Tropical Cyclone Freddy rips through south-eastern Africa
Lasting for over a month, Tropical Cyclone Freddy caused devastating floods and landslides across large areas of southern and eastern Africa. More than 400 people have died across Malawi, Mozambique and Madagascar, with thousands of homes destroyed (BBC, 2023). As of 17 March, 180,000 people were displaced and 200 were still missing in Malawi alone (FloodList 2022). Malawi President, Lazarus Chakwera, has called for immediate help from the international community (Al Jazeera, 2023).
The course of a month-long cyclone
Freddy has been described as a ‘record-breaking’ storm, having persisted for over 40 days. It now holds the record for the longest-lasting storm in the Southern Hemisphere and, during its journey across the Indian Ocean, accumulated more energy than an entire US hurricane season (NY Times, 2023; AP News, 2023).
On 30 January 2023, the Australian Bureau of Meteorology (BoM) recorded a tropical low-pressure system forming close to the Cocos (Keeling) Islands in the Indian Ocean. By 6 February, the system – now located off the west coast of northern Australia – began to strengthen; in response, BoM upgraded its status to a Tropical Cyclone (TC) and named the storm Freddy as it moved southwestwards across the ocean. By the next day, Freddy had intensified into a Severe Tropical Cyclone (STC) with sustained wind speeds of around 120 km/h, continuing to move southwestwards away from the Australian coastline (Paladino of Storms, 2023; NOAA, 2023a; NOAA, 2023b.).
By 9 February, despite favourable warm sea surface temperatures, STC Freddy weakened back to a TC as it encountered a disruptive easterly wind shear at its mid-levels. Over the course of the next week however, as the storm continued to travel west, Freddy quickly intensified back into a STC, at one point becoming a Category 5 storm with sustained wind speeds of 250 km/h (NOAA, 2023c; PDC, 2023).
Figure 1: Satellite-observed rainfall animation showing rainfall evolution between 20 February 2023 and 15 March 2023. Rainfall data source: NASA GPM, 2023. Tropical Cyclone Freddy track data source: IBTrACS, 2023. Animation produced by JBA Risk Management, 2023.
After travelling a distance of more than 7,000km, Freddy finally made landfall on the east coast of Madagascar on 21 February near Mananjary at around 7pm local time, weakening to a tropical disturbance as it moved west. As Freddy passed over the warm waters of the Mozambique Channel on 23 February, it underwent a further intensification into a Tropical Storm, with strong convective currents strengthening the circulation within its system (Twitter, 2023; Météo-France, 2023a).
The French national meteorological service Météo-France (MFR) recorded Freddy’s second landfall in Quelimane district, Mozambique on 24 February, with sustained wind speeds of 83 km/h. Over the course of the next week, Freddy weakened significantly as its supply of moisture from below was removed. By 2 March however, MFR reported yet another intensification as Freddy unexpectedly drifted back east into the Mozambique Channel, becoming a fully blown Severe Tropical Storm by 7 March with sustained wind speeds of 111 km/h (Météo-France, 2023b; Météo-France, 2023c.).
The storm made a third landfall in Zambezia Province in Mozambique on 11 March, bringing heavy rain and gales. Freddy then travelled north-west, reaching Malawi on 13 March. It was not until 15 March that Malawi’s Department of Climate Change and Meteorological Services were able to state that Freddy had officially dispersed (ReliefWeb, 2023a).
Impacts
Madagascar
According to the National Office of Risk and Disaster Management, over 16,000 people in Madagascar are thought to have been affected by the passing of TC Freddy, with around 4,500 homes flooded or damaged. Mananjary, the coastal town where Freddy made landfall, was still recovering from the devastation caused by Cyclone Batsirai last year (JBA, 2022). While there was some localised flooding, the majority of the impacts in Madagascar are thought to be related almost entirely to wind damage rather than flood (France24, 2023).
Mozambique
Intense rainfall was experienced across central and northern parts of Mozambique including the provinces of Zambezia, Sofala, Manica, Tete and Niassa, some of which reported daily rainfall totals exceeding their monthly average. Over 170,000 citizens are thought to have been affected by the heavy rain and resulting floods, with 10 reported fatalities and over 5,000 people displaced. In addition, over 90,000 hectares of crops were damaged by the storms, raising concerns over food security (ReliefWeb, 2023b; ReliefWeb, 2023c).
Malawi
The southern region of Malawi was hardest hit by the arrival of TC Freddy, with President Lazarus Chakwera declaring a state of emergency as the storms brought flooding, mudslides and strong winds across the area. Thousands of people were displaced across the districts of Nsanje, Chikwawa, Mulanje, Thyolo, Blantyre and Chiradzulu, leading to concerns over water and sanitation provisions in the face of an ongoing cholera epidemic. More than 300 fatalities have been reported, many of these in the southern district of Blantyre as a result of mudslides (ReliefWeb, 2023c; Al Jazeera, 2023).
What made Freddy such a unique TC
Tropical Cyclone Freddy is 2023’s strongest TC by far - equivalent to a Category 5 hurricane at its strongest - and has made several historical records:
- One of four recorded TC events ever in history to travel from east to west of the hemisphere
- The first TC in the Southern Hemisphere to undergo more than four rapid intensifications
- The most accumulated TC energy over its lifetime
- The greatest longevity in TC recorded history, surviving up to five weeks
Figure 2: Track of Tropical Cyclone Freddy with cyclone intensity from 6 February to 14 March 2023. TC Freddy track data source: IBTrACS, 2023.
It is very rare for TCs to travel such large distances from west to east and this may be linked to the ongoing La Niña phase of the El Niño Southern Oscillation (ENSO), a climate index based on sea surface temperature anomalies in the Southern Pacific Ocean. Other recent examples of far-travelling TCs are Leon-Eline and Hudah in 2000, also a La Niña year (WMO, 2023a). During a La Niña phase, sea surface temperatures in the eastern parts of the Southern Indian Ocean (where Freddy first formed) are warmer than average. Research suggests that TC genesis is enhanced in these regions during a La Niña phase (Ho et al., 2006; Kuleshov et al., 2009), and the additional heat fed into the cyclonic system from below may have helped to encourage Freddy in its progression across the Indian Ocean (UNSW, 2023).
The IPCC have reported that heavy precipitation and flooding has increased and is projected to increase more for south-east Africa and Madagascar (WMO, 2023b). The WMO has observed an increase in cyclone wind speeds, heavy precipitation and number of category 4-5 tropical cyclones. Global sea level rise is expected to contribute to the magnitude of storm surges that often accompany tropical cyclones making landfall, increasing the risk in coastal areas.
Modelling flood risk in southern Africa
JBA is the first in the industry to offer a truly global view of flood risk for every country in the world. Impacts can be assessed as people affected, economic loss or some other measure of risk, depending on the availability of suitable exposure data. We license high-resolution surface water and river flood hazard maps at return periods of 20, 50, 100, 200, 500 and 1,500 years for Malawi, Mozambique and Madagascar and, by combining these with our sophisticated event sets, exposure data and vulnerability descriptors, we can 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. This likelihood can be expressed as either:
- An exceedance probability (the percentage chance of occurrence)
- A return period (the reciprocal of exceedance probability: for example, a return period of 100 years - often termed a 1-in-100-year event - has an exceedance probability of 1%)
We have used population data representative of 2020 values (WorldPop Peanut Butter, 2020) and economic data based on country-level GDP in 2020 (World Bank, 2023) to generate national flood risk profiles for Malawi, Mozambique and Madagascar using JBA’s African Flood Model. These risk profiles assume that populations or properties are affected once flood depths exceed 0.2m and are shown in Figure 3.
Figure 3: National level flood risk profiles for Madagascar, Malawi and Mozambique, showing modelled (left) number of people affected and (right) economic loss by return period for a 0.2m flood depth threshold. Population data source: WorldPop Peanut Butter representing population in 2020. Economic data disaggregated based on country-level GDP values from World Bank (2023).
If you would like to learn more about our African Flood Model or our 30m river and surface water hazard maps, please get in touch.
References
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