The Western Cape province in South Africa experienced overall below average rainfall over the period 2015-2017. This led to the worst drought since 1904 and an unprecedented water shortage in the region. The capital city of the region, Cape Town was particularly affected by this rainfall deficit impacting the area directly surrounding the six large reservoirs that provide fresh water to the city of Cape Town and its ~3.7 million residents. The water crisis was so extreme at the beginning of 2018 that the city of Cape Town was expected to run out of water (“day zero”) in March 2018 (the extreme measure was ultimately averted).

This study used observed records and climate model output to assess the contribution, if any, of anthropogenic forcings to the frequency and severity of the event. The main factor behind the drought and the consequent water shortage was below-average rainfall rather than surface evaporation caused by high atmospheric temperatures. All the climate models used in the study (among which NCAR-DOE CESM) show the likelihood of droughts like the current one, although still very rare, will increase with further warming: the return time of such event is currently more than 100 years, but climate change has increased its likelihood more than three-fold already, compared to a pre-industrial climate, and the trend toward more frequent event of this type will continue in the future, tripling again the likelihood of such events under an additional degree of warming compared to present.