Increased Risk of “Day Zero” Droughts due to Climate Change

18 November 2020 Mervyn Piesse, Research Manager, Global Food and Water Crises Research Programme

Background

In 2018, Cape Town came within weeks of depleting its municipal water supplies. Years of below average rainfall resulted in less water entering the reservoirs that supply the bulk of its water. By the middle of that year, the reservoirs had declined to about 20 per cent of their capacity. If they had fallen to 13.5 per cent, most of the city’s water supply would have been disconnected, a scenario referred to as “Day Zero”. The population had also increased by 50 per cent over the preceding decade, adding further strain to water infrastructure.

Comment

While population growth, poor water management practices and insufficient spending on water infrastructure worsened the Cape Town water crisis, the 2015-17 drought was the main cause. A recent study published in the Proceedings of the National Academy of Sciences found that climate change increased the risk of that drought occurring by five to six times, compared to the early twentieth century. If global greenhouse gas emissions continue to rise, the likelihood of a drought of similar magnitude occurring by 2100 rises to 80 per cent.

The risk of severe and prolonged drought is also likely to rise in other parts of the world that are undergoing increased rainfall variability. There are at least 17 countries – home to about 25 per cent of the world’s population – that already face extremely high levels of water stress. The climate of southern Australia is expected to undergo shifts similar to those in South Africa. The 2020 State of the Climate report, prepared by the Bureau of Meteorology and CSIRO, indicates that winter rainfall in south-western Australia has declined by 16 per cent since 1970. Over the same time period, rainfall during the wettest part of the year (May-July) has declined by 20 per cent. A similar trend is evident in south-eastern Australia, where April-October rainfall has declined by 12 per cent since the 1990s.

While no major Australian city is at immediate risk of water shortages, several regional and rural towns in Australia were at risk of depleting their water supplies within three to six months at the beginning of 2020. There are several options to improve water security in South Africa, Australia and other parts of the world that are at risk of climate change-induced water shortages. They include: wastewater recycling, the adoption of desalination technology, the construction of surface water dams, groundwater extraction, the adoption of managed aquifer recharge schemes, stricter water demand management and the wider use of more water efficient technologies. As climate change is also expected to lead to higher temperatures, lower surface water runoff and greater surface water evaporation, some of those options are more appropriate than others. For instance, the construction of surface water dams is unlikely to be as effective as other options in a hotter, drier climate.

Without the adoption of measures to prepare and adapt to changing climatic conditions, it is likely that South Africa and Australia will face increased water insecurity over the course of the twenty-first century.

Any opinions or views expressed in this paper are those of the individual author, unless stated to be those of Future Directions International.

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