Climate change will crush Western Cape crops

The debate around whether global warming exists is well and truly over, says Dr Stephanie Midgley, a leading scientist in the field of climate change at the University of Stellenbosch. Her most recent research shows that climate change is already having a significant effect on agriculture in the Western Cape – the SA region that scientists predict will be hardest hit by rising temperatures and decreasing rainfall. Anneliese King reports.

What are the likely climate change scenarios? How bad are they really?
Globally, we are looking at least at a 0,4°C rise in temperature over the next 20 years, and around 1,8°C to 4,0°C by the end of the 21st century. It very much depends on international efforts to reduce emissions of carbon dioxide (CO2) and other greenhouse gases. For the Western Cape, the predictions are around 1°C to 1,5°C by the mid-2030s, and possibly as high as 2°C. All the Mediterranean regions of the world, including the Western Cape, will experience reductions in rainfall. Locally, we expect at least a 5% reduction, but it could be as high as 20%.

Tell us about your research into the effects of climate change in the Western Cape?
I looked at 12 weather stations,mainly situated on the Western Cape’s agricultural experimental farms close to the fruit and wine industries. I studied the minimum and maximum temperatures between 1967 and 2000 and found that in this 34-year period there had been an increase in temperature of about 1°C, on average. This is much more than the global average – 0,74°C over the last 100 years – and also the national average.

The Western Cape has shown the most significant warming in the country, and we also found that warming was dependant on seasons. In summer, for instance, it was night temperatures that went up quite significantly, while in autumn, the increase was during the day.

Other research has also pointed to changes in rainfall patterns. It seems our rainy season is getting shorter.
The first rains are starting later, and the rainy season is becoming concentrated into only two months – June and July. These are the kind of changes that will seriously affect farmers dependant on rainfall.

The timing of first rains are critical for grain plantings, so it’s not only volumes of water, but also the timing of rainfall that’s important. While timing is not quite as sensitive for irrigated farming, we remain dependant on rain coming in May and June, and continuing through the winter, so we have enough water for the next summer season’s irrigation.

How will this affect agriculture in the Western Cape?
Decreases in rainfall are serious and warming will affect soil moisture. For irrigated crops we can ensure a sufficient supply of water, but only for the medium term – up to the mid-2030s. For rainfed crops we are looking at faster, more serious effects. Even with mild warming and reduced rainfall, such crops will suffer more quickly than irrigated crops.

The Western Cape already has a water shortage problem without climate change and less rain due to and an ever-increasing urban population. How will this affect agriculture?
There are two sides to the water problem. There is supply-side management which is a government function. It needs to ensure water is available for urban users, for farmers and for what we call the ecological reserve which ensures that river systems stay healthy. So in terms of supply, volumes of water must be available and allocated equitably.

In the Western Cape we rely heavily on dams for our water – for irrigation and urban use. We are getting a new dam that should see us through to 2015 but after that we will need new sources of water. The Department of Water Affairs and Forestry is looking at future options such as recycled water and desalinisation plants at the coast. The other side, however, is demand-side management and this is where farmers come in. It is often said farmers should become more efficient in the way they use water. While some farmers are wasteful with water, on the whole, if you look at the highly intensified export crops in the Western Cape like fruit and wine, we are fairly efficient with our irrigation systems. There is room for improvement, but that option will not release huge volumes of water. People are generally going to have to get a lot more serious about water usage and wastage – both in urban and rural areas.

Should farmers be more concerned about global warming and climate changes?
Absolutely. There is a general awareness of global warming, but I think people are not really informing themselves as well as they should be. If you have a business or a farm, you need to plan in advance. I know there are very pressing challenges which everybody has on a year-to-year basis, especially farmers who work in a very high-risk environment with a variable climate. I often hear them saying “we just need to keep going for the next year or two”. Farmers often tend to think short term, but they need to think more long term if they are serious about planning for climate change. There are ways to adapt.

If we start now we could reduce the more serious impacts quite substantially. People are scared of doom and gloom talk and I understand that, but we need to look at this in a very level-headed way. We need to figure out how we can buffer ourselves and create opportunities in certain parts of the province or in certain sectors as result of climate change.

Is a single percentage point increase in global warming really that significant?
Yes, it is. In global climate systems terminology that’s a lot, especially for crops. We all know that on a day-to-day basis we have wide variations in temperatures, but we are talking here of a mean increase. That means if you wake up at 8am and it is usually 16°C, it will now be 17°C. If you have your lunch at 1pm and it is usually 30°C, it will now be 31°C. That is what it means to have a mean increase of 1°C. If you add up the effects of this on natural systems, there will be a huge impact on water resources and water losses to evaporation, for instance, or transpiration by plants. But it’s not only about mean increases. In the farming sector it is even more important to look at variability and at extreme events rather than just the means. Crops are probably quite capable of handling a 1°C mean increase, but during a heatwave or drought, the impacts are much stronger.

Say for instance there is a threshold of 40°C, but we have two or three days during the season where the temperatures go up to 42°C. This could just be enough to reduce the yield or quality of a crop by a substantial margin. Even just two or three hours of a heatwave at that temperature could destroy an export crop’s quality. So those highs and lows are very important. So are drought spells.

What crops will be most affected by these climatic changes?
Of all the irrigated crops, apples are most probably the most sensitive. They require what we call chilling units. As the temperature starts dropping in autumn, the tree starts sensing that it’s going into winter and basically comes to rest.

This is a very important time in the tree’s life cycle. If it doesn’t get the right signals in autumn, it will continue growing and this will have a very negative effect on the next season’s crop because that’s when the flower buds are forming. So if there has not been enough chilling, you’ll find poor flowering during spring, which will lead to poor fruit quality.

The industry is already battling with this as they have to produce in very warm areas compared to other production areas in the world.  We compete in a market with other production regions that have much colder autumns and winters and don’t have to struggle with this issue. So, with more warming, apple farmers will struggle to maintain yields and quality.

There are of course opportunities to introduce cultivars more resistant to high temperatures that don’t have the same chilling requirements as some of the older cultivars, but of all fruits, apples will be most at risk, particularly in the warmer areas. In Elgin and Grabouw, we are already seeing the effects of warming on apple production. The colder areas like the Koue Bokkeveld probably won’t see any negative effects for a couple of decades still – even with warming.

What about other agricultural sectors?
At this point the real negative effects are only being felt by the pome fruit farmers – apples and pears. Stone fruit and citrus are better adapted to high temperatures, while grapes are also a lot more resistant to higher temperatures and don’t require the amount of chilling that apples do. But when it comes to soil moisture, farmers are starting to pick up the effects of quicker soil drying. And then of course all the farmers relying on rainfall are already struggling.

The most vulnerable areas at this stage are the Swartland and Sandveld along the West Coast where warming has been substantial, and changes in rainfall have been experienced. If you are relying on rainfall, there is not much you can do except change your cultivar or crop or try to find irrigation water. Unfortunately irrigation water is limited and often not an option.

Or leave farming?
Yes. Some people are leaving, while others are buying up land in areas that will probably become more suitable to their crop in the future. There is talk that those farmers worst affected will move eastwards along the coast because predicted rainfall decreases will become less serious as one moves towards the Garden Route and the Eastern Cape.

There may even be slight rainfall increases in these regions, particularly during summer. Water issues in those parts will also be less serious as there is less strain on water resources due to lower demand by urban, industrial and agricultural users, coupled with more evenly distributed rainfall throughout the year.

What can the individual do in the fight against global warming?
Global warming is caused by CO2 and other greenhouse gases released into the atmosphere. In South Africa, as elsewhere, the most significant contributor comes from coal-powered energy plants burning fossil fuels to generate electricity. In South Africa more than 80% of all greenhouse gas emissions come from these stations. Cars also fall into this category, as petrol and diesel are fossil fuels, so all of us can reduce our energy consumption.

The second most important category of CO2 emissions is deforestation that often goes hand in hand with the clearing and burning of land. All the carbon that has been in that forest for so long is suddenly released as CO2 into the atmosphere. While not an issue in South Africa, it is a big contributor globally. Contact Dr Midgley on (021) 808 3939 or 083 652 9062.