What are the challenges in forecasting the impacts of tropical cyclones?

By: Liz Stephens

Last year I joined the Meteorology department in a joint-post between the University of Reading and the Red Cross Red Crescent Climate Centre (RCCC), but I still suspect most people have no idea exactly what it is that I do! Apart from the administrative team in the Netherlands, the Climate Centre is virtual, we have 40+ team members based all around the world which makes for a wonderful blend of cultures (and a sometimes confusing use of humour and local proverbs!).

My role is as the Science Lead for Anticipatory Action, which means I help steer efforts to use forecasts to take actions to support vulnerable communities in advance of a disaster. We develop so-called Early Action Protocols (EAPs, plans to secure pre-agreed financing in advance of a disaster) for taking actions before different types of hazard. These EAPs are required to show evidence of forecast skill, which is often a challenge where forecast archives or observational data is limited.

This work aligns very well with the research I have been leading under the Science for Humanitarian Emergencies and Resilience research programme. We have supported the assessment of flood forecast skill in Uganda, which has informed where in the country Anticipatory Action is feasible. We have also produced flood forecast bulletins for the Foreign Commonwealth and Development Office (FCDO), firstly, for Tropical Cyclone Idai in 2019, but then with continued funding to produce these for many tropical cyclones with associated flood impacts in vulnerable countries.

Figure 1: Mocuba District in Nampula Province. (c) Mozambique Red Cross Society

The intersection between my two roles has been even more apparent in the last year. Super typhoon Rai (Odette) in the Philippines caused enormous impacts just before Christmas in 2021, but due to rapid intensification the forecasts of the storm had limited accuracy beyond 12 hours before landfall; nowhere near enough time to trigger the release of financing. I spoke about this more on “Science in Action” for the BBC World Service (https://www.bbc.co.uk/sounds/play/w3ct1l4s, from 9 minutes in). I was invited to join a panel discussion at a workshop led by the Start Network in January to discuss how to address the challenges that rapid intensification gives us within our decision-making, commenting on research presented by the University of Philippines and PAGASA on rapid intensification. (The Reading link continues, with PhD researcher BA Racoma also joining the workshop, and with one of the presenters having Ed Hawkins’s climate stripes in the background).

Earlier this year we saw the devastating impact of a series of tropical cyclones in the Southern Indian Ocean (Ana, Batsirai, Emnati, Gombe), affecting Madagascar, Mozambique and Malawi. Along with the wider team of scientists from ECMWF, University of Bristol and HR Wallingford, we (University of Reading) produced flood forecast bulletins for FCDO to provide onto humanitarian partners. These bulletins provide support to humanitarians operating on the ground, and inform the release of funds by the government to support these operations (e.g. https://www.gov.uk/government/news/uk-provides-emergency-support-to-madagascar-after-cyclone-batsirai). With colleagues at RCCC we provided early awareness to the National Red Cross Societies that we support of the potential for impacts, providing interpretation of the forecast uncertainties and likely areas worse hit.

Figure 2: Global Flood Awareness System (GloFAS) forecasts for Tropical Cyclone Batsirai, February 2022. Colour saturation represents the probability of a 1 in 5 year return period flood.

The learning across all of these cyclones is that for early warning and humanitarian decision-making there is a massive need to improve the provision of multi-hazard early warnings – too often the forecast information coming in is fragmented, with one source for wind, another for river floods, another for storm-surge flooding and so on. To make robust decisions we need to combine the hazard forecasts to provide comprehensive assessments of exposure and vulnerability, giving us an overall assessment of risk that will help to prioritise resources, determine early actions and provide appropriate impact-based warnings. This of course needs to be led by the national meteorological, hydrological and disaster management authorities.

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