The Qinghai-Xizang Plateau is characterized as one of the key areas of global energy and water cycle and is known as Asian water tower.Climate change of the Qinghai-Xizang Plateau has significant impacts on the environmental changes of the its own and surrounding areas.This paper reviews the facts and mechanisms of recent 60 years’ climate change and its associated environmental impacts， emphasizing surface warming， change of surface radiation， precipitation variability among different seasons and regions， change of surface wind speed and surface environment.Changes of skin temperature， surface air temperature and surface wind speed and associated mechanisms during past decade over the Plateau are also analyzed based on reanalysis and site data.Finally， the issues that need to be solved have been sorted out.The conclusions are as follows： （1） The surface warming over Qinghai-Xizang Plateau was earlier and faster than that along the same latitude in Northern Hemisphere.The elevation-dependence warming and increase of clear sky downward longwave radiation caused by Interdecadal atmospheric humidification are the main causes of Qinghai-Xizang Plateau surface warming.However， the variations of surface temperature during past decade are concentrated on inter-annual scale.（2） Due to the continuous rapid warming of the plateau and the anomalies of sea temperature and atmospheric circulation， the precipitation in different regions and seasons presents various variability.（3） Interdecadal shift of surface wind speed is mainly drwen by the meridional difference in warming between the Qinghai-Xizang plateall and the mid-latitude Eurasian Continent and anomalous atmospheric circulation.（4） Environmental changes on the Qinghai-Xizang Plateau are mainly manifested as lake expansion， permafrost degradation， and advance of vegetation rejuvenation； Since the 1990s， glacier in the western Qinghai-Xizang Plateau have been stabilized or even partially recovered， while， glacier in the southeastern Qinghai-Xizang Plateau continue to retreat.The above results are mainly caused by the dipole pattern that precipitation increased and decreased over western and eastern Qinghai-Xizang Plateau， respectively.Meanwhile， the seasonal and intra-seasonal variations of the Summer Monsoon can be reasonable indicators to the vegetation growth and the spatiotemporal variations of vegetation rejuvenation period.（5） The mechanism and numerical simulation of surface temperature and wind speed changes in different seasons and regions need to be further investigated； performance of temperature and precipitation in climate models needs to the improved； high-resolution numerical simulation and data assimilation based on regional models need to be strengthened urgently.

三江源冻土、 植被二者之间存在着强烈的相互作用的关系， 并通过改变土壤水热特性以及地表-大气间的能量和水分交换过程影响局地气候， 加快或减缓气候变化， 源区的生态安全面临挑战。本文综述了近几十年来三江源区冻土、 植被特征及变化趋势、 冻土-植被相互作用过程以及冻土、 植被变化的气候效应， 在此基础上对未来研究方向进行了展望。主要认知如下： 三江源地区是季节性冻土和多年冻土的交汇带。植被类型有高寒草甸、 高寒草原、 高寒荒漠等， 植被生长季较短。近几十年来， 在全球变化影响下， 源区冻土和植被经历了快速的变化。冻土土壤温度明显升高； 多年冻土面积减小而季节性冻土面积增加； 多年冻土活动层厚度及融化期增加而季节性冻土最大冻结深度及冻结期减小。植被物候整体表现出返青期提前， 黄枯期推迟， 生长季延长的特征； 同时高寒植被生态系统的结构和功能也发生了明显变化。土壤的水、 热状态是连接冻土和植被相互作用的重要纽带。冻土的冻融状态， 土壤的水、 热过程对高寒植被的生长有着密切的影响； 同时位于冻土上层的植被， 又通过植被特征和生态系统的变化， 影响土壤温度、 湿度， 反作用于冻土的形成和发展。冻土和高寒植被作为三江源两种典型的下垫面， 在陆-气相互作用中是一个有机整体， 其变化将通过影响局地能量分配及水分过程对区域降水、 气温、 能量收支、 局地环流以及水汽循环等产生重要的影响， 需要统筹考虑二者协同变化的气候效应。未来面向整个区域的冻土-植被相互作用的综合评估及机理分析需进一步加强。利用观测、 耦合了动态植被模型的陆面过程模式、 区域气候模式以及人工智能等， 深入开展研究三江源区冻土冻融变化与高寒植被变化的内在联系， 将进一步提高对未来冻土及高寒植被变化的认识， 为三江源生态保护和建设提供重要科学依据。

The freeze-thaw process is one of the most prominent features of the land surface process on the Qinghai-Xizang Plateau， and quantifying the variation of the key variables that denote the soil freeze-thaw process has scientific significance for understanding the climate change， hydrological processes and ecosystems of the Qinghai-Tibetan Plateau.By using the ECMWF/ERA5 （European Centre for Medium-Range Weather Forecasts/ERA5） reanalyzed soil temperature， volumetric soil water and air temperature data， the temporal and spatial trends of the start date of soil freezing， the start date of soil thawing and the duration of the soil freezing and their relationships with the air temperature and altitude were investigated by using linear regression， Mann-Kendall test， moving t test and correlation analysis.These results demonstrated that the spatial distribution of soil freeze-thaw process in the Qinghai-Xizang Plateau is characterized by a trend of delaying freeze， advancing thaw and shortening freeze from the northwest to the southeast.The soil freeze-thaw process varied significantly on the Qinghai-Xizang Plateau from 1979 to 2018.The start date of soil freezing was delayed by 14.0 days with a rate of 0.17 d·a^-1， and the start date of soil thawing was advanced by 11.0 days with a rate of 0.07 d·a^-1， and the duration of the soil freeze was shortened by 25.0 days with a rate of 0.23 d·a^-1 over the past 40 years.The overall trend of soil freeze-thaw process is the same in the Qinghai-Xizang Plateau， while the local rate is different.Throughout the period of study， the duration of the soil freeze in the southern and the northern Changtang Plateau is shortened by 47.2 days and 32.9 days.The first date of the soil freeze， the first date of the soil thaw and the duration of the soil freeze are significantly correlated with temperature and altitude.If the air temperature rises by 1.0 ℃， the first date of the soil freeze will be delayed by 5.2 days， and the first date of the soil thaw will be advanced by 4.5 days， so that the duration of the soil freeze will be shortened by 9.8 days.In the high cold Tibetan climatological zone， the first date of the soil freeze will be advanced by 9.1 days， and the first date of the soil thaw will be delayed by 4.9 days， while the duration of the soil freeze will be increased by 13.9 days as the altitude increases by 1000.0 m.

Acting as the “Asian water tower”， the Qinghai-Xizang Plateau （QXP） can significantly influence the East Asian and global climate.This paper introduces some preliminary results of the Strategic Priority Research Program of Chinese Academy of Sciences （Grant No.XDA2006010301）.Focusing on the Pan Third Pole centered by the QXP， the dominant results include： （1） Dust， polluted dust， elevated smoke and polluted continental aerosols are the most important types over the Pan-Third Pole region.Among them， the dust emission and transport can significantly affect the atmospheric thermodynamic structure over the western QXP and the Qaidam Basin.（2） The occurrence frequency of supercooled water clouds and its role in adjusting the energy budget are greater than those of warm water clouds over the QXP.Precipitation is mainly produced by ice clouds and mixed phase clouds， especially in warm season.Although the QXP is warming and wetting， the water vapor arriving from outside the QXP could not effectively replenish the surface water storage， the water cycle over the eastern part of the QXP shows a weakening trend， while the one over the western part indicates opposite trend.（3） Due to the black carbon （BC）， a weak South Asian Summer monsoon is induced， leading less water vapor transported from the Indian Ocean to the QXP.Besides， BC addition can induce an intensified East Asian Summer monsoon significantly， consequently， more water vapor is transported from the east of QXP.Overall， due to the BC， the net water vapor is positive over the QXP， implying a net import of water vapor from the surroundings to the QXP.The eastward movement of convective clouds polluted by dusts over the QXP can merge with the local cloud clustering， leading to an intensified precipitation in the Yangtze River Basin and North China.In general， aerosols can directly affect radiation， or indirectly change the macro and micro characteristics of clouds by acting as cloud condensation nuclei， or by affecting the thermal structure required for cloud formation， thereby further affecting the surface energy budget and atmospheric heating rate profile of QXP.And ultimately affect the circulation system and the water vapor budget of the plateau.Being some parts of the program， the research on above results is beneficial to reveal the physical mechanism of the QXP influencing the surrounding water cycle， to understand the mechanism of aerosol-cloud-interaction affecting the water cycle of TP.Additionally， it may provide some evidence and guidance for the improvement of the efficiency of air water resources development and utilization.

Qinghai-Xizang Plateau Monsoon （QXPM） is a prevailing wind system with a seasonal reversal of wind direction， which is caused by the thermal effects of the plateau.QXPM plays a vital role in the energy budget and water cycle of the Qinghai-Xizang Plateau （QXP） and thus has profound impacts on the formation and variations of Asian climate and environment.The review on the QXPM and its climatic influence is not only the need for an in-depth understanding of the climatic and environmental of QXP but the requirements of the country's ecological civilization construction and social and economic development.This paper reviews the advances of studies in QXPM， emphasizing its multi-scale variability， factors affecting the QXPM， and its climate and environmental effects.The existing studies show that the formation of QXPM is an important sign of the beginning of Quaternary and related to the uplift of QXP closely.The variation in QXPM is significantly influenced by QXP heating， the tropical sea surface temperature， Atlantic Oscillation， and teleconnection patterns.Existence and variations in the Qinghai-Xizang Plateau Monsoon have notable impacts on the climate of the QXP and its surrounding area， such as Asian monsoon， South Asian high， mid-latitude westerlies， and so on.In the future， the relationship between the water vapor transport condition， thermal characteristics， and dynamic characteristics of the plateau monsoon system needs to be clarified.Studies on the interaction between the complex land surface process and the QXPM need to be strengthened.Moreover， under the background of global climate change， it's also necessary for us to analyze the response of QXPM to QXP warming.

Featured with high topography， the Qinghai-Xizang （Tibetan） Plateau （QXP） shows very significant dynamic and efficient thermal effects， and the land-atmosphere interaction and the atmospheric boundary layer processes are very important for the weather development and climate change over the QXP and its surrounding regions.Since the 1960s， especially after 1979， a series of observation and research programs have been conducted， including "the Qinghai-Xizang Plateau Meteorological Science Experiment （QXPMEX） "， " The Second Tibetan Plateau Scientific Experiment （TIPEX-Ⅱ）"， "the Global Energy and Water Cycle Experiment （GEWEX）， the Asian Monsoon Experiment on the Tibetan Plateau（GAME/Tibet）"， "the Coordinated Enhanced Observing Period （CEOP） Asia-Australia Monsoon Project on the Tibetan Plateau（CAMP/Tibet）"， "the Tibetan Observation and Research Platform （TORP）"， and "The Third Tibetan Plateau Atmospheric Scientific Experiment （TIPEX-Ⅲ）"， where the observation analysis， numerical simulation and satellite application of the land-atmosphere interaction and the atmospheric boundary layer processes are the most important contents.Here， we reviewed the major atmospheric scientific experiments over the QXP in the past 40 years and summarized the observation experiments of the land-atmosphere interaction and the atmospheric boundary layer processes systematically.The relevant results are briefly summarized in 5 aspects， including the land-atmosphere interaction process， the atmospheric boundary layer process， the surface and atmospheric heat sources， satellite application of land evapotranspiration， numerical simulation of land surface processes.

By using the ECMWF Re-Analyses version5 data， the water vapor transport type over the Yarlung Zangbo Grand Canyon area of southeastern Qinghai-Xizang Plateau（QXP）are categorized， the daily variation characteristics of land-atmospheric water heat exchange fluxes are analyzed at different locations under different water vapor conditions by choosing two observation stations in the Yarlung Zangbo Grand Canyon area， namely， the Pailong Station and the Motuo Station.The results show that： The plateau monsoon period is the period of strong water vapor transport and the warm-wet period in the Yarlung Zangbo Grand Canyon area， while the opposite is true for the Plateau non-Monsoon period.Daily variations of near-surface latent heat fluxes on typical sunny/cloudy days during the Plateau Monsoon/non-Monsoon period are more sensitive and consistent in response to atmospheric water vapor conditions at the Motuo and the Pailong stations.The daily variation of near-surface latent heat flux under strong water vapor conditions is stronger than that under weak water vapor conditions， and the most significant difference in daily variation of near-surface latent heat flux under different water vapor conditions is found at the low altitude and humid Motuo station， where the daily average of near-surface sensible heat flux under strong water vapor conditions （84.05 W·m^-2） is about 1.13 times of that under weak water vapor conditions on a typical sunny day during the non-monsoon period on the plateau， and the daily variation can reach 345.37 W·m^-2.Different characteristics of near-surface sensible heat fluxes at the two sites in response to different water vapor conditions during the highland monsoon and non-monsoon periods.The daily variation of near-surface sensible heat fluxes at the Pailong and the Motuo stations on typical clear days during the highland monsoon period is stronger under weak water vapor conditions than under strong water vapor conditions.The daily average and variation of near-surface sensible heat flux is most sensitive to the difference of water vapor conditions during the highland monsoon/non-monsoon period at the higher altitude Pailong station， and the daily average and diurnal range of sensible heat flux under weak water vapor conditions （32.71 and 191.1 W·m^-2） is about 1.66 and 1.26 times higher than that under strong water vapor conditions under a typical sunny day during the highland monsoon period.The weakening effect of cloud cover and water vapor on solar short-wave radiation is greater than its own greenhouse effect.The daily variations of near-surface sensible heat fluxes at the Motuo and the Pailong stations under weak water vapor conditions on typical cloudy days during the highland monsoon/non-monsoon period are stronger than those under strong water vapor conditions， and the daily average values of near-surface sensible heat fluxes at the Pailong station under weak water vapor conditions on typical cloudy days during the Plateau Monsoon/non-Monsoon period are 35.12 and 14.32 W?m^-2 which are 2.59 and 1.27 times higher than those under strong water vapor conditions， respectively.The existence of water vapor transport channels in the Yarlung Zangbo Grand Canyon area， the radiation forcing of atmospheric water vapor has significant effects on the land-atmospheric water & heat exchanges process， the energy parting at the surface is controlled by the land surface property.

Using the daily precipitation datasets from 64 meteorological monitoring stations in the Loess Plateau and NCEP/NCAR reanalysis data during the period of 1961 -2016， the spatial-temporal variations of the extreme precipitation were investigated in the Loess Plateau.In addition， the similarities and differences in atmospheric circulation situation corresponding to strong and weak years of extreme precipitation， and in different ages were compared.Results showed that extreme precipitation was the major type in summer in the Loess Plateau， which accounted for about 70% of the total summer precipitation， and presented spatial decreases from east to west of the plateau.Under the background of overall decline of summer precipitation in the Loess Plateau from 1961 to 2016， the proportion of extreme precipitation showed an increasing trend among almost 70% of the stations.Comparison of atmospheric circulation between strong and weak year indicated that when Baikal low strengthened and the subtropical high extended northward in summer， the warm and humid northward air flow from the Northwest Pacific Ocean and South China Sea intensified， leading to the convergence of cold and warm air over the Loess Plateau and consequently more extreme precipitation in summer.In strong extreme precipitation years， there were positive water vapor income anomalies in summer in the Loess Plateau.The positive contribution to water vapor mainly originated from the northern and southern boundaries in June.The water vapor at northern boundary was converted to an output part in July and August， while the water vapor input at the western and southern boundaries increased and more pronounced in August.The more obviously convergence of cold and warm air in summer was detected in strong extreme precipitation years， which was beneficial to the release of unstable energy and the increase of extreme precipitation in study area.Moreover， extreme precipitation in summer was found to have experienced a transition from wet condition to dry condition in the Loess Plateau in the 1980s， and had begun to increase in recent years.Based on the analyses of the characteristics of summer atmospheric circulation in different ages， it can be observed that positive net income of water vapor and obvious convergence of cold and warm air in summer typically resulted in more extreme precipitation in the Loess Plateau in the corresponding year， and vice versa.

Based on the in-situ observation of double-metal-sphere three-dimensional （3-D） electric field sonde and the comprehensive data of surface electric field， weather radar and lightning location， the electric field （E-field） and corresponding charge structure inside the stratiform region of a mesoscale convective system （MCS） in the North China Plain on 19 August 2016 were studied.The sounding system was released at 04： 30 （Beijing time） when the storm was at mature stage.The surface E-field was relatively weak （about +1.7 kV·m^-1） compared to that of other overhead strong thunderstorms （>5 kV·m^-1）.The lightning frequency of the whole MCS presented an obvious unimodal distribution and the peak occurred at about 06： 00.However， almost all lightning occurred in the convection region， while there was a few lightning within the stratiform.The complete sounding data during the ascent stage showed that there were six charge layers in the stratiform and the charge polarity altered in the vertical direction.The main positive charge region was at 8.2-9.5 km （-20~-14 ℃） and the main negative charge region was at 7.4~8.2 km （-14~-10 ℃）.A thin positive layer was just below， and a negative shielding charge region was near the top of thunderstorm.There were one positive and one negative charge layer near 0 ℃.The total net charge of the six layers was weakly positive （about +0.22 nC·m^-2）， that may be caused by the positive particles advected from the convection based on the 3-D dynamic field simulation of the MCS.The local electrification mechanism may also contribute to the charge layers near 0 ℃， that need more observation and simulation to study.When the sounding system flew down （about 1 hour later）， it still went through the stratiform region that was at the mature stage.The available sounding data between 4.6 to 9.0 km showed the maximum E-field was about +70 kV·m^-1， larger than that in the ascent stage， and four charge layers existed.The distribution of charge structure corresponded roughly to with that during the ascent stage， while the heights， thicknesses and charge densities of the charge layers were different.The differences may be caused by the changes of the sounding position relative to the thunderstorm， the development status， and the dynamic and microphysical field inside cloud.

By analyzing Soil Moisture Anomaly Percentage Index （SMAPI） at different soil layers， dry-wet evolution of the source region of the Yellow River （SRYR） during 2008 -2017 are investigated using observations from the Maqu-Ruoergai soil temperature and moisture monitoring network.To diagnose the water vapor transportation path and potential water vapor sources in different processes， the Lagrange Flexible Particle Dispersion Model （FLEXPART）， which is driven by reanalysis data （National Centers for Environmental Prediction Final， NECP FNL）， are used to simulate the backward trajectories of target particles.The results show that the water vapor transportation path can be divided into three categories： （1） South Branch transportation.The water vapor origins from the Indian Ocean and the Arabian Sea， and finally arrives at the SRYR by way of the Indian Peninsula and Bay of Bengal； （2） East Branch transportation.The water vapor is from the Pacific Ocean and the South China Sea， then passes through the Yangtze River Basin， and finally arrives at the SRYR from eastern and southern flank of the Tibetan Plateau； （3） North Branch transportation.The water vapor is from the Atlantic Ocean， the northern African continent， and the European continent， then arrives at the SRYR from the western or northern side of the Tibetan Plateau by way of the mid-latitude Eurasian continent.Moreover， the North Branch is dominant in dry period， whereas the South and East branches are prominent in wet period.The water vapor sources also show discrepancies for dry and wet periods.The water vapor sources of the Tibetan Plateau are mainly distributed around the Kunlun Mountains during wet period， and are scattered distributed from north to south during transitional period， and are located around the Tianshan during dry period.The intensity of the water vapor sources of the Iranian Plateau， Pamir Plateau， and the Bay of Bengal gradually strengthen from wet to dry period， the intensity of the water vapor sources of the Sichuan Basin-Qinling Mountains and south China enhanced first and then weakened， while the source of Qilian Mountain-Loess Plateau weakened after enhanced.The intensity of water vapor sources over the middle and lower reaches of the Yangtze River and around East China has been weakening from the wet period to the dry period.