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George Yates
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Thomas T. Warner, David N. Yates, and George H. Leavesley

A new community laboratory for fostering collaborative research between the atmospheric and hydrologic sciences communities is described. This facility, located at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, allows scientists from both communities to more easily focus resources and attention on interdisciplinary problems in atmospheric, hydrologic, and other related sciences. Researchers can remotely access the computing tools to use them or to download them to their own facility, or they can visit NCAR and use the laboratory with other scientists in joint research projects. An application of this facility is described, where scientists from NCAR, the University of Colorado, and the United States Geological Survey used quantitative precipitation estimates from weather radar to simulate a flash flood in the Buffalo Creek watershed in the mountainous Front Range near Denver, Colorado.

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David N. Yates, Thomas T. Warner, and George H. Leavesley

Abstract

Three techniques were employed for the estimation and prediction of precipitation from a thunderstorm that produced a flash flood in the Buffalo Creek watershed located in the mountainous Front Range near Denver, Colorado, on 12 July 1996. The techniques included 1) quantitative precipitation estimation using the National Weather Service’s Weather Surveillance Radar-1988 Doppler and the National Center for Atmospheric Research’s S-band, dual-polarization radars, 2) quantitative precipitation forecasting utilizing a dynamic model, and 3) quantitative precipitation forecasting using an automated algorithmic system for tracking thunderstorms. Rainfall data provided by these various techniques at short timescales (6 min) and at fine spatial resolutions (150 m to 2 km) served as input to a distributed-parameter hydrologic model for analysis of the flash flood. The quantitative precipitation estimates from the weather radar demonstrated their ability to aid in simulating a watershed’s response to precipitation forcing from small-scale, convective weather in complex terrain. That is, with the radar-based quantitative precipitation estimates employed as input, the simulated peak discharge was similar to that estimated. The dynamic model showed the most promise in providing a significant forecast lead time for this flash-flood event. The algorithmic system did not show as much skill in comparison with the dynamic model in providing precipitation forcing to the hydrologic model. The discharge forecasts based on the dynamic-model and algorithmic-system inputs point to the need to improve the ability to forecast convective storms, especially if models such as these eventually are to be used in operational flood forecasting.

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Guy Delrieu, John Nicol, Eddy Yates, Pierre-Emmanuel Kirstetter, Jean-Dominique Creutin, Sandrine Anquetin, Charles Obled, Georges-Marie Saulnier, Véronique Ducrocq, Eric Gaume, Olivier Payrastre, Hervé Andrieu, Pierre-Alain Ayral, Christophe Bouvier, Luc Neppel, Marc Livet, Michel Lang, Jacques Parent du-Châtelet, Andrea Walpersdorf, and Wolfram Wobrock

Abstract

The Cévennes–Vivarais Mediterranean Hydrometeorological Observatory (OHM-CV) is a research initiative aimed at improving the understanding and modeling of the Mediterranean intense rain events that frequently result in devastating flash floods in southern France. A primary objective is to bring together the skills of meteorologists and hydrologists, modelers and instrumentalists, researchers and practitioners, to cope with these rather unpredictable events. In line with previously published flash-flood monographs, the present paper aims at documenting the 8–9 September 2002 catastrophic event, which resulted in 24 casualties and an economic damage evaluated at 1.2 billion euros (i.e., about 1 billion U.S. dollars) in the Gard region, France. A description of the synoptic meteorological situation is first given and shows that no particular precursor indicated the imminence of such an extreme event. Then, radar and rain gauge analyses are used to assess the magnitude of the rain event, which was particularly remarkable for its spatial extent with rain amounts greater than 200 mm in 24 h over 5500 km2. The maximum values of 600–700 mm observed locally are among the highest daily records in the region. The preliminary results of the postevent hydrological investigation show that the hydrologic response of the upstream watersheds of the Gard and Vidourle Rivers is consistent with the marked space–time structure of the rain event. It is noteworthy that peak specific discharges were very high over most of the affected areas (5–10 m3 s−1 km−2) and reached locally extraordinary values of more than 20 m3 s−1 km−2. A preliminary analysis indicates contrasting hydrological behaviors that seem to be related to geomorphological factors, notably the influence of karst in part of the region. An overview of the ongoing meteorological and hydrological research projects devoted to this case study within the OHM-CV is finally presented.

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