The Sahara Desert, as defined by the World Wide Fund for Nature (WWF), includes the hyper-arid center of the Sahara, between latitudes 18° N and 30° N. The vast desert encompasses several ecologically distinct regions. The Sahara Desert ecoregion covers an area of in the hot, hyper-arid centre of the Sahara, surrounded on the north, south, east, and west by desert ecoregions with higher rainfall and more vegetation. 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 edges 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 Intertropical Convergence Zone moves up from the south. 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 ecoregions, the West Sahara desert and East Sahara desert, were designated in the hyper-arid center. The transitional North Saharan steppe and woodlands and South Saharan steppe and woodlands ecoregions were extended towards the central Sahara, and the South Saharan steppe and woodlands was renamed South Sahara desert.