Of all natural hazards, Europe suffers most from flooding. In the six years from 1998, Europe was hit by more than 100 floods. The flooding caused 700 deaths, displaced nearly 500 000 people, and resulted in €25 billion of damage.
Flash floods have a short response time – between 15 minutes and 2 hours (maximum 3 hours). They can occur anywhere in a basin and are the result of heavy rainfall. Flash floods are the most devastating of all floods at global level and the scale of casualties and damage is higher than for 'classic' riverine floods.
Flash floods are also more difficult to forecast accurately than hurricanes, blizzards or river floods. Rainfall is highly variable and the tools for forecasting heavy rain can only 'see' a couple of hours into the future. This is coupled with the challenge of predicting what water will do once it hits the ground – how it interacts with landscape and plant cover determines whether the water will flow off the surface or be absorbed. Providing residents and first responders with advance warnings is therefore a major challenge.
Floodwater’s capacity to trigger debris flow, mudflow and landslides in steep mountainous areas such as the Mediterranean coast and the Alps is yet one more complication.
Seeking to minimise the damage, a European Parliament directive of 2007 requires all EU countries to prepare detailed maps of flood risk by 2013, and create risk management plans by 2015.
The results of the EU-funded project IMPRINTS (IMproving Preparedness and RIsk maNagemenT for flash floods and debriS flow events) is helping governments do just that. The team was tasked with improving probability-based rainfall and flood forecasts, and developing tools that regional and national authorities could use to prepare their risk management plans – as well as their capacity to deal with flash flood emergencies and any resulting debris flow.
The IMPRINTS researchers to improved short-term rainfall forecasts as these are the best possible tool for anticipating flooding before it happens. Currently, there is a gap in our capacity to predict rainfall: meteorological models can forecast rainfall from six hours to few days in advance, while meteorological radars provide good short-term forecasts, up to two hours in advance. But the crucial window between two and six hours is a major challenge for rain and flash flood forecasts.
The IMPRINTS team developed a number of techniques to fill this gap. In mountainous areas, the NORA system (Nowcasting of Orographic Rainfall by means of Analogues) is one promising alternative. By comparing current radar images with archived radar images, it detects similarities to improve forecasts.
The team was also able to develop a high resolution Flash Flood module that has since been included in the European Flood Awareness System (EFAS). The module allows EFAS to anticipate flash floods more than 24 hours in advance, anywhere Europe.
The IMPRINTS team was also able to quantify the threshold for the amount of rainfall liable to produce flash flooding and/or debris flow in different landscapes and terrains. This information provides a very first warning of likely debris flow events.
The project resulted in an Early Warning operational platform that extends to hydrological warnings based on rainfall anticipated by meteorological models (a few days in advance) and by weather radar networks (a few hours in advance). The platform is able to transform the information provided by the rainfall forecasts into hydrological forecasts, as well as to combine these hydrometeorological forecasts with information about vulnerability and flooding risks. The Early Warning System for Flash Flood and Debris Flow can be used to support risk management – including through the implementation of the EU Flood Directive.
The platform design ensures that it can be easily adapted to any basin in Europe, and it has been already tested on six European river basins.
The IMPRINTS team disseminated the project’s results and produced audiovisual material for policy-makers, risk managers, water companies as well as for the local authorities. This material is accessible in the dissemination section of the project’s website: http://www.imprints-fp7.eu/en/dissemination.
Press Release available here