Desert climate (BWh/BWk in Köppen) is characterised by extreme aridity (<250 mm/year) and clear skies producing diurnal temperature ranges of 20–30 °C. Hot deserts (BWh: Sahara, Arabia) reach 50+ °C by day; cold deserts (BWk: Gobi, Patagonia) drop below −30 °C in winter.
In Spain, Almería and Cabo de Gata are closest to desert climate (200 mm/year). Subtropical subsidence is the main cause of desert aridity.