There has been widespread coverage of the current drought in the media: this leads one to speculate just how severe this drought is at Ingwelala, compared with previous droughts.
Rainfall records have been kept at Ingwelala since the early 1980s and, during this period, there have been three severe droughts including the current one.
The timing of these droughts is summarized below
- The drought of the early 1980s started in February 1982, after the good rains of the previous three months with a total of over 200mm. Below average rainfall (with the exception of March 1983) persisted until November 1983 saw the start of a good summer rainfall season.
- The drought of the early 1990s started in April 1991, following a good summer rainfall season. The drought persisted until good rains fell in November 1992, followed by high flood-producing rainfall in the following two months.
- The current drought started in January 2015, after good rains in November and December amounting to over 200mm. Ingwelala is still in the grip of this drought, although some relief was provided by above-average rainfall in March 2016.
Analysis of the rainfall
A spreadsheet was used to analyse the rainfall data for Ingwelala by performing the following steps.
• Listing the monthly rainfalls in mm for each drought
• Expressing the rainfalls as percentages of the mean rainfall for each month
• Accumulating the rainfall percentages since the start of the drought
• Accumulating the mean monthly rainfall percentages for each month of the drought
• Finally, calculating the accumulated deficit as being the difference between the accumulated rainfall and the accumulated mean rainfall (as percentages)
Calculation of the deficit in this way assumes there is zero deficit when the actual rainfall is equal to the average rainfall. The results are shown in the diagram below. Month 1 is January, so for the 1980s drought (green curve) it is January 1982, for the 1990s drought (red curve) it is January 1991 and for the current drought (blue curve) it is January 2015.
The diagram shows that the current and 1980s drought follow a similar pattern, even to the extent of some recovery in March (month 16). The 1980s drought is seen to persist until November 1983 (month 24), when good rains reduced the deficit to a degree. The 1990s drought has a different pattern, with a slow start but severe deficits from about month 12 (December 1991) and persisting until month 22 (October 1992), after which good rains brought about a significant recovery and even floods in the December, January period.
What is of interest is that all three droughts reached a maximum deficit of around 75 to 80 percent. However, it remains to be seen whether the current drought will also experience significant relief in the coming summer – let’s hope so.
by Bill Pitman