Editing IPCC:AR6/WGI/Chapter-10 (section)

==== 10.6.2.2 The Region’s Climate ====

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An evaluation of the relative role of rainfall and temperature signal in the 2015–2017 hydrological drought gives a strong indication that lack of rainfall was the primary driver ( [[#Otto--2018|Otto et al., 2018]] ) leading to the 2018 water crisis. Thus, the remainder of this section focuses on rainfall. [[IPCC:Wg1:Chapter:Chapter-11#11.6|Section 11.6]] offers a discussion of African drought over broader areas, including mechanisms relevant to them.

Cape Town is located at the south-western tip of Africa, within an approximately 100 km × 300 km region that receives 80% of its rainfall during the austral winter (March to October), with the largest portion in June to August. In the vicinity of Cape Town, rainfall is strongly heterogeneous, ranging from about 300 mm/year on coastal plains to &gt;2,000 mm/year in mountain ranges. The Cape Town water supply relies on surface water reservoirs located in a few small mountain catchments (about 800 km <sup>2</sup> in total). The Cape Town region receives 85% of its rainfall from a series of cold fronts forming within mid-latitude cyclones. The remainder is brought in by infrequent cut-off lows that occur throughout the year ( [[#Favre--2013|Favre et al., 2013]] ). This creates a very strong water resource dependency on a single rainfall delivery mechanism that may be strongly affected by anthropogenic climate change ( [[IPCC:Wg1:Chapter:Chapter-4|Chapter 4]] and [[#10.6.2.6|Section 10.6.2.6]] ).

The 2015–2017 drought had strong low-rainfall anomalies in shoulder seasons (March to May and September to November, though weaker in the latter), and average rainfall in June and July ( [[#Sousa--2018a|Sousa et al., 2018a]] ; [[#Mahlalela--2019|Mahlalela et al., 2019]] ). The anomaly resulted from fewer rainfall events and lower average intensity of events. The anomaly was strongest in the mountainous region where the water supply system’s catchments are located ( [[#Wolski--2021|Wolski et al., 2021]] ).

Although the 2015–2017 drought was unprecedented in the historical record, the Cape Town region has experienced other droughts of substantial magnitude, notably in the 1930s, 1970s and more recently in 2000–2003. Long-term (&gt;90 years) rainfall trends are mixed in sign, location-dependent, and weak ( [[#Kruger--2017|Kruger and Nxumalo, 2017]] ; [[#Wolski--2021|Wolski et al., 2021]] ); mid-term (about 50 years) trends are similarly mixed in sign ( [[#MacKellar--2014|MacKellar et al., 2014]] ). In the south-western part of the region, rainfall is mostly decreasing in the post 1981 period, particularly in December–January–February and March–April–May, although there is no trend or a weak wetting in June–July–August ( [[#Sousa--2018a|Sousa et al., 2018a]] ; [[#Wolski--2021|Wolski et al., 2021]] ). Rainfall trends of similar magnitude and duration to the post-1981 trend accompanied previous strong droughts in the region ( [[#Wolski--2021|Wolski et al., 2021]] ).

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