Flood Delta City Index
To help decision makers in delta areas to select appropriate adaptation and mitigation strategies it is necessary to have a clear picture of the main sources of risk and how this risk evolves under changing conditions. Because flood risk is often considered an urgent but almost never acute problem, it is difficult to keep flood risk on the investment agenda. Acknowledging these problems, the Delta Alliance and the TU Delft took the initiative to develop a new index that helps cities to better understand the dominant drivers of risk, formulate ambitions, and compare and share their results with other delta regions. The approach is based on previous work at TU Delft in collaboration with HKV and Deltares. The rankings goal is not to formulate an “exact” risk number, but aims to serve as a benchmark that supports the discussion and supports a peer learning process with other deltas. And that helps to better communicate risk within the political arena.
To test the proposed approach, a first ranking of 38 delta and coastal cities has been prepared. For practical reasons, the flood risk assessment is limited to coastal flooding and given data limitations not all Delta Alliance cities could be included. The list is dominated by the world's mega cities, leading by Buenos Aires. Looking at future risk scenarios, Asian cities in particular will face a strong increase in risk due to ongoing urbanization and further economic growth. This contrast with Japan's cities Tokyo and Osaka, who show more stable risk number due to the expected stagnant economic growth. Especially in the extreme scenario by 2030, cities of Tianjin, Taipei and Shanghai may expect a strong risk increase due to climate change. In terms of risk bridging between now and 2030, it is more interesting to look at cities that may not be in the top of the ranking but will experience explosive growth. One example is Dhaka who can expect a future increase of 4 to 9 times the current risk or Kolkata in India and Palembang in Indonesia with even more extreme projections.
As a next step the Delta City Index functionality will be further developed and tested in collaboration with the Delta Alliance and the new Global Centre of Excellence on Climate Adaptation. One of the shortcomings of using open data is that it generally lacks data that covers the scale of delta territory. To overcome this problem collaboration is sought with Delta Alliance delta regions to provide detailed data within a self-assessment process and to test and improve the ranking.