Has spring sprung or not?

01 September 2017 - 14:36 By Kgaugelo Masweneng
Yellow tulips.
Yellow tulips.
Image: iStock

September 1 and it’s officially spring‚ right?

Well‚ perhaps it’s not. People disagree about the starting dates of the seasons and many regard September 22 – the spring equinox – as the official start of Spring.

South Africa conventionally celebrates Spring Day on September 1‚ although there is no official designation of the starting dates‚ the South African Weather Service said.

In an article explaining how the seasons are worked out‚ the weather service says it can be done on an astronomical‚ climatological or phenological (relating to the natural seasonal behaviour of plants and animals) basis.

Earlier astronomical textbooks often defined the four seasons as starting on the dates of the corresponding equinoxes and solstices. But this is no longer the case.

“Apart from rejecting the astronomically-based seasons in compliance with modern astronomical usage‚ there are no firm grounds for choosing one set of dates rather than another for the starting dates of the seasons‚” said the weather service.

This year the spring equinox - when the sun crosses the Earth's equator‚ which occurs twice each year‚ in the Southern Hemisphere will occur on September 22.

Climatologically that’s when the season actually begins.

“One finds disagreement on the starting dates of the seasons at both the scientific and the lay level. South Africa does not really experience four distinct seasons. Throughout South Africa the transitional seasons of autumn and spring tend to be very short. Most analysis of climate is done using the assumption that January is mid-summer and July mid-winter‚” said the weather service.

Climatologists ignore the usual seasonal classification‚ using instead labels that are more appropriate to the climate of a particular region‚ such as hot season‚ cold season and post-rainy season.

“The durations of these seasons depend on the climate of the region‚ and have no direct relationship to either the astronomical seasons or the calendar months. Thus‚ September is spring-like in Gauteng‚ with cool mornings and warm afternoons‚ whereas it is still winter-like in the Western Cape‚ with the possibility of snow on the Eastern Cape mountains.

“Unfortunately the lay public would find it too confusing if a different set of seasonal dates was adopted for different parts of the country in order to encompass this variability‚” said the weather service.