Predicting Impacts of Cyclones in South-East Africa (PICSEA)

Lead Research Organisation: University of Reading
Department Name: National Centre for Atmospheric Science

Abstract

On average, 14 tropical cyclones per year form in the southern Indian Ocean, most in the months between November and April. Of these, about 2-3 cyclones per year make landfall in southeast Africa, most often in Mozambique and Madagascar. In these countries, tropical cyclones are associated with approximately one-third of all extreme daily precipitation events, defined as days with rainfall accumulations greater than 50 mm (2 inches). Tropical cyclone landfalls in Mozambique in 2012 caused severe flooding, resulting in US$65 million in damage and 150 deaths. Two cyclone landfalls in Madagascar in early 2018 resulted in 23 deaths and displaced 21,000. The Seychelles archipelago is also affected by tropical cyclones, including category 5 (the most severe) Fantala in 2016.

Despite the vulnerability of the southeast African population to tropical cyclones and related hazards, little is known about the ability of contemporary weather and climate prediction systems to forecast cyclone tracks, intensities, and wind and rain impacts. Further, there may be particular tropical atmospheric circulation patterns that provide "windows of opportunity" for more accurate cyclone forecasts. For instance, El Nino conditions (warm equatorial Pacific Ocean temperatures) may provide the backdrop for more accurate predictions of tropical cyclones and their impacts.

The "Predicting Impacts of Cyclones in South-East Asia" (PICSEA) project addresses these shortcomings by providing the most comprehensive assessment of forecast systems to date for tropical cyclones and their effects on southeast Africa. This assessment is needed desperately to give advice to national meteorological agencies, humanitarian organisations and the growing forecast-based finance community on how best to interpret forecasts of tropical cyclones in the southern Indian Ocean. Specifically, PICSEA will determine which forecast systems, lead times and background tropical circulations lead to relatively more or less accurate tropical cyclone predictions. When should disaster management agencies trust a forecast for a landfalling tropical cyclone, and when should they not?

Initially, PICSEA will assess the accuracy of predictions of tropical cyclone tracks, intensities and associated hazards (primarily wind and rain) from three weather forecasting centres: the UK Met Office, the European Centre for Medium-range Weather Forecasts and the US National Centers for Environmental Prediction. We have 10-30 years of forecast data for each centre, including multiple realisations of each forecast. We will determine to what extent, and how far in advance, contemporary prediction systems can forecast the extreme winds and rainfall associated with tropical cyclones in southeast Africa.

Next, PICSEA will determine whether there are particular background tropical conditions, such as El Nino or La Nina, that lead to more or less accurate forecasts. We will do this by evaluating forecast accuracy conditioned on the type of background conditions. Is skill for cyclone-related hazards greater during La Nina or El Nino? Are there particular circumstances under which forecasters and disaster-management agencies should trust these forecasts more, or less?

Finally, PICSEA will work together with partner organisations -- national meteorological organisations in Mozambique, Madagascar and the Seychelles, as well as the Red Cross / Red Crescent Climate Center, a key provider of scientific advice to humanitarian organisations and the forecast-based finance community -- to develop guidance for interpreting tropical cyclone forecasts. We will work with forecasters and disaster-management agencies to improve their understanding of when they can, and cannot, trust forecast information on cyclone impacts. PICSEA will also provide training in the use of this guidance, as well as background training on tropical meteorology, for forecasters in southeast African meteorological agencies.

Planned Impact

The "Predicting Impacts of Cyclones in South-East Asia" (PICSEA) project will benefit national meteorological agencies in southeast Africa, the United Kingdom, Europe and the US; humanitarian organisations, particularly those engaged in forecast-based finance initiatives; national governments in southeast Africa; and the general population of southeast Africa.

PICSEA will provide the most comprehensive analysis to date of prediction skill for South Indian Ocean tropical cyclones, particularly for the extreme wind and rainfall hazards associated with landfalling cyclones in southeast Africa. PICSEA will assess short-range numerical weather predictions (up to 14 days ahead) for individual cyclones, as well as seasonal predictions (up to six months ahead) for basin-wide activity in the South Indian Ocean. This assessment will benefit national meteorological agencies in southeast Africa, who currently lack information on how far in advance they can trust predictions of cyclones and their associated wind and rain hazards. PICSEA will also determine whether there are "windows of opportunity" for more skilful prediction - large-scale atmospheric conditions under which certain forecast models perform more accurately than they do on average. Combined with our overall skill assessment above, identifying these windows will allow national meteorological agencies to understand when they can and cannot trust predictions of the track and intensity of cyclones, as well their wind and rainfall extremes.

This improved understanding will translate directly into more accurate warnings of landfalling tropical cyclones, issued further in advance. These improved warnings will benefit disaster management agencies in national governments in the region, who will be able to mobilise resources further in advance of impending tropical cyclone landfalls. More accurate warnings will also reduce false-alarm rates, which will contribute to greater public trust in warnings and hence to a more robust public response to warnings and evacuation orders.

National meteorological agencies in the US, Europe and the UK will benefit from our assessment of their forecast systems for South Indian Ocean tropical cyclones and their impacts. Prediction skill for cyclone activity in the South Indian Ocean is subject to far less scrutiny than activity in other basins, such as the North Atlantic and West Pacific. No study has compared the performance of contemporary models for cyclone rain and wind hazards in the South Indian Ocean, or investigated how large-scale atmospheric variability affects prediction skill. PICSEA will provide this comprehensive assessment to inform modelling centres of the atmospheric circumstances under which their systems have relatively more or less skill than those of other centres. We will report these findings through papers and international initiatives, and thus contribute to pathways for model improvements.

We will collect our scientific results on forecast skill into a set of guidelines for interpreting cyclone forecasts, developed in collaboration with national meteorological agencies and humanitarian organisations involved in forecast-based financing. These guidelines will inform the development of standard operating procedures (SOPs) for forecast-based finance, which seeks to release funding for humanitarian assistance in advance of weather-related disasters. By informing humanitarian organisations of the models, forecast lead times and atmospheric circulations when forecasts are more or less accurate, PICSEA will contribute to the design and implementation of successful forecast-based financing activities in southeast Africa.

The general public of southeast Africa will benefit from PICSEA through improved warnings of cyclone impacts, improved disaster response efforts, as well as from forecast-based finance activities that will allow humanitarian aid to be marshalled further in advance of cyclone landfalls.

Publications

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