Abstract
Mounting evidence across South Africa’s southwestern winter rainfall zone (WRZ) reflects consistent drying since ~ 1980, and projected trends suggest this will continue. However, limited evidence exists for changes in the region’s rainfall seasonality. To improve our understanding of these WRZ drying trends, especially within the context of Cape Town’s 2015–2017 “Day Zero” drought, it is necessary to explore long-term rainfall seasonality trends. Thus, we use the longest WRZ meteorological record from the South African Astronomical Observatory (SAAO) in Cape Town to investigate rainfall seasonality shifts during 1841–2020. Consistent with recorded poleward migrations of the subtropical high-pressure belt and mid-latitude westerlies, known drivers behind the drought and drying trends, calculated trends demonstrate strengthening of WRZ conditions, primarily from a later start-date trend leading to a shorter wet-season. Long-term drying trends are quantified for the wet and dry seasons; however, analysis of trend evolution reveals much variability, reflecting that drying has only persisted since ~ 1892. Comparative analyses of the first and last 59 years of 1841–2020 reveal a rainfall decline of almost 10% across both seasons—highlighting that the extreme “Day Zero” drought was not only driven by wet-season rainfall declines. Results demonstrate that these drying trends were consistently driven by a long-term decline in rain day counts and a more recent decline in average rainfall per rain day. Correspondence between our results and projected rainfall seasonality trends suggests the trends we quantified will likely continue; thus, improvements and continuation of existing water conservation and management strategies are imperative for Cape Town.
Highlights
The southwestern region of South Africa’s winter rainfall zone (WRZ; Fig. 1) experienced below-average rainfall during the 2015–2017 April-September winter wet-seasons, which resulted in the worst drought and water shortages across the region since 1904 (Botai et al 2017; Wolski 2018)
Using the South African Astronomical Observatory (SAAO) meteorological record, we present the longest station-based rainfall seasonality record for Cape Town, within South Africa’s WRZ
Our results reflect that rainfall seasonality, expressed here by variables measuring the degree of seasonality and the duration, intensity, magnitude and timing of wet- and dry-season rainfall, has, for 1841–2020, undergone a significant change for some of the variables considered
Summary
The southwestern region of South Africa’s winter rainfall zone (WRZ; Fig. 1) experienced below-average rainfall during the 2015–2017 April-September winter wet-seasons, which resulted in the worst drought and water shortages across the region since 1904 (Botai et al 2017; Wolski 2018). These deficits, which were most pronounced for the autumn (March-May) and spring transition (September-November) seasons, led to supply dam water levels dropping to ~ 20% capacity during May 2018 (Burls et al 2019; Pascale et al 2020). This crisis highlighted that Cape Town is extremely vulnerable to multi-year droughts, which are expected to increase in frequency and magnitude under anthropogenically induced climate change (Otto et al 2018; Mahlalela et al 2019; Pascale et al 2020)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
