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The present paper introduces a new database for collection of flood-related damage and assessment at the local scale. Every year in France, recurring flood events result in several million Euros of damage, and reducing the heavy consequences of floods has become a high priority. However, actions to reduce the impact of floods are often hindered by the lack of damage data on past flood events. Even if partial data were available, data sharing within the research community is very limited and closely supervised to ensure the protection of individuals' personal information. In comparison, the growth of social and online media has provided access to broad information at the local and global scales. Therefore, the DamaGIS database offers an innovative bottom-up approach to gather and identify damage data from multiple sources, including new media. This paper also presents an easily reproducible method to assess the severity of flood damage. [ABSTRACT FROM AUTHOR]

Anticipating floods is a major challenge for communities at risk of flooding as the entire warning system – responsible for the safety of people and goods - relies on this anticipation. There is an existing monitoring system "Vigicrues" for flood damage for a fifth of the river network in France. But for four-fifths of this network, made of small rivers, no monitoring is available. Yet those rivers are the most affected by flash floods which especially requireanticipation for crisis management purposes. This is why at the beginning of 2017, the Vigicrues system for flood monitoring has been completed with a new flood warning system called Vigicrues Flash. This system provides automatic information in real-time on flood severity of ungauged basins for 10 000 French communities. Even if this new system is a real innovation for communities with no monitoring at all, the AIGA method which is used in Vigicrues-Flash has some limits. The first one is that the warnings are only based on the assessment of flood severity. But estimating flood severity is not enough to issue efficient flood warnings. To be able to do so, taking into account potential flood losses is essential. The main goal of this work is to enable an anticipated estimation of flood related damage, especially for ungauged basins. We offer a method to assess the risk of flood related damage based on flood severity assessed by the AIGA method and a territorial vulnerability assessment. This last one has been built on a bottom-up approach developed with crisis managers. Putting together this data has enabled a first assessment of the risk of flood risk damage as a dynamic risk index. By adjusting performance testing used in the meteorology field, we have been able to evaluate our risk index and to compare the results with the AIGA method. In order to do so, we have used existing damage data (CATNAT from the GASPAR database) as well as a specific multisource database (using notably social media data) which has been put together as part of this study (DamaGIS). The evaluation process has been tested for 12 communities in the Alpes-Maritimes, 69 in the Gard and 28 in the Var department. Two types of evaluation have been performed: a first comprehensive one continuously with CATNAT data on the1988-2016 period; and another one per flood event at a finer scale. Our results show that moving from hazard assessment to risk assessment has significantly increased the relevance of the warnings and mostly at a smaller scale than the community one. Though, there is a better detection of flood related damage as the false alarm rate has been significantly reduced. This work offers promising prospects to improve the current French warning system for floods and enable a more efficient emergency response. [ABSTRACT FROM AUTHOR]