Hydraulic, hydrologic and water resources engineers have been concerned for a long time about failure phenomena. One of the major concerns is the definition of a failure event E, of its probability of occurrence PtE), and of the complementary notion of reliability. However, as the stochastic aspects of hydraulics and water resources engineering were developed, words such as "failure," "reliability," and "risk" took on different meanings for different specialists. For example, "risk" is defined in a Bayesian framework as the expected loss resulting from a precisely defined failure event, while according to the practice of stochastic hydraulics it is the probability of occurrence of a failure event. The need to standardize the various concepts and operational definitions generated numerous exciting discussions between the co-editors of this book during 1983-84 when L. Duckstein, under sponsorship of the Alexander von Humboldt Foundation (FRG), was working with E. Plate at the Institute of Hydrology and Water Resources of the University of Karlsruhe. After consulting with the Scientific Affairs Division of NATO, an organizing committee was formed. This comittee - J. Bernier (France), M. Benedini (Italy), S. Sorooshian (U. S. A. ), and co-directors L. Duckstein (U. S. A. ) and E. J. Plate (F. R. G. ) -- brought into being this NATO Advanced Study Institute (ASI). Precisely stated, the purpose of this ASI was to present a tutorial overview of existing work in the broad area of reliability while also pointing out topics for further development."

If one surveys the development of wind engineering, one comes to the conclusion that the challenge of urban climatology is one of the most important remaining tasks for the wind engineers. But what distinguishes wind engineering in urban areas from conventional wind engineering? Principally, the fact that the effects studied are usually unique to a particular situation, requiring consideration of the surroundings of the buildings. In the past, modelling criteria have been developed that make it possible to solve environmental problems with great confidence, and studies validated the models: at least in a neutrally stratified atmosphere. The approach adopted in the book is that of applied fluid mechanics, since this forms the basis for the evaluation of the urban wind field. Variables for air quality or loads are problem specific, or even random, and methods for studying them are based on risk analysis, which is also presented. Criteria are developed for a systematic approach to urban wind engineering problems, including parameter studies. The five sections of the book are: Fundamentals of urban boundary layer and dispersion; Forces on complex structures in built-up areas; Air pollution in cities; Numerical solution techniques; and Posters. A subject index is included.

Studies of convection in geophysical flows constitute an advanced and rapidly developing area of research that is relevant to problems of the natural environment. Since the late 1980s, significant progress has been achieved in the field as a result of both experimental studies and numerical modelling. This led to the principal revision of the widely held view on buoyancy-driven turbulent flows comprising an organized mean component with superimposed chaotic turbulence. An intermediate type of motion, represented by coherent structures, has been found to play a key role in geophysical boundary layers and in larger scale atmospheric and hydrospheric circulations driven by buoyant forcing. New aspects of the interaction between convective motions and rotation have recently been discovered and investigated at the end of the 20th century. Extensive experimental data have also been collected on the role of convection in cloud dynamics and microphysics. New theoretical concepts and approaches have been outlined regarding scaling and parameterization of physical processes in buoyancy-driven geophysical flows. The book summarizes interdisciplinary studies of buoyancy effects in different media (atmosphere and hydrosphere) over a wide range of scales (small scale phenomena in unstably stratified and convectively mixed layers to deep convection in the atmosphere and ocean), by different research methods (field measurements, laboratory simulations, numerical modelling), and within a variety of application areas (dispersion of pollutants, weather forecasting and hazardous phenomena associated with buoyant forcing).

Studies of convection in geophysical flows constitute an advanced and rapidly developing area of research that is relevant to problems of the natural environment. During the last decade, significant progress has been achieved in the field as a result of both experimental studies and numerical modelling. This led to the principal revision of the widely held view on buoyancy-driven turbulent flows comprising an organised mean component with superimposed chaotic turbulence. An intermediate type of motion, represented by coherent structures, has been found to play a key role in geophysical boundary layers and in larger scale atmospheric and hydrospheric circulations driven by buoyant forcing. New aspects of the interaction between convective motions and rotation have recently been discovered and investigated. Extensive experimental data have also been collected on the role of convection in cloud dynamics and microphysics. New theoretical concepts and approaches have been outlined regarding scaling and parameterization of physical processes in buoyancy-driven geophysical flows. The book summarizes interdisciplinary studies of buoyancy effects in different media (atmosphere and hydrosphere) over a wide range of scales (small scale phenomena in unstably stratified and convectively mixed layers to deep convection in the atmosphere and ocean), by different research methods (field measurements, laboratory simulations, numerical modelling), and within a variety of application areas (dispersion of pollutants, weather forecasting, hazardous phenomena associated with buoyant forcing).

If one surveys the development of wind engineering, one comes to the conclusion that the challenge of urban climatology is one of the most important remaining tasks for the wind engineers. But what distinguishes wind engineering in urban areas from conventional wind engineering? Principally, the fact that the effects studied are usually unique to a particular situation, requiring consideration of the surroundings of the buildings. In the past, modelling criteria have been developed that make it possible to solve environmental problems with great confidence, and studies validated the models: at least in a neutrally stratified atmosphere. The approach adopted in the book is that of applied fluid mechanics, since this forms the basis for the evaluation of the urban wind field. Variables for air quality or loads are problem specific, or even random, and methods for studying them are based on risk analysis, which is also presented. Criteria are developed for a systematic approach to urban wind engineering problems, including parameter studies. The five sections of the book are: Fundamentals of urban boundary layer and dispersion; Forces on complex structures in built-up areas; Air pollution in cities; Numerical solution techniques; and Posters. A subject index is included.