Based on the China snow depth time series data set and high resolution ground meteorological element driven dataset， this study analyzes the spatial and temporal variation of snow depth on the Qinghai-Xizang （Tibetan） Plateau by watershed and elevation gradient during the 1980 -2020 snow season considering different river basins and elevation gradients.Additionally， the study investigates the response of snow depth to climate change in the context of hydrothermal factors.The results show that： （1） Spatial difference in snow depth on the Qinghai-Xizang （Tibetan） Plateau was obvious， showing a distribution pattern of high in the west and low in the east， and greater in the high-altitude mountain areas than in the basin plains， with the average snow depth in the high-altitude mountain areas generally greater than 10 cm.The average snow depth decreased at a rate of 0.25 cm/decade， 64.74% of the regions showed a declining trend， with statistically significant decreases in 29.09% on the Qinghai-Xizang （Tibetan） Plateau during the snow season from 1980 to 2020.（2） There is a clear vertical zonation of snow depth and its trend as influenced by altitude.Below an altitude of 4.2 km， average snow depth increased with elevation.Between 4.2 km and 4.8 km， average snow depth decreased as elevation rises.Above 4.8 km， average snow depth again increased with elevation.A decreasing trend in snow depth was observed across all elevation bands， with the rate of decrease initially increasing and then decreasing with elevation， exhibiting a threshold at approximately 5.0 km.The most rapid decrease in mean snow depth ［3.36 cm·（10a）^-1］occurred in the 5.0~5.2 km elevation band.The interannual variation of mean snow depth exhibited a pronounced altitude-dependent pattern， the rate of snow depth reduction was significantly higher at higher elevations than at lower elevations， especially at 4.8~5.5 km.（3） Climate change on the Qinghai-Xizang （Tibetan） Plateau is ‘warmer and wetter’ overall， but ‘warmer and drier’ in the north-west and south during the snow season from 1980 to 2020.However， there are watershed differences and elevation differences in the response of snow depth to climate change.Specifically， in the Nujiang， Ganges， Amu Darya， and Indus River basins， the warming and aridification of climate conditions have contributed to a reduction in snow depth.Conversely， temperature has a more pronounced effect on snow depth in the Yarlung Tsangpo River， the interior plateau， as well as the Yangtze River basins， the Qaidam Basin， and the Tarim Basin.Additionally， precipitation plays a more significant role in influencing snow depth in the Yellow River， Heihe River basin.In regions with altitudes below 3.5 km， climate conditions characterized by warming and aridification have led to a reduction in snow depth.However， in areas with altitudes above 3.5 km， temperature has a more pronounced influence on snow depth.The altitude-dependent warming of temperature accounts for the altitude-dependent reduction in snow depth.

Compound heatwave events are heatwaves that occur simultaneously during the day and at night， which not only threaten human health but also impede sustainable socio-economic and ecosystem development.In recent years， the frequency of compound heatwave events in the Sichuan-Chongqing （SC） region has increased significantly， and an advanced understanding of the plausible factors of compound heatwave variations over the SC region is of great importance for a better understanding of their impacts.Based on observational and reanalysis data， the relationship between the summer compound heat wave frequency （HWF） in SC and the anomalous atmospheric heat source （AHS） over the Qinghai-Xizang （Tibetan） Plateau （QXP） is statistically analyzed in the present study.Then， this study evaluates the performance of 28 climate models from the Coupled Model Intercomparison Project Phase 6 （CMIP6） in simulating the relationship between the SC HWF and the QXP AHS of 1985-2014 and explores the key factors causing the differences in the simulation capability among the models.The results show that both the climate mean and the standard deviation of the HWF have relatively large values in the eastern SC， where the HWF variability shows a significant negative correlation with the summer AHS over the southeastern QXP.When the AHS over the southeastern QXP is weaker in summer， an anomalous anticyclone is present over the eastern SC， leading to an anomalous downward motion.This anomalous descent induces cloud cover and surface shortwave changes， leading to the formation of heatwave events over the eastern SC.Most CMIP6 models can essentially simulate the spatial distribution characteristics of the observed climate states of the summer HWF in the SC region and the summer AHS in the QXP.However， the models perform better in simulating the standard deviation of the AHS over the QXP than in simulating the HWF in the SC regions.There are significant differences in the simulated relationship between the SC HWF and the QXP AHS between different models.This is mainly due to the different abilities of the models to simulate the anomalous vertical motions over the SC regions corresponding to the anomalous summer AHS over the QXP.Further analysis shows that a good performance of the models usually depends on their ability to simulate the anomalous vertical motions and cloudiness in the SC regions， which can lead to air temperature variations.Therefore， the simulated vertical motion and cloudiness anomalies in the eastern SC in response to the QXP AHS anomalies are the key circulation factors affecting the model’s performance in simulating the HWF-AHS relationship.

The freeze-thaw cycle of near-surface soil in the perennial permafrost region of the Qinghai-Xizang （Tibetan） Plateau plays a crucial role in regulating water and energy exchange between the soil and the atmosphere.Investigating its spatiotemporal characteristics and response to climate change is essential for understanding the mechanisms driving climate change on the plateau.In this study， we calculated near-surface freeze-thaw parameters-including the start and end times of soil freezing， thawing duration， and freezing duration-across the perennial permafrost region of the plateau from 1980 to 2017 using the Common Land Model 5.0 （CLM5.0）.We further analyzed their spatiotemporal variations and correlations with temperature， precipitation， snow depth， and vegetation index.The results show that： （1） The onset of near-surface soil freezing in the plateau’s permafrost region occurs between September and mid-to-late October， while the thawing period ends between February and May.Semi-humid regions have the longest thawing duration， whereas semi-arid regions have the shortest， with an average difference of 15 days.The freeze-thaw status of permafrost soil on the plateau exhibits significant changes.Except for areas near the Karakoram Mountains， most permafrost regions show a decreasing trend in freezing duration and an increasing trend in thawing duration.The average growth rate of soil thawing duration across the plateau is 2 d·（10a）⁻¹， with the most significant increase observed in semi-humid regions， reaching 4 d·（10a）⁻¹.（2） The freeze-thaw parameters of the plateau's permafrost are associated with geographical factors.In the latitude range of 29°N -36°N and longitude range of 82.5°E -103°E， the thawing duration shows an increasing trend； however， the rate of change decreases in some areas while increasing in others.Additionally， as elevation increases， the growth rate of thawing duration declines.（3） The duration of permafrost thawing is significantly correlated with snow depth， near-surface temperature， precipitation， and vegetation index， though these relationships vary across different climatic regions.Near-surface temperature exhibits a strong positive correlation across all regions， making it the primary driver of freeze-thaw changes.Precipitation and snow depth show positive and negative correlations， respectively， with particularly strong correlations in semi-humid areas.The vegetation index is positively correlated with thaw duration in all regions， with the strongest correlation observed in semi-arid areas.（4） The relationship between thawing duration and seasonal climatic factors varies.Near-surface air temperature exerts a significant influence on the freeze-thaw process at seasonal scales， with the most pronounced impact occurring in spring.Precipitation is positively correlated in summer but negatively correlated in winter.Both snow depth and vegetation index are significantly correlated with thawing duration in semi-arid and semi-humid regions during spring， exhibiting negative and positive correlations， respectively.（5） Near-surface temperature influences the freeze-thaw cycle in the plateau’s perennial permafrost region during both dry and wet seasons.However， the effects of snow depth， precipitation， and vegetation index are more pronounced during the wet season.

Using effective bias correction methods and transforming non-stationary data to stationary can enhance the scientific accuracy of temperature analysis， allowing for a deeper understanding of its temporal and spatial distribution characteristics and evolution patterns.This study utilizes the ERA5_Land near-surface （2 m） monthly mean temperature observation dataset covering the period from 1970 to 2014.Initially， it employs the Taylor diagram， Taylor index， interannual variability skill score， and rank scoring method to evaluate and select among six climate models from the International Coupled Model Intercomparison Project Phase 6 （CMIP6） and the multi-model ensemble （MME） average models.Subsequently， the superior models are refined using the Delta bias correction method and the Normal distribution matching method.Finally， the study analyzes the temporal and spatial temperature variation characteristics of the Qinghai-Xizang Plateau from 2015 to 2100 under the SSP1-2.6， SSP2-4.5， and SSP5-8.5 scenarios.The results indicate that： （1） Among the six CMIP6 models and the multi-model ensemble （MME） average models analyzed in this study， the EC-Earth3 model demonstrates the most effective performance in simulating temperature.（2） When comparing the Delta bias correction results of the EC-Earth3 model with observational data， the regional averages of the coefficient of determination （R²） and the Nash-Sutcliffe efficiency coefficient （NSE） are 0.992 and 0.983， respectively.After applying the Normal distribution matching method for correction， the regional average values of R² and NSE are 0.990 and 0.978， respectively.This comparison reveals that the Delta bias correction method exhibits superior correction efficacy for the model's monthly temperature.（3） According to the combination of EOF-EEMD， the annual temperature of the first typical field of the three scenarios changes uniformly in the whole region， and there is a common sensitive area of temperature change under SSP1-2.6 and SSP2-4.5 scenarios， that is， the central region of the Qiangtang Plateau.The temperature dynamics in the second typical field reveal a gradual reverse-phase change from the upper reaches of the Zhaqu River to surrounding areas.Under the SSP1-2.6 scenario， the plateau experiences overall cooling in the east and warming in the west.Conversely， under the SSP2-4.5 and SSP5-8.5 scenarios， the plateau initially warms in the east and cools in the west， followed by a subsequent cooling in the east and warming in the west.This study provides a reference for bias correction methods that enhance the accurate application of climate model data in the Qinghai-Xizang Plateau region and offers essential foundational information for a comprehensive assessment of the impacts of temperature changes on water resources， ecosystems， and the environment in this area.

The central Qinghai-Xizang Plateau is located in the transition zone between the mid-latitude westerlies and the Asian monsoon， with complex circulation systems and water vapor sources.In the studies of lake-atmosphere interaction in the Qinghai-Xizang Plateau， little attention has been paid to the dependence of lake effect on background circulation to understand the mechanism of lake affecting extreme precipitation.To further understand the mechanism of lake influence on extreme precipitation， this study objectively classifies the dominant synoptic patterns responsible for the regional extreme precipitation events in autumn over the central Qinghai-Xizang Plateau with lakes densely distributed to analyze the characteristics and differences of lake effects under different dominant synoptic patterns.Based on the CMFD precipitation data and ERA5 reanalysis data during 1979 to 2018， 1358 regional extreme precipitation events were detected in autumn over the central Qinghai-Xizang Plateau， and it was found that the regional extreme precipitation events contributed more than 40% of the total autumn precipitation in most parts of the central Qinghai-Xizang Plateau with the large centers of regional extreme precipitation amount mainly concentrated in the Nam co basin and the small lakes in the north， that is also the region with high occurrence probability of extreme precipitation when regional extreme precipitation event occurs.Then， the spectral clustering method was used to analyze the atmospheric circulation over the central Qinghai-Xizang Plateau during the regional extreme precipitation events and identified three dominant synoptic patterns responsible for the regional extreme precipitation events in autumn over the central Qinghai-Xizang Plateau： precipitation in the southern mountainous areas caused by weak convergence airflow （P1 type）， precipitation in the northeast downstream under the control of monsoonal southwest airflow （P2 type）， and precipitation near lakes under the influence of southwest airflow in front of the westerly trough （P3 type）.They lead to 48.8%， 42.3% and 8.8% of the total occurrences of regional extreme precipitation events in autumn， respectively.P1 and P2 types mainly occur in September， and P3 type mainly occurs in October.The physical mechanism of the regional extreme precipitation occurrences is explained by analyzing the high and low level configuration of large-scale circulation fields and their anomalies under different synoptic patterns.Furthermore， multiple sensitivity experiments were conducted to reveal the relative importance of the influence of lake clusters in the central Qinghai-Xizang Plateau on regional extreme precipitation events under different synoptic patterns， and found that the lake clusters can lead to the precipitation amount averaged over the central Qinghai-Xizang Plateau reduced by 2.37%， increased by 12.11% and increased by 138.37% under the P1， P2 and P3 types， respectively.The lake effect under the P3 type is the most significant among the three synoptic types， making it a synoptic pattern prone to lake effect.Further mechanistic analysis shows that the enhancement of low-level instability and water vapor convergence over the lake and surroundings areas induced by the heating and moistening effect of lake play an important role in the formation of the regional extreme precipitation under the synoptic pattern P3.This research has identified the dominant synoptic patterns responsible for the regional extreme precipitation events over the central Qinghai-Xizang Plateau in autumn and revealed the relative importance of lake effects on regional extreme precipitation under different dominant synoptic patterns， providing necessary reference for further improving the prediction level of regional extreme precipitation.

The Qinghai-Xizang Plateau summer monsoon is an important component of the Asian monsoon system， significantly influencing the energy and moisture cycles in the plateau and its surrounding regions.This study uses JRA-55 monthly reanalysis data from 1980 to 2020 and GPCC monthly precipitation data， combined with the Qinghai-Xizang Plateau Monsoon Index.Various statistical methods， including correlation analysis， regression analysis， composite analysis， and dynamic diagnostics， are used in this study.This paper focuses on the impact of the summer monsoon over the Qinghai-Xizang Plateau on water transport， such as precipitation， atmospheric circulation， and water budget.The results show that： （1） When the Qinghai-Xizang Plateau summer monsoon is strong （weak）， precipitation in the central and eastern parts of the plateau increases （decreases）.（2） From the perspective of water vapor transport， when the summer monsoon over the plateau is stronger， there is an anomalous anticyclonic circulation over central India， an anomalous westerly airflow to the south of the plateau， and the water vapor transport over the plateau is primarily dominated by the westerly water vapor transport channel.（3） Analysed in terms of moisture budget， when the Qinghai-Xizang Plateau summer monsoon is strong （weak）， moisture inflow at the southern and western boundaries of the plateau increases （decreases）， while moisture inflow at the northern boundary decreases （increases）， resulting in an increase （decrease） in regional net moisture budget.（4） The impact of the Qinghai-Xizang Plateau summer monsoon on moisture convergence/divergence is mainly driven by the contribution of the wind’s dynamic component， while the thermal component from moisture advection is relatively small.

This study evaluates the simulation capabilities of 16 models with varying resolutions from the High-Resolution Model Intercomparison Project （HighResMIP） in reproducing warm-season （May to September） precipitation over the eastern slope of the Qinghai-Xizang Plateau， using the CN05.1 dataset as observational reference.Through comparative analysis of outputs from multiple models against observational data， this study elucidates model strengths and limitations in capturing spatiotemporal variability， precipitation intensity， and terrain-related mechanisms.Results indicate that high-resolution climate models demonstrate reasonable accuracy in simulating annual and warm-season precipitation spatial patterns， though notable inter-model discrepancies persist.Three models （CMCC-CM2-HR4， CMCC-CM2-VHR4， FGOAL-f3-H） successfully replicate the observed increasing trend in annual precipitation， while others exhibit stable or decreasing trends.Persistent model deficiencies emerge in simulating precipitation frequency and intensity： all models systematically underestimate light precipitation events （<1 mm∙d^-1） while overestimating heavy precipitation frequency （>4 mm∙d^-1）.Medium-to-low-resolution models show a systematic phase lag of approximately 30 days in diurnal precipitation cycles compared to observations.In contrast， the high-resolution models performed better in simulating precipitation frequency than the medium low resolution group.Based on comprehensive evaluation of temporal distribution， frequency characteristics， and model skill scores， the ECWMF model demonstrates superior performance， whereas the FGOAL-f3-H model exhibits significant negative biases.

On August 13-14， 2022， an extreme rainstorm event occurred in Yuzhong region of Gansu Province， northeast of the Qinghai-Xizang Plateau.Accumulated daily precipitation reached 130.6 mm and the maximum hourly precipitation was 36.6 mm， breaking the heaviest daily precipitation records of the region and causing serious social impact and economic losses.Based on the data of surface minute observation and high altitude observation， Lanzhou Doppler radar and ECMWF Reanalysis v5（ERA5）， by analyzing the observation characteristics， environmental conditions， topographic effects and instability mechanism of the two heavy precipitation stages in this extreme rainstorm， the results show that： （1） The rainstorm was caused by the convergence of weak cold air brought by the shortwave trough in the westerlies and warm and humid air outside the subtropical high in the Longzhong area.The 700 hPa shear line provided the dynamic lifting conditions， and the surface cold front provided the triggering conditions.（2） The radar reflectance factor in the rainstorm process was characterized by persistent strong echoes accompanied by "backward propagation"， low-level jets and obvious convergence.In the second stage， the echo top height behind the cold front was similar to that in the first stage， but the scope was larger and the structure was more compact， and the convective cloud development was more vigorous.（3） The water vapor conditions of the rainstorm were abundant.In the first stage， there was significant convective instability due to strong convergence and upward movement at the lower level and high convective effective potential energy.In the second stage， the upward movement was weakened， the convective effective potential energy was 0， and the dynamic and convective instability conditions were weak.（4） The release of unstable energy triggered by cold front baroclinic frontogenesis was the main triggering mechanism of precipitation in the first stage.After the transit of the cold front， the precipitation in the second stage was formed by the combination of terrain， frontogenic secondary circulation and instability.Since the heavy precipitation after the summer cold front was not common in the northeast part of the Qinghai-Xizang Plateau， forecasters tended to ignore such kind of rainstorms.Therefore， we need to strengthen monitoring and early warning of such rainstorm events.

This study aims to improve the accuracy of simulating soil hydrothermal processes on the Qinghai-Xizang Plateau by introducing a novel soil stratification method combined with an integrated freeze-thaw gravel parameterization scheme.The region's unique topography and complex climate pose challenges for conventional numerical models in achieving precise simulations.The proposed scheme incorporates freeze-thaw parameterization， gravel parameterization， and refined vertical soil discretization， offering a more comprehensive representation of the soil characteristics and terrain complexity specific to the Qinghai-Xizang Plateau.To evaluate the effectiveness of the scheme， the BCC-CSM atmospheric circulation model， provided by the National Earth System Modeling Center， was used for testing.The results demonstrate that integrating freeze-thaw and gravel parameterization significantly improves the representation of soil hydrothermal distributions， especially during the winter and at greater soil depths.By refining the soil stratification to 20 and 30 layers， the simulations of soil temperature and moisture have been further enhanced.The 30-layer stratification yields the most accurate outcomes， followed closely by the 20-layer configuration.This approach notably reduces bias and root mean square error in soil temperature simulations， particularly in the central and western regions of the Qinghai-Xizang Plateau， with better performance in winter compared to summer.While soil moisture simulation accuracy lags behind temperature results， the stratification refinement reduces errors， particularly in shallow soil layers.The enhanced stratification also improves the correlation between simulated values and CRA data， strengthening the alignment between simulation and observation， especially in the central and western parts of the plateau.This research provides new insights into soil hydrothermal processes on the Qinghai-Xizang Plateau and offers critical methodology and technical support for future climate simulations and predictions.Moreover， the proposed integrated scheme holds significant potential for simulating soil hydrothermal processes in other plateau regions and may be applied across a wide range of fields.

The phenomenon of near-surface energy budget imbalance is widespread， especially in the complex underlying surface such as mountain lakes.Due to the heterogeneity of the surface， the energy closure is poor， and the influence of the energy storage term between the atmosphere of the high canopy vegetation in the mountain on the energy closure is often ignored.This paper is based on the gradient tower meteorological data， radiation observation data and turbulence observation data of the eddy covariance system of Mount Emei Atmosphere and Environment Comprehensive Observation Experimental Station of Chengdu University of Information Technology （hereinafter referred to as "Mount Emei Station"） from June 2022 to October 2022.The Ogive function was used to analyze the average time suitable for the turbulent flux calculation at the forest station， and the soil heat flux and energy storage between vegetation and atmosphere were calculated， and the changes of near-surface energy balance after considering the storage terms between vegetation and atmosphere were analyzed.The results show that extending the average time to calculate turbulent flux to 60 minutes can capture larger turbulent vortices at some moments to a certain extent， but the energy balance ratio is lower than the average time of 30 minutes， so it is considered that the average time of 30 minutes is still suitable for the calculation of turbulent flux at Emei Mountain Station.The energy storage item of vegetation atmosphere improves the energy balance ratio by about 3.65%.Considering that this item has the effect of improving energy closure in most of the time， the energy storage item of photosynthesis contributes the most to improving energy closure， followed by the heat storage item of vegetation canopy， followed by the sensible heat storage item， and the latent heat storage item contributes the least.All the energy storage items in the atmosphere of high canopy vegetation have obvious single-peak diurnal variation characteristics.The peak value of heat storage items in vegetation canopy can reach up to 26 W·m^-2， and the energy balance ratio can be increased by 1.57% when the heat storage items in vegetation canopy are considered.The peak value of the photosynthetic storage term can reach about 8 W·m^-2， and the average daily storage capacity is about 141.6 W·m^-2， which is the main energy storage term.Considering the photosynthetic storage term， the energy balance ratio can be improved by 1.65%， accounting for 45% of the overall effect.The peak value of sensible heat storage term is about 5 W·m^-2， the magnitude of latent heat storage term is very small， and the effect on energy closure is also small.Vegetation-atmosphere storage terms cannot be ignored except latent heat storage terms which are very small.When considering the energy storage between vegetation and atmosphere， the energy closure problem still exists.Therefore， in addition to the energy storage term， the influence of large-scale vortices induced by the underlying mountain surface on the near-surface energy budget also needs to be further studied.

We bias-corrected and assessed summer precipitation data over the Qinghai-Xizang Plateau （QXP） based on 18 models from the Coupled Model Intercomparison Project Phase 6 （CMIP6）.Our assessment of CMIP6 data， conducted for the period 1979-2014， centered on the performance of both the ensemble and individual models.We evaluated the CMIP6 data before and after bias correction， according to considering mean precipitation and extreme precipitation.The results highlight the correction method's dependence on ERA5 reanalysis data quality over the QXP.Although corrected mean summer precipitation over the QXP shows improvement in bias and bias rate， it exhibits inferior interannual time-varying characteristics compared to pre-corrected data.Most of the models were able to better simulate the spatial variability characteristics of mean precipitation over the QXP， gradually increasing from northwest to southeast from 1979 to 2014.Pre-correction precipitation data overestimates precipitation over the QXP with a bias rate of 60.4%， while corrected data is relatively underestimated with a deviation rate of -13.9%.The mean bias of the corrected data from ERA5 is only 0.003 mm·d^-1， with a spatial correlation as high as 0.999.Spatial trend analysis of observed data indicates a slight increase in summer precipitation over most of the TP from 1979 to 2014， with a significant decreasing trend only along the eastern edge.Both pre- and post-corrected data generally capture this spatial distribution， though pattern correlation coefficients of most individual uncorrected CMIP6 models do not exceed 0.5.Comparing with the interannual variability of the precipitation data obtained from observations， the pre-corrected data overestimate the precipitation on the QXP， while the post-corrected data are underestimated in comparison with the observation results.Extreme precipitation is selected by determining the 95% thresholds， a revealing a spatial distribution similar to the mean annual precipitation， increasing from northwest to southeast.This feature is well captured by some models， such as MRI-ESM2-0 （The Meteorological Research Institute Earth System Model version 2.0） and ACCESS-CM2 （Australian Community Climate and Earth System Simulator Climate Model Version 2.0）.Earth System Simulator Climate Model Version 2）， the spatial correlation coefficients are 0.851 and 0.821， respectively， compared with the observations， but the spatial correlation of the corrected data decreases from 0.861 to 0.730， failing to accurately characterize the stepwise increase of extreme precipitation on the QXP.The deviation distribution of the corrected extreme precipitation data is similar to pre-correction data， with lower areas concentrated in the southern hinterland and eastern part of the QXP.The analysis of extreme precipitation contribution shows that both the observation results and the CMIP6 precipitation data indicate that the trend of extreme precipitation contribution is not obvious during 1979-2014.Among individual models， EC-Earth3-Veg （European Community Earth-Vegetation model version 3） and EC-Earth3 （European Community Earth Model version 3） and CanESM5 （The Canadian Earth System Model version 5） ranked high in several parameters， showing better simulation capability， while IPSL-CM6A-LR （Institute Pierre-Simon Laplace Climate Model 6A Low Resolution） ranked high in the mean precipitation deviation and extreme precipitation deviation.

The Qinghai-Xizang Plateau （QXP） is an important herbage producing area， ecological barrier and water conservation area， the vegetation ecological process on which can directly affect the changes of China and even East Asia.With global warming， the phenological period of vegetation on the QXP is constantly changing， affecting climate and ecosystem through carbon cycle and hydrothermal cycle， etc.The study of phenological change and its influencing factors has become a key issue， and the construction of models that can realize future phenological prediction is of great scientific significance.In this paper， based on the Normalized Difference Vegetation Index acquired by satellites during 2000 -2020 （MODIS NDVI）， the dynamic threshold method was used to extract the start of growing season （SOS） on the QXP， and its spatiotemporal variation was analyzed in combination with vegetation types， so as to construct multiple phenological models of SOS， air temperature and soil moisture， exploring the hydrothermal conditions required for different regions and types of vegetation to start growing.The results showed that： （1） From 2000 to 2020， the overall SOS advance trend of the QXP was most significant in the eastern part of the region， where the SOS advance rate exceeded 10 d·（10a）^-1.Coniferous forests， scrub， meadows， and alpine vegetation cover areas had a high percentage of SOS advance， and grasslands had about 50 % of slightly delayed areas.（2） The eastern and northern regions of the QXP showed an obvious warming and humidification trend.The average annual temperature rise rate was about 0.36 ℃·（10a）^-1， and the average annual soil moisture increase rate was about 3.8×10^-4 m³·m^-3 （p<0.01）.（3） The parameters of the four phenological models showed that the vegetation growth in the eastern and southern QXP required higher hydrothermal conditions.The main controlling factor for vegetation SOS in the south was air temperature， while in the north it was soil moisture.The temperature and soil moisture thresholds and main controlling factor of different vegetation types were also closely related to their spatial distribution locations.（4） The cumulative temperature and cumulative soil moisture threshold model established in this paper has the best simulation effect for the main vegetation types （grassland， meadow and alpine vegetation） on the QXP， and the root-mean-square error is only about 8 days， which has reference significance for the future SOS prediction and the interaction mechanism between phenology and climate on the QXP.

In the context of global warming， the Qinghai-Xizang Plateau is altering atmospheric circulation through sensible heat absorption and latent heat release.This not only impacts the water and energy balance of the plateau's ecosystem but also plays a crucial role in regulating Asian and global climates.In order to explore the change characteristics and influencing factors of evapotranspiration in different regions of alpine grassland ecosystem on the Qinghai-Xizang Plateau， and deepen understanding of plateau climate change and hydrological-ecological processes， based on the observed eddy and meteorological data in 2022， the variation characteristics and environmental influencing factors of actual evapotranspiration of alpine grassland ecosystems at the same altitude in Sijinlacuo （seasonal permafrost） and Tuotuo River （permafrost） on the Qinghai-Xizang Plateau were compared and analyzed.The results show that： （1） Significant differences existed between environmental factors at these two sites， particularly in wind speed， air temperature， and precipitation.The wind speed at Tuotuo River station greatly exceeded that at Shijinlasuo station； annual average air temperature and precipitation were lower at Tuotuo River station.（2） The average hourly evapotranspiration of Sijinlacuo Station at night was higher than those recorded at Tuotuo River Station， however， this trend reverses during daytime hours.The variation characteristics of daily evapotranspiration at the two stations had a similar trend.The date of sharp increase and maximum of evapotranspiration at Sijinlacuo Station were earlier than those at Tuotuo River Station.The monthly evapotranspiration of the two stations were unimodal， with the maximum value appeared in July in summer and the smaller value appeared in December， January and February in winter.（3） Wind speed and ground radiation showed differing correlations with evaporation across both stations.Wind speed had a stronger correlation with evaporation at Tuotuo River Station due to higher wind speeds compared to weaker correlations observed for Sijinlasuo Station where winds were less intense.Conversely， ground radiation showed opposite correlations with evaporation between both locations.Air temperature， water vapor pressure， and atmospheric longwave radiation demonstrated strong correlations with evaporation across both locations while air humidity， saturated water vapor pressure difference， and precipitation displayed weaker associations.Precipitation exhibited the weakest correlation.（4） Although precipitation served as the primary source of evaporated water content， sources such as glacier melt water and thawing permafrost played significant roles as well on the Qinghai-Xizang Plateau， resulting in subdued influence of precipitation on the evaporative process at both locations.These results contribute valuable insights into understanding regional variations in high-altitude grassland ecosystems' response to changing climatic conditions on the Qinghai-Xizang Plateau.

The Coupled Model Intercomparison Project （CMIP） provides reliable scientific data for predicting ecology， hydrology and climate under the backdrop of global change.However， there are large biases in current climate models， especially on the Qinghai-Xizang Plateau （QXP）.In this study， we employed Detrended Quantile Mapping （DQM） and Quantile Delta Mapping （QDM） methods to correct and evaluate the precipitation and temperature data of eight CMIP6 models with better simulation performance， utilizing the China Meteorological Forcing Dataset （CMFD）.The results showed that Both methods had corrected the simulation biases of the models， and the correction effects for temperature and precipitation data over the QXP were relatively consistent between the two methods.Then， based on the corrected multi-model ensemble mean （MME） results from QDM method， we analyzed the spatial and temporal variation characteristics of extreme high temperature events， low temperature events， atmospheric dryness and precipitation over the QXP in the early 21^st century （2015 -2057） and later 21^st century （2058-2100）.Under different emission scenarios in the future， extreme high temperature events strengthen， especially in the southeast of the QXP.Extreme high temperature events enhance with the increase of radiation.Extreme low temperature events decrease， with no occurrence in the later 21^st century under high emission scenarios （SSP370 and SSP585）.Under different emission scenarios， precipitation and saturated vapor pressure difference both exhibit a significant increasing trend on the QXP.With global warming， the increase of precipitation does not mitigate atmospheric drought.The atmospheric dryness increases significantly under the future scenarios， especially in summer， at 1.3 to 2 times compared to annual average.

Based on 109 hourly rain-gauge stations from June to August during 2005 -2020， the spatial and temporal distribution of annual rainfall amount， occurrence， rainfall intensity， and duration of summer hourly extreme rainfall events in the region of Southeastern Xizang Plateau-Western Sichuan Basin （28°N -33°N， 90°E - 105°E） are analyzed.Additionally， the diurnal variation of rainfall amount， rainfall intensity， and rainfall frequency during hourly extreme rainfall events in the region of Southeastern Xizang Plateau-Western Sichuan Basin are also explored.Results show that the hourly extreme the rainfall threshold， the annual rainfall amount， the rainfall intensity， and the duration of summer hourly extreme rainfall events in the region of Southeastern Xizang Plateau are lower than those in the region of Western Sichuan Basin， with the occurrence showing the opposite pattern.The annual rainfall amount and occurrence， and duration of summer hourly extreme rainfall events in the region of Southeastern Xizang Plateau increase over time.The annual rainfall amount and occurrence of hourly extreme rainfall events in the region of Western Sichuan Basin also increase， while the duration of hourly extreme rainfall events in the region of Western Sichuan Basin change insignificant.The rainfall amount’， the rainfall intensity’ and the rainfall frequency’ peak time of the summer hourly extreme rainfall events in the region of Southeastern Xizang Plateau -Western Sichuan Basin exhibit the eastward delayed features， and their peak time in the region of Western Sichuan Basin are 3 h， 4 h and 2 h later than those in the region of Southeastern Xizang Plateau， respectively.The most evident delayed feature exists in the rainfall intensity in June， with the peak time in the region of Western Sichuan Basin being 11 hours later than that in the region of Southeastern Xizang Plateau.However， both the Southeastern Xizang Plateau and Western Sichuan Basin regions exhibit insignificant interannual variation in the peak time of the rainfall amount， the rainfall intensity， and the rainfall frequency during summer hourly extreme rainfall events.

Photosynthetically Active Radiation （PAR） spectrum， in visible light， is the wavelength range sensitive to plants and can be absorbed by them for photosynthesis.The characteristics of ground PAR spectrum directly affect the growth， development， morphology， physiological metabolism， yield， and adaptability of plants.In order to further understand the distribution characteristics of PAR in high-altitude areas of Xizang， this study utilized the International High-Precision Solar Spectroradiometer to conduct field observations of the PAR spectrum characteristics in the Mt.Everest， Shigatse， Lhasa， and Nyingchi regions of the Qinghai-Xizang Plateau from 2021 to 2022.The observations found that during the winter and summer solstices on the Qinghai-Xizang Plateau， the variation in PAR was significant.The peak monochromatic radiation illuminance of PAR at Mt.Everest during the summer solstice ［1251 mW·（m²·nm）^-1］ to the winter solstice ［1935 mW·（m²·nm）^-1］ fluctuated by up to 684 mW·（m²·nm）^-1.The winter solstice integrated value of PAR spectrum at Mt.Everest （309.86 W·m^-2） was 41.61% lower than the AM0 standard spectrum integrated value of PAR （530.67 W·m^-2）， and 28% lower than the AM1.5 standard spectrum integrated value of PAR （429.83 W·m^-2）.During the summer solstice， the PAR spectra at Mt.Everest， Shigatse， and Lhasa in Xizang all exceeded the AM1.5 standard spectrum at noon and were close to the AM0 standard spectrum.In Shigatse， Xizang， during the spring equinox and autumn equinox， the peak PAR spectra were 1699 mW·（m²·nm）^-1 and 1696 mW·（m²·nm）^-1 respectively， with peak values being nearly identical.This similarity is due to the same local solar altitude angle at noon （e.g.， 59.84 radians in Shigatse） during the equinoxes at the same observation point on the Tibetan Plateau， assuming other factors affecting the spectrum are the same.Comparison of observations between the Qinghai-Xizang Plateau and low-altitude areas such as Beijing， Anhui's Lu'an， and Henan's Puyang revealed that on a clear day near the winter solstice （November 20， 2021）， the integrated value of PAR spectrum at high-altitude Mt.Everest （309.86 W·m^-2 was 17.19% higher than that in low-altitude Lu'an， Anhui （264.41 W·m^-2）； on a clear day near the summer solstice （June 3， 2021）， the integrated value of PAR spectrum at high-altitude Mt.Everest （487.41 W·m^-2） was 23.66% higher than that in low-altitude Beijing （394.15 W·m^-2）； near the autumn equinox （September 19， 2021）， the integrated value of PAR spectrum in low-altitude Beijing （315.23 W·m^-2） was only 71.24% of that at high-altitude Mt.Everest （442.49 W·m^-2）； near the spring equinox （March 19， 2021）， the integrated value of PAR spectrum in high-altitude Shigatse （413.34 W·m^-2） was 64.75% higher than that in low-altitude Puyang， Henan （261.82 W·m^-2）.The results indicate that the integrated value of PAR spectrum is positively correlated with altitude， with higher altitudes corresponding to larger integrated values.Additionally， through observations of PAR spectra on clear days throughout the year， it was found that there are certain temporal variations in spectral radiation illuminance.Specifically， the spectral radiation illuminance is lowest at the winter solstice， then increases daily until reaching its peak the following year after the spring equinox， decreases daily after the summer solstice， reaches its lowest point again at the winter solstice after the autumn equinox， with the spectral radiation illuminance characteristics being basically the same during the spring equinox and autumn equinox.

The China Meteorological Forcing Dataset（0.1°×0.1°） from 1979 -2018 was used as atmospheric forcing data to drive CLM5.0 （Community Land Model version 5.0） to simulate soil temperature and moisture changes in the Qinghai-Xizang Plateau region from 1979 to 2018.Divide the soil freeze-thaw process into two stages： freezing period and thawing period.By comparing and validating CLM5.0 simulation with site observation data， assimilation data （GLDAS-Noah）， and satellite remote sensing data （MODIS soil temperature data and ESA CCI-COMBINED soil moisture data） in two stages， this study explores the applicability of CLM5.0 simulation of soil temperature and moisture in the Qinghai-Xizang Plateau.The results indicate that： （1） CLM5.0 can accurately describe the dynamic changes in soil temperature and moisture at stations on the Qinghai-Xizang Plateau.The soil temperature and moisture simulated by CLM5.0 have consistent variation characteristics with the observed data and are numerically close.The accuracy of CLM5.0 simulation is higher than that of GLDAS Noah.CLM5.0 provides a more accurate description of soil temperature at the stations.（2） CLM5.0 can accurately describe the soil temperature and moisture characteristics during the freeze-thaw process in the Qinghai-Xizang Plateau.CLM5.0 simulated soil temperature and moisture show a significant positive correlation with MODIS and ESA CCI-COMBINED remote sensing data on the Qinghai-Xizang Plateau， with correlation coefficients mostly above 0.9.CLM5.0 has relatively better simulation ability for soil temperature in Qinghai-Xizang Plateau areas.CLM5.0 has better simulation ability for soil moisture during thawing periods than during freezing periods.CLM5.0 overestimates the soil temperature of the Qinghai-Xizang Plateau as a whole， with an average deviation mostly between 0~4 ℃.The average deviation of soil moisture simulated by CLM5.0 is mostly between -0.1~0.1 m³·m^-3， and the average deviation of soil moisture during thawing period is relatively small.（3） The soil temperature and moisture data from CLM5.0 simulation， GLDAS-Noah， MODIS， and ESA CCI-COMBINED remote sensing all have similar spatial distribution characteristics， with higher similarity in the spatial distribution characteristics of soil temperature.CLM5.0 has higher spatial resolution and more precise soil stratification， which can better describe the details of soil temperature and moisture.（4） The CLM5.0 simulation data shows an overall warming and drying trend in the Qinghai-Xizang Plateau， while the MODIS and ESA CCI-COMBINED remote sensing data show an overall warming and moistening trend.The trend of soil temperature changes simulated by CLM5.0 is relatively accurate， while there is a greater deviation in the trend of soil moisture changes.

High-precision and long time-series soil moisture （SM） data are crucial for quantifying the land-atmosphere interactions on the Qinghai-Xizang Plateau （QXP）.However， most of current studies on the Tibetan Plateau mainly focus on retrieving surface SM based on the satellite data， with relative lack of studies on estimating rootzone SM （RZSM）.Based on data collected from five SM observation networks on the QXP （i.e.， Shiquanhe， Pali， Naqu， upper reaches of Heihe River， and Maqu）， this paper systematically evaluates the applicability of the exponential filter model for estimating RZSM （i.e.， 10， 20， 40 cm） in different climatic and land areas of the QXP.In addition， we explore the impacts of different environmental factors （e.g.， soil properties， climate， and vegetation） on the estimated key model parameter， i.e.， characteristic time length T.Moreover， the reliability of regional-scale T-value obtained using three methods （i.e.， using the median value of optimal T-value obtained for each observation network or the whole Qinghai-Xizang Plateau， or the random forest model） for estimating RZSM on the QXP was assessed.The results showed that： （1） With the increase of soil depth， the correlation between rootzone and surface SM decreased while its spatial heterogeneity increased.This results in a decrease in the accuracy of the exponential filter model， but the obtained T-value and its spatial heterogeneity increased.（2） Spatially， with the increase of precipitation and SM content， the correlation between rootzone and surface SM increased while its spatial heterogeneity decreased.This leads to an increase in the accuracy of the exponential filter model， while the difference in accuracy of the model applied to different sites shows a decreasing trend.（3） Soil properties， especially the sand content， are the main factors controlling the spatial distribution of T-value on the QXP.（4） The different methods for obtaining regional-scale T-value have little influence on the accuracy of the exponential filter model in estimating the RZSM on the QXP.Specifically， both the commonly used methods， such as using the median value of optimal T-value or the random forest model， can obtain reasonable regional-scale T-value and achieve consistent and accurate RZSM estimations.These findings are expected to promote the use of the exponential filter model to accurately obtain the RZSM on the TP using satellite-based surface SM data.

The Qinghai-Xizang Plateau， distinguished by its vast array of lakes， exhibits marked seasonal lake ice coverage， which is highly responsive to climatic shifts.This ice coverage plays a crucial role in the dynamic interchange of fluxes between the lake surfaces and the atmosphere.Despite the significance of these ice phenomena， the limited availability of extensive， long-term observational data on plateau lake ice has led to a reliance on reanalyzed ice datasets， particularly ERA5-Land.This study aims to rigorously evaluate the effectiveness and potential enhancements of ERA5-Land's lake ice data in the distinct environment of the Qinghai-Xizang Plateau.Focusing on data collected from 2010 to 2022 for Qinghai Lake and Ngoring Lake， this research meticulously examines the ERA5-Land reanalysis data's ability to accurately capture the intrinsic characteristics of plateau lake ice.The study uncovered that ERA5-Land tends to overestimate the ice thickness by about 0.54~0.62 m and erroneously prolongs the freezing period by roughly 68 days per year for these lakes.This notable discrepancy necessitated an in-depth error analysis， which synthesized ERA5-Land data with direct observational data from Ngoring Lake， revealing that inaccuracies primarily originated from the FLake one-dimensional lake model within the ERA5-Land system.In an effort to address these inaccuracies， the study employed the MCD43A3 surface albedo product for both Qinghai Lake and Ngoring Lake over the same period.This innovative approach significantly refined the FLake model by incorporating both a multi-year average albedo and a dynamic daily average albedo.These methodological improvements led to a substantial reduction in the average bias of ice thickness， by 85% and 90% respectively， and narrowed the deviation in the modeled freezing period by about 6 and 8 days per year.The enhancements were particularly notable in lakes with longer periods of snow cover， where the dynamic albedo adjustment proved to be highly effective.This research has successfully identified the albedo parameter within the FLake model as a key source of error in ERA5-Land's lake ice characterizations and has implemented practical adjustments to rectify this.These enhancements have markedly increased the model's precision in simulating lake ice， thereby significantly improving the accuracy of ERA5-Land reanalyzed lake ice data.This advancement is particularly pertinent for the unique climatic and geographical conditions of Qinghai Lake and Ngoring Lake on the Qinghai-Xizang Plateau and offers invaluable insights for future research and practical applications in this domain.The findings of this study contribute profoundly to our understanding and modeling of lake ice phenomena in high-altitude regions and have broader implications for climatological research and environmental monitoring on the Qinghai-Xizang Plateau.

Based on NCEP/NCAR reanalysis data and the daily precipitation data from 105 meteorological stations in the central and eastern Qinghai-Xizang Plateau from 1982 to 2020， we investigate the spatiotemporal anomalous characteristics and major falling areas of warm season extreme precipitation and typical circulation of large-scale extreme precipitation in the central and eastern Qinghai-Xizang Plateau.The results show that： （1） Total precipitation of central and eastern Tibetan Plateau in the warm season shows statistically significant increasing at the rate of 10.7 mm·（10a）^-1 （P<0.05） during 1982 -2020， but there are obvious interdecadal trend shifts in the late 1990s and late 2000s.The increase in extreme precipitation of central and eastern Qinghai-Xizang Plateau is most prominent after 2009， and the climate tendency rate is of 4~5 times greater than that of during 1982 -2020.In terms of the distribution of spatial climate tendency rates， the trend of extreme precipitation in the southern Qinghai-Xizang Plateau is opposite to that in the central and northern Qinghai-Xizang Plateau in the three periods.The increase of extreme precipitation in the northern Qinghai-Xizang Plateau is the most prominent during 1998 -2009， and the extreme precipitation in the southern Qinghai-Xizang Plateau experiences the interdecadal trend shifts of significant increase， significant decrease and significant increase.（2） The small-scale extreme precipitation in central and eastern Qinghai-Xizang Plateau shows statistically significant decreasing trend （P<0.1）， while the large-scale extreme precipitation exhibits statistically significant increasing trend （P<0.05） during 1982 -2020.According to the locations of precipitation center， the level 4 large-scale extreme precipitation can be divided into three types， that is， northeast type （A type）， southern type （B type） and southeastern type （C type）.（3） The difference of location and intensity of the West Pacific Subtropical High is the main factor， which leads to the difference of water vapor sources and the locations of large-scale extreme precipitation falling areas.When the A-type large-scale extreme precipitation occurs， the West Pacific Subtropical High is anomaly weaker and eastward， which leads to the water vapor mainly transported from the Pacific Ocean and the westerlies.When the B-type occurs， the West Pacific Subtropical High is anomaly stronger and extending westward and southward， consequently， the water vapor mainly transported from the Indian Ocean and the Bay of Bengal.When the C-type occurs， the West Pacific Subtropical High is anomaly stronger， extending from the westward and northward， resulting in the water vapor mainly transported from the northwest Pacific Ocean， the South China Sea and the Bay of Bengal.

Plant diversity significantly affects the structure and function of ecosystems and plays a crucial role in soil organic carbon sequestration.In the past， the effects of plant diversity on soil organic carbon were mostly carried out under artificial plant diversity control， indicating that high plant diversity significantly promoted soil organic carbon accumulation.However， in natural grassland ecosystem， the research on the effect of plant diversity on soil organic carbon is relatively weak.In this study， 15 typical alpine meadows in the northeastern part of the Qinghai-Xizang Plateau were selected as sample sites.By measuring plant above-ground and subsurface biomass， soil pH value， soil microbial biomass carbon and nitrogen， soil organic carbon， granular organic carbon， mineral-bound organic carbon， total nitrogen and total phosphorus， etc.， the effects of plant diversity on soil organic carbon sequestration under natural conditions were explored.It provides theoretical basis for the change of soil carbon storage and scientific management of grassland.The results showed that plant diversity significantly increased plant coverage and aboveground biomass （P < 0.01）， but had no significant effect on underground biomass in different soil layers （0~20 cm and 20~40 cm）.In 0~20 cm and 20~40 cm soil layers， the increase of plant diversity significantly increased soil microbial biomass carbon and organic carbon contents （P<0.05）， but had no effect on microbial biomass nitrogen in different soil layers.According to the classification of soil organic carbon， there was a significant positive correlation between plant diversity and soil mineral bound organic carbon content （P<0.01）， but no correlation with soil particulate organic carbon content.In conclusion， in the alpine meadow of the Qinghai-Xizang Plateau， higher plant diversity under natural conditions has a significant promoting effect on soil organic carbon content， which is mainly reflected in the increase of mineral binding organic carbon content.This study provides new insights and theoretical basis for the relationship between plant diversity and soil carbon pool in grassland ecosystem.

The Qinghai-Xizang Plateau Vortex is a mesoscale low-pressure vortex system generated within the boundary layer of the Qinghai-Xizang plateau in summer， which not only has an important influence on the weather patterns and precipitation dynamics across the plateau， but also profoundly impacts the surrounding regions.In this study， the database of the plateau vortex obtained from an objective analysis method， along with ERA5-land reanalysis data， was utilized to conduct a comprehensive statistical and analytical investigation of the vortex's activity from 1950 to 2021.Various analytical methods， including correlation analysis， regression analysis， Bayesian time series analysis algorithm， and probability statistics were used.Furthermore， the intensity and path of the plateau vortex during the years 1950 and 2021 were specifically examined to identify the areas most sensitive to its activity during this time span.Results reveal a noteworthy increasing trend （at a 95% confidence level） in both the annual number and duration of the plateau vortex， with climate tendency rates of 0.16·a^-1 and 1.25 h·a^-1， respectively.However， the growing trend for the total number and duration of the plateau vortex during the active period （May to August） is not statistically significant.The sensitive areas that affect the activity of the plateau vortex are located on the north side of the northern Qinghai-Xizang Plateau and near the Hoh Xil Mountains， corresponding to the main mountains in the central and western Qinghai-Xizang Plateau.Furthermore， the study investigates the relationship between land surface parameters and the vortex's characteristics， showing positive correlations between latent heat， surface longwave radiation， and surface soil moisture （0~7 cm） with the number and duration of the plateau vortex.Conversely， sensible heat exhibits a negative correlation， it is further found that the plateau vortex is relatively consistent with precipitation when the time scale of the study is inter-annual， while on the daily scale， the sensible heat is positively correlated with the number， duration， and intensity of the plateau vortex mainly in the sensitive areas and to the east of the sensitive areas， with the most significant correlation being in the months of May and June.In conclusion， the results derived from this study provide a solid theoretical foundation for further exploration of the land-atmosphere interaction mechanism in the identified sensitive area.Moreover， these findings lay a critical foundation for enhancing numerical simulations and data assimilation studies of the Qinghai-Xizang Plateau Vortex.

The snow cover in winter and spring on the Qinghai-Xizang （Tibetan） Plateau has a significant inter-annual variation， which has a certain indicative significance for the prediction of summer precipitation in eastern China.Due to the special complex terrain， the distribution of meteorological stations on the Tibetan Plateau is sparse and uneven.The uncertainty of the plateau snow cover information provided by reanalysis data and satellite data is a key issue affecting and constraining the study of snow variability and its weather-climate effects.Based on the multi-source snow data from station observations， reanalysis （ERA5 and NOAA-V3）， and satellite inversion （MODIS snow cover and IMS snow cover） on the Qinghai-Xizang （Tibetan） Plateau， this paper highlights the uncertainties of the multi-source plateau snow data in characterizing the inter-annual variability of the snow cover by means of multivariate statistical methods such as bias analysis， root-mean-square error and correlation analysis.By comparing the spatio-temporal distribution and variation characteristics of various snow data， we aim to improve the knowledge of the applicability of multi-source plateau snow data and provide meaningful references for subsequent related studies.The results show that： （1） In terms of the snow data given by the reanalysis data， the ERA5 snow depth exhibits a better depiction of the observed snow depth at the plateau stations compared to the NOAA -V3 snow depth.The mean bias and root-mean-square error of the ERA5 snow depth data are relatively small， except for some stations in the central-eastern part of the plateau， while NOAA-V3 snow depth is to some extent overestimated throughout the plateau； （2） Both reanalysis （ERA5 and NOAA-V3） and satellite inversion （MODIS as well as IMS snow cover） snow data and the station-observed snow depth on the plateau show good consistency in terms of interannual variability characteristics； Where the ERA5 reanalysis is more similar to the observed snow data on the plateau station in terms of long-term trend； In addition， decadal trend in Northern Hemisphere snow cover and station-observed snow depth appear more similar； （3） The spatial discrepancies in the distribution of snow depth and snow cover on the plateau was observed in the reanalysis data （ERA5， NOAA-V3）， in which the large value areas of NOAA-V3 in the years of more and less snow are located in the southern and northern margins of the plateau and in the central-eastern part of the plateau， while the large value of ERA5 are mainly distributed in the central-eastern， western and southern margins of the plateau.However， the differences between the respective snow depth and snow cover for each reanalysis data are relatively small， and the difference distribution between the snow anomalies years is relatively consistent， with the positive anomaly areas located in the central， western and southern margins of the plateau and the negative anomaly areas in the northern part of the plateau for both snow depth and snow cover； （4） The large value areas of snow cover for all three satellites in snowy years are located in the central-eastern and southern part of the plateau as well as in the western region.The difference distribution of snow cover in the increased anomalies years is also consistent for each type of satellite data， but the negative anomalies at the northern edge of the plateau reflected in the reanalysis data are not reflected in the satellite snow cover data， which may be related to the short coverage time of the satellite inversion snow data and different processing methods.

The Qinghai-Xizang Plateau has complex terrain and climate， which is a great challenge to the airdrop parachute landing and aviation safety.This research focuses on Qinghai-Xizang Plateau wind field simulation in boundary layer based on numerical calculation method.Firstly， the study built a WRF-LES system and scaled down to 40 m horizontal resolution based on the large eddy simulation （LES） scheme of WRF （Weather Research and Forecasting） model， and undertook the application study of large eddy simulation on the Qinghai-Xizang Plateau.Based on a strong wind case over the Qinghai-Xizang Plateau， the impacts of LES scheme and terrain elevation data on wind field simulation were evaluated through sensitivity tests.Then， the parameters in the standard sub-grid turbulent stress models of LES scheme were analyzed， and the optimal schemes for wind field simulation on the Qinghai-Xizang Plateau was obtained.Finally， a batch test was conducted to verify the applicability of the optimal schemes to the Qinghai-Xizang Plateau wind field simulation.The test results show that the WRF-LES system with a resolution of 40 m can simulate more precise and accurate wind field information， and the MAE （Mean Absolute Error） of simulated wind speed is reduced by 1.4 m·s^-1 and the RMSE （Root Mean Square Error） is reduced by 1.81 m·s^-1 compared with the ACM2 scheme； The high-precision ASTER terrain data can also improve the effect of wind field simulation， and the error is approximately deduced by 0.2 m·s^-1； The LES scheme that use 1.5-order turbulent flow energy scheme and set parameter coefficient 0.1 has the best simulation result， and the MAE is 1.56 m·s^-1 and RMSE is 2.06 m·s^-1； The batch test verifies that the large eddy simulation scheme is fit for the wind simulation on the Qinghai-Xizang Plateau， and the wind field simulation results in the 40 m resolution is significantly better than in the mesoscale resolution.The result shows that WRF-LES system can provide accurate wind field information for the parachute landing on the plateau.

Reliable precipitation information is particularly important for understanding the water balance and water cycle processes in the Qinghai-Xizang Plateau.As a new generation of satellite precipitation data， IMERG （Integrated Multi-satellitE Retrievals for Global Precipitation Measurement） represents an advanced iteration in satellite precipitation data， characterized by expanded coverage and heightened spatiotemporal resolution.However， due to the complex terrain in the Qinghai-Xizang Plateau， IMERG still has great uncertainty in the plateau region.In view of this， this study performs bias correction of IMERG daily precipitation data based on the Quantile Delta Mapping （QDM） method.The transfer function is established seasonally using CMFD （China Meteorological Forcing Dataset） precipitation and IMERG daily precipitation data during 2001 -2010 to correct IMERG daily precipitation during 2011 -2014.The results show that： （1） The QDM method can effectively correct the frequency， value， and spatial distribution of IMERG precipitation products， and the corrections are more effective for extreme precipitation and large negative deviation regions.The probability distribution of corrected IMERG daily precipitation is closer to that of the observations， and the precipitation deviation is more in line with the normal distribution.Monthly precipitation and the spatial distribution characteristics of annual and seasonal precipitation are improved.（2） The root mean square error of the corrected daily precipitation is reduced from 1.49 mm·d^-1 to 1.26 mm·d^-1 with an improvement by 15.44%.The critical success index CSI， probability of detection POD， false alarm rate FAR， precision rate， and F_score of the corrected daily precipitation in different precipitation intensities are improved， and the Bias score of tiny and torrential precipitation is enhanced.（3） After correction， the extreme precipitation is significantly improved， and the mean values of the simple daily intensity index （SDII） and percentile-based threshold indices （R95p and R99p） are closer to the observed values.The spatial distribution of extreme precipitation is effectively displayed， and the bias of extreme precipitation is reduced from over 30% to within 5%.The root mean square error of SDII， R95p， and R99p is reduced from 1.59， 6.54， and 14.89 mm·d^-1 to 0.65， 3.01， and 8.99 mm·d^-1 with the accuracy improved by 59.12%， 53.98%， and 39.62%， respectively.This study verifies the applicability of the Quantile Delta Mapping method in the Tibetan Plateau， which is beneficial for obtaining more accurate precipitation data for meteorological and hydrological studies in the region.

Extreme wind events （EWEs） not only are a kind of meteorological disaster， but also serve as an important natural resource.The Qinghai-Xizang Plateau （QXP）， well known as the "roof of the world"， is vulnerable to global and regional climate change.However， the characteristics and mechanism of variability of extreme wind events over this region and associated mechanisms remain elusive.Under the background of global change， Chinese Sichuan-Tibetan Railway construction， the exploration on changes in the EWEs could deepen our scientific understanding the regional climate.In order to explore the spatial-temporal distribution characteristics of regional extreme wind events （REWs） over the central and eastern QXP for the period of 1982 -2021， daily data of maximum wind speed are utilized to define REWs.Further， with the aid of thermal - thermodynamic diagnosis and the multiple statistical methods， such as trend analysis， EOF and composite analysis， we explore the potential causes leading to the decreased frequency of RWEs.The results show that： （1） The REWs over the QXP significantly decreased since 1980， varied consistently throughout the QXP and occurred mostly in the northeastern QXP.The REWs as defined in the 95^th and 99^th percentiles decline with the rate of 44d/10a and 11.6d/10a.（2） During periods of REWs， the circulation pattern is "high in the west and low in the east" in the middle and high latitudes and "low in the west and high in the east" in the low latitudes.The main characteristics are as follows： the abnormal positive geopotopic in Mongolia-Siberia， the abnormal cyclonic circulation in Mongolia， the abnormal westerly wind in the northeast of the plateau， and the abnormal negative surface temperature in Mongolia.（3） In the context of global change， the weakening of the Siberian high in spring and the strengthening of the East Asian trough in winter leads to decreasing pressure gradient between the north and south sides of the QXP， the weakening of the westerly jet stream leads to decreasing momentum downdraft， and the rise of non-uniform surface temperature in Asia leads to the decreasing temperature gradient between the north and south sides of the QXP.At the same time， the abnormal cyclonic circulation weakened in Mongolia.It may be resulted from the co-influence of these large-scale circulation and local thermal factors that reduce the frequency of regional extreme wind events in the central and eastern parts of the QXP.

Based on the meteorological observational data over Qinghai-Xizang （Tibetan） Plateau and atmospheric reanalysis dataset during 1961 to 2020， the snowfall variation characteristics over the Qinghai-Xizang （Tibetan） Plateau and its related corresponding circulation system were analyzed in this paper.Main conclusions are drawn as following： the spatial distribution of snowfall shows a uniformity with less in the northwest and more in the southeast.The characteristics of interannual and interdecadal variability are very evident.The interannual variability of the snowfall over Qinghai-Xizang Plateau was strong.The first mode of Qinghai-Xizang （Tibetan） Plateau snowfall anomalies is regional uniformity.In terms of the key circulation systems that affect Qinghai-Xizang （Tibetan） Plateau snowfall， when the snowfall over Qinghai-Xizang （Tibetan） Tibetan Plateau is more， the upper troposphere corresponds to the positive phase of the southern Eurasian （SEA） teleconnection， characterized as positive anomalies over the southwestern Europe， the Arabian Sea， and the northeast Asia， and negative anomalies over the Middle East and the Qinghai-Xizang （Tibetan） Plateau， while the Middle East jet is stronger； the positive （negative） phase of North Atlantic Oscillation （NAO） is conducive to more （less） snowfall over Tibetan Plateau， via modulating the SEA teleconnection and key circulation systems such as the Middle East jet stream.

To promote the understanding of precipitation microphysical characteristics and differences in the central and eastern Qinghai-Xizang （Tibetan） Plateau and the Sichuan Basin， disdrometer measurements collected at Naqu， Yushu， Linzhi， Batang， Luding， and Chengdu from July to August 2019 and 2020 are utilized to comprehensively investigate the characteristics and differences of raindrop size distributions （RSDs） among the six different areas.Meanwhile， local empirical relations between the Gamma shape parameter and slope parameter and between the reflectivity factor and rain rate are proposed and compared.The results show that RSDs in the basin and adjacent areas （Chengdu and Luding） are generally wider and have higher number concentrations of medium-to-large raindrops （diameter ≥1.0 mm） than those in the plateau areas （Naqu， Yushu， Linzhi， and Batang） due to the contribution of more strong convective precipitation.In contrast， RSDs in the plateau areas are narrower and possess higher number concentrations of small raindrops （diameter <1.0 mm） due to more occurrences of stratiform and weak-convective precipitation.RSDs gradually become wider with higher number concentrations as the increase of rainfall intensity both in the six observation areas.The RSD differences among the six observation areas can also change with the rain rate.Specifically， when the rain rate exceeds 0.1 mm·h^-1， the increase of the number concentration of small raindrops with increasing rain rate is significantly greater in Naqu and Linzhi than in other areas， and can gradually exceed that in Chengdu.When the rain rate exceeds 5 mm·h^-1， the differences in the number concentrations of medium-to-large raindrops between Chengdu and Luding and other plateau areas also gradually become larger.With the same shape parameters， the slope parameters in Chengdu and Luding are smaller than in other areas， indicating that they possess a slower decreasing rate of raindrop number concentration with increasing particle size than that in other plateau areas.Under the same radar echo intensities （reflectivity factor）， rain rates of stratiform precipitation in Naqu and Linzhi are greater than in other regions.The rain rate of convective precipitation in Linzhi is also greater than that in other areas when the radar echo is below 40 dBZ， but the rain rate of convective precipitation in Naqu can be smaller than that in other areas when the radar echo is greater than 40 dBZ.

Using radiosonde and ground mapping data from conventional observations， FNL analysis data （1°×1°） and quality controlled hourly precipitation data of Yunnan regional automatic station， diagnosed the function of the Qinghai-Xizang Plateau’s eastern slope topography in the PLV （plateau vortex） affected precipitation in Yunnan during 2-3 July 2017.While the latest WRFv4.0 numerical model is used to conduct the topographic sensitivity test of this process.The results show that PLV which generated in the Yajiang region of Sichuan province （NO.C1735） is an important system influenced on this heavy rainfall in Yunnan； This low-vortex system maintain warm core structure in the middle and high altitude during the process period， corresponding with remarkable alternately distribution of ascending and descending movements； Distribution of process accumulated rainfall present two obvious NW-SE rain belts parallel to the mountain trend and the precipitation on the rain belt have intensity interlaced fluctuation characteristics； The heavy rainfall mainly occurred within two periods： one from afternoon to evening and other at the first half of the night， and all located besides the terrain slope （the east and south slopes）， especially in areas with steep terrain， large slopes， and trumpet-shaped topography， and then propagates downstream alone with the PLV； The South Asian High， northwest divergent airflow， Western Pacific subtropical high and Yunnan-Myanmar high provides favorable upper flow field for the eastward movement and development of the PLV， besides the position of 500 hPa positive vorticity and 700 hPa water vapor flux convergence can well indicates the heavy rainfall area； There exist β-mesoscale gravity wave during the period of precipitation， which stimulated by the Qinghai-Xizang Plateau’s eastern slope， and propagate between 300~200 hPa； Non geostrophic equilibrium motion and vertical wind shear at high-altitude are beneficial to the occurrence and propagation of gravity wave； The gravity wave propagate downstream before the PLV and precipitation， its wave ridge corresponds to the upward motion and divergence center， whereas the wave trough corresponds to the descending motion and convergence center， the heavy precipitation and the wave ridge are all located at the southwest side of PLV， the area of strong convergence and upward movement； After reduced the terrain height， its mechanical blocking and lifting effect weakened， the gravity wave and PLV disappears， leading to significant changes in the intensity and spatial distribution of the rain belt； Thus， the topography of the eastern slope of the Plateau plays important role both on the formation and development of PLV and precipitation in Yunnan under the influence of PLV.

As a climate-sensitive region， precipitation over the Qinghai-Xizang （Tibetan） Plateau significantly impacts the water cycle and the climate of East Asia.Therefore， it is important to study its changes.Precipitation is an important variable in the global hydrological cycle and one of the major climate systems affected by climate change.To investigate the ability of the global climate models to simulate precipitation over the Qinghai-Xizang （Tibetan） Plateau and examine possible changes in future precipitation under the new model and scenarios， this paper uses the latest monthly precipitation data from the 31 climate models of the Coupled Model Intercomparison Project 6 （CMIP6） and the CN05.1 precipitation observation data set provided by the National Climate Center to evaluate the ability of the CMIP6 model to simulate precipitation over the Qinghai-Xizang （Tibetan） Plateau.Furthermore， better models are selected to project the future precipitation of the Qinghai-Xizang （Tibetan） Plateau under different Shared Socioeconomic Pathway （SSP） scenarios.The results show that the model distribution of observed precipitation over the Qinghai-Xizang （Tibetan） Plateau from 1995 to 2014 is characterized by a decrease from southeast to northwest and a summer precipitation concentration.Most of the models can simulate the precipitation distribution and seasonal trend， but almost all of them overestimate the precipitation phenomenon， and the average precipitation of multiple modes is 102% higher than that observed.In general， the latest model of CMIP6 has a poor ability to simulate precipitation over the Qinghai-Xizang （Tibetan） Plateau， and the average relative deviation index of the model from the observation is 102%， indicating that most of the models are not satisfactory， and EC-Earth3-Veg-LR， MPI-ESM1-2-LR， EC-Earth3-Veg， and MRI-ESM2-0 are selected as the better modes after quantitative analysis of all the models， which can roughly reflect the precipitation characteristics of the Qinghai-Xizang （Tibetan） Plateau.Climate models show the slowest increase of precipitation over the Qinghai-Xizang （Tibetan） Plateau under the SSP1-2.6 scenario and the fastest increase under SSP5-8.5.From SSP1-2.6 in the small radiative forcing scenario to SSP5-8.5 in the large scenario， the recent （from 2021 to 2040） precipitation increase on the plateau is difficult to find a large difference in each scenario， but there is a significant increase in the mid （from 2041 to 2060） and late （from 2081 to 2100） scenarios， indicating that carbon emission intensity has a small impact in the short term and a large impact in the long term.The future increase in precipitation mainly occurs in the area south of the Nianqing Tanggula Mountains， from a seasonal point of view， the summer increase is the largest， followed by spring and autumn， the smallest increase is in winter， so we should pay attention to the future summer and spring precipitation changes over the Qinghai-Xizang （Tibetan） Plateau and take coping measures.