Decision support system for flood warning in urban areas

A number of urban areas have experienced severe flooding in the past. The problem has worsened in southern Europe in the past decades mainly due to urbanisation, which has lead to the paving of natural ground surfaces and the blocking of natural watercourses by the infrastructure. In some areas this has aggravated the situation by shortening the hydrological response time, often triggering flash floods within few hours after the occurrence of heavy precipitation. The short time between the occurrence of heavy rain and corresponding flooding makes it difficult to forecast, especially when the meteorological conditions are such that it is difficult to forecast the rainfall. This is especially the case for coastal cities in mountainous terrain. In order to get sufficient lead time to alarm inhabitants and plan reactive measures, it has been found important to use advanced forecasting and monitoring techniques and a decision support system to assist authorities in their decision making. This article contains a concise presentation of a decision support system (DSS) developed to assist public authorities plan emergency activities when flooding is expected and to give guidance for restoration activities after the flood subsides. The DSS is designed mainly to work for areas with steep topography. Such areas are known to experience flash floods only a few hours after the occurrence of a severe precipitation event. The target areas are Liguria Region in Italy and the Greater Athens catchment in Greece. Severe and devastating flooding has occurred at both sites several times in the past two decades. The study shows that the problem of flood warning based on forecasts is one of great complexity and uncertainty. It is believed that results can be improved with better forecasting techniques, improving catchment models, with experience using the DSS, and increasing experience of the public about the meaning of flood warnings. The system developed can be easily applied in other areas with similar flooding problems.