Flood Risk Evaluation

Abstract

River floods are considered one of the most important natural disasters and causes huge damages every year, both in economic consequences and fatalities. Out of historical perspectives, human settlements are located in fertile and economic attractive delta regions. Deltas tend to be constantly changing nodes of economic and urban growth leading to increasing exposure to flooding. Climate change may lead to a higher intensity and magnitude of flood events in the future. This development puts huge pressures on government and other decision-making authorities to cope with these threat by developing adequate flood mitigation plans. It is recognized that prevention is not possible and a shift towards integrating flood management into urban planning making it both robust and adaptive to future uncertainties is required to reduce the risk. Finding the set of measures appropriate for the risk situation of a city is difficult, because for a lot of non-structural measures the benefit is not yet defined in a quantitative way. Flood risk assessments are useful tools for indications of economic damage and identifying the most vulnerable cities worldwide. However, only considering economic damage as flood indicator will lead to an one-sided quantification of flood risk. Therefore, other risk indicators need to be considered to give a more comprehensive indication of flood risk. In this research, a framework is suggested to get a quick overview of the flood risk management of a city containing preventive, spatial, emergency, recovery and adaptive status. The economic risk is extended with the risk indicators; individual risk, household risk and a damage distribution. Based on this, an evaluation of the flood risk situation of a city can be derived, resulting in a preliminary advice for the appropriate measures and measures where the highest cost benefit ratio can be achieved. Focusing on the most beneficial measures could save a lot of time and resources. Next to that, this framework could eventually lead to a more proper flood risk assessments for identifying vulnerable cities and a way to communicate flood management status leading to some sort of competition between cities to come up with sustainable solution to be as safe as possible. Two historical flood events are being used as case study, namely the 2011 Thailand Flood and the 2013 Central Europe flood focusing on Germany. Both events are being assessed using the Flood Risk Assessment Tool (FIAT), where the calculated damages of the events are compared with the official reported damages. This gives an indication of the validity of this tool for damage calculations. After that, a closer look into the flood management of Bangkok by looking at the risk reduction plans after the flood event is conducted related to our suggested framework. For Germany, the cities of Hamburg and Dresden are being assessed by combining the flood risk indicator and smart city flood risk framework to come up with a qualitative assessment if the cities recognized their shortcomings and turned the tables. This is also done for Rotterdam and Vienna eventually leading to a comparison between these two cities and Hamburg and Dresden to assess the multi-layer flood management status. In the end, the calculated damages compared to the reported damages were in the same order of magnitude for both events within a 10% boundary. However, looking more closely at the German state, results are less accurate. A closer look at the city of Bangkok showed that the weak spots of the urban flood management are still not recognized and focus on preventive measures still dominates. Including individual risk, household risk and damage distribution led to evaluation of the top 25 German cities, where differences between cities led to different advises. For instance, the city of Bonn has really high individual risk and high share of residential damage making insurance, precautionary measures and flood prove building appropriate measures. The city of Dresden managed to reduce its vulnerability from 25% to only 4.5% by finding appropriate measures. Hamburg is the frontrunner for flood risk management integrated into urban planning by shifting to an adaptive flood risk approach. By comparing the four citieswith approximately the same economical and individual risk showed that each city has managed to incorporate measures from different flood mitigation layers into the urban footprint. Rotterdam and Vienna largely rely on the high protection standards, where the German cities shift the responsibility more to household level. Rotterdam and Hamburg are inspirational cities how flood mitigation measures could be implemented in urban planning to cope with increasing urbanization rates and climate change threat. However, shortcoming are also recognized for all cities which makes room for improvements possible in the future.