31 August 2005

South Africa has been growing warmer each year - study

South Africa has been getting warmer over the past 44 years and the season that has been getting the warmest is autumn.

A study in the International Journal of Climatology by Andries Kruger and Stephen Shongwe of the South African Weather Services shows that the country's average yearly temperatures have increased by 0,13°C a decade between 1960 and 2003.

The scientists analysed climate data from 26 weather stations around the country.

Of these, 23 stations showed that the average annual maximum temperatures had increased, 13 of them significantly.

Average annual minimum temperatures also showed increases, of which 18 were significant.

But the study found that although temperatures had been warming during the past 44 years, these increases were not consistent between the seasons.

The average trend for the country during autumn was an increase of 0,21°C a decade, for winter it was 0,13°C a decade, spring 0,08°C and summer 0,12°C.

The season with the highest warming trend is autumn and the lowest warming trend is spring.

When the figures were analysed on a monthly basis, it was found that April showed the warmest trends at most of the weather stations.

The months which showed the least temperature increases were September to December, with the exception of the stations in the extreme eastern part of the country at Skukuza and St Lucia, where the least temperature increases occurred in January.

The weather stations also record the number of days and nights with maximum and minimum temperatures in defined categories, such as "hot days" which have temperatures over 35°C, or "cold nights" which have temperatures below freezing. They also record "events" where temperatures stay hot or cold for between three and five days.

Analysis showed that days with warmer temperatures had generally increased while the number of cooler days had decreased. Most stations showed an increase in "hot-day events", where temperatures stayed above 30°C for three to five days. "Cool day events" declined, some quite substantially.

There have been more warmer nights and fewer cooler nights.

The number of hot nights, over 20°C, has increased significantly in the interior around Upington and on the east coast from East London to St Lucia.

Warm nights, between 15°C and 20°C, have increased significantly on the Western Cape coast and in areas in the Eastern Cape like Addo.

There was a significant increase in "warm night events" throughout South Africa, where temperatures stayed above 15°C for three to five nights.

Globally, the 1990s have been substantially warmer than previous decades. When Kruger and Shongwe analysed South Africa's data to see if this was true here, they found it was not. The average warming trend between 1960 and 1990 was 0,11°C a decade, while between 1991 and 2003 it was 0,09°C.

Source: www.iol.co.za


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