Flooding risks are becoming more apparent. There have been numerous disastrous floods recently, and their frequency and intensity are increasing as a result of climate change. For example, in summer 2021 heavy precipitation led to extreme river flooding in Germany and Belgium. More recently, Pakistan has been the victim of deadly floods that have already engulfed a large part of the country, damaging over 1.7 million houses, causing over 1,500 deaths and billions of dollars of damage.

This month, UN General Secretary Antonio Guterres called on major polluters to reduce their fossil fuel consumption as quickly as possible, since the use of fossil fuels is largely responsible for climate change and natural disasters. On a visit to Pakistan, he called for the need for adaptation, “to build resilient infrastructure and to support resilient communities and to create conditions for those that are in the hotspots of climate change”.

Climate risks mitigation and adaptation is necessary to avoid the worst consequences of climate change for humans and the environment.

In our last article on flooding, we have focused on how climate change leads to more flood events, their impacts and potential adaptation options.  In this article we will expand on flood risk assessment products EcoAct is currently offering.

The flooding risk definition for an entity

At EcoAct, we have developed a holistic approach to assess the exposure and vulnerability of a site or a region to different flood risks, and to estimate potential loss and damages.

The flood risk to a system (eg. a business) is defined here as a combination of:

• Flood hazards
• Exposure of a system (location of the system, affected infrastructure)
• Vulnerability (eg. design and maintenance of the system’s infrastructure, flood protection measures, early warning systems)

 

Our pluvial and river flooding

To assess the exposure of a site or region to pluvial & river flooding, the two most important factors to consider are:

• Precipitation
• Topography (the arrangement of the natural and artificial physical features of an area)

These two factors largely determine the potential extent of the flooding.

The first step in our flood exposure product is to define the extreme precipitation event that might occur and lead to flooding, e.g. a 1-day extreme precipitation event where 150mm of rain falls within 24 hours. Using regional high-resolution climate model data on precipitation, we can determine the probability of such an extreme precipitation event occurring in the future depending on the climate scenario. We then identify the relevant extreme precipitation events and choose the relevant climate scenarios and future time horizon for analysis for our client.

 The second step in our flood exposure product is to collect and process high-resolution topographical data. High spatial resolution is crucial for an accurate quantification of the floodable areas, and flood depths. At EcoAct, we have developed a 3D flood model that outlines the potential flood zones and provides a flood depth map at a 1m spatial resolution. When 1m spatial resolution elevation data is not available, we propose an alternative product based on a 30m spatial resolution elevation data.

To complete the flood risk exposure assessment, we also consider two important factors that affect the proportion of rainfall that is converted to direct surface runoff: drainage, along with land cover and land use.

To convert all this high-resolution data into flood risk maps and flood depths we use a static hydrology model, and adopt a 2D diffusion scheme where flood water can flow in multiple directions based on the topography of the area. The advantage of our model is that it is independent of the region of interest and can be applied anywhere. The 3D modelling approach we use allows for accurate flood risk mapping, an impact assessment, and provides the possibility to scale flood protection measures.

 

Figure 2: EcoAct local flood risk assessment & inundation modelling 

 

To assess the vulnerability of a site or region to future pluvial and river flooding, our tool allows for the integration of local flood protection measures such as storage basins, levees, pumping, etc. During this stage, we organise interviews and work closely with the local site managers and engineers to fine-tune the flooding results.

 

Our coastal flood product

For coastal flooding, high resolution topography is also key in determining accurate flood risk exposure. We offer a highly compatible global product with a spatial resolution of 30m (highest spatial resolution globally available), which is based on the most accurate global coastal topography dataset and the sea level rise scenarios from the latest IPCC report (ref: Climate Central).

Here we make the distinction between permanent flooding, annual flooding and flooding with a 10-year return period. We can also assess the flood exposure of the surrounding area and infrastructure of a particular site. To assess the vulnerability of a site or region to coastal flooding, we organise interviews to collect data on local flood protection measures and past impacts.

 

Loss and damage estimation

To estimate the damage costs related to either river, pluvial or coastal flooding, we use flood depth -damage curves that connect a specific flood depth to a damage fraction of the asset per m². These functions are specific per asset, sector and geographical region. To get an estimation of the overall damage costs per m² of the asset area, we use the current value of the client’s assets.

 

Figure 3: Flood depth – damage costs example for a building in the hospitality sector (EcoAct product) 

 

The next step after a flood risk assessment is the assessment of flood protection and adaptation measures that are already in place or could be put in place. Generally, a multi-layer safety approach is advised for the development of flood mitigation and adaptation measures. These multiple layers consist of flood protection measures, waterproof spatial planning and disaster management.