This article is written by Iris Uijttewaal, with contribution from Dr. Mario Lebrato.
Lasting over 5 weeks, and traversing the Indian Ocean from Australia to Mozambique, C4 Cyclone Freddy hit Mozambique two times in 2023; the Bazaruto Archipelago and Vilankulos at the end of February, and again mid-March, making landfall northwards, near Quelimane. Sustained winds between 220 and 270 km/h caused devastation wherever they touched land, but substantially weakened while crossing Madagascar, although wind speeds were in excess of 140 km/h when hitting Mozambique. Rainfall exceed predictions, reaching in some areas 400 mm, causing extreme flooding events, erosion, and landslides. The system did not deteriorate after making landfall, and it bounced back to the Mozambique Channel, to then move north, hitting again, and eventually losing power inland.
Onsite Benguerra Island, the terrain got extremely wet, with the water table rising very quick, followed by wetlands and lakes overflowing, causing road closures and blocking access to the beaches. As a result, an increased number of crocodiles was observed moving beyond their normal ranges. Over 100 trees collapsed on the east side of the island due to the waves reaching near 6 m on long period swells, further eroding the sand cliffs inland.
The BCSS station suffered limited damage due to its conceptual design to blend in with nature, whereby the trees and bush buffer the wind’s impact. Though the station was partially flooded – measurements were swiftly put in place and all damage has since been repaired. (Photo by Dr. Mario Lebrato)
The BCSS station suffered limited damage due to its conceptual design to blend in with nature, whereby the trees and bush buffer the wind’s impact. BCSS building materials being local wood also flex and resist wind and water well. Though the station was partially flooded – measurements were swiftly put in place and all damage has since been repaired. The flooded terrain has been converted into wet mud, which is rich in nutrients and soil and therefore beneficial for our permaculture gardens.
The flooded terrain has been converted into wet mud, which is rich in nutrients and soil and therefore beneficial for our permaculture gardens. (Photo by Dr. Mario Lebrato)
The impact on the marine environment
Very few marine life was seen from boats or diving in the aftermath of the cyclone likely following major water column and seawater transient physicochemical shifts. Sea Surface Temperature (SST) was monitored via satellite undergoing major anomalies, and suffering complete heat shifts side to side in the Mozambique Channel. Sporadic seawater measurements from BCSS boats also witnessed disolved oxygen levels abnormally low in the water masses inshore/offshore, likely as a consequence of particle resuspension, and water column fluxes. The cyclone brought long periods of swells stirring up the seafloor and bringing up large amounts of sand, mud and debris. During the first boat inspection water column visibility was reduced to 4-6 m out to 200 m total depth, and it was down to 50 cm out to 30 m depth. For a few weeks, animals likely adopted a protective/refugee behaviour given the circumstances.
Change in Sea Surface Temperature (SST) measured over time during cyclone Freddy. Source: State of the Ocean (SOTO) App – NASA
After the cyclone, ocean dynamics returned to normal, though it took almost 3 weeks for the system to settle. Several days of calm weather, with seawater rising temperatures and ocean stratification, caused massive plankton blooms seen for, further depleting dissolved oxygen in the upper water mass. Immediately after that, animals moved in to feed, and large shoals of tuna were seen, also bringing massive amounts of shark underneath. Manta rays were again regularly spotted on the dives. Overall, it took almost a complete month for the system to recover normality.
For questions about this article, please contact:
Iris Uijttewaal, Bazaruto Center for Scientific Studies
Iris.Uijttewaal@bcssmz.org
Bazaruto Center for Scientific Studies
Host of the first permanent Ocean Observatory focused on multi-ecosystem time series research in Africa, the Bazaruto Center for Scientific Studies (BCSS) was established in 2017 as in independent, non-profit organisation with a mission to protect and support the fragile ecosystems of the Bazaruto Archipelago, Mozambique. The research station is located on Benguerra Island, off the coast of Mozambique.
