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In 2018, powerful tropical cyclones continue to make headlines. In August, Tropical Cyclone Lane caused massive damage in the United States; he was quickly followed by Hurricane Florence.
Most tropical cyclones – the word is used interchangeably with
"Hurricanes" – of this type originated in the North Atlantic Ocean, where
they are powered by the heat of the Gulf Stream.
The South Indian Ocean has been relatively well protected, which means
tropical cyclones are rarer in southern Africa. Those who strike
the area tends to be of fairly low intensity on the Saffir Simpson scale.
This scale is used to classify tropical cyclones on the basis of a
the speed and pressure of the storm wind: the low intensity storms are rated "1" on
scale, while "5" represents the most intense and damaging tropical climate.
cyclones. Category 1 storms have a smaller diameter (50 to 100 km) and have a
minimum wind speed of 119 km / h, while category 5 storms have a wind speed
252 km / h or more and can reach 500 km in diameter. A debate is ongoing as to whether a category "6" should be added to the scale.
Like my new search
shows that the trend in the South Indian Ocean is changing. Category 5
tropical cyclones did not exist in this ocean until 1994. They were
recorded for the North Atlantic Ocean, North Pacific Ocean and South Pacific Ocean
throughout the 20th century. But since 1994, Category 5 storms
in the south of the Indian Ocean have become more common.
On the basis of the gradual trend of the last three decades, their frequency should continue to increase.
This happens because the sea surface temperatures are rising.
Tropical cyclones require a minimum sea surface temperature of 26 ° C
form. These temperatures are recorded more often and over a period of
larger area of the ocean than in the past. It's because the air
Temperatures that warm the sea surface are increasing due to greenhouse gas emissions.
Southern African governments must proactively respond to this new threat.
Dig in the data
I established all this by studying a global historical tropical cyclone database maintained by the National Oceanic and Atmospheric Administration.
Heavy rains caused by a cyclone in Sanaa, Yemen.EPA-EFE / YAHYA ARHAB
The search used databases from a number of sources. These include ship and harbor records from the 1800s and early 1900s, aircraft reconnaissance records from the mid-1900s, and satellite data from the 1970s.
Tropical cyclone Guillaume, north-east of Mauritius and Reunion, Indian Ocean.Shutterstock
The first tropical cyclone category 5 recorded in the South Indian Ocean and recorded in this record relates to the year 1994 – 70 years after the first Category 5 storm in the North Atlantic Ocean.
Over the past 30 years, I have seen a gradual increase in the number of tropical storms of high category. In the southern Indian Ocean, my study found that a sea surface temperature of 29 ° C resulted in the intensification of storms to a severity degree of 5. And these very hot ocean temperatures are now recorded over a much larger area, increasing the likelihood of these high intensity storms.
These Category 5 storms also moved the poles back to their place of origin and landing during this 30-year period. This means that previous storms in the equatorial waters of the south central Indian Ocean, far from any continent, are now occurring more and more often in the southern tropical region. This is a threat to the northern half of Madagascar, Mozambique and the islands of Reunion and Mauritius.
A region in difficulty
The last Category 5 storm that hit southern Africa took place in April 2016, when tropical cyclone Fantala crossed the southwestern Indian Ocean passing north of Madagascar and landed on the island of Farquhar, Seychelles.
Remarkably, despite the fact that the storm was the strongest ever recorded in the South Indian Ocean, a relatively small $ 4.5 million in damages was recorded and no deaths occurred. 39, has been registered.
This contrasts sharply with the last Category 5 storm that hit Madagascar, the tropical cyclone Gafilo, in March 2004. The storm – which kept the wind speed in tropical cyclones for six days – killed at least 250 people, sinking of a ferry and left 300,000 people homeless.
Unfortunately, southern Africa is struggling to cope with the effects of tropical cyclones, even Category 1. This suggests that governments are ill-equipped to cope with the most powerful category 5 variety.
But there are things to do to proactively manage this new climate reality. For example, coastal buildings, roads and bridges must be built to withstand high winds, heavy rains and possible storms to avoid costly infrastructure damage.
Better forecasting systems need to be put in place so that cities can actually evacuate the premises before a storm hits the ground in order to avoid loss of life. Spatial planning must take into account this increased threat and, to the extent possible, discourage development along high-risk coasts.
Jennifer Fitchett, Lecturer in Physical Geography, University of the Witwatersrand
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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