Permafrost have a critical impact on the infrastructure construction， hydrology and ecology in the cold region.Under the background of global warming， it is of great significance to explore soil freeze-thawing cycle over the Western China.Based on the natural geographical and permafrost characteristics， the western region of China is divided into four sub-regions as the study region of this investigation.The ERA-5 surface temperature， soil volumetric water content and monthly air temperature data from January 1981 to June 2020 are to be deployed in analyzing the spatio-temporal distribution of soil freeze-thawing status， the active layer thickness and maximum freezing depth over the western China in the past 40 years.the correlationship between variables of freeze-thawing cycles and air temperature and altitude are discussed.The results show that： the spatio-temporal distribution of the start date of freezing and thawing has the characteristics of delayed freezing and early thawing from high-altitude areas to low-altitude areas over the western region.The high-altitude northern Tibetan plateau freezes the earliest， thaws the last， and freezes the longest.The sporadic areas on the Kunlun Mountains can last for more than 300 days.The Tarim Basin in the west-northwest with low altitude and low soil moisture content freezes the latest， melts the earliest， and lasts the longest.The melting in the Taklimakan Desert can last for more than 280 days.The thickness of the permafrost active layer is basically more than 2.0 m， only the area near the Karakoram Mountains has a large area with a thickness of less than 2 meters.the seasonal frozen soil of the Qinghai-Tibet Plateau has the largest freezing depth， and the thickness can reach more than two meters， and the Tarim Basin shows a shallowest freezing depth， and the thickness is less than 0.6 m.The start date of freezing was delayed over the western region， and the start date of thawing was advanced.The date of start freezing and the date of completely frozen increased at a rate of 0.089 d·a-1and 0.061 d·a-1.The date of start thawing and the date of completely thawed decreased at a rate of 0.102 d·a-1 and 0.156 d·a-1.When the freezing trend is rising and the thawing trend is declining， the duration of completely thawed increased by about 12 days at a rate of 0.256 d·a-1， and the duration of completely frozen is shortened by about 11 days with a rate of 0.164 d·a-1， during the study period， the start date of completely thawed was mutated in 1996.The date of start freezing and the duration of completely thawed were abrupted changed in 1997.The overall change trend of the start date of the freezing and thawing is the same over the western region， but there are locally slight differences.The duration of start freezing and completely frozen of the Loess Plateau decreased the fastest at the rate of 0.166 d·a-1 and 0.405 d·a-1.The duration of start freezing and the duration of completely frozen were shortened by around 7 and 16 days.The trends in the duration of completely melt period in all four regions showed an upward trend.However， the duration of completely frozen rises rapidly at a rate of 0.435 d·a-1 over the Loess Plateau， and increase about 17 days during 1981 -2020.There is a significant correlation between the start dates of freezing and thawing and the annual average temperature and altitude.The correlation between the annual average temperature and all freeze-thaw times exceeded 0.79， and the negative correlation between the date of completely thawed and the annual average temperature was as high as 0.963.The start date of freezing was delayed by 2.03 days per 1.0 ℃ increase， the start date of complete freezing was delayed by 2.12 days， and the start dates of completely thawed and frozen were advanced by 5.10 and 5.17 days， respectively.The start dates of freezing and completely frozen are advanced by 6.1 days and 4.5 days per 1000 m rise in altitude， respectively， and the start dates of thawing and freezing are delayed by 14.4 days and 19.9 days， respectively.This research clarifies the situation of soil freezing and thawing and its variation in the past years over the western China， and provides a scientific supports for the ecological system and infrastructure construction over the western region.

Precipitation has a significant influence on the topsoil moisture and further impacts the land-atmospheric water and heat exchange process over the Yarlung Zangbo Grand Canyon region (YGC) where exhibits one of the highest frequencies of convective activity in China. The simulated performance of the Community Land Model version 5.0 (CLM5.0) on turbulent fluxes under seven roughness heights for heat transfer (Z 0h ) schemes at Motuo and Pailong stations over the YGC was evaluated. The results indicate that the CLM5.0 significantly overestimates the surface sensible heat flux (H) while the simulation performance of surface latent heat flux (LE) is better than H. By comparing and analyzing the simulation results, the Z 0h schemes suitable for the YGC are selected optimally. The Zeng et al. (J. Hydrometeorol., 2012, 13, 1359–1370) scheme (Z12) is more suitable for the simulations of H, with the simulated RMSE of H at Motuo and Pailong stations on typical sunny days being only 21.63 and 15.13 W m−2, respectively, 81.51% and 76.96% lower than the original Z 0h scheme of CLM5.0. The Garratt, J., R and Francey, R., J (Boundary. Layer. Meteorol., 1978, 15, 399–421) scheme (G78) is more suitable for simulating LE in the YGC. The simulated BIAS and RMSE of LE at Motuo station were 9.80% and 21.90% lower than that under the default scheme of CLM5.0 on typical cloudy days. In addition, except for the G78 and CLM5.0 default scheme, the Z 0h under the other schemes showed obvious diurnal variation characteristics, and H was positively sensitive to Z 0h , while LE was the opposite. Consequently, the optimal Z 0h schemes are of great application value for further comparative analysis of the water and heat exchange process between the Grand Canyon land surface and the atmosphere, to better reveal the mechanism of land-atmosphere interactions in the YGC.

The Source Region of the Three-River （SRTR） lies in the hinterland of the Qinghai-Xizang （Tibetan） Plateau （QXP） and is one of the sensitive regions to climate change in East Asia.It is of great significance to study the distribution， transport， and budget of water vapor for understanding the characteristics of the regional precipitation.This research is based on the ERA5 reanalysis data of the European Centre for Medium-Range Weather Forecasts （ECMWF） from 1980 to 2019， combined with the data of 9 radiosonde stations in the National Meteorological Data Center from 1981 to 2010.The temporal and spatial variation characteristics of water vapor distribution， water vapor transport flux and budget of each boundary over the SRTR and its surrounding areas are analyzed.The results show that there are significant differences in the spatial distribution of water vapor content， which presents a high value region in the southeastern QXP and a low value region in the northwest of the QXP.The distribution and value of water vapor content are different in four seasons， which exhibit the largest in summer， followed by autumn and spring， and the least in winter.The annual cycle of water vapor content manifests the single peak over the SRTR and the Brahmaputra River basin.Water vapor is mainly concentrated in June to August and its maximum appears in July with a value of 41.6 mm.The inter-annual variation shows an increasing trend with a rate of 0.4 mm·（10a）-1.The Arabian Sea and the Bay of Bengal are the main sources of water vapor over the SRTR， followed by the western airflow from the middle latitude and the northwestern airflow.Three kinds of airflows form obvious convergence of water vapor transport flux over the Brahmaputra Grand Canyon.There are seasonal discrepancies in the intensity of water vapor transport.Among the water vapor import boundaries， the western boundary has the largest import （815.3×106 kg·s-1）， followed by the southern boundary （724.9×106 kg·s-1） and the seasonal variations of the two boundaries are significant.The northern boundary has less import （317.9×106 kg·s-1）， while the eastern boundary is the export boundary of water vapor flux， and the maximum water vapor export is in September with a value of 140.5×106 kg·s-1.The net water vapor import is greater than the export， thus the water vapor flux is in surplus， which is about to affect the variations of precipitation and the regional water cycle over the SRTR.