Flash Flood Forecasting Over Complex Terrain

The nation's network of more than 130 Next Generation Radars (NEXRADs) is used to detect wind and precipitation to help National Weather Service forecasters monitor and predict flash floods and other storms. This book assesses the performance of the Sulphur Mountain NEXRAD in Southern California, which has been scrutinized for its ability to detect precipitation in the atmosphere below 6000 feet. The book finds that the Sulphur Mountain NEXRAD provides crucial coverage of the lower atmosphere and is appropriately situated to assist the Los Angeles-Oxnard National Weather Service Forecast Office in successfully forecasting and warning of flash floods. The book concludes that, in general, NEXRAD technology is effective in mountainous terrain but can be improved.

Flash floods typically develop in a period a few hours or less and can arise from heavy rainfall and other causes, such as dam or flood defence breaches, and ice jam breaks. The rapid development, often associated with a high debris content, can present a considerable risk to people and property. This book describes recent developments in techniques for monitoring and forecasting the development of flash floods, and providing flood warnings. Topics which are discussed include rainfall and river monitoring, nowcasting, Numerical Weather Prediction, rainfall-runoff modelling, and approaches to the dissemination of flood warnings and provision of an emergency response. The book is potentially useful on civil engineering, water resources, meteorology and hydrology courses (and for post graduate studies) but is primarily intended as a review of the topic for a wider audience.

This book provides readers with a broad understanding of the fundamental principles driving atmospheric flow over complex terrain and provides historical context for recent developments and future direction for researchers and forecasters. The topics in this book are expanded from those presented at the Mountain Weather Workshop, which took place in Whistler, British Columbia, Canada, August 5-8, 2008. The inspiration for the workshop came from the American Meteorological Society (AMS) Mountain Meteorology Committee and was designed to bridge the gap between the research and forecasting communities by providing a forum for extended discussion and joint education. For academic researchers, this book provides some insight into issues important to the forecasting community. For the forecasting community, this book provides training on fundamentals of atmospheric processes over mountainous regions, which are notoriously difficult to predict. The book also helps to provide a better understanding of current research and forecast challenges, including the latest contributions and advancements to the field. The book begins with an overview of mountain weather and forecasting chal- lenges specific to complex terrain, followed by chapters that focus on diurnal mountain/valley flows that develop under calm conditions and dynamically-driven winds under strong forcing. The focus then shifts to other phenomena specific to mountain regions: Alpine foehn, boundary layer and air quality issues, orographic precipitation processes, and microphysics parameterizations. Having covered the major physical processes, the book shifts to observation and modelling techniques used in mountain regions, including model configuration and parameterizations such as turbulence, and model applications in operational forecasting. The book concludes with a discussion of the current state of research and forecasting in complex terrain, including a vision of how to bridge the gap in the future.

"A flash flood is a flood in which the rapid rise in stream level and the resulting inundation follows the observable causative event by about four hours or less. For rain-caused flash floods meteorology is complex, and limited amounts of real-time data make timely forecasts of exact location very difficult. Lack of reports of flash-flood occurrences adds to the difficulty. Many occur that are never reported to the National Weather Service (NWS)"--Introduction.

The aim of this book is to contribute to understanding risk knowledge and to forecasting components of early flood warning, particularly in the environment of tropical high mountains in developing cities. This research covers a challenge, taking into account the persistent lack of data, limited resources and often complex climatic, hydrologic and hydraulic conditions. In this research, a regional method is proposed for assessing flash flood susceptibility and for identifying debris flow predisposition at the watershed scale. An indication of hazard is obtained from the flash flood susceptibility analysis and continually, the vulnerability and an indication of flood risk at watershed scale was obtained. Based on risk analyses, the research follows the modelling steps for flood forecasting development. Input precipitation is addressed in the environment of complex topography commonly found in mountainous tropical areas. A distributed model, a semi-distributed model and a lumped model were all used to simulate the discharges of a tropical high mountain basin with a pramo upper basin. Performance analysis and diagnostics were carried out in order to identify the most appropriate model for the study area for flood early warning. Finally, the Weather Research and Forecasting (WRF) model was used to explore the added value of numerical weather models for flood early warning in a pramo area.

Recent flood events in Europe, the USA and elsewhere have shown the devastating impact that flooding can have on people and property. Flood warning and forecasting systems provide a well-established way to help to reduce the effects of flooding by allowing people to be evacuated from areas at risk, and for measures to be taken to reduce damage to property. With sufficient warning, temporary defences (sandbags, flood gates etc) can also be installed, and river control structures operated to mitigate the effects of flooding. Many countries and local authorities now operate some form of flood warning system, and the underlying technology requires knowledge across a range of technical areas, including rainfall and tidal detection systems, river and coastal flood forecasting models, flood warning dissemination systems, and emergency response procedures. This book provides a comprehensive account of the flood forecasting, warning and emergency response process, including techniques for predicting the development of flood events, and for issuing appropriate warnings. Related topics, such as telemetry and information systems, and flood warning economics, are also discussed. For perhaps the first time, this book brings together in a single volume the many strands of this interesting multidisciplinary topic, and will serve as a reference for researchers, policy makers and engineers. The material on meteorological, hydrological and coastal modelling and monitoring may also be of interest to a wider audience.