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Growing concern over impact climate change may have on water security

UNCERTAINTY While there is a degree of uncertainty about the net effects of climate change on water availability, rainfall is expected to become more variable, with extreme events such as flooding and droughts increasing

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MIKE MULLER The impacts of climate change on rainfall and water resources are still unclear; however, the proper management of climate variability will assist in the mitigation of climate change

Photo by Creamer Media

7th February 2020

By: Natasha Odendaal

Creamer Media Senior Deputy Editor

     

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As the world scrambles to mitigate the anticipated impact of climate change and global warming and strives to limit the temperature increase to below 1.5 ºC above that of the preindustrial period, solutions to ensure South Africa’s own water secure future need deeper scrutiny.

Many climate change projections are based on probable future outcomes, with some uncertainties; however, the impact of global warming is increasingly starting to show and developing countries, including South Africa, are especially vulnerable to climate variability and change.

Some of the likely scenarios proponents have forecast include flash floods and regional floods, heightened droughts, more intense and more frequent storms, higher temperatures, increases in aridity, rising sea levels and glacier and snow melt, besides others.

The National Climate Change Adaptation Strategy indicates that climate change is likely to increase the frequency and magnitude of many extreme events, which will increase the risk of slow-onset events, such as sea level rise and drought.

“Global warming and related climate changes are increasingly better understood, and there is growing consensus on their likely scale. These are no longer merely potential threats but an inevitable reality,” says University of the Witwatersrand visiting adjunct professor Mike Muller.

“However, the impacts on rainfall and water resources are still unclear.”

South Africa is believed to be at higher risk, owing to its geographical location in the dry subtropics and its socioeconomic landscape, a 2017 Water Research Commission and South African Weather Service Climate Change Reference Atlas shows.

The Long-Term Adaptation Flagship Research Programme (LTAS), which responds to South Africa’s National Climate Change Response (NCCR) White Paper, shows South Africa’s mean annual temperatures have increased at least 1.5 times the observed global average of 0.65 ºC over the last five decades.

The Department of Environment, Forestry and Fisheries-led research programme says this raises the “very real possibility” that, in a world of a 2 ºC temperature change, South Africa could experience changes of 3 ºC.

Council for Scientific and Industrial Research (CSIR) researcher Mavhungu Muthige explains that temperatures within most of the Southern African region are projected to increase between 4 ºC and 6 ºC above the preindustrial average by the end of the century under the low mitigation scenario.

September 2019 was the warmest on record, with last year one of the five warmest years in Earth’s recorded history, CSIR meteorologist Dr Johan Malherbe says.

The six warmest years on record globally since 1880 will be the last six years – 2014 to 2019 – with the peak occurring during the strong El Niño year of 2016.

“We have analysed the data of our reliable long-term temperature stations and there seems to be a tie between 2015 and 2019 being the two hottest years in South Africa since at least 1951,” says South African Weather Service chief scientist Dr Andries Kruger.

Various studies of rainfall and temperature undertaken, going back to 1921 and 1931, show that most of the country experienced significant warming, with signals of significant drying along the far western and southern parts, particularly along the coast, as well as the far north-eastern interior.

Daily rainfall has also become more intense, with signs of increased rainfall in the southern interior, especially during summer.

The National Climate Change Adaptation Strategy also notes that there is evidence that extreme weather events in South Africa are increasing, with heat wave conditions found to be more likely, dry spell durations lengthening slightly and rainfall intensity increasing.

Large parts of South Africa have also been experiencing a serious drought since 2015, resulting in crop losses, water restrictions and impacts on food and water security.

Water Impact

Research continues into how climate variability and climatic extremes are impacting on both water quality and availability, potentially through changes in rainfall patterns, characterised by intense storms, floods and droughts; changes in soil moisture and runoff; and the effects of increasing evaporation and changing temperatures on aquatic systems.

The NCCR White Paper indicates that, while there is a degree of uncertainty about the net effects of climate change on water availability, rainfall is expected to become more variable, with an increase in extreme events such as flooding and droughts resulting in a much more variable runoff regime.

An LTAS study, the ‘Economics of Adaptation to Future Climates in South Africa’, notes that climate change will have a limited impact on water supply at national level, but could be “quite significant” at regional levels, particularly under drier futures.

The NCCR White Paper highlights how downscaled climate modelling suggests that the western and interior parts of the country are likely to become drier, and the eastern parts of the country wetter.

Muller notes, however, that South Africa’s rainfall has always been variable and unpredictable.

“Globally, there is much that is not yet well understood about the overall impacts of climate change on freshwater resources,” he continues.

While the trend of rising temperatures is confidently predicted by forecasters, it is not certain what that temperature increase will do to water availability.

“Although modelling of the impact of increased temperatures on rainfall has been done, there is still considerable lack of clarity in most regions. The effect on river flows and the recharge of underground waters are even less certain.”

One exception is that, in colder regions, the melting of snow and glaciers will first increase and then reduce river flows, first causing floods, then droughts.

“More generally, to understand the impacts of climate change on water supply to large urban communities, we need to be able to predict average rainfall and stream flows to determine water availability and storage requirements, as well as extreme flows and storms, to design infrastructure to withstand them,” he explains.

“The effects of climate change on water availability, as opposed to rainfall, are more difficult to predict because a number of effects combine,” he says.

Hotter temperatures will see more evaporation from the land surface and less water will flow into rivers or seep into the soil; but, if rainfall is more intense, a larger proportion of water will flow off the ground and flood into rivers and dams or infiltrate the soil and recharge groundwater reserves.

Also, as temperatures rise, more water will evaporate and be ‘stored’ in the atmosphere; as a result, when it rains, more is likely to “come down”, faster and more intensely, flooding into the rivers.

In addition, the frequency and intensity of weather systems such as cyclones are predicted to increase, leading to more, and more intense, rainfall.

Tropical cyclones that form over the South West Indian Ocean and reach landfall over Southern Africa are typically associated with flooding in Mozambique, Zimbabwe and South Africa, Muthige notes.

However, he adds that, while tropical cyclones bring much-needed moisture to the region, the expected hike in the intensity of storms will ultimately cause extensive damage and destruction, including damage to water supply and treatment infrastructure.

This will affect supply if the infrastructure is unable to withstand such extreme events.

“These systems, therefore, are sources of both damage, especially along the coast, and much-needed rainfall over large parts of the interior.

“There are many interlinked issues that lead to pressure on the system,” Muthige says.

“The different challenges faced in different places may look like a single crisis. But the fact is that the underlying problems are often not the same,” Muller adds, noting that, while climate change adds to the uncertainties, shortages attributed to extreme weather or climate change are still more often the result of poor management.

“If we focus on managing the variability and uncertainty, we can manage the change; so, it is vital to keep our planning people well resourced and our data up to date, and that we take and implement decisions when needed to address growing demands and increasing risks.”

LTAS research shows that, in general, areas of concern are the isolated systems that are dependent on a single resource, including small farm dams in headwater catchments and water supply schemes for rural towns.

Further, rapid urban growth means that many more places will face similar challenges as they compete with surrounding regions for water.

Muller says that, in most parts of South Africa, reliable supplies can still be provided for urban and industrial water users and irrigation farmers, if storage infrastructure is built with enough capacity to cope with regular dry periods and is properly managed.

“We should not be concerned about dam levels falling and rising. Dams are built to store water in wet periods to draw on when it is needed; they rise in the rainy season and fall when it is dry.

“It is exactly what the dams have been designed for,” he explains. “But we do need to understand how much water can be taken from such systems and when restrictions on use need to be introduced and when systems need to be expanded.”

Cape Town is one area where, owing to its geography and small catchment areas, climate change is predicted to impact on water availability. Nevertheless, the city’s near-Day Zero disaster could possibly have been mitigated had the region developed sufficient infrastructure to withstand a severe drought.

“We may be seeing the effects of climate change there,” he says, referring to predictions that rainfall patterns will move a bit south and potentially fail to reach the city’s small catchment area.

For the rest of the country, data [does not show] much outside the normal variability.

“We know climate change is happening. Global warming is happening – it could affect rainfall, it could affect water availability, but it could be good or bad, or just stay the same,” Muller notes.

This is why a focus on managing climate variability is the best way of addressing the potential impacts of climate change on the water sector.

“This is the best way forward to deal with any uncertainties.”

Muthige agrees with this view; he says that infrastructure development and water storage and spatial planning, besides others, are increasingly important, with enough information available to start planning around climate change and developing climate-smart cities.

Edited by Martin Zhuwakinyu
Creamer Media Senior Deputy Editor

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