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202312 Fresh Quarterly Issue 23 09 Keeping Clear Day Zero Web
Issue 23December 2023

Keeping clear of Day Zero

The 2015–2017 drought was a wake-up call for the Western Cape. We need a plan to prevent future water shortages. By Anna Mouton.

Below-average rainfall in 2015–2017 led to the worst drought in the Western Cape since 1904. The rest of the world was gripped by Cape Town’s seemingly unstoppable slide to Day Zero — the day when the taps would finally run dry. We all know that this story has a happy ending. But what happens next time?

Planning for a drier future

Based on historical rainfall data, droughts such as the 2015–2017 event are likely to affect the Western Cape Water Supply System (WCWSS) on average once in every 244–548 years and other parts of the province once in every 14–60 years. But studies have shown that this type of event is now three times more likely due to climate change.

However, low rainfall is not the only driver of drought. “When temperatures rise, you lose more water through evaporation, but you also need more water to meet the transpiration demands of your crops,” explains Dr James Cullis, Technical Director at Zutari. Zutari recently completed a 15-year Integrated Drought and Water Response Plan for the Western Cape Government.

Cullis says the consensus is growing that the Western Cape will become drier on average. “That doesn’t mean we’re not going to have floods. It could be drier on average, but we could still have big wet years, and when the rain comes, it will likely be more intense.”

Changing rainfall patterns can contribute to droughts even if total rainfall stays the same, adds Anya Eilers, Senior Scientist at Zutari. “The intensity and duration of rainfall have a big impact. Heavier rainfall in shorter periods gives less time for the water to absorb into the soil and groundwater, and more is lost through run-off.”

Although the drought focussed our attention on rainfall — the origin of our water — the demand side is the biggest threat to water security. As populations grow, we have more people who need water, and as living standards improve, individual water use increases. Cullis notes that migration makes this a particular challenge in the Western Cape.

“There won’t necessarily be additional water to allocate to increasing demands, and we’ll potentially start to lose some of the existing availability,” says Cullis. “And it’s also a question of affordability. For example, we can generate fresh water from the sea, but it becomes uneconomical and unsustainable.”

Balancing supply and demand

The award-winning 15-year Integrated Drought and Water Response Plan developed by Zutari for the Western Cape Government is structured around municipal water resource planning. Zutari has done similar work on a national level, evaluating climate impacts on water security for all South African municipalities as part of the CSIR Greenbook, which includes other municipal climate-related risks.

“The Drought and Water Response Plan looked primarily at municipal water security and not necessarily at the needs of agriculture or other industries,” says Eilers, “but we did look at which sources had a potential conflict between agricultural and domestic uses.”

Determining the current and future supply and demand is the first step in water resource planning. “We assessed how much water at what level of assurance of supply we have based on our dams, rivers, and groundwater,” says Eilers.

“The Western Cape has lots of existing dams, but their capacity is limited, and there are not a lot of sites for new dams,” she adds. “So, we need to start looking at other sources such as rainwater harvesting, groundwater, desalination and reuse.”

Exploiting alternative water sources makes economic sense, but Cullis points out that we should also do more with what we have by resolving inefficiencies such as losses from leaks and the impact of alien and invasive plants. Addressing these inefficiencies is far more cost-effective than replacing wasted water with alternative sources.

Nonetheless, rising demand will increase the competition for water. Agriculture uses about 85% of the water in the Western Cape Province, making it the single largest user. When considering only the water in the WCWSS — representing only part of the total Western Cape water supply — nearly a third goes to agriculture, with the remaining two-thirds going to the City of Cape Town and other urban and industrial users.

One of the findings in Zutari’s report is that the WCWSS is already over-allocated by about 29 million m3 or 5% per year. “Possibly more — we don’t know yet,” comments Cullis. “What were considered reliable yields on a 150-year timeframe have to be re-evaluated as a result of the drought. The Department of Water and Sanitation is currently undertaking a study to update the available yield and future water demands for the WCWSS.”

Augmenting the water supply from the WCWSS makes sense, according to a recent World Bank study demonstrating the economic benefits even with more expensive options such as seawater desalination.

A strategy for fruit growers

Agriculture is especially vulnerable to water shortages because it’s at the bottom of the hierarchy when water allocations are made. “Agriculture is seen as more able to adjust to reduce demand than domestic consumption,” notes Cullis. “However, this does depend on the crop type. Many agricultural users, particularly horticulture, are less able to adapt to water restrictions than, for example, cash crops.”

Hortgro recognises water as a critical risk, so they recently approved funding for Zutari to conduct a water status quo assessment and develop a water response strategy specifically for the deciduous-fruit industry.

The project’s first phase will be the status quo assessment of current water resources, use and availability in the different areas, including allocations to different users, planned infrastructure, climate change scenarios, water quality, groundwater, ecosystem health, and alien and invasive plants.

The second phase will incorporate stakeholder inputs to determine risks and opportunities around water resilience.

Zutari will then develop a water and irrigation strategy, including a proposed action plan in the final phase. In addition to sharing the results in a virtual meeting, the outputs will be summarised as a reference guide for stakeholders.

“We want to bring flexible thinking into how the industry manages water,” says Cullis. “The more integrated you are — the more options you have to manage water on the supply and demand side — the more flexible you can be. But we also realise that most farmers are already very aware of the increasing constraints on water availability and use advanced methods to adapt to these increasing environmental stresses.”

He would like to see growers look further than their fruit trees when it comes to water. “There is a strong link between climate resilience and the impact of alien and invasive plants, and agriculture can play a big role in managing that, not only by growers on their own land but also by investing in clearing the catchment and riparian areas.”

The status quo assessment and water response strategy are set to run until September 2024. The project focuses on the Western Cape, but other production areas, such as the Langkloof, will also be included.

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