Friday, September 24, 2021

The current downpours aren’t a new phenomenon – Meteorologist

Rainfall intensity and distribution both in space and in time increased over most areas due to the enhancement from the two tropical cyclones Chalane and Eloise that made landfall at the end of December 2020 and January 2021.

Department of Meteorological Services (DMS) Deputy Director Radithupa Radithupa informed Sunday Standard that, so far, the season has been wet and in agreement with the department’s forecast.

Following the advent of the two tropical cyclones that gripped Botswana, the country has been receiving heavy amounts of rainfall.

“Tropical Cyclone Chalane made landfall towards the end of the year over the eastern coast of Mozambique and it weakened to be a depression as it moved overland depositing heavy rains over the eastern and northern parts of Botswana all the way to the Ghanzi District where it caused flooding in the Ncojane areas,” Radithupa said.

Radithupa stated that the depression on its way to Gantsi also developed an easterly wave about 5000 meters into the lower atmosphere and this enhanced rainfall over the northeast such that all the Dams in the north were reported to be filled to capacity thereafter.

“Tropical Cyclone Eloise also followed, although it took a slightly different track moving towards the north-eastern parts of South Africa. It also did influence the weather over the Bobirwa and Tswapong area by enhancing the ‘overland through’ which resulted in rains spreading to the rest of the country,” Radithupa stated.

In the past, Botswana experienced Tropical Cyclone Eline in 2000 which according to Radithupa, flooded the Ghanzi areas but moved further south as the depression and filled up the Gaborone Dam. Tropical Cyclone Dineo came in 2017, resulting in floods in the northern parts of the Central Districts. Radipthupa said the tropical cyclones would differ in their strength depending on the meteorological conditions during cyclogenesis and/or during their track.

Of the three tropical cyclones mentioned, Eline in the year 2000 was the strongest also confirmed by the amount of devastation or rainfall it caused in Mozambique and ultimately flooding in Zimbabwe and Botswana filling up the Gaborone Dam.

DMS rainfall analysis dates to 40 years, or the beginning of the nineteenth century. The weather department classifies Botswana rainfall into wet, normal and dry years.

“We will only refer to the wet years because we are comparing with this year’s good rains that surprised Batswana,” Radithupa explained.

Botswana’s extremely wet years are 1999/00, 2005/06, 1987/88, 2007/08 and very wet years are 1980/81,2013/14, 1995/96 and 1990/91. Radithupa said that during these wet years, Gantsi recorded 231 mm on the 25th of Jan 1963 and Letlhakane recorded 144 mm on the 18th February 1995.

“It is becoming evident that indeed we are having good rains thus far and the year might turn out to be wet or extremely wet when we analyse data by the end of March 2021,” Radithupa said.

“However, so far, we have not broken the records for the data that we have hence the conclusion that this rainfall occurrence is not the first of its kind as some people might think,” he added.

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