QUANTIFYING VULNERABILITY

Humans and the ecosystems on which they depend are vulnerable to a variety of natural hazards and responses to those hazards. Vulnerability is the degree to which human and environmental systems are likely to experience harm due to a perturbation or stress. Vulnerability occurs on many spatial scales ranging from local to global, and many temporal scales ranging from seasonal to geologic. For large-scale, rare events, such as volcanic eruptions or large earthquakes, we rely on traditional geological, geophysical, and geochemical techniques to try to avoid catastrophe. For more frequent events involving human time scales, new techniques for quantifying vulnerability have been developed. These involve not only geologic and physiochemical considerations, but ecosystem considerations , as well as human moral and economic values. Several examples of this are the Environmental Kuznets curve (Kuznets, Amer. Econ. Rev., 45, 1-28, 1955; and many subsequent discussions and controversies); The Research and Assessment Systems for Sustainability Program (http://sust.harvard.edu); and methods such as those of Luers et al. (Global Environ. Change, 13, 255-267, 2003). We discuss these models and progress in quantifying vulnerability, and discuss the specific case of the vulnerability of wheat yields in the Yaqui Valley, Mexico, to climate variability and change. We also present a preliminary analysis of a simple one-dimensional system of commodity flow based on shock wave theory that looks at temporal and spatial fluxes of a commodity. It is optimized to examine nonlinearities and thresholds in the flow of commodities by quantifying the relations of temporal and spatial fluxes of a commodity, and may provide a way to examine, at least qualitatively, both the physical variables that geologists are familiar with, and the economic factors that influence management and policy decisions. We compare this model with other vulnerability analyses.