More than 135 dead amid flooding and landslides in Rwanda and Uganda.

One hundred and twenty nine people have now been confirmed dead in Rwanda, and another six in neighbouring Uganda, amid heavy and relentless rains which have been falling in the area since the beginning of March, triggering a series of floods and landslides. Landslides are a common problem after severe weather events, as excess pore water pressure can overcome cohesion in soil and sediments, allowing them to flow like liquids.  Approximately 90% of all landslides are caused by heavy rainfall.

A landslide blocking a road at Mushubati in western Rwanda. Miriam Kone/AFP/Getty Images.

Sixteen people are known to have died in a flash flood in Karongi District in Western Province,  Rwanda, which swept away a number of houses at about 2 am local time on Wednesday 3 May 2023, and it is feared that more people may have died in the event and not yet been discovered. The River Sebeya, in northwest Rwanda, close to the border with Uganda, is reported to have burst its banks, leading to widespread flooding Six people, five of them from a single family, are reported to have died in a landslide in Kisoro District in the southwest of Uganda, with a number of other landslides causing disruption in mountainous areas of southern Uganda.

The remains of a home which collapsed amid flooding in Rubavu District, Western Province, Rwanda. Jean Bizimana/Reuters.

Rwanda has a wet montane climate, with a long rainy season which lasts from mis-September to mid-May, with two peaks in rainfall in October-November and March to April. Such a double Rainy Season is common close to the equator, where the Sun is highest overhead around the equinoxes and lowest on the horizons around the solstices, making the solstices the coolest part of the year and the equinoxes the hottest. Like other areas of East Africa, Rwanda has suffered from exceptionally high levels of rainfall this year, driven by unusually warm weather over the Indian Ocean, which means that much of the ground is now waterlogged, and cannot absorb any more water, with the effect that any further rain is likely to run over the surface leading to flooding.

The high temperatures and exceptional rainfall are thought to be associated with a developing el Niño weather-system over the South Pacific. The El Niño is the warm phase of a long-term climatic oscillation affecting the southern Pacific, which can influence the climate around the world. The onset of El Niño conditions is marked by a sharp rise in temperature and pressure over the southern Indian Ocean, which then moves eastward over the southern Pacific. This pulls rainfall with it, leading to higher rainfall over the Pacific and lower rainfall over South Asia. This reduced rainfall during the already hot and dry summer leads to soaring temperatures in southern Asia, followed by a rise in rainfall that often causes flooding in the Americas and sometimes Africa. Worryingly climatic predictions for the next century suggest that global warming could lead to more frequent and severe El Niño conditions, extreme weather conditions a common occurrence.

Movements of air masses and changes in precipitation in an El Niño weather system. Fiona Martin/NOAA.

The development of an el Niño weather-system this year is considered particularly alarming by climate scientists, as the world has had several consecutive years in which average global sea-surface temperatures have equaled or slightly surpassed the hottest previous average temperatures recorded, despite the climate being in a la Niña phase. As sea surface temperatures are typically significantly warmer during an el Niño phase than a la Niña phase, the development of such a phase could push temperatures into areas not previously encountered on Earth since Modern Humans first appeared, potentially triggering or accelerating other climatic problems, such as glacial melting, droughts in tropical forests, and changes in ocean circulation, which might in turn take us further into unfamiliar climatic territory.

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Malawisaurus dixeyi: The braincase and inner ear of a Southern African Titanosaur.

Titanosaurs were a group if exceptionally large Sauropod Dinosaurs that dominated many faunas in the Southern Hemisphere during the Cretaceous. The group includes the largest known Dinosaurs, with species such as Argentinosaurus and Puertasaurus thought to have weighed close to 90 tonnes. However the group was quite diverse, and also contained many smaller species, as well as both long and short-necked forms, suggesting a wide range of ecological specialisations.

Titanosaur remains from Malawi, Southern Africa, were first described under the name Gigantosaurus dixeyi in 1928. These fossils underwent several name-changes as our understanding of Dinosaur taxonomy changed and grew during the twentieth century, eventually gaining the current name, Malawisaurus dixeyi, in 1993. The beds which produced these fossils are of Cretaceous age, though a more precise date has eluded geologists to date; biostratigraphic studies using Ostracods (small Crustaceans with distinctive shells and high species turnover), and the beds are closely related to carbonates that have been dated to between 123 and 111 million years old, based upon potassium-argon geochronology (argon is a noble gas, and cannot be incorporated into rocks, but unstable isotopes of potassium, which decay into argon can, and will then remain in the rock; since this happens steadily at a known rate, geochemists can date rocks by establishing the ratio of radioactive potassium to argon within them), but studies of the Vertebrate fauna preserved within these rocks has suggested a Late Cretaceous origin.

In a paper published in the journal PLoS One on 13 February 2019, Kate Andrzejewski, Michael Polcyn and Dale Winkler of the Roy M. Huffington Department of Earth Sciences at Southern Methodist University, Elizabeth Gomani Chindebvu of Culture and Community Development at the Ministry of Civic Education in Malawi, and Louis Jacobs, also of the Roy M. Huffington Department of Earth Sciences at Southern Methodist University, describe new Malawisaurus dixeyi material from Malawi, including a reconstruction of the inner ear and endocast (cast of the inside of the braincase, this is not the same as the brain, but can give information about it), and draw conclusions from this.

The described specimen, Mal-202-1, comprises a nearly complete basicranium and associated parietals, ectopterygoid, quadrate, cervical vertebrae, and post cranial elements, all assigned to Malawisaurus dixeyi, recovered from near Mwakasyunguti in Karonga District, northern Malawi, by the Malawi Dinosaur Project in the 1980s and 90s.

The specimen was scanned at the University of Texas High Resolution X-ray CT facility, enabling Andrzejewski et al. to construct a three dimensional computer model of the brain endocast and inner ear. The bones of the braincase are well preserved, and all show fully ossified sutures, suggesting that the specimen was a mature adult at time of death. An estimate of its size based upon the circumference of the humerus, suggests a living weight of 4.73 tonnes.

Braincase of Malawisaurus dixeyi. (A) lateral view; (B) lateral view with endocast; (C) posterior view. Abbreviations: BO, basioccipital; BP, basipterygoid process; BT, basal tuber; CAR, canal for cerebral carotid artery; FO, fenestra ovalis; LABYR, labyrinth; LS, laterosphenoid; OC, occipital condyle; PFO, pituitary fossa; PP, paroccipital process; SO, supraoccipital; SPHA, canal for sphenopalatine artery; III, oculomotor nerve; IV, trochlear nerve; V, trigeminal nerve; VI, abducens nerve; VII, facial nerve; IX-XI, shared canal for glossopharyngeal, vagus, and spinal accessory nerves; XII, hypoglossal nerve. Scale bar equals 10cm. Andrzejewski et al. (2019).

Andrzejewski et al.’s reconstruction lacks the olfactory and cerebral regions, or caudal dural expansion, a prominent venous feature of Sauropods. Like most Sauropod endocasts it shows a lack of distinction of gross regions of the brain, presumably obscured by the presence of overlying thick meninges and extensive venous sinuses in life, but does show typical Sauropod features such as a large pituitary fossa. The reconstruction does show the connections of the veinous canals (canals through which the veins pass) and cranial nerves, the general pattern of which are consistent with the interpretation of Malawisaurus as a Titanosaur.

Cranial endocast and vestibular labyrinth of Malawisaurus dixeyi. (A) left lateral view; (B) caudal view; (C) ventral view; (D) dorsal view; dashed line represents reconstruction of full endocast based on the endocast of Sarmientosaurus. Endocast represented by purple colouring; cranial nerves by yellow colouring; vestibular labyrinth by pink colouring; carotid artery by red colouring. Scale bar equals 5cm. Andrzejewski et al. (2019).

The inner ears of several Sauropods have been described previously, with a general pattern observed of larger vestibular labyrinths in early members of the group, and smaller in more derived Titanosaurs; that of Malawisaurus dixeyi appears to be intermediate in size, which is roughly what would be expected based upon current interpretations of its phylogenetic position as a Titanosaur that split from the group early in their history. It also shows uneven size of the semicircular canals, something which is found in earlier Sauropods, but not more derived Titanosaurs, again consistent with the current interpretations of the phylogenetic position of the species.

Left vestibular labyrinth of Malawisaurus dixeyi. (A) lateral view; (B) posterior view; (C) dorsal view. Abbreviations: C, cochlea; CRC, crus commune; CSC caudal (posterior) semicircular canal; FP, fenestra perilymphatica; FV fenestra vestibuli; LSC, lateral semicircular canal; RSC, rostral (anterior) semicircular canal; VE, vestibule of inner ear. Scale bar equals 2cm. Andrzejewski et al. (2019).

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Crocodile kills man in Karonga Distriict, Malawi.

A 28-year-old man has been killed by a Crocodile in Karonga District in northern Malawi. Hussein Zibeli was apparently attempting to swim out to a boat where some friends were fishing, when he was seized by the animal and dragged under at about 8 pm local time on Thursday 30 November 2017. His body was later recovered, and an autopsy revealed he had died of a mixture of drowning and blood-loss. This is fairly typical of Crocodile attacks, with prey typically dragged under the water and drowned, but often not eaten immediately. This is at least the fifth Crocodile-related death in Malawi this year.

Wounds on the body of Hussein Zibeli, who was killed by a Crocodile on 30 November 2017. Nyasa Times.

Lake Malawi is home to a large population of Nile Crocodiles, Crocodylus niloticus. These are large animals, reaching about five meters in length, and are ambush predators capable of taking large prey, including, on occasion, Humans. The animals are thought to be at their most dangerous around in the dry season (December to March in Malawi), when the water is lowest, and females are guarding eggs buried in nests by the river.

 A Nile Crocodile on Lake Malawi. Birding for Pleasure.

Nile Crocodiles are considered to be of Least Concern under the terms of the  International Union for the Conservation of Nature’s Red List of  Threatened Species, but are still protected in many countries, including Malawi, due to historic hunting which decimated populations in many areas. However, the rising number of attacks on Humans, which is thought to have been driven by rapidly rising populations of both Humans and Crocodiles, combined with a sharp decline in the numbers of many natural prey species, has led to calls for regulated hunting to be introduced to control the population.

The approximate location of the 30 November 2017 Malawi Crocodile attack. Google Maps.

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