|
Early warning systems for the detection and response to severe floods
William J. R. Alexander
Abstract: However, there are many large rivers in developing countries, and small rivers in many other countries where no such warnings can be issued in time to prevent a tragedy occurring. In South Africa for example, the largest loss of life due to floods is in communities located on the banks of a small rivers that rise within a matter of hours after a severe storm. Sophisticated flood routing procedures are of no use in these situations. The paper describes a simple but effective method based on antecedent precipitation indices. Most floods in South Africa are caused by large area, long duration rainfall of the order of more than 500 mm in four days, culminating in a severe rainfall event. By observing the extent and severity of rainfall, communities at risk can develop their own flood watch systems based on the build up of rainfall as an indicator of the likelihood of floods developing. |