GLOBAL SCALE DRIVERS AND FUTURE PROJECTIONS OF THE TERRESTRIAL WATER BUDGET

Abstract

Projected changes in the hydrological cycle have raised significant concern over future water availability and the sustainability of the world’s terrestrial ecosystems. In Chapter 2, I used a recently compiled dataset of observed terrestrial evapotranspiration (ET) to estimate global fields of ET as a function of land-cover (LC) type and meteorological variables. I determined the primary driving variables to be temperature, precipitation and short-wave radiation through statistical analysis and found that these relationships varied by LC type. In Chapter 3, I analyzed global climate model data to examine projected changes in the terrestrial hydrological budget; in particular, the regional balance between precipitation, runoff, and evapotranspiration. To diagnose hydrologically significant change, I applied the concept of ‘climate departure’ which compares the size of the projected trend to the magnitude of historical variability. I then used the climate departure analysis to test and demonstrate support for the controversial hypothesized pattern of change, known as ‘wet-get-wetter, dry-get-drier’ (WWDD), whereby regions with characteristically high (low) available water receive more (less) precipitation input under climate change. In particular, I develop a spatial meta-analysis framework across individual models which demonstrates stronger support for WWDD than previously recognized. The results of this thesis provide new insights into the observed drivers of hydrological flux (Chapter 2) and model-based projections of future change (Chapter 3). Such knowledge is critical for understanding the hydrological consequences of environmental change now and into the future.