Abstract

JURY, Mark R. Climate trends in the Cape Town area, South Africa. Water SA [online]. 2020, vol.46, n.3, pp.438-447. ISSN 1816-7950.  http://dx.doi.org/10.17159/wsa/2020.v46.i3.8654.

Climatic conditions near Cape Town, South Africa (34°S, 19°E) are analysed for historical trends in station measurements in the 20^th century and in modern satellite-blended datasets. Despite the variety of datasets and record lengths, all show a steady drying trend. Faster rates of warming, 0.1°C∙yr^-1, are found in land surface temperatures during the period 2000-2017. Drying trends are most acute to the northwest of the Hottentots Holland mountains. Hydrology station measurements in the Upper Berg River catchment since 1956 reveal a decline in streamflow of −0.012 m³∙s^-1∙month^-1, and an upward slope in potential evaporation of +0.020 W∙m^-2 ∙month^-1. Rainfall has declined most in May and September, indicating a shorter winter wet season. Features supporting the drying trend include an increase of easterly winds and low-level subsidence during summer. The clockwise circulation trend around Cape Town entrains dry air from the Karoo interior and the south coast upwelling zone, leading to negative sensible heat flux, a capping inversion and diminished orographic rainfall.

Keywords : Cape Town; climate trend; water deficit.

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