Emergency Bulletins – Forecasting flood inundation and exposure to recent tropical cyclones in East Africa

Neal, J. and Archer, L. and Chuter, S. and Cooper, T. and Devitt, L. and Hawker, L. and Grey, S. and Janes, T. and Savage, J. and Stephens, E. (2023) Emergency Bulletins – Forecasting flood inundation and exposure to recent tropical cyclones in East Africa. In: AGU23, 11-15 December 2023, San Francisco, CA and online.

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Tropical cyclones can be especially devastating due to their multi-hazard nature and potential to generate exceptional flood magnitudes. In Africa, a combination of high vulnerability to flooding and limited pre-emptive action can exacerbate a disaster. Accurate and timely forecasts of tropical cyclone flooding can potentially aid humanitarian response and save lives and livelihoods. However, impact forecasts always include significant uncertainty that complicates their use by decision makers. We present a summary of efforts to forecast population exposure to tropical cyclone flooding for the UK Foreign and Commonwealth Development Office and various humanitarian partners via the production of Emergency Bulletins. Bulletins were produced for eight tropical cyclones (Idai, Kenneth, Eloise, Ana, Batsirai, Emnati, Gombe and Freddie), with bulletins often issued or updated over multiple days. Our approach uses a combination of ensemble river discharge forecasts from the GloFAS system and 30 m resolution pluvial, fluvial and coastal flood inundation mapping provided by Fathom. Given these data, a bulletin will summarise and map the likelihood and location of flooding and the number of people directly affected. The performance of previous ensemble forecasts was evaluated using inundation extents from satellite data and user feedback. We find that the inundation mapping could identify the most exposed districts once uncertainty in the track and landfall location was sufficiently low, often around a day before landfall. Longer 2-5 day forecasts could be highly uncertain but were not disinformative. Key components of our bulletin production process include: 1) expert interpretation of the discharge forecasts and inundation model outputs, 2) comparative analysis with previous events, and 3) post event appraisal aimed at understanding how the bulletin was used. We believe that each of these add significant value over automated modelling outputs available online and that the value of fully automated bulletin and flood forecast services for decision makers should be considered carefully.

Item Type: Conference or Workshop Item (Paper)
Subjects: Maritime > General
Divisions: Maritime
Depositing User: Helen Stevenson
Date Deposited: 15 Dec 2023 13:35
Last Modified: 15 Dec 2023 13:35
URI: http://eprints.hrwallingford.com/id/eprint/1602

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