The climate of Ethiopia varies mainly according to elevation. The tropical zone below approximately 1,800 m (approximately 6,000 ft) has an average annual temperature of about 27°C (about 80°F) and receives less than about 500 mm (about 20 in) of rain annually. The subtropical zone, which includes most of the highland plateau and is between about 1,800 and 2,400 m (about 6,000 and 8,000 ft) in elevation, has an average temperature of about 22°C (about 72°F) with an annual rainfall ranging from about 500 to 1,500 mm (about 20 to 60 in). Above approximately 2,400 m (approximately 8,000 ft) is a temperate zone with an average temperature of about 16°C (about 61°F) and an annual rainfall between about 1,300 and 1,800 mm (about 50 and 70 in). The principal rainy season occurs between mid-June and September, followed by a dry season that may be interrupted in February or March by a short rainy season.