Tropic of Capricorn - Geography and Environment

Geography and Environment

The Tropic of Capricorn is the dividing line between the Southern Temperate Zone to the south and the tropics to the north. The northern hemisphere equivalent of the Tropic of Capricorn is the Tropic of Cancer.

The position of the Tropic of Capricorn is not fixed, but rather it varies in a complex manner over time; see under circles of latitude for information.

As with the Tropic of Cancer, most places along the Tropic of Capricorn have arid or semi-arid climates, though with the Tropic of Capricorn this unfavourable environmental state is exacerbated by the fact that in Australia and Southern Africa tectonic activity and glaciation have been largely absent since the Carboniferous 300 million years ago, so that the aridity is compounded by extremely infertile soils. This results in a generally scrubby vegetation, with perennial grasslands occurring in less infertile cracking clay soils. In Australia, areas on the Tropic have the most variable rainfall anywhere in the world and thus even the wetter areas cannot be generally farmed since irrigation sources invariably dry up in drought years. In southern Africa, where rainfall is more reliable, farming is possible though yields are low even with fertilisers.

In South America, whilst in the continental cratons soils are almost as old as in Australia and Southern Africa, the presence of the geologically young and evolving Andes means that this region is on the western side of the subtropical anticyclones and thus receives warm and humid air from the Atlantic Ocean. As a result, areas in Brazil adjacent to the Tropic are extremely important agricultural regions, producing large quantities of crops such as coffee, and the natural rainforest vegetation has been entirely cleared. In and west of the Andes, however, the Humboldt Current makes conditions extremely arid, creating one of the driest deserts in the world, so that no glaciers exist between Volcán Sajama at 18˚30'S and Cerro Tres Cruces at 27˚S. Vegetation here is almost non-existent, though on the eastern slopes of the Andes rainfall is adequate for rainfed agriculture.