Hydrological indices and triggers, and their application to hydrometeorological monitoring and water management in Texas




Ward, George H.

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Center for Water and the Environment, University of Texas at Austin



Assessing and responding to variations in hydroclimate require some immediate quantitative measure of surface-water conditions, not only of surfeits or deficits in rainfall, of volumes of flow in the streams and rivers, and of the storage in reservoirs, but how these relate to normal conditions and their likelihood of meeting regional water demands. A metric that summarizes surface-water conditions in a compact and intuitive way is an indicator or index (the latter generally being more mathematically complex). Specific values, or thresholds, of an index can be associated with levels of surface-water availability and, in turn, tied to specific management actions, in which case they are referred to as “triggers.” The overall objectives of this project are to survey the literature on hydroclimatological indices, with emphasis on the international literature for case studies of trigger formulations, then to use Texas examples to explore and contrast different indices of hydroclimate and their thresholds. The indices specifically addressed in this review are selected because either they appeared to offer some potential for utility in Texas water management, or because they have acquired some level of acceptance in hydrometeorology and water-resources.

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