Pamir Plateau | in July 2021 Source: Fu Yunfei
Introduction
Recently, there have been views that warming, rising sea levels, and shifting precipitation lines to the north are beneficial and harmless to many continental countries, including China. At the end of July, "Taklamakan Desert Flood" appeared on the hot search, and many netizens even issued the feeling of "the northwest water and grass have recovered, the desert has become plugged into Jiangnan, and China has returned to the Han and Tang Dynasties".
Why did extreme rainstorm fall in southern Xinjiang, which has always been dry and rainy? Does this indicate that Northwest China is experiencing warm humidification? If so, will the desert become an oasis? Will the ecological environment change retroactively?
"Intellectuals" interviewed Zhang Junlan, chief forecaster of Xinjiang Meteorological Bureau, He Qing, researcher of Urumqi Desert Meteorological Research Institute of China Meteorological Administration, Zhou Tianjun, researcher of Institute of Atmospheric Physics, Chinese Academy of Sciences, Chen Yaning, researcher of Xinjiang Institute of Ecology and Geography of Chinese Academy of Sciences and director of State Key Laboratory of Desert and Oasis Ecology, and Zhang Qiang, chief engineer of Gansu Meteorological Bureau and director of Key Open Laboratory of Drought Climate Change and Disaster Reduction of China Meteorological Administration, to interpret the above issues for the public from the perspective of scientific research.
Interview | Feng Hao
Written | Feng Hao
Responsible editor| Chen Xiaoxue
● ● ●
Why are there floods in desert areas?
Intellectual: In mid-to-late July this year, floods occurred in parts of the desert in southern Xinjiang. Why?
Zhang Junlan: There are three causes of flooding in the Xinjiang desert, one is the convergence of flash floods caused by heavy precipitation and heavy rain in the mountains of southern Xinjiang, the second is the melting of snow (ice) in high mountains due to heating and sustained high temperatures, and the third is the mixed flood of heavy rain and melted snow (ice) in the upper mountainous areas. It can be seen that desert flooding is not caused solely by local precipitation in desert areas.
"Intellectuals": From the perspective of precipitation, what are the characteristics of southern Xinjiang this year?
Zhang Junlan: This year,s weather and climate in southern Xinjiang are relatively abnormal, and extreme precipitation events occur frequently.
From March to July, the frequency and intensity of extreme rainstorms hit a new high in the past five years, and the extreme precipitation weather showed the characteristics of early onset, frequent occurrence and intensity, and so far there have been 5 heavy rainstorms, of which 4 have reached the level of extreme rainstorms, and precipitation in many places has exceeded historical extremes.
Among them, on March 30, the two stations of Yanqi and Pegatron in northern Bazhou broke the historical extremes of the maximum daily precipitation of the year, reaching 62.4 mm and 61.1 mm respectively. The two stations of Yuli and Korla broke the maximum daily precipitation extremes in spring, reaching 43.4 mm and 24.2 mm respectively. In this rainstorm, the precipitation of the five national meteorological stations in Bazhou, Yanqi, Pegatron, Korla, Yuli and Ruoqiang, was 15 to 40 times more than that of the same period of the year, which was the first in the history of precipitation in March. On April 2, baicheng broke the maximum daily snowfall of the year, with a snow depth of more than 20 centimeters, and the new snow depth of the county town reached 40 centimeters.
On May 14, the daily precipitation of the station in the desert hinterland was 34.0 mm, and the maximum daily precipitation of the year was extreme, which was equivalent to 1.4 times the average annual precipitation of the station.
On June 16 (20:00 on the 15th to 20:00 on the 16th), the daily precipitation of Luopu County, Moyu County and Hotan City in Hotan District reached 74.1 mm, 59.6 mm and 56.0 mm respectively, breaking through the historical extreme of daily precipitation and exceeding its annual average annual precipitation, of which the daily precipitation of Luopu County was 1.7 times the average annual precipitation of the station.
From July 18 to 22, from the northern mountainous area of Kezhou in the southern foothills of the Tianshan Mountains to the northern part of the Aksu region, there was a cumulative rainfall of 107.3 mm, a maximum daily rainfall of 78.5 mm and a maximum hourly rain intensity of 50.9 mm, all of which reached the level of heavy rainstorm.
From July 18 to 22, from the northern mountainous area of Kezhou in the southern foothills of the Tianshan Mountains to the northern part of the Aksu region, there was a cumulative rainfall of 107.3 mm, a maximum daily rainfall of 78.5 mm and a maximum hourly rain intensity of 50.9 mm, all of which reached the level of heavy rainstorm | Courtesy of respondents
"Intellectuals": The torrential rains in southern Xinjiang in mid-to-late July occurred almost at the same time as the heavy rainstorms in Zhengzhou, what is the meteorological connection between the two?
Zhang Junlan: The main atmospheric circulation systems affecting zhengzhou's heavy rains include the location of the subtropical high pressure in the northwest Pacific Ocean, the northerly, the water vapor transport of typhoons "Fireworks" and "Chapaka", and the anchoring of the local terrain.
Almost at the same time as the heavy rain in Zhengzhou, on July 18-22, heavy rain occurred in the western part of the southern foothills of the Tianshan Mountains, and the main atmospheric circulation system was the 100hPa South Asian high pressure at a high altitude from "east high and west low" to "uniform bibody" distribution, and the qinghai-Tibet high pressure developed significantly. When the South Asian high pressure is "high in the east and low in the west", the Arab sea steam first moves westward along the bottom of the Iranian high pressure, then folds to the north, and then moves east into southern Xinjiang; when the South Asian high pressure is "uniform", the water vapor in Central Asia enters southern Xinjiang along the west wind or the southwest wind, and when the south wind of the Qinghai-Tibet Plateau strengthens, part of the water vapor of the plateau can also enter southern Xinjiang along the south wind.
Regarding the connection between the heavy rain in southern Xinjiang and the heavy rain in Zhengzhou, we have noticed that the two occurred nearly at the same time, in addition to the impact of the high-altitude westerly wind belt system, there is also the participation of the weather system in the northern Indian Ocean, but the specific process has yet to be studied.
Zhang Junlan, chief forecaster of the Xinjiang Meteorological Bureau, | Courtesy of respondents
What factors affect precipitation in desert areas?
Intellectual: Drought is the general understanding of Xinjiang. Flooding, is this year more special, or has there been such a trend recently?
He Qing: The frequent occurrence of extreme rainstorms is a significant feature of the climate in southern Xinjiang in the past 10 years, accounting for 36% of the meteorological disasters in southern Xinjiang. The rainstorms in southern Xinjiang are characterized by great intensity and increasing persistence.
For example, from June 24 to 28, 2019, there were heavy to heavy rains in the arid area of southern Xinjiang for four consecutive days, which was extremely rare, and on the 25th, 28 meteorological stations in The Hotan region went to Bazhou and the last county observed heavy rainfall, and the last station broke the historical extreme of the daily precipitation with 48.7 mm (26 days) of precipitation, and the maximum hourly rain intensity was located at the Tajik Acoshaw Station in Pishan County, reaching 30.9 mm.
From April 17 to 24, 2020, a total of 17 rainstorms and 3 heavy rainstorms were observed in Kashgar, of which the cumulative precipitation in 5 villages of Kyzyl Township in Ingisha County was 169.5 mm, and the precipitation in 5 hours reached 103.0 mm.
He Qing, researcher at the Urumqi Desert Meteorological Research Institute of the China Meteorological Administration, | Courtesy of respondents
Intellectual: What are the main reasons for the increase in precipitation?
He Qing: First, the background of global warming, and second, the large-scale circulation situation, water vapor transmission and aggregation mechanism that affect the weather in southern Xinjiang have changed, making arid southern Xinjiang more and more humid and precipitation more and more.
Zhou Tianjun: Simply put, the factors that affect climate anomalies include two categories. One is natural factors, which include changes in solar irradiance, the effects of volcanic aerosols, and natural oscillations within the climate system, particularly in the oceans [4]; On longer timescales, both natural shadows and anthropogenic factors have an impact on the climate of the Northwest.
But in the case of warming and humidification in the northwest in recent decades, studies have shown that observed changes in precipitation are influenced by two processes. First, the thermal process, accompanied by global warming, the atmospheric water holding capacity is enhanced, which is conducive to the increase of precipitation, and the relative increase in atmospheric precipitation in Xinjiang observed by the meteorological sounding station data can reach 5%/10 years; the second is the dynamic process, that is, the change of atmospheric circulation, and its impact on precipitation varies from region to region [1].
The studies show that the main atmospheric circulation type that determines the humidity of Xinjiang and the drying out of northern Central Asia is the southward shift of the subtropical westerly rapids and the weakening of their intensity. Attribution simulation studies based on climate patterns have shown that the southward shift of the westerly wind jets is the result of global warming, while the weakening of intensity is affected by increased anthropogenic aerosol emissions, that is, human activities have significantly affected changes in atmospheric circulation, thereby affecting precipitation in Central Asia, including Xinjiang [2-3].
The above research work is mainly aimed at the increase in average precipitation. As for whether an extreme precipitation, such as this year's heavy rain in southern Xinjiang, is affected by human activities, this remains to be studied. The "event attribution" in climate change research is the answer to whether the impact of human activities on a particular record-breaking weather event changes the probability of it occurring. Such studies require high-quality observations of sufficient length of time and high demands on the performance of climate models.
Climatic distribution of summer precipitation in the Northwest Territories (left column, unit: millimeters/day) and its trend from 1961 to 2010 (right column, unit: millimeters/day/per 50 years)
First row: observations from 99 weather stations;
In the climate average chart, only 18% of the observatories have an average summer precipitation of more than 2 mm/day, and about 65% of the stations have an average summer precipitation of less than 1 mm/day; in terms of long-term changes, 70 of the 99 stations have significantly increased precipitation, and 27 stations have shown a decreasing trend | Source: Literature[1]
Intellectual: How did the observations change about the second factor in flood formation, seasonal alpine snowmelt (ice) ?
Zhang Junlan: There are significant differences between the snowmelt floods in southern Xinjiang and northern Xinjiang, the frequency of snowmelt floods in northern Xinjiang accounts for 75% of the whole of Xinjiang, the main flood period is in the spring, the main flood season in southern Xinjiang is in the summer, the snowmelt (ice) flood mainly appears in the Pamir Plateau, the northern slope of Kunlun Mountain and the western part of the southern foothills of the Tianshan Mountains, and the high incidence of snowmelt (ice) floods in northern Xinjiang and snowmelt (ice) floods in southern Xinjiang in March and July are respectively.
In recent years, satellite remote sensing has monitored changes in alpine snowmelt in stages, and there have been no reports of a significant increase in snow cover in mountainous areas and long-term maintenance. Specifically, snowmelt changes are related to specific precipitation and high temperature weather processes - when there is a large-scale precipitation process, the snow cover in mountainous areas will increase significantly; when the southern xinjiang encounters high temperatures in summer, the snow in the mountains will melt and the snow area will decrease.
Intellectual: What challenges do these extreme events pose to infrastructure?
He Qing: Flash floods caused by torrential rains pose a serious threat to road traffic and water conservancy facilities.
In 2018, the precipitation in the center of the 7.31 exceptionally heavy rainstorm in Hami reached 105.4-115.5 mm, and the flash flood triggered the flooding of the Sheyuegou Reservoir and the partial collapse of the dam, resulting in the death of 28 people, more than 8,700 houses and farmland, roads, railways, power and communication facilities were damaged, the loss of the Sheyuegou Reservoir alone was 170 million yuan, and other economic losses were as high as 796 million yuan.
On July 28-29, 2021, heavy precipitation and meltwater of ice and snow triggered mudslides, causing three landslides on the line from Oyigaizi to Baisha Lake Scenic Area in Kashgar Region, and the China-Pakistan Highway was interrupted.
At present, the risks caused by extreme weather have become an important part of meteorological forecasting and early warning, and are included in the emergency operation system. In the future, extreme weather and its derivative disasters are issues that must be taken into account in regional development planning, and from a specific regional point of view, northern Xinjiang needs to focus on preventing snowmelt floods in the spring in the middle and low mountain seasons of Ili Prefecture, while southern Xinjiang should pay close attention to the summer alpine glacial lake collapse type and snow and glacial meltwater type two types of snowmelt (ice) type floods.
From June 16 to 17, 2013, heavy rains in Keping and Wensu in southern Xinjiang | Courtesy of respondents
What is "Northwest Warm humidification"?
"Intellectuals": Recently, the Internet has been talking about "warming and humidification in the northwest" and its impact, what is the overall trend of meteorological conditions in terms of southern Xinjiang, the whole territory of Xinjiang and the northwest region?
Zhou Tianjun: This is not a completely new argument. As early as 2002, Mr. Shi Yafeng, a pioneer in modern glaciology research in China, jointly with the Chinese Academy of Sciences and the China Meteorological Administration, organized an assessment of the transition of the northwest climate from "warm dry to warm and wet" [4].
At that time, through a large number of investigations and studies, Chinese scholars found that since 1987, there was a strong climate change signal in the northwest climate zone - from the 1950s to the late 1980s, the temperature in western China fluctuated and changed, and the upward trend was not obvious; but after 1987, there was a continuous warming tendency; in the second half of the 20th century, it rose by about 1.0 °C, and the rising rate reached 0.2 °C/10 years. Among them, northern Xinjiang is one of the most obvious warming areas.
On the other hand, climate humidity has increased. For example, after more than 30 years of falling water levels, the water level of Bosten Lake in the middle of the Tianshan Mountains rose by 3.5m between 1987 and 2000. In August 2002, the water level reached an altitude of 1049.26 meters, exceeding the highest water level (1958) since the recorded water level of 1958, and the lake area also expanded to more than 1000 km2.
The latest monitoring data of the Xinjiang Climate Center shows that from 1961 to 2019, the average temperature in all four seasons in Xinjiang showed a significant upward trend, and the annual average temperature increased by 0.30 °C every 10 years. The winter warming trend is the most obvious, with an average increase of 0.38 °C every 10 years, followed by an average increase of 0.32 °C and 0.30 °C every 10 years in spring and autumn, respectively, and the summer heating rate is the smallest, with an average increase of 0.23 °C per 10 years [6].
In terms of precipitation, there is an overall increase trend, of which summer is the most significant, with the central value increasing by 2.5 to 3.5% every 10 years [3]. However, since entering the 21st century, the changes have been stable and the increase trend has not been as significant as in the previous period. There has been a marked increase in heavy precipitation events, with the number of storm days increasing by 12% every 10 years and the amount of rainstorms increasing by about 13% every 10 years [6].
That is to say, the trend of warming and wetting in the northwest is indeed an indisputable fact, although the total amount of precipitation is still very limited.
Figure 2: Standardized regional mean precipitation time series (black line: gridded observation data, black dot line: station data, red line: reanalysis data), the average summer precipitation of 99 stations in the northwest region was 0.713 mm/day, and the summer precipitation increase trend between 1961 and 2010 was 0.025 mm/day/per 10 years.
Figure a: Regional average results for the northwest (35-50N°, 74-96E°) and Figure b: Regional mean results for the western northwest (WNW: 35-50N°, 74-96E°) region | Source: Literature[1]
Intellectual: Since "warm humidification in the northwest" is supported by meteorological observation data, will it change the overall climate pattern of the region?
Zhou Tianjun: There is a larger background to the warming and humidification of the northwest region, including Xinjiang, which is not a local phenomenon, and observational data show that the area of increased precipitation can extend westward to the east of Central Asia, while Kazakhstan in northern Central Asia has a significant drought trend. It should be emphasized that although there is a trend of increasing precipitation in the northwest region, including Xinjiang in recent decades, the pattern of Xinjiang's arid climate will not change due to the low annual precipitation in the region, with an average annual average of only 50-70 mm.
The long-term trend of summer precipitation in Central Asia between 1958 and 2014 (in mm/month/per 10 years) | Source: Literature[3]
He Qing: There are sub-regional differences in the characteristics of dry and wet changes in Xinjiang. Tacheng, Altay region, western southern Xinjiang and the Pamir Plateau in northwestern Xinjiang are dominated by continuous humidification. After 1997, due to the temperature jump, the potential evapotranspiration increased, resulting in more than 70% of the sites drying out.
Zhang Qiang: First of all, we should not exaggerate the degree of change in the climate of the northwest region, at present, the precipitation in the western part of the northwest region, including Xinjiang, has increased by only about 10 mm per 10 years on average, and the cumulative amount of more than 35 mm in more than 30 years has not exceeded the current precipitation.
Secondly, because the warming in the western part of the northwest region is very significant, and the degree of warming is still accelerating, which will cause a significant increase in ineffective evaporation in the region, and a considerable part of the wetting effect of the precipitation increase will be offset by the increase in ineffective evaporation, so the actual degree of wetness will be much smaller than we think.
At the same time, the increase in temperature will cause alpine glaciers and snow melting to accelerate, which will convert some solid water resources into liquid water resources, resulting in an increase in evapotranspiration in the region, which will contribute to the trend of increasing precipitation, but this will not only not make the water resources in the region substantially increased, but may be reduced.
Third, the spatial difference in the trend of precipitation change in the northwest region is very large, the precipitation in the eastern part of the northwest region has been continuously reduced before the last century, only in the past ten years there has been an increase in fluctuations, and it is only a little more than the valley bottom period (the 90s of the last century), which is basically the same as the 70s and 80s of the last century, and it belongs to different time scales and different formation mechanisms with the trend of precipitation increase in the western region in the past 30 years. From the perspective of interdecadal or longer time scales, the precipitation changes in the western and eastern parts of the western region showed the opposite trend of change, with a certain "seesaw" effect. The former warms and wets, while the latter may warm dry [11].
In addition, the precipitation changes in the northwest region have obvious fluctuations and uncertainties, even in the trend of warming and humidification, there will be years with little rain and drought or low temperature and cold years, and it is difficult to determine how long this wet trend can last and what range it can maintain.
Zhang Qiang, chief engineer of Gansu Meteorological Bureau and director of the Key Open Laboratory of Drought Climate Change and Disaster Reduction of China Meteorological Administration, | Courtesy of respondents
Intellectual: From the perspective of the impact on local vegetation, does the trend of warming and wetting mean that the desert becomes an oasis, and the arid areas in the northwest will become "plugged into the good Jiangnan"?
Chen Yaning: The slight increase in precipitation in the arid region of northwest China is difficult to change the pattern of desert landscape and the state of drought and water shortage in northwest China. This is because the slight increase in precipitation is difficult to counteract the negative effects of warming and increasing evaporation.
Since 1998, the arid northwest has seen a "jumping" warming, with temperatures rising by an average of 0.93–1.11ºC compared to the previous 35 years, and has been at a high level of oscillation [13]. The increase in temperature increases the evaporation capacity, and the precipitation increase is not enough to compensate for the water loss caused by the increase in temperature and evaporation.
In addition, although the precipitation in the northwest region has increased, the number of precipitation days has not increased significantly, and the increase in precipitation is largely due to the increase in the intensity of single precipitation or heavy rain. The increase in the probability of such extreme precipitation will exacerbate climatic disasters and increase the risk of drought and localized heavy rains and floods in the northwest region.
Our latest research and analysis results show that the arid region of northwest China, with Xinjiang as the main body, has been developing in the direction of aridization since about 2000, and the natural vegetation in the desert area has shown a significant degradation trend [12].
With the increase in temperature and evaporation capacity, soil moisture dissipation increases, and some plants with shallow roots and poor drought tolerance die. The number of species has decreased, the vegetation coverage has decreased, the vegetation index has reversed in 1998, from increasing to decreasing, grassland has been shrubized, and ecological concerns have become prominent.
Central Asia exhibits the same pattern of wet and dry variations. Since 2000, the Pamir Drought Index has shown a clear downward trend, with about 65% of the region showing increased aridization, with the northern region of Kazakhstan in Central Asia particularly prominent [15].
It is worth mentioning that spring phenological advance is common in the arid areas of northwest and Central Asia. Spring phenological advance may disrupt the dynamic equilibrium of the land-gas-water heat exchange process between different seasons, causing an increase in vegetation transpiration and accelerating the loss of water from the land surface soil. At the same time, spring phenological advances may have a feedback effect on the trans-season of the climate, resulting in an intensification of soil drought in summer, and by changing the surface energy budget, promoting near-surface warming, resulting in an increase in the frequency and intensity of summer heat wave events.
Chen Yaning, researcher at the Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, and director of the State Key Laboratory of Desert and Oasis Ecology, | Courtesy of respondents
What is the reason for the "resurrection" of the desert river?
"Intellectual": The natural vegetation in desert areas shows a clear trend of degradation, so what is the reason for the observation of the "resurrection" of some lakes and the improvement of ecosystems?
Chen Yaning: Recently, some of the water in the lower reaches of the river channel and the "resurrection" of lakes are mainly caused by artificial ecological water transmission in the past 20 years, and it is not due to "local climate changes, increased precipitation, and desert changes in Jiangnan", as many self-media articles exaggerate.
For example, in the lower reaches of the Tarim River, as of 2020, the Tarim River Basin Management Bureau has implemented 21 ecological water transfers to the lower reaches of the Tarim River, with a cumulative water delivery of 8.445 billion cubic meters. The surface water area of The Tail Lu Lake- Taitma Lake "died and came back to life", with a surface water area of 455.27 square kilometers [14]; the middle and lower reaches of the Tarim River's sister river, the Peacock River, were greatly improved through ecological water transport, and the water system connectivity was greatly improved, the dry river channel crossed more than 600 kilometers, and the area of natural vegetation along the river increased by 181 square kilometers; the three key poplar forest reserves in the middle reaches of the Tarim River (Shaya, Luntai, Bachu) were improved to a certain extent through ecological water replenishment.
Intellectual: Global warming has brought about global weather extremes, such as an increase in heavy rains, why is the response in the Northwest particularly sensitive?
Zhang Junlan: Climate-sensitive areas and ecologically fragile areas are particularly sensitive to extreme weather events. Xinjiang is an arid climate area, and southern Xinjiang is even more arid, with an average annual precipitation of 50-70 mm in the plain area, and the ecological environment is fragile. Over the past few decades, with global warming, the warming of arid areas is higher than that of humid areas, the amount of atmospheric precipitation can increase accordingly, and the rapid increase in water vapor content in the northwest region has provided favorable conditions for heavy rainfall.
In recent years, the probability of extreme events of heavy precipitation has increased significantly, and heavy rains have occurred frequently. The reason why southern Xinjiang is particularly sensitive to extreme weather such as heavy rain is that southern Xinjiang has a long-term drought and little rain, the ecological environment is fragile, and since the establishment of the station in the 1950s, it has mainly prevented the harm of wind and sand and dust, but in recent years, meteorological data show that the climate has warmed and wettened, the rainstorm events have increased significantly, and the local heavy rain in the mountainous areas is easy to cause geological disasters such as flash floods, mudslides, landslides, etc., so that southern Xinjiang must face more complex weather and climate conditions for a considerable period of time.
Zhou Tianjun: According to the results of the Sixth Assessment Report (AR6) of the First Working Group of the United Nations Intergovernmental Panel on Climate Change (IPCC), which was released on August 9, from a global perspective, most of the land areas with observational data since the 1950s have experienced an increase in the frequency and intensity of extreme precipitation (the results are highly reliable), and human-induced climate change may be the main driver [7].
On a global scale, observational data show that the increase in extreme precipitation in humid areas is still much greater than in total in arid areas. The same is true of the China region, where analysis based on existing station data shows that the humid area in the east is much larger than the arid area in terms of the increase in the absolute value of extreme precipitation, but the relative percentage increase is large due to the low climatic state of precipitation in the arid area [8].
It should be noted that the current research work is based on the existing network of meteorological stations, and the existing surface meteorological observation station network is mostly distributed around the low mountain belt and the low-altitude plain area, the stations in the alpine canyon area are very rare, the observation stations are almost blank, and we cannot monitor the changes in mountain precipitation and then explore its causes. Some of the extreme precipitation changes we are noticing now may have existed in their own right, only because of the improvement of the observation network in recent years.
At the same time, there are many extreme precipitation events that may have occurred or are occurring, but are difficult to monitor by current observation networks. The issue of information is particularly important here.
The Terrestrial-Air Interaction Observatory in the Pamir Plateau | Source: He Qing
What are the impacts of climate change on the Northwest Territories?
Intellectual: What gains or losses will climate change bring in terms of the Northwest?
He Qing: With the global warming, the increase in heat has increased significantly, which has a significant impact on the growth process, yield quality, planting system, variety layout and climate resource utilization rate of forest fruits in Xinjiang, but at the same time, the frequent occurrence of extreme weather and climate events has also increased the instability of the production of characteristic forest fruits.
Taking fragrant pear as an example, the climatic conditions of fragrant pear cultivation tend to be better, and the most suitable planting areas move south to west, but the threat of wind disaster and overwintering frost damage is higher; while the suitable planting areas for red dates are also significantly expanded, and the climate yield is increasing, but the frequency of overwintering frost damage is reduced.
Zhang Qiang: From the perspective of the overall long-term development of the northwest region, it is certainly beneficial, because it is conducive to the improvement of ecological vegetation and can also supplement water resources for all aspects of social economy.
However, in the short term or locally, warm and humid climate will increase the frequency and intensity of heavy rain disasters. Generally speaking, relatively stable non-extreme precipitation will not cause disasters, and only extreme climates are prone to disasters. What is climate extremes? Even as drought increases, torrential rain increases, that is, non-precipitation periods are longer, but each precipitation intensity is greater.
Zhou Tianjun: I very much agree with researcher Zhang Qiang's point of view. The volatility of precipitation is an important part of the climate change response. There is a technical term here - precipitation variability, refers to the possible fluctuations or oscillations of precipitation events, the greater the variability, the more frequent the occurrence of abnormal precipitation, the stronger the unevenness of precipitation, the stronger the extreme events, and the greater the impact on people's livelihood and social and economic development. A recent study by the LASG State Key Laboratory at the Institute of Atmospheric Physics of the Chinese Academy of Sciences showed that with global warming, about two-thirds of the world's land will face a "wetter and more volatile" hydrological situation in the future, which should be paid attention to [9].
Zhou Tianjun, a researcher at the Institute of Atmospheric Physics of the Chinese Academy of Sciences, | Courtesy of respondents
Zhang Junlan: The impact of climate change on the ecological environment of desert oases is multifaceted.
First of all, extreme weather and catastrophic weather have increased, and catastrophic weather such as heavy rain, high temperatures, strong winds, sandstorms, cold waves, low temperatures and hail has occurred from time to time, especially extreme rainstorms have increased significantly;
Second, the continuous high temperature causes the snow (ice) in the mountainous areas to melt and form floods;
Third, strong convective small- and medium-scale weather such as high winds, sandstorms, cold waves, and strong convective small-scale weather such as hail and thunderstorms have seriously affected agriculture and animal husbandry, facility agriculture, forestry and fruit industry, transportation, tourism and public life. Specifically, spring torrential rains, strong winds, sandstorms and other catastrophic weather will make spring crops late sowing, re-sowing, affecting the pollination of forest fruits during flowering, etc., summer torrential rains lead to flash floods, mudslides, landslides and urban waterlogging and other meteorological disasters and derivative disasters frequently, flooding farmland, destroying cottages, greenhouses, etc.; the impact on urban operation and public life is also greater, especially affecting traffic safety travel, tourism operations, etc.
Chen Yaning: The "warming and humidification" that has increased precipitation in recent years cannot fundamentally change the basic pattern of drought, water shortage and desert landscape in the northwest region with Xinjiang as the main body. Moreover, with global warming, extreme climate hydrological events will be further enhanced, and the threat of extreme heavy rain floods and mudslide disasters will further increase. In the process of economic and social development, the pressure on water resources and ecology will continue to exist, and the risk of drought will be further aggravated.
"Intellectuals": In view of the current climate situation, what adjustments should be made to the arid areas in the northwest as a whole?
Chen Yaning: Insufficient water resources remain a key factor restricting Xinjiang's economic and social development. Arid areas must insist on how much water and how much to do. Afforestation on the edge of the desert (desert-oasis transition zone) is not advisable.
Where does the water come from? The large amount of groundwater pumped will lead to a decline in the groundwater level and the death of natural vegetation. The natural vegetation distributed on the edge of the desert, that is, the desert-oasis transition zone, is very drought-resistant, cold-resistant and sand-buried, and does not require special manual management. Afforestation activities on the edge of the desert need to be watered and nurtured, because the precipitation in the plain area is scarce, mostly about 50 mm, which has no ecological significance, and it costs water and electricity instead, which not only increases the regional water dissipation, but also aggravates the contradiction between regional water supply and demand, and increases the burden of ecological construction.
Xinjiang is an arid area, this climate pattern will not change, from the perspective of the scientific concept of development, we must adhere to the suitable agriculture, suitable forest and forest, suitable for grazing and grazing, suitable grass for grass, suitable for sand and sand. To this end, I solemnly suggest: We must fix the land with water, the city with water, the green with water, and the development with water.
Zhang Qiang: In view of this climate situation, for large and major engineering facilities, we must consider the impact of extreme climate changes and actively do a good job in drought and flood disaster prevention. At the same time, the current heavy rain is also a severe test for the city's infrastructure, and the scientific demonstration of meteorological disaster risks should be fully carried out in the urban flood control and drainage planning.
Zhang Junlan: In the future, the situation of meteorological disaster defense will become more complex, and the task of meteorological disaster defense will face new challenges, and the government and the public need to pay close attention to and deal with them as soon as possible. The layout of disaster defense needs to be expanded from the focus on drought and wind and sand hazards to the prevention of rainstorms and floods, and to do a good job in preparing for the floods of small and medium-sized rivers caused by heavy rainstorms and the melting of snow in mountainous areas, and the various preparations for the prevention of flash floods and geological disasters derived from them.
Zhou Tianjun: In the context of global warming, it is estimated that the scope of the impact area of extreme precipitation events on China will be greatly expanded, but there is still a gap in cognition of complex terrain areas [10]. Southern Xinjiang has a vast territory, complex terrain and large altitude differences, and the ground weather stations, high-altitude detection stations and radar monitoring stations are relatively sparse, and the spatial distribution is extremely uneven. It is recommended to strengthen the capacity building of various meteorological disaster monitoring, scientifically lay out the meteorological monitoring network in southern Xinjiang, improve the layout of automatic meteorological stations in mountainous areas, fill in the monitoring blanks, and improve the monitoring level of meteorological disasters in southern Xinjiang. At the same time, strengthen the research and technical support of rainstorm weather in southern Xinjiang, and improve the understanding of the formation mechanism and disaster mechanism of complex meteorological disasters in southern Xinjiang.
He Qing: The possibility of flooding in desert areas mainly comes from extreme precipitation and meltwater of ice and snow in the upper mountains. Extreme rainstorms and floods have a great impact on local agricultural and animal husbandry production, transportation, energy production and urban operation. It is recommended to organize experts to tackle key scientific and technological problems, improve the refined level of fixed-point, timed and quantitative forecasts of heavy rainstorms in southern Xinjiang, so that forecasts are accurate, early warnings are timely, services are in place, and the role of meteorological disaster prevention, mitigation and relief is brought into full play.
At the same time, strengthen the linkage of multi-departmental meteorological disaster defense. Transportation, water conservancy and government departments at all levels should attach great importance to meteorological disaster prevention, form a departmental linkage mechanism, and revise and improve the linkage mechanism for emergency response to meteorological disasters. Meteorological and water conservancy and other relevant departments should rely on the national emergency early warning information release system and one-click release platform to timely release relevant meteorological early warning and risk early warning products. It is necessary to pay attention to strengthening the building of soft power for disaster prevention and mitigation at the grass-roots level. Continue to expand and promote the coverage of meteorological early warning information, establish a rapid and efficient response mechanism with early warning information as the guide, and realize the accurate delivery of meteorological early warning information to the "last mile".
Resources
1. Peng D, Zhou T. Why was the arid and semiaridnorthwest China getting wetter in the recent decades? [J]. Journal ofGeophysical Research: Atmospheres, 2017, 122(17): 9060-9075.
2. Peng D, Zhou T, Zhang L, et al. Human contributionto the increasing summer precipitation in Central Asia from 1961 to 2013[J]. Journalof Climate, 2018, 31(19): 8005-8021.
3. Jiang J, Zhou T. Human-induced rainfall reductionin drought-prone northern Central Asia[J]. Geophysical Research Letters,2021, 48(7).
4. Jiang J, Zhou T, Chen X, et al. Central Asianprecipitation shaped by the tropical Pacific decadal variability and theAtlantic multidecadal variability [J]. Journal of Climate, 2021, https://doi.org/10.1175/JCLI-D-20-0905.1
5. Shi Yafeng, Editor-in-Chief, Assessment of the Transition of Climate from Warm dry to Warm and Wet in Northwest China, China Meteorological Press, Beijing: Meteorological Press, 2003, 1-124pp, ISBN 7-5029-3538-X
6. Taixi Zhang, 2021: Characteristics and impacts of warm and humidified climate in Xinjiang. Invited Report of the Academic Symposium on "History and Scenario Estimation of Climate Change in Extreme Weather In the Great Lakes Region of Central Asia" special project of the "Silk Road Environment" Strategic Pilot Technology Of the Chinese Academy of Sciences, Beijing, August 5, 2021.
7. IPCC,2021: Summary for Policymakers. In: Climate Change 2021: The PhysicalScience Basis. Contribution of Working Group I to the Sixth Assessment Reportof the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P.Zhai, A. Pirani, S. L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L.Goldfarb, M. I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T. K.Maycock, T. Waterfield, O. Yelekçi, R. Yu and B. Zhou (eds.)]. CambridgeUniversity Press
8. Zhang, W., Zhou, T. 2019. Significant increases inextreme precipitation and the associations with global warming over the globalland monsoon regions. Journal of Climate, 32, 8465-8488,https://doi.org/10.1175/JCLI-D-18-0662.1
9. Zhang Wenxia, Kalli Furtado, Peili Wu, TianjunZhou*, Robin Chadwick, Charline Marzin, John Rostron, David Sexton. 2021.Increasing precipitation variability on daily-to-multiyear timescales in awarmer world. Science Advances. DOI: 10.1126/sciadv.abf8021
10. Zhang, W., T. Zhou, Increasing impacts from extremeprecipitation on population over China with global warming, ScienceBulletin (2019), doi: https://doi.org/10.1016/j.scib.2019.12.002
11. Zhang, Q., Yang, J., Wang, W. et al. ClimaticWarming and Humidification in the Arid Region of Northwest China: Multi-ScaleCharacteristics and Impacts on Ecological Vegetation. J Meteorol Res 35,113–127 (2021). https://doi.org/10.1007/s13351-021-0105-3
12. Li Zhi, Chen Yaning*, Li Weihong, et al. Potentialimpacts of climate change on vegetation dynamics in Central Asia. Journal ofGeophysical Research – Atmospheres, 2015, 120(24): 12345–12356
Chen Yaning*, Li Zhi, Fang Gonghuan, et al. Impact of climate change on water resources in Tianshan Mountains, Central Asia. Acta Geographica Sinica, 2017, 72(1):18-26
14. CHEN Yaning, WUMAILJIANG WUBULI, Akremu Abra, et al. Monitoring and analysis of the ecological benefits of water transmission in the lower reaches of the Tarim River in the past 20 a years[J]. Arid Land Geography, 2021, 44(03): 605-611.]
15. Li Zhi, Chen Yaning*, Fang Gonghuan, et al. Multivariate assessment and attribution of droughts in Central Asia. ScientificReports, 2017,7:1316.