Changing rainfall brings more cattle production to Karoo’s sheep regions
Justin du Toit, a scientist in pasture research at Grootfontein Agricultural Development Institute in Middelburg, spoke to Roelof Bezuidenhout about his analysis of rainfall records in the Central Karoo and how farmers can adapt to climate change.
How WOULD YOU DEFINE A DROUGHT?
Long-term records allow us to build a historical picture of drought in an area. This can be tricky as drought is influenced by many variables, including the amount of rainfall, its timing, run-off, temperature and humidity, season and the environment. However, because these factors are seldom properly recorded, we mostly use weather data, notably rainfall, to define drought. Simply put, drought is an unusually dry period.
Arguably, the best way to classify an area as experiencing drought is by its effects on the ground, such as crop failure, scarcity of drinking water, fodder shortages, reduced stream flow, and plant and animal mortality.
Droughts are, of course, a feature of semi-arid rangelands owing to the high rainfall variability typical of such areas. It’s small wonder that rainfall is a key driver of ecosystem processes, especially vegetation dynamics, in this type of veld.
With climate change, parts of South Africa are predicted to get wetter, others drier. Perhaps more importantly, variation in rainfall is set to increase, and the number of rain days to decrease. This indicates a future of heavier showers when it rains, with longer dry periods between rains. Here, as elsewhere, droughts and storms are predicted to become more intense, the highest temperatures higher, and snowfalls greater.
Some research suggests that our winters will be drier; springs will be mainly drier but in some places wetter; summers will be mainly wetter, except in the far west; and autumns will be drier.
de scri be your current re sear ch at the Agricultural Development Institute
Some climate change studies predict that the eastern Karoo, and areas to the east and north of it, will experience increased rainfall in future. Certainly, the
rainfall here in Middelburg has generally been higher than expected for the past 30 years or so. Since the mid-1980s, the average annual rainfall has been 430mm. Contrast that with the 30 preceding years when the average rainfall was only 350mm.
If we look at the historical rainfall over the past 130 years or so for the region, there is quite strong evidence of an approximately 20-year cycle, and weaker evidence of a longer cycle. This 20-year cycle is well known, and if it holds true, we should be in a dry period at the moment, with rainfall increasing over the next 10 years. But these are only trends in average rainfall; they are not predictions of how much rain we’ll get from one year to the next. In the eastern Karoo, rainfall seasonality has not varied much over the past century. Since the mid-1980s, rainfall has generally peaked in mid-summer, just after Christmas. Before that, in the late 1960s and early 1970s, rains peaked later in the year, as late as mid-March or early April.
Local farmers also say that the rains are coming but at the ‘wrong’ time of the year. In the past, autumn rains were felt to be higher, and were very welcome as they allowed the shrubs in the veld to green up to provide fodder into winter.
Mid-summer rain, on the other hand, increases grass production, sometimes to the point where grasses actually outcompete the bossies [shrubs] and push them out of the system.
Rainfall has also become more concentrated in recent years; in other words the same amount of rain is falling over a shorter season. This is not useful for livestock farmers, as they’d prefer rain to be spaced more evenly over the year.
Middelburg lies roughly on the boundary between the Karoo and the Grassland Biome, and this boundary moves west and east depending on rainfall.
In dry times, grasses die out and shrubs thrive, and the boundary moves east. During wetter times, grasses thrive and the boundary moves west. At the institute, we have examples of some areas that were typical bossieveld [shrub veld] in the 1960s, and have shifted to become grassland with some remains of Karoo vegetation.
have these changes influenced farming systems in the karoo?
As vegetation changes, so do farming practices. The increase in grass has led to an increase in cattle farming over large areas in the Karoo. Where 30 years ago only sheep would have been seen, cattle are now a common sight.
The early 1900s had the densest grouping of very dry seasons. These were difficult times due to the very low average rainfall. Other periods during the century were also dry, at least in certain seasons. For example, spring was very dry in the early 1900s, the 1960s had a clump of very dry summers, and from 1980 to 2000 autumn was often dry.
The high levels of variation and complex causal factors make it difficult to discriminate between natural variation and possible effects of climate change on rainfall.
In future, we’ll most probably still have the same cycles that we’ve always had, but their nature is likely to change to some degree.
What can farmers do to adapt to these changes?
It’s difficult to give advice to farmers on what to expect and how to cope with climate change because of the huge variation in weather patterns. That being said, Australian farmers already live with high variation in weather. What we call a drought, they would call a temporary dry spell.
It may be useful for our farmers to see how their Australian counterparts cope, and perhaps consider adopting their style of management to some extent.
Dealing with drought simply by buying in feed is unlikely to be the answer because of cost. If possible, it’s better to sell animals and then restock following the drought. Of course, the number of animals that can be sold is limited because it’s important to retain on-farm genetics.
One shift that a farmer could make is to retain more animals in good years and sell off more in poor years. This has the advantage of matching stocking rate to food availability, but the downside of disrupting herd and flock management. It’s also problematic in terms of cash flow and taxes.
Other management strategies include increasing fodder reserves (to my mind, spineless cactus is the only real winner here in dry areas) and lowering the stocking rate. With the latter, more food is available to the animals, and the farmer is better able to push through a drought. Decreasing the stocking rate need not mean decreasing productivity; fewer animals performing better can be more productive than more animals performing worse.
In the US, some remarkable work has been done with breeding animals to eat lesspalatable plants. Hopefully there is scope for this in South Africa, particularly if these species increase in number in the future. • Email Justin du Toit at justindu[email protected]
‘ to my mind, spineless cactus is the only real winner as fodder reserve in the karoo’
Rainfall is highly variable in semi-arid regions such as the Karoo, and this largely defines the vegetation dynamics.
Justin du Toit