Southern Africa needs flood modelling now more than ever before

In the years between 2017 and 2023, Southern Africa experienced three of its deadliest tropical storms: Cyclone Idai (2019, 1 300 deaths); Cyclone Freddy (2023, 500+ deaths) and tropical storm Dineo (2017, 250 deaths). It also experienced Cyclone Kenneth (2019), Africa's strongest cyclone ever recorded.

Madagascar, Mauritius, Mozambique, Zimbabwe and Malawi are in the direct path of these devastating Indian Ocean storms, which are on track to increase in both frequency and severity in the future. Risk modelling is an instrumental tool that can prepare communities and businesses in these countries for what's to come.

Cyclone Freddy: a warning

On 6 February 2023, the Australian Bureau of Meteorology - a regional centre of the World Meteorological Organisation (WMO) - upgraded a tropical low pressure system spotted a few hundred kilometres off the northwest coast of Australia to a tropical cyclone, and named it Freddy.

Meteorologically, Freddy was a remarkable storm. It tracked across the entire Indian Ocean from east to west, affecting Mauritius and La Réunion on its journey to Madagascar. Super zonal tracking by a tropical cyclone like this is rare, with the most recent recorded cases being tropical cyclones Eline and Hudah, both in 2000.

After travelling more than 7 000km, Freddy made landfall on the east coast of Madagascar, weakening to a tropical disturbance as it moved west but then intensifying into a tropical storm over the Mozambique Channel. It made a second landfall in Mozambique with sustained wind speeds of 83 km/h. Over the next week, Freddy weakened significantly, but intensified again over the Mozambique Channel, becoming a severe tropical storm. It made a third landfall in Mozambique before hitting Malawi two days later.

In the end, 16 000 people were affected in Madagascar, 170 000 people in Mozambique, and more than 550 000 in Malawi, where the death toll rose to 507, with at least 537 people still missing (as at 21 March 2023).

Destructive winds, storm surge and extreme rainfall resulting in flooding were the main events recorded. The WMO said ongoing rainfall exacerbated flooding from Freddy's first passage as well as from heavy seasonal rains, which had already seen rivers reach maximum capacity. Southern Mozambique, for instance, received more than a year's worth of rainfall in one month, while Madagascar received three times the monthly average in the space of a week.

Freddy is most likely the longest-lasting and highest accumulated cyclone energy (ACE)-producing tropical cyclone ever recorded worldwide. But it won't be the last.

More frequent storms for Southern Africa

Tropical cyclones require a sea surface temperature of 26.5°C to form, while the highest intensity storms require temperatures of 28-29°C. Jennifer Fitchett, Associate Professor of Physical Geography at Wits University says this is one of the reasons why Southern Africa is experiencing more intense tropical cyclones.

'The South Indian Ocean is warming rapidly. This means that regions that previously experienced the temperatures of 26.5°C that facilitated tropical cyclone formation are now experiencing temperatures as warm as 30-32°C. Simultaneously, regions further from the equator which didn't previously have sufficiently warm water for tropical cyclone formation, are more regularly experiencing the threshold temperature. This increases the range in which these storms occur, making storms like Tropical Cyclone Dineo, which made landfall in February 2017 in southern Mozambique, more common,' she explains.

The African Centre for Strategic Studies also notes that warmer ocean temperatures combined with greater energy driving these storms will see Indian Ocean cyclones increasingly making landfall over a wider swathe of Africa's east coast. Beyond historical storm paths affecting Madagascar and northern Mozambique, this is expected to include countries as far north as Tanzania, and as far south as South Africa.

It says these cyclones are more likely to impact densely populated urban areas such as Maputo, Durban and Dar es Salaam, with a direct hit on one of these centres potentially affecting millions of people and causing acute economic costs.

Forewarned is forearmed

The WMO maintains that while Cyclone Freddy had a major socio-economic and humanitarian impact on the communities affected, the death toll was limited by accurate forecasts and early warnings.

'Advance warnings of the storm by the WMO's Regional Specialised Meteorological Centre La Réunion (Meteo-France) and by the national meteorological and hydrological services of Madagascar, Mozambique and Malawi, allowed the disaster management and humanitarian communities to mobilise in advance, with evacuations and pre-positioning of food supplies,' it says.

This is where risk modelling comes into its own. In the same way technology enables these communities to prepare for severe weather, so it empowers businesses and their insurers to understand and manage the risks of the properties they insure and underwrite.

Highly sophisticated technology

The latest technology available allows risk modelling agencies to provide a global view of flood risk for every country, around the planet. This includes Southern African countries.

This enables the impact of this risk to be assessed from the humanitarian perspective, economic loss or other measures of risk, depending on the availability of suitable exposure data.

Some service providers license high-resolution surface water and river flood hazard maps at return periods of 20, 50, 100, 200, 500 and 1 500 years for Southern African countries. When combined with other data, this information enables these agencies to generate flood risk profiles that indicate the likelihood of flood impacts of a particular magnitude occurring in a given year at a national or sub-national level.

Using this information, insurers and their reinsurers can accurately inform their clients of specific flood and storm risks, and the potential impact on their businesses and employees. Infrastructural damage and business disruption are the two biggest losses associated with flood risk, with cyclones being among the top three natural hazards with the highest losses.

This is critical, as multinationals gradually expand into these territories in Southern Africa and seek to secure their operations, and as local business partnering with these larger corporations in their supply chain, attempt to steady themselves against the increasingly destructive effects of a changing climate.

Reinsurance is a useful tool for catastrophe risk mitigation. At Reinsurance Solutions, our modelling expertise allows us to assess the vulnerabilities inherent in our client's portfolio to various perils, such as cyclones, flood, earthquake and hail. This enables us to recommend and place bespoke reinsurance structures, promoting improved financial resilience within clients' organisation as well as more efficient economic recovery from such disasters.