What is the environment like in Lhasa?

Unique plateau climate. Due to the peculiar and diverse topography, high-altitude air environment and weather system in Tibet Plateau, a complex and diverse unique climate has been formed. In addition to the general trend of cold and dry northwest and warm and humid southeast, there are various regional climates and obvious vertical climatic zones.

(1) The air is thin, the air pressure is low, and there is little oxygen. At sea level, the air density is 1292g per cubic meter, and the standard air pressure is1013.2mg. The air density and air pressure in the plain area are almost the same as those at sea level. In Lhasa, Qinghai-Tibet Plateau (at an altitude of 3,658 meters), the air density is 8 10g per cubic meter, and the annual average air pressure is 652mg, which is 62.64% and 64.35% of that in the plain area respectively, less than or more than one third lower than that in the plain area. There is plenty of oxygen in the plains, with an oxygen content of 250-260 grams per cubic meter, while the air in Tibet Plateau only contains oxygen 150- 170 grams per cubic meter, with the lowest temperature in summer. Especially in northern Tibet, the temperature is below 8 degrees Celsius in summer and July.

Judging from the temperature difference, the characteristics of small annual temperature difference and large daily temperature difference in Tibet are particularly obvious. The annual temperature difference between Lhasa, Qamdo and Shigatse is 18-20 degrees Celsius, while Wuhan and Nanjing with similar latitudes are 26 degrees Celsius. The annual average daily range of Lhasa, Qamdo and Shigatse is 14- 16 degrees Celsius, while that of Chengdu, Changsha and Nanchang is only 7 degrees Celsius. The diurnal range of heliostats is 18.2 degrees Celsius, which is about 2.5 times that of Nanchang at the same latitude. In places above 5000 meters above sea level in Ali area, the daytime temperature can reach 10 degrees Celsius in summer and August, and the nighttime temperature drops below zero degrees Celsius. Lhasa and Shigatse, located in the Yarlung Zangbo River basin, have the highest temperature of 27-29 degrees Celsius at noon in June, giving people the feeling of midsummer. The temperature drops in the evening and the air is crisp in autumn; At midnight, the temperature drops to 5 degrees Celsius, and the quilt should be covered all night; After sunrise in Rosty Yi, the temperature rises, giving people a feeling of spring. It's really "cold clothes are prepared all year round".

Tibet's small annual temperature difference and large daily temperature difference are favorable climatic conditions. There is little change throughout the year, and the temperature in winter will not be too low. At a certain height, overwintering crops can overwinter smoothly, and crops such as winter wheat and highland barley can be planted in a large area. The diurnal range is large, and the daytime temperature is high, which is beneficial to plant photosynthesis; Low temperature at night can reduce the respiratory loss of plants and is beneficial to the accumulation of plant nutrients.

(4) The dry season and rainy season are distinct, and it rains many nights. Due to the different sources, properties and control time of winter westerly wind and summer southwest monsoon, the seasonal distribution of precipitation in Tibet is very uneven, and the division between dry season and rainy season is very obvious.

Every year 10 to April, the westerly jet is over the Qinghai-Tibet Plateau, and the ground is controlled by cold and high pressure. It is dry and windy, with low temperature and little rain and snow. Precipitation only accounts for 10-20% of the annual precipitation. For example, the precipitation in Lhasa/KLOC from October to April only accounts for 3% of the annual precipitation, so it is called dry (dry) season or windy season.

From May to September, the surface of the plateau is controlled by low pressure, and the southwest monsoon climbs the plateau. Under its control, rainfall in all parts of Tibet is very concentrated, generally accounting for about 90% of the annual precipitation. For example, the precipitation in Lhasa from May to September accounts for 97% of the total precipitation in the whole year, so it is called rainy season or wet season. In the rainy season, there are many nights of rain, thunderstorms and hail. Night rain is dominant in all parts of southern Tibet, which can account for more than 80% of the precipitation in rainy season. Thunderstorms and hail often occur in the rainy season in the northern Qinghai-Tibet Plateau. For example, Naqu and Suoxian have more than 85 thunderstorm days a year, which is the region with the most thunderstorm days at the same latitude in the northern hemisphere. The number of hail days in Tibet Plateau ranks first in China. The average number of hail days in Naqu is as many as 35 days, and it rained for 64 days in 1954, which is rare in the world.

(5) The climate type is complex and the vertical variation is great. Tibet is high in the northwest and low in the southeast. The plateau in northern Tibet is 4500-5000m above sea level, and the valley in southeastern Tibet is below1000m above sea level. Its climate characteristics are divided into tropical mountain monsoon humid climate-subtropical mountain monsoon humid climate-plateau temperate monsoon semi-humid and semi-arid climate-plateau sub-cold monsoon semi-humid, semi-arid, arid climate-plateau cold monsoon dry climate and other climate types from southeast to northwest.

In the alpine valleys and the southern slopes of the Himalayas in southeastern Tibet, from bottom to top, due to the rising terrain, the temperature gradually drops, and the climate changes vertically from tropical or subtropical climate to temperate, cold temperate and frigid climate. From south to north, the plain area shows a natural scene of heat, temperature and cold for thousands of kilometers, while from low to high, it appears within a horizontal distance of only tens of kilometers. It's really "four seasons in one mountain, ten miles different."

According to the distribution of climate types, the areas below 1 100 meters above sea level in southeastern Tibet and the southern slope of Himalayas belong to tropical mountain monsoon humid climate. The average temperature in the warmest month here is above 22 degrees Celsius, and the average temperature in Leng Yue is below 13 degrees Celsius, which is higher than that in eastern China at the same latitude. The annual precipitation is 2,500 mm, reaching 4,495 mm in some places, which is the most rainy area in Tibet and one of the rainy areas in China. Here, the trees are lush, the seasons are evergreen, all kinds of tropical plants grow luxuriantly, vines are entangled, and the wild banana, wild lemon forest and bamboo forest all over the mountains constitute a beautiful tropical scenery. Tropical cash crops can be planted here and harvested three times a year.

These areas are located at an altitude of 1 100-2500m, and belong to subtropical monsoon humid climate. The average temperature in the warmest month is 18-22 degrees Celsius, and the annual precipitation is about 1000 mm. It is warm and rainy all year round. Subtropical evergreen broad-leaved trees grow and crops are harvested twice a year.

The Yarlung Zangbo River basin, north of Himalayas, south of Gangdise Mountain and Nyainqentanglha Mountain, is 500-4200m above sea level, and belongs to the semi-humid and semi-arid climate of plateau temperate monsoon. The average temperature in the warmest month is 10- 18 degrees Celsius, and the annual precipitation is 400-800 mm. It can be used to grow cool crops such as wheat, highland barley and potato and temperate fruit trees, and the crops can be harvested once a year.

The lake basin area in the south of northern Tibet Plateau, north of Gangdise Mountain-Nyainqentanglha Mountain, is 4200-4700 meters above sea level, and belongs to the semi-arid and arid monsoon climate in the plateau sub-cold zone. The average temperature in the warmest month is 6- 10 degrees Celsius, and the annual precipitation is100-300mm. It is a prairie in Tibet, with animal husbandry as its main industry.

The plateau in northern Tibet is 4700-5500 meters above sea level, which belongs to the monsoon dry climate in the cold region of the plateau. The average temperature in the warmest month is below 6 degrees Celsius, and the annual precipitation is100-150 mm. This is a vast natural pasture. The area above 5500 meters above sea level is covered with snow all year round, which is a world of ice and snow with crystal clear as pearls and broken jade.