at a time, and can even soar to . In desert rocky mountains such as the Tibesti in Libya or the Hoggar in Algeria, average highs in summer are slightly moderated by the high elevation and are between at elevation. Daily variations may also be extreme: a swing from has been observed. Typical temperature swings are between . Precipitation in the Sahara Desert is scarce, as the whole desert generally receives less than of rain per year except on the northernmost and southernmost edge as well as in the highest desert mountains. More than half of the desert area is hyper-arid and virtually rainless, with an average annual precipitation below and many consecutive years may pass without any rainfall. The south of the Sahara Desert, along the boundary with the hot semi-arid climate (BSh) of the Sahel, receives most of its annual rainfall during the highest-sun months (summer) when the Inter-Tropical Convergence Zone moves up from the south. Wind- and sandstorms occur in early spring. Local inhabitants protect themselves from the heat, the sunshine, the dry air, the high diurnal temperature ranges and the sometimes dusty or sandy winds by covering their heads, such as the cheche garment worn by Tuareg. History and conservation The Sahara was one of the first regions of Africa to be farmed. Some 5,000 years ago, the area was not so arid and the vegetation might have been closer to a savanna. Previous fauna may be recognised in stone carvings. However, desertification set in around 3000 BCE, and the area became much like it is today. The Sahara is largely undisturbed. The most degradation is found in areas where there is water, such as aquifer oases or along the desert margins where some rain usually falls most years. In these areas, animals such as addaxes, scimitar-horned oryxes, and bustards are over-hunted for their meat. Only one area of conservation is recorded in the Sahara: the Zellaf Nature Reserve in Libya. Ecoregion delineation In 2001, WWF devised Terrestrial Ecoregions of the World (TEOW) "a biogeographic regionalization of the Earth's terrestrial biodiversity". The 2001 regionalization divided the deserts of the Sahara into several ecoregions. The Sahara desert ecoregion included the Sahara's hyper-arid center, and the more humid Saharan mountains and southern, northern, eastern, and western deserts were separate ecoregions. In 2017, the authors of the 2001 system proposed a revised ecoregion system for the Sahara. Two new