Farmers’ weather records are a valuable source of data

Farming in South Africa is very dependent on weather, which influences the amount of food and water available to livestock, the success or failure of crops, the potential of veld fires and other factors that are of daily concern to the farming community (Picture: Gowar family) The farm Bassonskloof in the Eastern Cape is situated in the magisterial district of Somerset East in the Kommadagga area, where winter and summer rainfall regions overlap (Picture: Gowar family) The dwelling at which the rainfall has been measured is at the northern foot of the Zuurberg mountain range and was built about 200 years ago. Daily rainfall has been monitored continuously since 1937 except for a five year period when data were mislaid (Picture: Gowar family) The farm covers mountainous area and also extends north of the mountain into the Karoo. The mountain is mainly sour veld comprising of grass and fynbos, while the lower portion is made up of thicket, grass and karoo veld (Picture: Gowar family) River after a period of good rainfall (Picture: Gowar family) If anyone has rainfall or climate data that they would like to archive at SAEON, please contact Victoria Goodall, Data Scientist at SAEON.

- Victoria Goodall, Data Scientist, SAEON Fynbos Node & Mervin Gowar, Bassonskloof Farm

Long-term climate records are extremely valuable, particularly in light of the ongoing investigations, debates, analyses and discussions around the topic of climate change.

Many new research projects include intensive weather monitoring programmes which measure variables such as rainfall, temperature, humidity, evaporation, solar radiation, wind speed and direction, using automated weather stations. However, this intensive monitoring is only delivering data from recent times.

To understand the changes that are happening around us, longer-term data are needed. Some very long-term monitoring projects such as the Jonkershoek streamflow and weather monitoring sites have over 70 years’ worth of rainfall data from a number of different stations within the Jonkershoek valley. However, long-term monitoring sites like Jonkershoek are uncommon and they are often situated a long way from other similar sites.

Farming in South Africa is very dependent on weather, which influences the amount of food and water available to livestock, the success or failure of crops, the potential of veld fires and other factors that are of daily concern to the farming community. Many farmers have been collecting rainfall data for decades, often spanning multiple generations on one farm.

Valuable resource

These data provide an extremely valuable resource for studying the changes in climatic patterns in our country. In order to preserve this valuable source of data, SAEON is archiving rainfall data sets collected by the farming community. These data sets are made publicly available via the SAEON Metacat repository.

The potential for data integration and comparison will become greater as more long-term rainfall records are archived with SAEON. So far, rainfall data from the Eastern Cape, Western Cape and Limpopo are archived with SAEON and many of these will be updated as the recent data are received from the farmers.

Bassonskloof data

An example of one of these data sets was received from the Gowar family from the farm Bassonskloof in the Eastern Cape. The farm is situated in the magisterial district of Somerset East in the Kommadagga area, where winter and summer rainfall regions overlap.

The dwelling at which the rainfall has been measured is at the northern foot of the Zuurberg mountain range and was built about 200 years ago. The farm covers the mountainous area and also extends north of the mountain into the Karoo. The mountain is mainly sour veld comprising of grass and fynbos, while the lower portion is made up of thicket, grass and karoo veld.

Rainfall monitoring began on the farm shortly after EV Gowar bought the farm in 1935 from his father in law. The current owner, Mervin Gowar became the third generation of Gowars to own the farm when he took over in 1975.

Daily rainfall has been monitored continuously since 1937 except for a five year period when data were mislaid. Fortunately rainfall data for this period are available from the neighbouring farm, Glenn Cumming, 5 km east and also situated at the foot of the Zuurberg.

Farming has focused mainly on Merino sheep, Angora goats and cattle, but in the 1970s wheat was planted rather successfully. Wheat is no longer planted, which Mervin attributes to changes in rainfall patterns and input costs.

There is a decline in annual rainfall for both periods over which rain data is available for the Bassonskloof farm (Figure 1). Interestingly, the low point at the end of the 1950s (just above 300 mm) is much lower than the starting point for the curve in 1976 (just below 600 mm), which indicates that the same rate of decline did not continue through the period when the data were lost for Bassonskloof.

We need to look at the Glenn Cumming data to understand what may have happened to rainfall in this period. These data suggest that although inter-annual rainfall remained highly variable there was a trend to increased rainfall over the period when data are missing (Figure 6). This accounted for the good wheat harvests in the 1970s and their subsequent decline as annual rainfall decreased.

The monthly rainfall recorded at the farm since 1937 is very variable from month to month and does not show a strong seasonal cycle (Figure 2). This is confirmed by the lack of association found in the auto correlation plots shown in Figure 3. There is very little significant correlation between the rainfall in successive months, and certainly the plots do not show a strong cyclic pattern. A clear pattern would be expected for rainfall data obtained in a region with clearly defined seasons.

An analysis of the monthly rainfall patterns shows no clear change in seasonality over the years based on the trend lines, shown in Figure 4 and Figure 5. Large rain events have occurred in most months of the year, while there is a greater variability in the rainfall for the early summer months.

In the recent period between 1976 and 2010, January and March show a slight increase in monthly rainfall. February, September, November and December show a declining trend. July is usually a dry month, although the two highest rainfall months occurred in this month in 1979 and 1983. Both instances received special mention in the farmer’s rainfall recording system. No July rainfall total has come close to these levels since 1983.

What is noticeable across the years is the spiky nature of all the monthly graphs – no month seems to be consistently good or bad in terms of rainfall, and in particular for the months of September through to November, a high rainfall month one year is normally followed by a poor rainfall month in that same month the following year.

Importance of long-term monitoring

These analyses highlight the importance of long-term monitoring. Climate data are highly variable, and depending on the time period being analysed, very different trends can be found. Farmers’ weather records such as these, can provide a very valuable source of data spanning many decades.

The longest farm record in SAEON’s archives spans 115 years from near Graaff Reinet. There is the potential for citizen data sets such as these, to be integrated with similar data sets from nearby areas and across the country to allow for both small scale and large scale analyses of the rainfall trends over the past century in our country.

These rainfall data are also useful to researchers and conservation managers who may want local climate data to support their research or decision making. The preservation of these data is critical for ensuring that long-term records are available for scientific research.