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April 2017 Climate Summary

The Western Cape has been experiencing drought conditions for some time.  In addition, the winter rainfall that normally starts off round about April was absent this year (slide 1).  There were some areas that received 30-50mm, mostly in the eastern side of the Central Karoo and the western side of the Cape Winelands and the Overberg.  It should be stressed that poor rains (0-10mm) were experienced in the western and northern areas of the West Coast, parts of the Cape Winelands including the western side of the Karoo regions.     

When taking the historical long term statistics into account (slide 2), then most of the province indicated below normal rains for April, excluding the mid to eastern side of the Central Karoo showing normal to above normal rains.  Parts of the West Coast, Cape Winelands, Little Karoo, Overberg and southern coastal areas received up to 50% (orange areas) of its normal rains.  The red areas in the latter revealed more extreme situation (0 to 25% of normal rainfall), mostly evident in mid to northern areas of the West Coast, though also present in the Cape Winelands and Eden districts. 

Slide 1

Slide1

Slide 2

Slide2

Slide 3 consists of data taken from 35 weather stations, depicting total monthly rainfall, mean monthly maximum (Tmax) and minimum temperatures (Tmin) for April 2017, including corresponding historical long term means.  The overall mean rainfall for April 2017 (calculated as the average of the 35 weather stations) was 15mm, meaning 50% of the long-term mean rainfall for April (calculated similarly).  Half of the weather stations recorded total monthly rainfall of ≤13mm, of which 4 weather stations indicated ≤1mm to no rain.  Conversely the highest monthly rainfall of 46mm (long-term 25mm) was recorded at Murraysburg.

The monthly mean Tmax at the various weather stations ranged between 23.1 ºC (Bredasdorp) to 33.2 ºC (Citrusdal), compared to the long term averages ranging from 22.4 ºC (Koue Bokkeveld) to 30.9 ºC (Klawer).  From the latter it is evident that the high extreme Tmax was 2.3 ºC warmer this year compared to the corresponding long term average, while the low range Tmax remained reasonably similar.  In addition, the overall average Tmax of 28.1 ºC was 2.3 degrees higher than the corresponding long term mean.  All but one weather stations resulted in positive Tmax anomalies (≥ +0.5 ºC), of which the highest monthly anomalies were recorded at Mossel Bay (+4.3ºC) and Rawsonville (+3.9ºC).

Monthly mean Tmin at the same weather stations ranged between 6.9 ºC (Murraysburg, long term 6.2 ºC) to 16.8 ºC (Klawer, long term 14.5 ºC) with an overall average of 12.2 ºC (long term 11.3 ºC).  Most of the weather stations (excluding eight) resulted in positive Tmin anomalies (≥ +0.5 ºC), of which half indicated anomalies of at least +1 ºC.  The most extreme Tmin anomaly (2.3 ºC) was recorded at Klawer.

 

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Slide 3

Slide 3

The state of provincial dam levels (slide 4) dropped to an overall average of 20% (last year 30%) on the 1st of May, indicating a further downward trend for most dams in the province.  The Theewaterskloof Dam, decreased to a water level of 16% (last year 32%).

The persistent below normal rainfall accompanied by high temperatures, brought about further deterioration with regard to plant growth conditions in the province (slide 5).

ENSO remains neutral, the possibility of El Niño to appear later this year is less evident but still achievable.  According to SAWS, statement released 3rd May, above normal rainfall and above-normal temperatures are forecasted for the Western Cape for the period May to July.   Due to high uncertainty in forecasts, users are advised to regularly review updated medium and short term forecasts to identify any intermediate change.

Slide 4

Slide4

Slide 5

Slide5


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Agri-Oulook April 2017

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