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ing the economic impacts of windstorm damage; ~ development of improvcd techniques for pre- dicting storm surge vulnerability and risk; ~ design of storm shelters and refuges to savc lives while minimizing the need for massive evacuation; and ~ enhancement of programs to aid local officials and emergency managers in deciding when and how to evacuate during severe storms. FLOODS Flooding is any abnormally high water flow that overtops the natural or artificial confining bound- aries of a waterway. Each year, floods take an increasing number of lives and property. Single events can result in heavy tolls of death and property damage, as in the Sichuan, China, flood of 1983, when more than 1,300 died, 1.5 million were left homeless, and damages totaled $1.1 billion. In the United States alone, rainstorms and their resulting flooding (including mud and debris flows) accounted for more than 63 percent (337 out of 531) of the federally declared disasters from 1965 to 1985. These floods caused 1,767 deaths. Internationally, floods take an even greater proportional toll. From October 1, 1985, to September 30, 1986, a year when no exceptional flood disaster occurred, floods took 626 lives and affected more than 1.6 million others in six countries. The number of deaths is significantly higher in developing countries than in indus- trialized countries because communications are often poor and warning systems and evacuation plans inadequate. Further, the number of flood deaths is expected to increase as population pressures force people into vulnerable areas such as low-lying agricultural areas or overcrowded urban slums on flood plains. Floods are caused not only by rain but also by man-made changes to the earth's surface: farm- ing, deforestation, and urbanization, for example. These actions increase runoff from rains, and storms that previously would have caused no flooding inundate vast areas today. In addition to the human contribution to the causes of floods, disaster conditions are created by reckless build- ing in vulnerable areas, poor watershed manage- ment, and failure to control flooding. Flash floods are local floods of great volume and 41 short duration. A flash flood generally results from a torrential rain or cloudburst on relatively small and widely dispersed streams. Runoff from the intense rainfall results in high flood waves. Discharges quickly reach a maximum and dimin- ish almost as rapidly. Flood flows frequently contain high concentrations of sediment and debris. Flash floods also result from failure of a dam or the sudden breakup of an ice jam. Flash floods are particularly common in mountainous areas and desert regions, but they are a potential threat wherever the terrain is steep and when surface runoff rates are high, streams flow in narrow canyons, and severe thunderstorms occur. Riverine floods are caused by precipitation over large areas, the spring snow melt, or both. They differ from flash floods in extent and duration. Whercas flash floods are of short duration in small streams, riverine floods take place in river systems whose tributaries may drain large geographic areas and encompass many independent river basins. Floods on large river systems may continue for periods ranging from a few hours to many days. Flood flows in large river systems are influenced primarily by variations in the intensity, amount, and distribution of precipitation. The condition of the ground (amount of soil moisture, seasonal variations in vegetation, depth of snow cover, imperviousness to water due to urbaniza- tion) directly affects runoff. Floods damage human settlements, force evacu- ation, damage crops and food stocks, strip farm- land, wash away irrigation systems, erode large areas of land or make them otherwise unusable, and change the course of streams and rivers. Alleviating the harmful effects of floods globally requires action on three fronts: reducing the vulnerability of human settlements and resi- dences, reducing the vulnerability of local and national economies, and strengthening the social structure of communities so that they can absorb the impacts of a disaster and recover rapidly. The first step in vulnerability reduction is to identify the high-risk areas through risk maps showing flood probabilities. Once these maps are complete, specific mitigation measures can com- mence. These include: . development of extcnsivc public awareness programs to inform the public about flood haz- ards and illustrate what can be done to prevent a disaster;