Report of a Workshop on Predictability and Limits-To-Prediction in Hydrologic Systems (2002) / Chapter Skim
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1. Background and Goals
1. Background and Goals
Pages 1-11
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As a result observing systems and conceptual understanding are the engine behind operational prediction systems. In this way hydrologic science and operational hydrology work together to reduce the hazards faced by the public.
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The first goal is the identification of predictable patterns on all pertinent spatial and temporal scales in the water cycle. Because the water cycle is composed of components with varying memory (e.g., mean residence time in atmosphere is about nine days whereas in the active groundwater system the memory may be decades)
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Background and Goals 3
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The third and final major goal posed in NRC (1999) for predictability research in the unique context of hydrologic sciences is to understand how variability in hydrologic processes change with spatial scale.
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Background and Goals 5
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Because analysis budgets are the main link bet~veen models and observations, they should be rigorously tested against all observations, especially those hydrometeorological observations developed to cover broad space and time scales. New continental and global hydrometeorological data sets will be required to support these activities.
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These include surface soil moisture at high resolution (~10 km for hydrometeorology applications, ~40 km for hydroclimatology applications) , surface freeze/thaw condition, diurnal cycle of precipitation, river and water bodies altimetry, and snow cover and water equivalent.
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Nonetheless the two goals for predictability research are distinguished here because they often require different driving science questions, data, and metrics of progress. Progress in predictability research directed towards improving operational prediction is measured in terms of increased prediction accuracy or forecast skill.
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In this context the goal is less to improve the immediate forecast skill but to develop the foundations for a future system. in fact, in the short term there may be a drop in forecast skill as a new paradigm is introduced but the paradigm shift sets a new trajectory that promises great gains (see Figure A..
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As the prediction system and its supporting science paradigm mature, the system again experiences slower rates of skill increase with time. In this phase the prediction system has essentially reached it highest potential for characterizing and predicting hydrologic phenomena.
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This prediction did not effectively convey the associated uncertainties, rather indicated a fixed value for the flood crest, which was only marginally larger than the previous high water mark. The river crested at a height of 54 feet, resulting in extensive damage to the unprepared communities, which had prepared for river crests of no greater than 49 feet.
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