Dealing with drought
By Jamie Goode | 12th November 2020
As of the beginning of October 2020, the six main dams in the Western Cape were 99.5% full for the first time in five years, after a winter of good rainfall. The worst drought in over a century seems to be over – for now.
This is a part of the world not unused to droughts. The Western Cape has a Mediterranean-style climate, with dry summers followed by short but wet winters. There’s a lot of climatic variation here that has to do with the El Niño Southern Oscillation that affects the Pacific Ocean. There are two phases: the colder La Niña, and the warmer El Niño. It’s the latter that is associated with drought, as the weather systems that would normally bring rain to this tip of Africa end up depositing their precious cargo out at sea, rather than where it’s needed.
The drought began in 2015, and thus impacted the 2016 wine vintage (grapes are usually picked in February in South Africa, and so the growing season extends across two calendar years). It ran for three consecutive years, and the levels in the dams dropped lower and lower. After a second dry winter, by May 2017 the drought was declared the worst in a century. Level 4 water restrictions were introduced in Cape Town, restricting people to 100 litres of water per day. [This sounds a lot, but think of how many times you flush the toilet each day, and how much water is used in a shower, let alone other uses such as washing clothes and cars, filling swimming pools and watering plants.] In September, level 5 restrictions came in.
I remember a visit in October 2017 when the water restrictions were very apparent. Showers had to be fast, and taps in public places were restricted to a trickle. Tourism was being impacted. In February 2018 I worked in a winery over vintage we were acutely aware of our water use. At this stage, level 6B restrictions were in place, limiting people to 50 litres a day, and there was talk of Day Zero – level 7 restrictions when municipal water would be shut off. This was set for April 12, but because people stopped using as much water, everything limped on until there were some good winter rains in 2018. Cape Town very nearly became the first major city in the world to run out of water.
The vineyards have been particularly hard hit by these three years. Vines can be quite miserly in their water requirements, and thrive in areas where other plants would struggle. The drought was so bad, though, that some vineyards died, and in those that survived, yields were significantly reduced. The conditions one year can also affect the crop the following year, though: if the vine doesn’t have sufficient reserves going into the next season and the soils are dry in the spring, these can cause also impact yield.
Many of the vineyards of the Cape are irrigated. This can moderate the effects of a drought season. The problem is that this time round, the usual sources of irrigation water were threatened. For many, irrigation is via small privately owned dams, or boreholes. These mostly ran dry. And for others, water comes from the large dams or rivers, which would normally be a steady source of supplementary water. By the time the drought entered its second year, allocations were restricted. Irrigated vineyards also tend to be less resilient: the roots grow where the water is, and with irrigation, this is in the upper layers of the soil – these are the first to dry out.
There are many areas in the Cape where the vines are ‘dry grown’, without any extra water. The advantage these vines have is that they get used to periodic droughts and sink their roots deep. It makes them more resilient, but with this severe once-in-a-century drought they were reaching their limits. The famous hilltop Stellenbosch vineyard that Chris Alheit used to make his Radio Lazarus wine died in the 2018 vintage, after two hard years of drought: 2017 is the last vintage of this wine.
How much water does a vine need? Generally speaking, around 500 mm rain in a growing season is enough. But when it falls matters, as does the soil type. Some soils are good at retaining water (clay and chalk both do this well), whereas others are much freer draining and don’t hold on to it for long (such as sandy or stony soils). Wind increases the rate of evaporation from the leaves, and temperatures are obviously very important: more water is lost on hot sunny days than overcast cool ones. It seems that well-farmed soils with a good amount of organic material are able to retain more water, so the use of cover crops and avoiding the use of herbicides is likely to make a vineyard less prone to drought stress.
And some drought stress can be beneficial, at least for red wines. Top red wines come from vineyards where there is a steady water supply that tapers off after veraison, the point in grape development where the berries change colour and enter the later stages of ripening. This means that the canopies stop growing and the vine concentrates on ripening fruit. But if the stress is excessive, the vine ends up sacrificing the leaves that otherwise would provide some shade for the fruit zone, and the grapes can be damaged by direct sun exposure in hot conditions. Without enough leaves, and enough water to be able to open the stomata, photosynthesis is limited – then, not only is ripening grapes a problem, but also the vine struggles to build up the carbohydrate reserves needed to get the next growing season underway after dormancy.
When I last visited South Africa, in November 2019, the drought was still on peoples’ minds, despite better winter rains earlier in the year. ‘The drought is still taking a toll and it will for the next three, four or five years unless it gets broken properly,’ said Jaco Englebrecht, a consultant viticulturalist. ‘At least we had a better winter in terms of temperatures. The year before we only got 7-10 mm of rain in July. This year we had about 80-100 mm.’ But he says that some areas are still heavily impacted. ‘I was up in Skurfberg last week and they have only had 255 mm of rain in the whole year, where their average is 400. I can still see the effect.’
For many, the drought has been a push to alter farming methods to be better adapted to the dry conditions of the Western Cape. ‘For me, the best thing about the drought has been it might have taken 30% of the last three crops, but what we gained from the drought in knowledge and pro-active farming is worth it,’ says Eben Sadie. Many of the vineyards planted in recent decades have been high-density (with lots of vines, close together) trellised on what is called a vertical shoot position (VSP) system. The VSP creates a canopy that looks a bit like a wall. It’s very efficient and produces good yields, but may be better adapted for cooler climates where there’s less water stress. Sadie thinks that old-school unsupported bush vines might be better adapted to hot, dry conditions. ‘We’ve only been trellising for 100 years,’ he says. I’m more inclined to trust the past 6900 years. If you put vines on a trellis system in our climate it increases your foliage spread. The only thing you put up on plates like that is solar panels. You capture a lot of sun, a lot of energy. But you must do something with that energy. You need more water and nutrients. I don’t view this as sustainable over the long term.’
‘The drought has taught us a lot and we are farming differently,’ agrees Engelbrecht. ‘We are looking differently at how we manage our cover crops. We bought two weather stations for Eben [Sadie, who he works with]. One we set up on the west coast and one on his farm. We also set up soil moisture probes: normally no one sets up soil moisture probes in dryland vineyards, but we want to see how much the cover crop is taking up and what is going on. We started this year, and the weather station has shown us a lot.’
Some varieties are also better suited to very dry conditions. Sadie explains that vines can be isohydric and non-isohydric. The former regulate their stomata well and deal well with warm conditions, while the latter just keep going, and consequently use more water. ‘We must plant isohydric vines,’ he says. ‘Non-isohydric vines is like that guy who at 2 o’clock in the morning is swinging on the chandeliers, partying it hard, going all out. But the next day you don’t see him until 4 in the afternoon. He’s not very productive as a person. Then you have that other friend who at 10 o’clock throws a ninja bomb and he’s out of there. You wake up and he’s done a marathon, he’s done the dishes and he’s made breakfast for everybody. That’s isohydric. Being realistic about tomorrow.’
‘If we look at the drought, Grenache and Mourvèdre were the two varieties that thrived,’ says Johan Meyer, who makes wines in the Swartland. The yields for these varieties weren’t down as much for Syrah. ‘They love the heat.’
Hopefully, now the dams are full, and the soil water is replenished, the 2021 vintage should be a good one. But in this part of the world, droughts are not unusual, and with climate chaos may be more frequent and more severe. It’s a good time to make the vineyards more water efficient, and to think about changes that might increase the resilience of dry-grown vines.