Botswana has a hot, semi-arid climate dominated by the Kalahari and a strong west-to-east rainfall gradient. Most of the country is classified as hot semi-arid under Köppen, with the driest conditions in the southwest and somewhat higher rainfall in the north and northeast. Rain falls mainly in the summer wet season from about October or November to April, while the dry winter from April or May to September is usually sunny and rain-free. For residents and expats, the main practical issues are heat, water availability, and large day-to-night temperature swings rather than persistent humidity or long periods of cloud cover.