Rainfall


Rainfall

The average annual rainfall in South Africa is around 497 mm, compared to a world average of around 860 mm. Droughts and water shortages are a severe and regular problem in South Africa.

Rainfall in South Africa is very unpredictable and unevenly spread across the country, as the map below illustrates.

Only a narrow region on the eastern coastline receives good rainfall, while the majority of the interior and western part of the country receives much less. Many parts of South Africa are classified as arid (dry) or semi-arid.

About 65% of the country receives less than 500 mm of rain on average per year, and around 20% of the country receives less than 200 mm. 


 

The map above shows that more rain falls in the east of the country and this gradually decreases towards the west, with very little rainfall and semi-desert areas on the west coast. The eastern coastal areas are affected by moist, warm air moving in from the Indian Ocean in the east and south-east.

In the north-west of the country, many places receive below 200 mm of rain per year, whereas the eastern Highveld region receives rainfall in the range of 601 to 800 mm per year.  The interior of the country receives rainfall in the range of 201 to 400 mm per year.

The amount of annual rainfall impacts on the farming practised in different regions, for example, most crops cannot grow well in areas with less than 400 mm of annual rainfall, without being irrigated. Therefore, the western regions of South Africa are more suitable for livestock farming and the eastern regions are generally more suited to crop farming.
 


Sheep Farming in the Karoo
 
  
Carrot Crop
 

The highest rainfall areas in South Africa are in the mountains of the South-west Cape and the Drakensberg, where the annual rainfall can reach 3000 mm in some places. The moisture-laden air that forms over the mountains results in the high rainfall in these areas. The highest ever rainfall recorded in one year (1950) was 3874 mm, in Jonkershoek in the Western Cape.

Rainfall Regions in South Africa

In South Africa, it usually rains only in summer, or only in winter, with most of the country, in particular in the interior, receiving only summer rainfall. Some areas of the south-east and north-east coastlines receive rain throughout the year.  

The map below shows that the country is divided into the following main rainfall regions:

  • Summer rainfall region
     
  • Winter rainfall region
     
  • Rain throughout the year
     
  • Dry regions (arid region and very dry region) – very little rain

Summer Rainfall Region


Thunderstorm

The summer rainfall areas receive rain right up until autumn. This area covers most of the interior of the country and occurs due to warm, moist air being drawn into the north and north-east in summer months. The hot temperatures cause the Earth’s surface to heat up, resulting in upward air currents (convection). As the hot air rises, it then cools down and forms large clouds which bring rain.

Moderately heavy rain will fall and can last for several days. Thunderstorms with short heavy downpours and thunder and lightning storms occur frequently. Hail can also accompany these storms and cause damage to vehicles, buildings, vegetation and crops.

Areas in the summer rainfall region do not receive the same amount of rain, with the east being much wetter than the west. This is due to the air that is blown across the escarpment from the east, which contains a lot of moisture.

To the west, the air does not contain as much moisture, and so it becomes increasingly drier the further west you go, where there are areas with very little or hardly any rainfall.


 

The graph above shows that Johannesburg receives most of its rain in the summer months, mainly from October to March, and very little in the winter months of May, June, July and August.

Winter Rainfall Region

The winter rainfall area is a small area on the western and south-western coasts of the Western Cape.

The climate in this area is Mediterranean, and in winter, snow can often be seen on the mountains of the Cape.


Storm Across False Bay, Cape Town
 

The rainy season is from May / June to August / September with minimum rain for the rest of the year. The type of rainfall is cyclonic, which occurs when two air masses of different temperatures meet. As the different air masses cannot mix, the warmer air rises above the colder air and forms clouds that produce rain. These different air masses are caused by the two ocean currents that meet, the cold Benguela current and the warm Aghulas current.

Cold fronts from the Atlantic Ocean bring winter rain to the Western Cape. The amount of rainfall in the winter rainfall area varies greatly from place to place and is influenced by the regional topography (the mountains and plains). Clouds form over the mountainous areas, for example, from a south-easterly wind and bring rainfall.

In some areas, there is more than 2000 mm of annual rainfall, while in other areas, for example, slightly further up the coastline, some places only receive around 300 mm of rain per year.


 

The average monthly rainfall graph for Cape Town above shows that most of the rain in Cape Town falls in the winter months, mainly from May to August and very little rain falls from November to March.

Rain Throughout the Year

The south-east coastline of South Africa, from Mossel Bay in the Eastern Cape to northern KwaZulu-Natal, receives rain all year round, during every season. In some areas, this may be more in summer than in winter and vice versa.

The consistent rainfall in this coastal region is due to the winds formed from the warm Mozambique and Agulhas currents, which are blocked by the escarpment and forced upwards.

The type of rainfall in this region is known as relief rain and usually occurs in coastal areas where hills or mountains and form a barrier along the coastline, so air condenses over the mountains and forms clouds that create rain.

In some areas, the difference in the amount of rainfall between summer and winter is not great, with similar amounts falling throughout the year.


 

The average monthly rainfall graph for George above shows that there is rain throughout the year in George, with only a small difference between the maximum and the minimum rainfall seasons.

The Dry Regions

To the west part of South Africa, the arid and very dry regions occur. Rainfall in most areas is less than 200 mm, making the growing of crops without irrigation, very difficult.

The cold Benguela current from the Atlantic Ocean influences the lack of rainfall in this area. The cold ocean current causes cold air above the sea with very little moisture. Fog forms on the west coast but there is very little rainfall.

When there is rainfall, it is infrequent and often in the form of thunderstorms, which bring little rain.

There is limited vegetation in these areas due to lack of rainfall.


 The Arid Karoo

 

The average monthly rainfall graph above is for Upington on the banks of the Orange River in the Northern Cape. The town is situated in an arid area with an average annual rainfall of around 189 mm. The little rainfall that the town gets is mainly in autumn and winter, from April to August.

ACTIVITIES

Activity 1

Rainfall Regions of South Africa

Activity 2

Making a Rainfall Graph
  1. Make a bar graph of the rainfall in millimetres in the table below to show the average monthly rainfall for Richards Bay, using the graph paper provided and a suitable scale.

    Months Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec
    Rainfall in mm 172 167 107 109 109 57 60 65 77 105 114 86
    Click here to download the graph paper.
  2. What is the average annual rainfall for Richards Bay?

  3. Locate Richards Bay on your atlas. Which rainfall area does Richards Bay fall into – summer, winter or all year?

  4. Describe the rainfall pattern in Richards Bay.

Activity 3

Rainfall Regions in South Africa
  1. For each of the rainfall regions in South Africa listed in the table below, list the area that falls within that region.

    Rainfall Region Area in South Africa
    a. Winter rainfall area
    b. Summer rainfall area
    c. Rain throughout the year area
  2. In which rainfall regions would you experience the following types of rain?

    Type of Rain Rainfall Region
    a. Cyclonic rainfall
    b. Thunder showers
    c. Relief rainfall
  3. Use your atlas to look up the towns in the table below and decide if they are summer, winter, all year rainfall or dry / arid.

    Town
    Summer Rainfall
    Winter Rainfall
    All Year Rainfall
    Arid / Very Dry
    a. Durban
    b. Polokwane
    c. Cape Town
    d. Pretoria
    e. Port Elizabeth
    f. Springbok
    g. Port Nolloth
  4. Print the blank map below and colour in the rainfall regions. Use a different colour for reach region and insert a key.

  5. Which rainfall region do you live in?

Activity 4

Average Annual Rainfall in South Africa

Study the map below and answer the questions that follow.

  1. Using your atlas and the map above, decide which of the following places receive the least rainfall?

    Place The Least Rainfall
    a. Johannesburg or Durban?
    b. Upington or Kimberley?
    c. Mafikeng or East London?
    d. Pretoria or Polokwane?
  2. Using your atlas and the key on the map, write down the amount of rainfall that the towns and cities in the table below receive on average every year.

    Place Amount of Annual Rainfall
    a. De Aar
    b. Bloemfontein
    c. Saldanha Bay
    d. Port Shepstone
    e. Pietermaritzburg
    f. Midrand
    g. Port Nolloth
  3. Study the two rainfall graphs of Durban and Alexander Bay and answer the questions that follow.

    1. Which place has the most rainfall in a year?

    2. In which season does the most rainfall fall in Durban?

    3. What do you notice about the rainfall in Alexander Bay in October and November?

    4. Which rainfall areas do these places fall into?

      1. Durban:
      2. Alexander Bay:
    5. Refer to the map scale in the rainfall map of South Africa and identify how much annual rainfall these places receive.

      1. Durban:
      2. Alexander Bay:
    6. What influences the amount of rainfall in each of these areas?

      1. Durban:
      2. Alexander Bay: