Climate

Exposed to topography and terrain unique to Xizang and air currents, the climate in Xizang is complicated and diversified. Overall, the Tibetan climate features frigid and dry air in the northwest and warm and humid in the southeast, forming climatic zones (southeast-northwest) such as the tropical, subtropical, plateau temperate, and plateau sub-frigid climatic zones. Giving rising elevation, the southeastern Xizang and the southern slope of the Himalayas see lowering temperature, with the temperature pattern featuring changes of going from tropical/sub-tropical to temperate, cold temperate and cold temperate.

With the rise in elevation, reduced air pressure and density, the oxygen content per-cubic meter of air correspondingly declines. At an elevation of 3,000 meters, the oxygen content is already only 73 percent of that at sea level, declining to 62-65.4 percent at 4,000 meters, 59 percent at 5,000 meters and 52 percent at 6,000 meters.

Dominated alternatively by westerly wind in winter and southwesterly wind in summer, Xizang has a clear distinction between dry and wet days. Generally speaking, the months from October to April are a dry season while the months from May to September are a wet season, with precipitation during the period accounts for some 90 percent of the annual total. Rainfall is unevenly distributed in different places of Xizang, with a remarkable demarcation line between dry and rainy seasons. Annual precipitation amounts to 5,000 mm in the low-lying area in the southeastern part, dropping to 50 mm in the northwest.

There exists great difference in climate between southern and northern Xizang. Under the impact of warm humid air currents from the Indian Ocean, the valleys in southern Xizang enjoy warm and wet weather, with the annual average temperature fluctuating between 8-16 degrees Centigrade at the height of summer and -16 degrees Centigrade in the depths of winter. The northern Xizang Plateau enjoys a continental climate, with the annual temperature staying above zero. However, the icing period extends over the bulk of the year. The "hottest" month is July when the average temperature is only 10 degrees Centigrade, however. The period of June-August features warm weather but more rain at night. Spring is windy. March-October is the ideal season for visits and June-September the best season of all. Receant years see the rise in the number of domestic and overseas people who visit Xizang in winter.

Xizang boasts more solar radiation than any other part of China, about 100 percent or one-third more than in plains at the same latitude. In addition, Xizang enjoys longer duration of sunshine, reaching 3,021 hours annually in Lhasa. However, it is 1,186.84 hours in Chengdu and 1,932.5 hours in Shanghai. The difference in temperature between day and night is enormous in Xizang; however, so far as the whole year is concerned, the seasonal difference is small. Both the annual average temperature and the highest temperature in Lhasa and Xigaze are 10-15 degrees Centigrade lower than in Chongqing, Wuhan and Shanghai, which lie on a closer latitude. The seasonal difference in temperature in Lhasa, Qamdo and Xigaze is 18-20 degrees Centigrade. In the Ngari area, some 5,000 meters above sea level, the temperature in August reaches 10 degrees Centigrade or higher during the day, but falls to below zero at night.