After the storm: assessing flood impact

Extreme weather events are growing more intense and more frequent. They are testing both the resilience of our infrastructure and our assumptions about which areas of the world will be hit the hardest.

In April 2024, record-breaking flash floods struck Al Ain in the UAE, serving as a wake-up call that even semi-arid regions could be vulnerable. The city was deluged by 250mm of rainfall in just a few hours. Hakim Saibi, professor in the Department of Geoscience at the United Arab Emirates University, was impelled to act, and launched a research study into the event. It was a chance to apply his expertise locally and make a difference.

“As scientists, we have to put our scientific knowledge towards understanding this flood and how we can do something for the community of Al Ain,” says Saibi. His research team conducted a geospatial assessment of the Al Ain flash flood that explored the city’s vulnerability to such events and offered crucial insights for policymakers to prepare for future rainstorms. 

To put the study together, Saibi needed to collect a range of different data sets. “We have remote sensing, which is the Sentinel-2 satellite data, and we also used climatic data or meteorological data provided by the National Centre of Meteorology (NCM) of the UAE,” he says. “We received temperature and precipitation data, and we added elevation or topographic analysis data.”

In total, data from 16 of the NCM’s meteorological stations were combined with the satellite imagery. Saibi integrated this data with his recently developed Index of Turbid Waters (ITW) – a spectral index that distinguishes between turbid floodwaters and permanent water bodies. He found what he was looking for, identifying the link between the extent of the flooding and the geomorphological vulnerabilities on the ground in Al Ain. It offered insights into the impact of flooding in areas across the city, highlighting just how serious these events are becoming. 

The ITW was critical to the analysis. Scientists have achieved good results through modelling, but by applying the ITW and real-world data, Saibi could be very confident of its accuracy. “This method has made a significant contribution to understanding the flood impact in arid and semi-arid regions, like in the UAE or Al Ain,” he says. “It provides a quite accurate flood map based on real data.”

This study is essential reading for policymakers in Al Ain. But it is also attracting interest elsewhere. Al Ain is not alone in being vulnerable to flash flooding. Saibi’s team is collaborating with scientists in Italy and Spain, and has applied the index to areas in northeastern Algeria. “Hopefully, it can be developed and enhanced in the near future to get better results,” says Saibi, and he knows how it can be improved. Better access to higher resolution satellite data would be a start. Hyperspectral satellite data does not come cheap, but if it underpins a new model of flood risk management, it could be money well spent.

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