University of Boulder, and he also holds a master’s degree in Environmental Science and Management, from the Bren School at University of California, Santa Barbara. In previous work he has investigated the way water supplies are managed from the Nor Yungus, in Bolivia, to here in Burbank, California. In his free time, Christopher enjoys journeying through the landscapes he researches, whether that be through backpacking, cycling, paragliding.