An investigation into the coupled dynamics of rainfall climatology, ecosystem structure, and biophysical functionality

Abstract

This dissertation is an investigation into the coupled dynamics of rainfall climatology, ecosystem structure, and biophysical functionality. The interconnected nature of the water, carbon, and energy cycles presents fundamental questions of how climate change will alter ecosystems, and how these alterations in ecosystems structure and function will feedback into global cycles. In chapter 1, climate change is introduced and the inability of current global climate models to accurately reproduce the observed frequency and intensity of rainfall events is demonstrated. Patterns of satellite derived rainfall and forest cover are used in chapter 2 to show that the frequency and intensity of rainfall are the key determinates of ecosystem structure. Given that rainfall climatology determines ecosystem structure, a new modeling framework able to represent the complex three-dimensional nature of ecosystems is presented in chapter 3. The accurate representation of canopy allometry, species density, landscape dispersion, and size distributions are shown to provided improved estimates of the biophysical functions of photosynthesis and transpiration. In order to validate models of ecosystem functionality, detailed measurements of hydrologic fluxes, particularly the separate fluxes of evaporation and transpiration, are required. No standard methods exist for the partitioning of evapotranspiration and information beyond the bulk flux is required to attribute evapotranspiration components. The stable isotopes of water fill this observational need, and chapter 4 is a study of the measurement of the isotopic composition of evapotranspiration and its associated uncertainties. Isotope flux composition is used in chapter 5 to partition evapotranspiration fluxes and attribute the partitioning to biophysical and micro-meterological conditions. Finally, in chapter 6, partitioned evapotranspiration flux over a multi-year record shows how vegetation structure and rainfall climatology alter the partitioning of evapotranspiration, and shape the dynamics of moisture feedback into the global hydrologic cycle.