By ROGER ROWSWELL
The rainfall for February at Darling Street was a meagre 37.3mm over 9 raindays. The long term average (LTA) over 36 years for February is 72.1mm and LT Median at 57.7mm. .
Looking at the graph below, comparing Darling Street monthly rainfall 2021 with that of the Old Gaol in 1922 99 years ago, the year Grahamstown had its last big deluge and flooding, it can be seen that although different, they are following a similar trend – although it is still very early in 2021 to draw conclusions.
It must be stated that the long term average (LTA) for Old Gaol is for a period of 76 years (1900 to 1975), while that of Darling St has entered its 36th year (1986 to 2021). The Darling St monthly LTA’s are notably higher then those of Old Gaol due to the fact that the Darling Street record includes a period of high rainfall from 2001 to 2012 where the annual rainfall exceeded 1000mm on three occasions. This is not evident in the Old Gaol early 1900 data.
Based on the Ocean Nina Index (ONI) which in December 2020 had a value of -1.2 it was declared that a La Nina phase was in progress. Values were less than -0.5 for a period of five months. The value for December was -1.2
The January value is -1.1 and this is likely to taper off and then rebuild in the latter half of the year.
- Editor’s note: Roger Rowswell says contractors putting in fibre optic cables in Cathcart Street damaged the underground Telkom lines on Tuesday 23rd February and these were only reconnected on Friday 12 March around 1pm. Next month we hope to share the monthly totals of all the local rain-measurers at the same time.
