If by dry you are referring to a desert, it receives less than 10 inches (250 mm) of rainfall per year on average.
Cape Town receives winter rainfall because it has Mediterranean Climate. In Mediterranean Climate, summers are hot and dry and winters are wet.
Africa is an expansive continent and climate varies from hot humid tropic jungle with daily rainfall to dry deserts that receive almost no rainfall. See related links
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Dry climate regions include arid and semiarid climates. They get less than 30 millimeters of rainfall per year.
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Some sort of desert.
Savannas and grasslands are generally considered as semiarid. They are dry but receive more rainfall than a desert.
The Atacama has a cool and very dry climate. Some areas have received no rainfall in historic times.
Hot and dry most of the year and there is barely any rainfall
One major feature of the Mediterranean climate is hot, dry summers with mild, wet winters. This climate is characterized by its distinct seasonal pattern of rainfall and temperature.
Zero. The Dry Valleys are generally below freezing temperature, so whatever moisture may blow into them from the Polar Plateau will be ice crystals.
Plants in certain rain forests require certain adaptation due to the amount of rainfall received and the seasonality of the rainfall. For example rainforests in sub-tropical region receive seasonal rainfall, this means that when it rains (in the wet season) it pours, but there is also a "dry" season where it still rains, but much less. For this reason the plants have to be adapted to be able to survive in both conditions. Equatorial rainforests receive pretty much constant rainfall throughout the year, so the plants are adapted for this