 Mozambique's fourth-largest city has been flooded after being hit by a tropical cyclone. Tropical Cyclone Desmond was formed in the Mozambique Channel on Sunday night and drifted slowly northwest towards the coast. Strong convective activity persisted for several days near Mozambique which was fed by the flow of monsoon that sinked deeply to the south of the Mozambique Channel. It made landfall in the province of Zambezia, near the border with the Sofala province. While there were no casualties in Mozambique, atleast 9 people were killed in Madagascar. The landfall took place just after 18:00 UTC, January 21, about 40 km S of Chinde and 200 km N of Beira, Mozambique with maximum sustained winds up to 65 km/h.
The winds in the upper atmosphere were much stronger than those near the surface which fortunately slowed down the storm's growth and prevented it from becoming too intense. Although the winds were not too strong when it made landfall, the rain was extremely heavy and the seas were very rough. Some 277 millimetres of rain was reported in Beira in the 24 hours until 06:00 GMT on Tuesday, more than the 250mm expected for the whole month of January. According to Al Jazeera, large waves smashed over the top of sea defences and the torrential rain transformed roads into rivers. Cars were submerged up to their windows and dirty floodwater rushed into people's homes and businesses. The remnants of Tropical Cyclone Desmond are expected to bring more flooding to central Mozambique and southern Malawi as it disintegrates above the region. Over the next 24 hours, some places could see as much as 200mm more rainfall, and it looks like Madagascar could be hit by even worse conditions. Tropical Cyclone Desmond did not hit Madagascar, but it did enhance the rains in the northwest of the island and more severe weather is expected as another circulation in the Mozambique Channel is expected to develop over the coming days. This system is expected to track south, off the coast of Madagascar, and is likely to pull a trail of heavy downpours across the northwest of the island. This would bring further torrential rain to a region that is already waterlogged, which could easily lead to flooding and landslides. To learn more about other climate-related stories occurring across Africa, be sure to click here! © 2018 Oceanographer Daneeja Mawren
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 Tropical cyclone Funso (Cat-4) captured by the MODIS instrument, Image Credit: NASA’s Aqua satellite on Jan, 25 2012 battering the Mozambique coast. Although tropical cyclones are rare to southern Africa, Jennifer Fitchett, a Senior Lecturer in Physical Geography at the University of the Witwatersrand, believes that this may not last for long. Results indicate warmer waters along the east coast of South Africa leading to more conducive conditions for these natural disasters to occur. The increase in the frequency of occurrence of intense cyclones may pose a heightened risk of storm damage for countries neighbouring the Southwestern Indian Ocean as a result of strong winds, heavy rainfall and storm surges associated with these systems. Her research showed that Category 5 storms were not present in the South Indian Ocean prior to 1994, but had now become more frequent.
An increase in the ocean temperature is now being recorded over a much larger area, increasing the probability of these high intensity storms. These category 5 storms have also shifted more poleward in their location of origin and landfall over the last three decades. This means that storms which previously existed in the equatorial waters of the central South Indian Ocean, far from any landmasses, are now increasingly occurring in the southern tropical region. That poses a threat to the northern half of Madagascar, Mozambique and to the islands of Reunion and Mauritius. The last time a category 5 storm hit southern Africa was in April 2016, when tropical cyclone Fantala moved through the southwest Indian Ocean passing north of Madagascar and making landfall on the island of Farquharin the Seychelles. Remarkably, despite being the strongest storm ever to have occurred in the South Indian Ocean, a relatively low $4.5 million in damages was recorded and no deaths were registered. This is in stark contrast to the last category 5 storm that made landfall on Madagascar – Tropical cyclone Gafilo, in March 2004. This cyclone sustained tropical cyclone intensity wind speeds for six days and left at least 250 dead, the sinking of a ferry and left 300,000 people homeless. Unfortunately, southern Africa struggles to cope with the effects of even category 1 tropical cyclones. This suggests that governments are ill equipped to deal with the more powerful category 5 tropical cyclones. Better forecasting systems need to be put in place so that cities and towns can effectively evacuate before a storm makes landfall to prevent loss of human life. Spatial planning needs to consider this heightened threat, and where possible, discourage development along high-risk coastlines. Detailed information can be obtained from the following journal : Fitchett, J.M., 2018. Recent emergence of CAT5 tropical cyclones in the South Indian Ocean. South African Journal of Science, 114(11/12). To learn more about other climate-related stories occurring across Africa, be sure to click here! © 2018 Oceanographer Daneeja Mawren  The Sahara Desert is known to have undergone major, and abrupt, hydrological fluctuations and was vegetated at times in the past. During a wet phase in the Early Holocene known as the African Humid Period (AHP), the region currently occupied by the Sahara desert was vegetated, contained forests, grasslands, permanent lakes, and was occupied by human populations. When the AHP ended, the Sahara was transformed into a hyperarid desert. On orbital time scales, the large hydrological fluctuations in North Africa are linked to changes in the African monsoon, which is related to precession-forced variability in low-latitude summer insolation. The abrupt transitions between humid and arid conditions observed in marine and terrestrial paleoclimate records from North Africa, however, cannot be explained solely by gradual orbital forcing; thus, other nonlinear feedback processes are required to explain the abrupt climate responses to orbital forcing.
Every year, winds from the northeast sweep up hundreds of millions of tons of Saharan dust, depositing much of this sediment into the Atlantic Ocean, off the coast of West Africa. Layers of this dust, built up over hundreds of thousands of years, can serve as a geologic chronicle of North Africa’s climate history: Layers thick with dust may indicate arid periods, whereas those containing less dust may signal wetter eras. Scientists have analyzed sediment cores dug up from the ocean bottom off the coast of West Africa, for clues to the Sahara’s climate history. These cores contain layers of ancient sediment deposited over millions of years. Each layer can contain traces of Saharan dust as well as the remains of life forms, such as the tiny shells of plankton. Layers of dust deposited off the west coast of Africa over the last 240,000 years were analysed. The researchers measured the concentrations of a rare isotope of thorium in each layer to determine how rapidly dust was accumulating on the seafloor. Thorium is produced at a constant rate in the ocean by very small amounts of radioactive uranium dissolved in seawater, and it quickly attaches itself to sinking sediments. As a result, scientists can use the concentration of thorium in the sediments to determine how quickly dust and other sediments were accumulating on the seafloor in the past. During times of slow accumulation, thorium is more concentrated, while at times of rapid accumulation, thorium is diluted. The pattern that emerged was very different from what others had found in the same sediment cores. Researchers found that some of the peaks of dust in the cores were due to increases in dust deposition in the ocean, but other peaks were simply because of carbonate dissolution and the fact that during ice ages, in this region of the ocean, the ocean was more acidic and corrosive to calcium carbonate. It might look like there is more dust deposited in the ocean, when in the face this is not the case. Once the researchers removed this confounding effect, they found that what emerged was primarily a new “beat” in which the Sahara vacillated between wet and dry climates every 20,000 years, in step with the region’s monsoon activity and the periodic tilting of the Earth. Apparently, the increased solar flux in North Africa can intensify the region’s monsoon activity which makes the Sahara Desert wetter. However, when the planet’s axis swings toward an angle that reduces the amount of incoming summer sunlight, it produces a drier parched climate like what we see today. David McGee, an associate professor in MIT’s Department of Earth, Atmosphere and Planetary Sciences found that analysing this time series will help understand the history of Sahara desert and investigate what period could contribute to amenable conditions for humans to settle the Sahara desert and allowing them to cross this otherwise inhospitable region. “We can now produce a record that sees through the biases of these older records, and so doing, tells a different story,” McGee says. “We’ve assumed that ice ages have been the key thing in making the Sahara dry versus wet. Now we show that it’s primarily these cyclic changes in Earth’s orbit that have driven wet versus dry periods. It seems like such an impenetrable, inhospitable landscape, and yet it’s come and gone many times, and shifted between grasslands and a much wetter environment, and back to dry climates, even over the last quarter million years.” Detailed information can be obtained from the following journal : Skonieczny, C., McGee, D., Winckler, G., Bory, A., Bradtmiller, L.I., Kinsley, C.W., Polissar, P.J., De Pol-Holz, R., Rossignol, L. and Malaizé, B., 2019. Monsoon-driven Saharan dust variability over the past 240,000 years. Science advances, 5(1), p.eaav1887. To learn more about other climate-related stories occurring across Africa, be sure to click here! © 2018 Oceanographer Daneeja Mawren |
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