Decreasing rainfall trends are linked to broader changes in the atmospheric and oceanic circulation, including the poleward shift of the Southern Hemisphere moisture corridor between 2015-17, displacement of the jet-stream and an expansion of the semi-permanent South Atlantic high pressure system.
Phase 3 would have been the point at which the City would no longer be able to draw water from surface dams in the Western Cape Water Supply System and there would have been a limited period of time before the water supply system fails.
On 1 January 2018 the City declared Level 6 water restrictions of 87 litres per person per day.
The immediate cause of the water crisis was the extreme drought from 2015-2017 that exceeded the planning norms of the Department of Water and Sanitation.
Research on long-term weather data done by the Climate System Analysis Group at the University of Cape Town determined that the low rainfall between the years 20 was a very rare and extreme event.
The Cape Town water crisis in South Africa was a period of severe water shortage in the Western Cape region, most notably affecting the City of Cape Town.
While dam water levels had been declining since 2015, the Cape Town water crisis peaked during mid-2017 to mid-2018 where water levels hovered between 15 to 30 per cent of total dam capacity.In mid-January 2018, previous Cape Town Mayor Patricia de Lille announced that the City would be forced to shut off most of the municipal water supply if conditions did not change.Level 7 water restrictions, "Day Zero", would be declared when the water level of the major dams supplying the City reached 13.5 per cent.For farmers who get water from the Western Cape Water Supply System, they are metered and monitored by irrigation boards and water user associations.Many farmers also join shared irrigation distribution schemes (from a specific river flow), and have on-site private storage dams and boreholes.The City of Cape Town implemented significant water restrictions in a bid to curb water usage, and succeeded in reducing its daily water usage by more than half to around 500 million litres (130,000,000 US gal) per day in March 2018.The Cape Town region experiences a Mediterranean climate with warm, dry summers and winter rainfall.The Western Cape Water Supply System relies almost entirely on rainfall, which is captured and stored in six major dams situated in mountainous areas.The dams are recharged by rain falling in the catchment areas, largely during the cooler winter months of May to August, and dam levels decline during the dry summer months of November to April during which urban water use increases and irrigation takes place in the agricultural areas.Phase 1 compromising "water rationing through extreme pressure reduction" was implemented immediately.In Phase 2, post "Day Zero", water would have been shut off to most of the system except to places of key water access.