South Africa at increased risk from tropical cyclones

Money Web (South Africa): Wits University scientists have debunked two big myths around climate change by proving firstly, that despite predictions, tropical storms are not increasing in number. However, they are shifting, and South Africa could be at increased risk of being directly impacted by tropical cyclones within the next 40 years.

Secondly, while global warming is causing frost to be less severe, late season frost is not receding as quickly as flowering is advancing, resulting in increased frost risk which will likely begin to threaten food security.

According to Jennifer Fitchett, a PhD student in the Wits School of Geography, Archaeology and Environmental Studies (GAES), there has been an assumption that increasing sea surface temperatures caused by global warming is causing an increase in the number of tropical cyclones. But looking at data for the south-west Indian Ocean over the past 161 years,

....The big surprise came when Fitchett and Grab looked at where storms have been happening. As the oceans have warmed and the minimum sea surface temperature necessary for a cyclone to occur (26.5 degrees Celsius) has been moving further south, storms in the south-west Indian Ocean have been moving further south too.

Most cyclones hit Madagascar and do not continue to Mozambique, and those which hit Mozambique develop to the North of Madagascar, but in the past 66 years there have been seven storms which have developed south of Madagascar and hit Mozambique head-on. More notable is that four of them occurred in the past 20 years. "This definitely looks like the start of a trend," says Fitchett.

South Africa is already feeling the effects of this shift. The cyclones that hit southern Mozambique cause heavy rain and flooding in Limpopo. But according to Fitchett, the trend becomes even more concerning when one considers that the 26.5 degrees Celsius temperature line (isotherm) has been moving south at a rate of 0.6 degrees latitude per decade since 1850. "At current rates we could see frequent serious damage in South Africa by 2050," she says....

Tropical cyclone Feling near Madagascar in 2013, from the International Space Station