Seasons, climate resources and rivers

In Uzbekistan seasons are determined not by the calendar but by the mean daily temperature: spring begins when the mean daily temperature rises above +5°C and summer when it rises above +20°C; autumn begins when it falls below +20°C and winter when it falls below +5°C. So spring begins in February, summer from the end of May lasts about five months, and true autumn comes from October. In winter the weather changes quickly; the coldest 40 days are called the “winter chilla” (25 December to 5 February) and the hottest 40 days the “summer chilla” (25 June to 5 August). In spring about 40 percent of annual precipitation falls, sometimes in downpours that bring mudflows at the foot of mountains; 21 March, when day and night are equal, is Navruz. Climate resources: 225–266 days are frost-free, the sum of temperatures above +10°C is 4500–5900°C and the Sun shines 2500–3000 hours a year. This allows fine-fibre cotton, melon, watermelon, grapes and fruit to be grown, and makes the use of solar and wind energy possible.