La Niña ‘won’t affect winter’

EXPERT: PHENOMENON SHOULD ALSO HAVE NO IMPACT ON AUTUMN RAINFALL OR TEMPS ➽ Tshwane tries making the invisible visible on World Water Day.

The heavy downpours during the summer may have helped restore surface and underground water levels, with above-average rainfall recorded, but they will have little impact on the winter season.

The South African Weather Service Regional Weather and Climate of Gauteng report showed the ’50s were a wet period, the ’60s were dry, the ’70s were wet, followed by another dry period in the ’80s. The late ’80s were wet, followed by the dry early ’90s, with the 1991-02 drought being one of the harshest recorded.

Vox Weather forecaster Annette Venter said she saw no correlation between a heavy rainy season and a cold winter.

“Weather phenomena and elements play a role in whether it will be a particularly cold, wetter or warmer winter,” she said.

Venter said the latest seasonal forecast showed the country would be in a La Niña state throughout autumn.

“But during autumn, the La Niña state has no impact on the rainfall or the temperature,” she said.

Venter added the seasonal forecast indicated temperatures were likely to be average to warmer than average over the central-eastern parts, which included Gauteng, while cooler temperatures were forecast for parts of the Cape.

Associated professor in meteorology at the University of Pretoria Liesl Dyson said during the summer rainy season of 2021-22 – from October to February – rainfall was near normal to above normal.

“December and January were particularity wet, but the western extremes of the country also received copious rainfall,” she said.

Dyson said the southwestern Cape, a winter rainfall area, received above-normal rainfall from October to December.

Water expert Professor Mike Muller said the good rains across most of the country had recharged groundwater, raised the water table and filled dams.

Water resource management specialist Professor Anthony Turton said surface water was found in the root zone of plants, while groundwater was deeper and went beyond the root zone.

“Very cold winters indicated the increased influence of the southern ocean system on weather in South Africa,” he said.

Turton said that system drove cold fronts deep inland, hence colder winters.

“The fact that these fronts are so deep is an indicator of an extreme pressure gradient in the atmosphere, which also correlates to more extreme rain in summer, when the cyclones from the Indian Ocean penetrate deeper and are more frequent,” he said.

Turton said at a loose level of generalisation, heavier prolonged rain created more soil water and resulted in extreme pressure gradients, which meant it correlated to a colder winter.

City of Tshwane spokesperson Sipho Stuurman said the city’s theme for this year’s World Water Day, celebrated on Tuesday, was Groundwater – Making the Invisible Visible.

“This seeks to inform people that the preservation of groundwater, although invisible, is critical for human survival,” he said.

Stuurman said groundwater could be found in many areas and was often used for drinking water in rural areas.

More soil water may correlate to a colder winter