What’s the climate like over there in Tibet?
Unique plateau climate
Due to the unique and diverse topography, high-altitude air environment and weather system of the Tibetan 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 also various regional climates and obvious vertical climate zones.
(1) The air is thin, the air pressure is low, and there is little oxygen. The density of air at sea level at zero degrees Celsius is 1292 grams per cubic meter, and the standard air pressure is 1013.2 milligrams. The air density and pressure values in plain areas are almost the same as those at sea level. In Lhasa City, which is located on the Tibetan Plateau (3,658 meters above sea level), the air density is 810 grams per cubic meter, and the annual average air pressure is 652 milligrams, which are 62.64% and 64.35% of those in the plain area, respectively, which is one-third less than that in the plain area. . Oxygen is relatively abundant in plain areas, with 250-260 grams of oxygen per cubic meter of air. The Tibetan Plateau only contains 150-170 grams of oxygen per cubic meter of air, where the temperature is the lowest in summer. Especially in northern Tibet, the temperature in July in summer is below 8 degrees Celsius in large areas.
From the perspective of temperature difference, Tibet has particularly obvious characteristics of small annual temperature range and large daily temperature range. The annual temperature range in Lhasa, Qamdo, Shigatse and other places is 18-20 degrees Celsius, while that in Wuhan and Nanjing with similar latitudes is 26 degrees Celsius. The annual average daily range is 14-16 degrees Celsius in Lhasa, Qamdo, Shigatse and other places, while it is only 7 degrees Celsius in Chengdu, Changsha and Nanchang. The diurnal range of Tingri reaches 18.2 degrees Celsius, which is about 2.5 times that of Nanchang, which has a similar latitude. At an altitude of more than 5,000 meters in the Ali region, the daytime temperature in August in summer can reach over 10 degrees Celsius, and the nighttime temperature drops below zero degrees Celsius. In Lhasa, Shigatse and other places located in the Brahmaputra Valley, the maximum temperature at noon in June can reach 27-29 degrees Celsius, giving people a feeling of midsummer; in the evening the temperature drops, and people feel the coolness of autumn; at midnight the temperature drops to 5 degrees Celsius, and the temperature drops to 5 degrees Celsius all night Everyone must cover themselves with quilts; after sunrise the next morning, the temperature rises, giving people the feeling of spring again. It is true that "although there are four seasons in a year, be prepared for cold weather all year round."
Tibet has small annual temperature range and large daily temperature range, which is a favorable climate condition. The annual range is small, the winter temperature is not too low, and overwintering crops below a certain height can successfully survive the winter, and winter wheat, highland barley and other crops can be planted in large areas. The diurnal range is large and the temperature is high during the day, which is conducive to photosynthesis of plants; the temperature is low at night, which can reduce the respiratory loss of plants and is conducive to the accumulation of plant nutrients.
(4) The dry season and the rainy season are distinct, with many nights of rain. Because the winter westerly and summer southwest monsoon have different origins, properties, and control times, the seasonal distribution of precipitation across Tibet is very uneven, and the distinction between the dry season and the rainy season is very obvious.
Every year from October to April of the following year, there is a westerly jet stream over the Tibetan Plateau, and the ground is controlled by cold and high pressure. It is dry and windy, with low temperatures and little rain and snow. The precipitation only accounts for 10-20% of the annual precipitation. For example, the precipitation in Lhasa from October to April of the following year only accounts for 3% of the annual precipitation, so it is called the dry (dry) season or windy season.
From May to September, the near-surface layer of the plateau is controlled by thermal low pressure, and the southwest monsoon reaches the plateau. Under its control, rainfall is very concentrated in various parts of Tibet, 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 annual precipitation, so it is called the rainy season or wet season. In the rainy season, there are many nights of rain, thunderstorms and hail. Night rain mainly occurs in various parts of southern Tibet, accounting for more than 80% of the rainfall in the rainy season. Thunderstorms and hail are frequent in the rainy season on the Northern Tibetan Plateau. For example, Nagqu, Suoxian and other places 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 Tibetan Plateau has the highest number of days with hail falling in the country. Nagqu has an average of thirty-five hail days per year. In 1954, there were sixty-four hail days, which is rare in the world.
(5) The climate type is complex and the vertical changes are large. The terrain of Tibet is high in the northwest and low in the southeast. The northern Tibetan plateau is 4,500-5,000 meters above sea level, and the southeastern Tibetan valley is below 1,000 meters above sea level. Its climate characteristics are divided from southeast to northwest: tropical mountain monsoon humid climate - subtropical mountain monsoon humid climate - plateau temperate zone monsoon semi-humid and semi-arid climate - plateau subarctic monsoon semi-humid, semi-arid and arid climate - plateau frigid zone monsoon drought climate and other various climate types.
In the alpine canyon areas of southeastern Tibet and the southern slopes of the Himalayas, from bottom to top, due to the repeated rise of the terrain, the temperature gradually drops, and the climate occurs vertically from tropical or subtropical climate to temperate zone, cold temperate zone and frigid zone climate. change. The natural scenes of hot, warm and cold zones can only be seen in plain areas thousands of kilometers apart from south to north, but here from low to high they appear within a horizontal distance of only tens of kilometers. It is true that "a mountain has four seasons. The sky is different even if it’s ten miles apart.”
From the distribution of climate types, areas in southeastern Tibet and the southern slopes of the Himalayas below 1,100 meters above sea level have a tropical mountain monsoon humid climate. The average temperature in the warmest month here is above 22 degrees Celsius, and the average temperature in the coldest month 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. It is the area with the most rainfall in Tibet and one of the rainiest areas in the country. The forest here is lush and evergreen all year round. Various tropical plants grow luxuriantly, vines are intertwined, and wild plantains, wild lemon groves and bamboo groves are all over the mountains and plains, forming a beautiful tropical scenery.
Tropical cash crops can be grown here, and the crops are harvested three times a year.
The above-mentioned areas with an altitude of 1100-2500 meters have a humid subtropical monsoon climate. The average temperature in the warmest month is 18-22 degrees Celsius, and the annual precipitation is about 1,000 mm. It is warm all year round, with abundant rainfall. Subtropical evergreen broad-leaved tree species grow, and crops are harvested twice a year.
The Brahmaputra Valley north of the Himalayas and south of the Gangdise Mountains and Nyenchen Tanglha Mountains has an altitude of 500-4200 meters and has a plateau temperate monsoon semi-humid and semi-arid climate. The average temperature in the warmest month is 10-18 degrees Celsius, and the annual precipitation is 400-800 mm. It can grow wheat, highland barley, potatoes and other cool-loving crops and temperate fruit trees. The crops ripen once a year.
The lake basin area in the southern part of the Northern Tibetan Plateau, north of the Gangdise Mountains and the Nyainqentanglha Mountains, has an altitude of 4200-4700 meters and has a semi-arid and arid climate in the plateau subarctic monsoon. The average temperature in the warmest month is 6-10 degrees Celsius, and the annual precipitation is 100-300 mm. It is a prairie in Tibet and is dominated by animal husbandry.
The area in the northern Tibetan Plateau at an altitude of 4,700-5,500 meters has a plateau frigid monsoon arid climate. The average temperature in the warmest month is below 6 degrees Celsius and the annual precipitation is 100-150 mm. It is a vast natural pasture. Areas above 5,500 meters above sea level are covered with snow all year round, making it a world of ice and snow like crystal beads and broken jade.