Geo data: mapping the real risk of flooding

Flooding affects more people worldwide than any other natural disaster. And when it occurs, affected communities are often caught off guard – not just by the event itself but also by the extent of it.

Flooding affects more people worldwide than any other natural disaster. And when it occurs, affected communities are often caught off guard – not just by the event itself but also by the extent of it. This was again demonstrated in recent weeks by the devastating floods in the Indian state of Kerala and Western Japan, which left a trail of destruction in their wake that many people underestimated. Long embraced by the insurance industry, geo data is a particularly valuable asset to better understand and respond to this risk. Modern radar satellites may give a useful snapshot of a disaster footprint at different stages of an event. But satellite imagery cannot show the potential maximum impact of a flood that is still unfolding and so says little about the risk faced by the affected community. Such analysis requires more time and more investigation. So how can geo data help?

In the early stages of impact assessment, a useful approach is to use flood hazard maps like the high-resolution data Swiss Re provides with its #CatNet® tool. CatNet® plots flood-affected locations, whether it be cities or entire regions, against 50 to 500-year flood hazard zones to provide a good first insight. It is important to keep in mind that hazard maps do not show the extent of a disaster event itself but only the risk in a given location. This provides a remarkably accurate depiction of the threat it poses to the local community and highlights potential weak spots in disaster preparedness, such as the absence of appropriate flood protection measures. Let me demonstrate this point with a comparison between the hazard zones from CatNet® and the footprints generated by radar and aerial images of Kerala (India) and Japan.

Flooding in Kerala state as of mid-August (Source: NRSC/ISRO Hyderabad, 18 Aug 2018; map no. 2018/09) compared with CatNet® 50 to 500 year hazard zones (Source: Swiss Re, Google). The event is currently labeled as the worst monsoon flooding in 100 years.

Flooding in Kurashiki in Western Japan (Source: GSI Geospatial Information Authority of Japan, Google, Swiss Re CatNet). Again a very good match, with the 500y hazard zones in the lower map being rather not affected. This example shows as well that the dams protecting the urban area often influence the affected area substantially. This is why, for example, the area at risk in the upper right corner of the map was not affected.


Managing climate and natural disaster...

Re/insurance plays an important role in managing climate and natural disaster risk, and that's why it's part of Swiss Re's core business.

Read the whole story

How to rethink flood risk and...

Flash and river floods– increasingly taking many lives and putting economies under severe stress. We can help ensure the best possible outcome for your clients.

Read the whole story