A leading weather expert says the recent heavy rainfall and flooding in parts of the Western Cape were driven by various atmospheric circulation-type air that generally flows from west to east, causing high winds, heavy rainfall and storms.
This is according to the University of Western Cape’s Department of Earth Science chairperson and associate professor Michael Grenfell.
Grenfell said these conditions were associated with intense low pressure such as cut-off lows and more widespread low-pressure systems involving a connection between low pressure in the interior and low pressure at the coast.
This comes after the Western Cape experienced a series of floods and rainfall incidents in which townships such as Langa and Samora Machel were severely affected.
In December, another series of floods affected areas in the Drakenstein Municipality district, where a hospital roof collapsed and severe damage was caused to roads in towns like Paarl.
In another incident, two fatalities and four people are still missing across the King Sabata Dalindyebo Municipality (Eastern Cape) and in the same province, one person is still missing in Komani (formerly Queenstown).
Two weeks ago, Coffee Bay on the Wild Coast also saw flooding in which a 6-year-old child died, and the body of a missing female was found on Thursday by OR Tambo District Municipality’s disaster management team, with more bodies yet to be recovered.
Grenfell told IOL that on the south and east coasts and interior, warm, moist air from the Indian Ocean is drawn into these low-pressure systems, and forced to rise, cool and condense, bringing heavy rainfall.
These systems tend to last for a few days, and move relatively slowly, so they can bring large amounts of rainfall to the areas they affect.
In terms of what can we expect, he said that projections varied for different parts of the country, but warming was expected everywhere.
“This acts like a boiler; more heat, more power, more evaporation and higher intensity rainfall events. Sub-escarpment areas in the east are likely to get a bit wetter due to increased advection of moisture off a warmer Indian Ocean.
“These changes can enhance the effects of existing natural oscillations associated with El Niño (more intense drought) and La Niña (more intense floods). The strong La Niña that has prevailed over the past three years has enhanced rainfall in KwaZulu-Natal,” he said.
“However, regions such as the Western and Southwestern Cape are expected to become drier overall, with fewer rain days and shorter rainfall events due to changes in the atmospheric circulation that drives cold fronts and there will be increased variability from year to year, making predictions difficult,” Grenfell said.
He said South Africa has a fairly good understanding of the atmospheric circulation-types that lead to heavy rainfall, but predicting exactly where and when these circulation-types will develop long in advance of their occurrence was difficult.
“We can provide a few days’ warning, and must do more to raise awareness within communities and avert loss of life.
“In general, we need to prepare for a warmer and more variable atmosphere, which in some cases will provide less rainfall than expected (drought) and in other cases will provide much more (floods).
“In areas that do not experience floods on a regular basis, there is a lack of institutional and social ‘memory’ of how to respond and how to adapt. These areas can learn from areas that are better adapted to flood risk, and municipalities should share knowledge and expertise to help each other to adapt,” Grenfell said.
He said these recent weather conditions were crippling infrastructure, and this was so widespread that the government had declared a national state of disaster.
“Flood risk is calculated on a scale of probability, and infrastructure is typically designed to withstand floods of a certain risk probability (in a 50-year event). With extreme rainfall events more likely in a warmer world, we need to shift our probability scales accordingly.
“We need to build back better, and replace what was lost with designs that can withstand larger events in future, but more importantly we also need to re-evaluate where infrastructure is developed, and avoid flood-risk parts of the landscape,” Grenfell said.
IOL