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SA now experiencing half-year summers

12 October 2020 | Story Leonie Bolleurs | Photo Supplied

Although several international studies have used temperature metrics to statistically classify their seasonal divisions, a study in which Adriaan van der Walt was involved, would be the first known publication in a South African context using temperature as classification metric.

Gone are the days when we as South Africans would experience a three-month spring season, easing into summer, and then cooling off for three months before we hit winter.

Adriaan van der Walt, Lecturer in the Department of Geography at the University of the Free State (UFS), focuses his research on biometeorology (a specialist discipline exploring the role and climate change in physical and human environments) as well as climatology and geographic information systems.

He recently published an article: ‘Statistical classification of South African seasonal divisions on the basis of daily temperature data’ in the South African Journal of Science.

In this study, which Van der Walt undertook with Jennifer Fitchett, a colleague from the University of the Witwatersrand, data on daily maximum and minimum temperatures was collected from 35 meteorological stations of the South African Weather Service, covering the period between 1980 and 2015.

They went to great lengths to ensure that they had a complete set of data before presenting it to demonstrate seasonal brackets.

First for South Africa

Their statistical seasonal brackets indicate that South Africans now experience longer summers (from October to March), autumn in April and May, winter from June to August, and spring in September.

Although considerable work has been done using rainfall to determine seasonality in Southern Africa, Van der Walt believes that these methods did not work well as there are too many inconsistencies in this approach, as identified by Roffe et al. (2019, South African Geographical Journal). To make matters more complicated – as a semi-arid region, and with desert conditions along the west coast – some regions do not have enough rainfall to use as a classifier.

Temperature, on the other hand, worked well in this study. “Temperature, by contrast, is a continuous variable, and in Southern Africa has sufficient seasonal variation to allow for successful classification,” says Van der Walt.

He continues: “Although several international studies used temperature metrics to statistically classify their seasonal divisions, this study would be the first known publication in a South African context using temperature as classification metric.”

Van der Walt says what we understand as seasons largely relates to phenology – the appearance of blossoms in spring, the colouration and fall of leaves in autumn, and the migration of birds as a few examples. “These phenological shifts are more sensitive to temperature than other climatic variables.”

Seasonal brackets

According to Van der Walt, they believe that a clearly defined and communicated method should be used in defining seasons, rather than just assigning months to seasons.

“One of the most important arguments of our work is that one needs to critically consider breaks in seasons, rather than arbitrarily placing months into seasons, and so we welcome any alternate approaches,” he says.

A number of sectors apply the temperature-based division to their benefit. “For example, in the tourism sector it is becoming increasingly important to align advertising with the season most climatically suitable for tourism,” says Van der Walt.

Temperature-based division is also used to develop adaptive strategies to monitor seasonal changes in temperature under climate change. However, Van der Walt points out that each sector will have its own way of defining seasons. “Seasonal boundaries should nevertheless be clearly communicated with the logic behind them,” he says.

News Archive

UFS study on cell development in top international science journal

2008-09-16

A study from the University of the Free State (UFS) on how the change in the packaging of DNA with cell development influenced the expression of genes, will be published in this week’s early edition of the prestigious international, peer-reviewed science journal, the Proceeding of the National Academy of Sciences of the USA (PNAS).

The PNAS journal has an impact factor of 10, which means that studies published in the journal are, on average, referred to by ten other scientific studies in a two year period. The South African Journal of Science, by comparison, has an impact factor of 0.7.

The UFS study, funded by the Wellcome Trust and the National Research Foundation (NRF), looked at how the change in the packaging of DNA with cell development influenced the expression of genes. It is very relevant to research on stem cells, an area of medicine that studies the possible use of undifferentiated cells to replace damaged tissue.

Prof. Hugh Patterton, of the Department of Microbial, Biochemical and Food Biotechnology at the UFS, who led the study, said: "We are extremely proud of this study. It was conceived in South Africa, it was performed in South Africa, the data were analysed in South Africa, and it was published from South Africa."

When a gene is expressed, the information encoded in the gene is used to manufacture a specific protein. In eukaryotes, which include humans, there is approximately 1m of DNA, containing the genes, in every cell. This length of DNA has to fit into a cell nucleus with a diameter of only about 10 micrometer. In order to fit the DNA into such a small volume, eukaryotic cells wrap their DNA onto successive protein balls, termed nucleosomes. Strings of nucleosomes, resembling a bead of pearls, is folded into a helix to form a chromatin fiber. The study from the UFS investigated how the binding of a specific protein, termed a linker histone, that binds to the length of DNA between nucleosomes, influenced the formation of the chromatin fiber and also the activity of genes.

"We found that the linker histone bound to chromatin in yeast, which we use as a model eukaryote, under conditions where virtually all the genes in the organism were inactive. It was widely believed that the binding of the linker histone caused the inactivation of genes. We studied the relationship between the amount of linker histone bound in the vicinity of each gene and the expression of that gene for all the genes in yeast, using genomic techniques. We made the surprising discovery that even through the linker histone preferentially bound to genes under conditions where the genes were shut off, this inactivation of genes was not caused by the binding of the linker histone and folding of the chromatin,” said Prof. Patterton.

He said: “Instead our data strongly suggested that the observed anti-correlation was due to the movement of enzymes along the DNA molecule, involved in processing the information in genes for the eventual manufacture of proteins. This movement of enzymes displaced the linker histones from the DNA. This finding now requires a rethink on aspects of how packaging of DNA influences gene activity."

Prof. Patterton said that his research group, using the Facility for Genomics and Proteomics as well as the Bioinformatics Node at the UFS, was currently busy with follow-up studies to understand how other proteins in nucleosomes affected the activities of genes, as well as with projects to understand how chemicals found in red wine and in green tea extended lifespan. "We are certainly having a marvelous time trying to understand the fundamental mechanisms of life, and the UFS is an exciting place to be if one was interested in studying life at the level of molecules," he said.

Media Release
Issued by: Lacea Loader
Assistant Director: Media Liaison
Tel: 051 401 2584
Cell: 083 645 2454
E-mail: loaderl.stg@ufs.ac.za
18 September 2008

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