Societal Relevance of Flood Risk Modelling
By Wouter Jan Klerk 12 January, 2016
Deltares' Klerk shares cases from Vietnam, Indonesia & Netherlands on emergency management & urban planning
Global economic losses due to flooding amounted up to 19 billion USD in 2012, and are increasing, due to rapidly urbanizing flood prone areas and increasing sea levels. Unfortunately, this isn’t likely to stop anytime soon.
Global economic losses due to flooding amounted USD19 bn in 2012
Deltares is a Dutch research institute that has been a global leader in development of techniques for modeling and managing flood related risks. We’ve applied our knowledge in countries around the world, including China, Vietnam, Singapore, United Kingdom, United States, Bangladesh and many more. In this article we’ll share some of our experiences as well as some illustrative examples of situations where flood risk modeling can make a real difference.
What is the point of flood risk modeling?
Flood risk can be expressed in many ways, but an essential part of any flood risk model is a hydrological/hydraulic model which answers the question: “Where does the water go?” The answer to this question can be obtained from physical models which result in flood depth maps (see image below) which shows water depths for a certain rainfall event.
“… an essential part of any flood risk model is a hydrological/ hydraulic model which answers the question: “Where does the water go?””
However, although very indicative, water depths do not show you how bad the presence of flood water at certain locations actually is. There could be a piece of unused grassland or a city at the same place: it yields the same picture but obviously not the same consequences. Therefore flood risk is usually expressed as the product of:
- Hazard: the probability that a flood occurs, this can be lowered by flood protection.
- Exposure: the location of economic assets or people in a flood-prone area. This can be influenced by spatial planning.
- Vulnerability: the susceptibility of those assets or people to suffer damage and loss. This can for instance be lowered by flood-proof building or use of flood early warning systems.
“The importance of quantifying the vulnerability differs per application…”
Flood risk is usually expressed in damage in $/year or number of casualties per year. The importance of quantifying the vulnerability differs per application: for planning it can be very important, but for other applications a good flood depth map might suffice. In the remainder of this article we’ll discuss three applications where Deltares has modeled these three aspects of flood risk in different (types of) cases.
Case 1: Flood forecasting for emergency managers: Ning Bo City, China
The first important application for flood (risk) modeling is for emergency management. Deltares has developed a hydrological forecasting system (Delft-FEWS), which is capable of forecasting hydrological extreme events and thus gives emergency managers an early warning that a flood might be imminent. It has been applied in more than 35 countries around the world, and an example application is the implementation of Delft-FEWS at the Nan Chang catchment in Ning Bo, China.
The existing model for storm and waste water has been implemented in a FEWS system and now provides valuable information which will lead to a more adequate response in extreme situations (see Figure 2). It relates real time rainfall predictions to overflow volume predictions for the drainage system. This enhances the emergency planning and enables the municipality to take the right actions. In this case the flood hazard is modeled, but it already gives a lot of useful and interesting information which reduces the vulnerability of the community.
The first important application for flood risk modeling is for emergency management
Deltares has developed a early warning hydrological forecasting system that has been applied in more than 35 countries
Case 2: Flood risk modeling for urban planning: Ho Chi Minh City, Vietnam
Flood risk modeling is also very useful for spatial planning. In flood prone areas an important aspect of planning new developments is the flood risk that it will incur. Deltares, together with local and international partners developed a strategy for urban flood risk management based on a flood risk model for Ho Chi Minh City, Vietnam. By first analyzing the hydrological conditions flood depth maps for different events were generated.
Flood risk modeling is also very useful for spatial planning
By analyzing development and the potential damage at different locations the total annual flood risk was determined. This was put to use in the advice on robust development strategies for the city and in the comparison of different flood mitigation measures and their benefits.
This led to a significantly cheaper plan for the future flood protection of Ho Chi Minh City
Due to this information a strategy has been developed which will keep Ho Chi Minh City safe for the future (see more info here and here).In this case also the exposure is modeled, which provides valuable additional information. This project led to a significantly cheaper plan for the future flood protection of Ho Chi Minh City.
Case 3: Flood risk modeling and policy making: The Dutch Delta programme
In 2008 it was advised that the safety standards for flood defences in the Netherlands should be increased by a factor 10. Deltares and other parties investigated this and based on a cost-benefit analysis of flood defences, based on flood risk modeling, a EUR7.8 billion reduction in investment costs was achieved (N.B.: a saving of approximately 200% of the total investment!), this research project was rewarded with the prestigious Franz Edelman Award.
The risk was estimated using different indicators such as economic damage, local individual risk (i.e. probability of death of an individual continuously present at a certain location) and societal risk (i.e. probability of an x amount of casualties).
The map below shows an individual risk map for 3 large polders in the Netherlands. This map was obtained by combining flood simulations, land use data and mortality functions. From the map a clear priority can be seen: reducing the risk in the easternmost (brown shaded) areas where the risk is highest. The information, such as from the risk map shown was used to determine new safety standards for the Dutch flood defences, and enables tailor-made and optimized planning. This is an example where hazard, exposure and vulnerability are all taken into account, and put to good use in developing efficient planning strategies.
Based on flood risk modeling, a EUR7.8 bn reduction in investment costs was achieved
The information in the map enables tailor-made & optimized planning
Trends & other implications
In this article a few applications of flood risk modeling have been shown. Obviously there are more applications for flood risk information. Deltares has for instance been involved in the development of flood risk models for insurance companies. We’ve also been working on global flood risk models (see examples here and here) for quick-scanning flood risks anywhere in the world, based on globally available data. The variety of different scales, detail levels and applications give an indication of the rapid growth in possibilities for flood risk models.
“…flood risk models are necessary for achieving robust growth and safe societies, and the investments in it are small, compared to the devastating consequences it can prevent.”
In recent years flood risk modeling has become increasingly popular around the world, for instance in the EU Floods Directive, which demands from all European Union member states to quantify their flood risks and develop plans for managing them. In other countries, including China, similar initiatives are ongoing. In the case of the Dutch Delta programme it was shown that smart use of flood risk information can yield large benefits. Especially in rapidly growing urban areas it is of importance to have insight in flood risk.
An article in Nature shows for instance that, only due to socio-economic change, flood risk will increase from US$6 billion to US$52 billion in 2050. This emphasizes the importance of good flood risk information, especially in regions with rapid socio-economic change. Especially in those areas, flood risk models are necessary for achieving robust growth and safe societies, and the investments in it are small, compared to the devastating consequences it can prevent.
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