Cause of drought shifts
SCIENTISTS: HUMAN INFLUENCE CHANGES WAY WATER CYCLE WORKS
Cape Town’s Day Zero is in a new category: a ‘human induced drought’.
There’s growing concern in South Africa about what’s being portrayed as “a national drought disaster”. There have been suggestions that drought could see many cities and towns facing Day Zero. This happened during the water crisis in Cape Town as fears mounted that the taps would run dry.
Concerns were reinforced when it was announced the tunnels that bring water from the Lesotho Highlands Water Scheme to the country’s economic hub, Gauteng, would be shut for a few months. From a technical perspective, the threat has been exaggerated. In summer rainfall areas, there has been a slow start to the rainy season. And while dam levels are lower than last year, they’re not at critical levels. An analysis of the Integrated Vaal River System found no need for water restrictions this summer.
The panicked reaction suggests many people don’t fully understand South Africa’s climate, or how it affects the way the water supply systems work. In particular, there’s limited recognition of the different types of drought and how they affect different sectors of society.
For example, dry periods can devastate agriculture without affecting water supplies to cities and industries. Plants in fields and livestock grazing on natural pasture depend on moisture in the soil’s top layers. Cities and towns have large reserves of water in dams or tap it from aquifers, which are effectively underground reservoirs.
It would be wrong to suggest there are no drought problems at present. Parts of the Northern, Western and Eastern Cape are officially in drought. This means prolonged dry conditions are seriously threatening farming activities. But across SA’s 1.2 million square kilometres, there are also areas where rainfall has been well below average for a year or more.
The SA Weather Service’s rainfall map for the 2015-16 season shows a mixture of very dry and very wet areas, some quite close to each other. The 2018-19 season showed the western half of the country much drier than the eastern, and parts of the Northern Cape getting less than 25% of average rainfall.
Climate scientists, hydrologists and disaster management specialists distinguish between three different kinds of drought: a meteorological drought occurs when rainfall is less than average over a significant period, often a month; an agricultural drought is when lack of rainfall leads to a decline in soil moisture affecting pastures and rain-fed crops; and an hydrological drought is when a meteorological drought significantly reduces the water in rivers, lakes and underground.
Currently, except in a few places, there is not yet a hydrological drought in SA. So the immediate problems are those affecting farmers, not municipal water supply.
A meteorological drought is usually simply an alert to warn farmers and water managers to be ready to act in case it continues. Responses to an agricultural drought depend on the kind of farming that is undertaken. Livestock farmers are advised to reduce herds or buy more feed, to compensate for lost grazing. Dry land crop farmers may delay planting or space crops so each plant has a better chance of getting enough water. They may also take out insurance against crop failure. In a hydrological drought, water managers responsible for supplying towns and cities need to implement plans to restrict water use as storage levels decline.
A group of international academics point out that human action has changed the way the water cycle works by damming and diverting rivers and pumping water from underground. They argue that human influence is as integral to drought as climate variability. Drought research should no longer view water availability as a solely natural phenomenon and water use as a purely socio-economic phenomenon, and instead consider the multiple interactions between both.
From this perspective, Cape Town’s Day Zero would fall into a new category: a “human induced drought”. And, if the citizens of Gauteng don’t heed the warning to reduce water use to what the Integrated Vaal River System can provide over the next five or six years, they might also suffer a “human induced drought”.
As the World Water Council puts it: the crisis is not about having too little water to satisfy our needs, it’s about managing water so badly that billions of people – and the environment – suffer.
Mike Muller: Visiting Adjunct Professor, University of the Witwatersrand. – Republished from TheConversation.com
Many don’t fully understand SA’s climate