Location context
Xizang Autonomous Region is located in the southwest of China, southwest of Qinghai-Tibet Plateau. It spans 26 50' ~ 36 53' north latitude and 78 25' ~ 99 06' east longitude, covering an area of 1.2028 million square kilometers, accounting for about one-eighth of the total area of China, second only to Xinjiang Uygur Autonomous Region.
The widest from north to south is about 1000 km, and the longest from east to west is 2000 km. It is the highest plateau in the world and is known as the "roof of the world". Xinjiang in the north, Qinghai in the northeast, Sichuan in the east, Yunnan in the southeast, Myanmar, India, Bhutan and Nepal in the south and west respectively. The border line is 3842 kilometers long and is an important gateway to the southwest border of China.
Climatic characteristics
Due to the influence of topography, landforms and atmospheric circulation, the climate in Xizang Autonomous Region is unique, complex and diverse. Generally speaking, the climate in the northwest is cold and dry, and the climate in the southeast is warm and humid. So from southeast to northwest, the climate types are tropical, subtropical, temperate plateau, sub-frigid plateau, frigid plateau and so on.
In the alpine valleys and southern slopes of the Himalayas in southeastern Tibet, due to the repeated uplift of the terrain, the temperature gradually drops, and the climate changes vertically from tropical or subtropical climate to temperate, cold temperate and frigid climate.
With the increase of altitude and the decrease of air pressure and air density, the oxygen content per cubic meter of air gradually decreases, which is equivalent to 73% of sea level at an altitude of 3,000 meters, 62% ~ 65.4% at 4,000 meters, 59% at 5,000 meters and less than 52% above 6,000 meters.
Under the alternating control of winter west wind and summer southwest monsoon, the difference between dry season and rainy season in Xizang Autonomous Region is very obvious, and the general dry season is 10 to April of the following year; May to September is the rainy season, and the rainfall generally accounts for about 90% of the annual precipitation. The precipitation in different places is also seriously uneven, and the annual precipitation is gradually reduced from 5000 mm in the southeast lowlands to 50 mm in the northwest.