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.

Near-surface energy budget closure has been a trending topic in land surface processes research, especially on the underlying surfaces of heterogeneous wetlands. In this investigation, the horizontal thermal advection caused by thermal inhomogeneity over the alpine wetland is calculated based on the eddy covariance data observed at the Flower Lake observation field and WRF modelling data over the Zoige alpine wetland, China. The contribution of horizontal thermal advection to the near-surface energy closure is analysed. The results show that the mean horizontal heat advection of the Zoige wetland is 20.2 W·m−2, and the maximum value reached 55.0 W·m−2 in the summer of 2017. After introducing thermal advection into the near-surface energy balance equation, the near-surface energy closure ratio increased from 72.3% to 81.0%.

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 soil freeze-thaw phenomenon is one of the most distinguishing peculiarities of the land surface processes over the Qinghai-Tibetan Plateau. By utilizing soil temperature/moisture and air temperature data from the GLDAS-NOAH product, 4 observing networks and 10 meteorological stations over the Qinghai-Tibetan Plateau, the spatio-temporal distribution of the start/end date and the duration of soil freezing and their relationships with air temperature and altitude were investigated with the analytical methods of linear regression model, correlation analysis, sliding t-test and Mann-Kendall test. As a result, the spatial distribution of top-layer soil freeze-thaw processes was characterized by a trend of delaying freezing and advancing thawing from the northwest to the southeast throughout the Qinghai-Tibetan Plateau. Moreover, in the period 1948-2019, the begin date of soil freezing was delayed at a rate of 1.2 d/10a (p-lev < 0.0001, R-2 = 0.40), and the end date of the soil freezing was advanced at a rate of 0.5 d/10a (p-lev = 0.105, R-2 = 0.04). The duration of the soil freeze was shortened with a rate of 2.1 d/10a (p-lev < 0.0001, R-2 = 0.23) in the southern Changtang but 0.4 d/10a (p-lev < 0.0001, R-2 = 0.47) in Qinghai and the southern Tibet Plateau. Additionally, the start date of the soil freeze is to be delayed by 2.8 days (p-lev < 0.0001, R-2 = 0.53), and the end date of the soil freeze is to be advanced by 3.6 (p -lev < 0.0001, R-2 = 0.61) days as the air temperature rises by 1.0 C. In the high cold climatological zone on the Qinghai-Tibetan Plateau, there is a trend toward earlier start date of soil freezing by 9.9 days (p-lev < 0.0001, R-2 = 0.36), and later end date of soil freezing by 14.4 days (p-lev < 0.0001, R-2 = 0.56) as the altitude increases by 1000.0 m. Furthermore, the seasonal variations of soil temperature and moisture were significantly different from typical strong and weak freezing years, which were defined according to the duration of soil freezing period. These results are of great significance for understanding the soil freeze-thaw process and its variation over the Qinghai-Tibetan Plateau.

Precipitation is one of the most important meteorological factors affecting the water cycle and ecological system over the Source Region of the Three-River (SRTR), where the Yangtze River, Yellow River, and Lantsang River originated. The characteristics of water vapor transport and budget in annual and summer over the SRTR are analyzed using monthly observational and reanalysis datasets during 1980-2019. The linkage between water vapor transport and summer precipitation is also explored in this study. The results show that the Global Precipitation Climatology Project (GPCP) data are in agreement with the measured precipitation well. The SRTR is a sink region for water vapor, where the water vapor content shows an increasing trend with a rate of 0.2 mm/10a in annual and 0.3 mm/10a in summer. The water vapor mainly flows into the SRTR from the lower (521.2×106 kg s−1) and the middle (195.7×106 kg s−1) layers of the southern boundary in summer, while it exports from the middle (208.1×106 kg s−1) layer of the eastern boundary. The abnormal wind convergence and the low-pressure system, combining with the effects of the Western Pacific Subtropical High and the Mongolian High, provide conditions for the transport of water vapor and precipitation over the SRTR. A close relationship is found between water vapor flux and precipitation from the Singular Value Decomposition (SVD) analysis. The Brahmaputra River basin is the key region of water vapor transport over the SRTR, which contributes to further understanding the mechanisms of water vapor transport and the regional water cycle.

The seasonal characteristics of water and heat exchange in the alpine grasslands are significant， and the freezing‐thawing process has an important impact on the land‐atmospheric water and heat exchange.Based on the observation data of the land surface process in the Tangchama small watershed in the source area of the Yellow River from May 2014 to May 2015， this research divides the soil freezing‐thawing process into thawed stage （TT）， frozen stage （FF）， thawing to freezing （T-F） and freezing to thawing （F-T）， and the changes in the different states and period of the net radiation， sensible heat flux， latent heat flux and surface heat flux of the underlying surface of the alpine grassland are analyzed to explore the characteristics of water and heat exchange between the land‐atmosphere in the soil freezing‐thawing process.The results are as follows： （1） The average value of the net radiation flux in the thawed stage is generally greater than that of the other three stages， and the maximum value reaches 203.7 W·m-2.The frozen soil melts in the freezing‐thawing stage， and the soil moisture content gradually increases.The radiation ratio increased significantly during the frozen stage， the net radiation diurnal variation was the largest in the thawed stage， reaching 717.6 W·m-2， and the frozen stage was the smallest， followed by the freezing‐thawing stage.（2） The proportion of sensible heat flux and latent heat flux is different in the thawed and frozen stages.When completely thawed， due to precipitation and soil moisture content， the net radiation is mainly converted into latent heat flux.The maximum diurnal variation of latent heat flux is 193.7 W·m-2， while the sensible heat flux is only about 80.0 W·m-2.The diurnal average of sensible heat and latent heat in the thawing‐freezing phase， the freezing‐thawing period and the frozen period is not much different.The mean latent heat in the three period is 21.9 W·m-2， and the sensible heat is 20.3 W·m-2； The diurnal variation is greater than the latent heat in the three period， the soil suffers a freezing‐thawing cycle， the soil temperature difference is small， and the water content changes， and the net radiation is mainly converted into sensible heat during this period； the diurnal variation of sensible heat was greater than that of latent heat in the three stages.The freezing-thawing cycle occurred in the soil， the difference between ground and air temperature was small， and the moisture content changed.During this period， the net radiation was mainly converted to sensible heat.（3） The soil heat flux is positive （negative） in thawed （frozen） state， indicating that the surface soil absorbs （releases） heat from the atmosphere， and its daily variation range is large （small）.The above results show that the state and process of soil freezing and thawing have different characteristics for the water and heat exchange process between the land and atmosphere.

土壤冻融过程对气候变化非常敏感,如何准确监测土壤冻融过程具有重要的科学意义.利用2017年6月至2018年6月中国科学院若尔盖高原湿地生态系统研究站玛曲观测场地基微波辐射计观测数据、浅层土壤温度和近地面气温数据,通过构建归一化极化比值冻结因子、极化差值冻结因子、组合水平极化差值冻结因子和组合垂直极化差值冻结因子等不同土壤冻结因子,评估了黄河源区草原下垫面土壤冻融过程.结果表明:L波段微波辐射计监测土壤冻融状态的结果与近地面气温和浅层土壤温度表征的土壤冻融过程基本一致.当入射角为50°时,归一化极化比值冻结因子和极化差值冻结因子与实测数据的一致性分别达到83.6％和82.8％.每种冻结因子具有明显的季节性变化,四种冻结因子在春季时的准确度低于夏、秋、冬三个季节.归一化后的相对冻结因子的标准差在秋季最大,可达0.3;在冬季和夏季最小,值小于0.2.在土壤发生冻结和融化转换时,垂直极化和水平极化下的亮温同时下降,其差值较完全冻结或者完全融化时的亮温差大.研究结果可为微波遥感监测土壤冻融过程提供技术参考.

Tropical cyclones (TCs) have devastating impacts and are responsible for significant damage. Consequently, for TC-induced direct economic loss (DEL) attribution all factors associated with risk (i.e. hazard, exposure and vulnerability) must be examined. This research quantifies the relationship between TC-induced DELs and maximum wind speed, asset value and Gross Domestic Product (GDP) per capita using a regression model with TC records from 2000 to 2015 for China's mainland area. The coefficient of the maximum wind speed term indicates that a doubling of the maximum wind speed increases DELs by 225% [97%, 435%] when the other two variables are held constant. The coefficient of the asset value term indicates that a doubling of asset value exposed to TCs increases DELs by 79% [58%, 103%]; thus, if hazard and vulnerability are assumed to be constant in the future, then a dramatic escalation in TC-induced DELs will occur given the increase in asset value, suggesting that TC-prone areas with rapid urbanization and wealth accumulation will inevitably be subject to higher risk. Reducing the asset value exposure via land-use planning, for example, is important for decreasing TC risk. The coefficient of GDP per capita term indicates that a doubling in GDP per capita could decrease DELs by 54% [39%, 66%]. Because accumulated assets constantly increase people's demand for improved security, stakeholders must invest in risk identification, early warning systems, emergency management and other effective prevention measures with increasing income to reduce vulnerability. This research aims to quantitatively connect TC risk (expected DELs, specifically) to physical and socioeconomic drivers and emphasizes how human dimensions could contribute to TC risk. Moreover, the model can be used to estimate TC risk under climate change and future socioeconomic development in the context of China.

Exploring precipitation threshold from an economic loss perspective is critical for rainstorm and flood disaster risk assessment under climate change. Based on the daily gridded precipitation dataset and direct economic losses (DELs) of rainstorm and flood disasters in the mainland of China, this paper first filtered a relatively reasonable disaster-triggering daily precipitation threshold (DDPT) combination according to the relationship between extreme precipitation days and direct economic loss (DEL) rates at province level and then comprehensively analyzed the spatial landscape of DDPT across China. The results show that (1) the daily precipitation determined by the combination of a 10 mm fixed threshold and 99.3th percentile is recognized as the optimal DDPT of rainstorm and flood disasters, and the correlation coefficient between annual extreme precipitation days and DEL rates reached 0.45 (p < 0.01). (2) The optimal DDPT decreases from southeast (up to 87 mm) to northwest (10 mm) across China, and the DDPTs of 7 out of 31 provinces are lower than 25 mm, while 5 provinces are higher than 50 mm on average. These results suggest that DDPTs exist with large spatial heterogeneity across China, and adopting regional differentiated DDPT is helpful for conducting effective disaster risk analysis.

The relationship between natural hazard-induced disasters and macroeconomic growth has been examined widely on global and national scales, but little research has been focused on the subnational level, especially in China.We examined the impacts of natural hazard-induced disasters on the regional growth in China based on subnational panel data for the period from 1990 to 2016. First, we used the number of people affected and the direct economic losses as the measures of the scale of disasters. Then, we used the direct damages of meteorological disasters and earthquakes as disaster measures separately to examine the impacts of different disaster types. Finally, we performed intraregional effects regressions to observe the spatial heterogeneity within the regions. The results show that the adverse short-term effects of disasters is most pronounced in the central region, while the direct damage of disasters is a positive stimulus of growth in the whole of China.However, this stimulus is observed in a lagged way and is reflected differently—meteorological disasters in central and eastern China and earthquakes in western China are related to regional growth. The results demonstrate that the short-term macroeconomic impacts of these disasters in the three geographical regions of China largely depend on regional economic development levels and the disaster types.

On the tenth anniversary of the 2008 Wenchuan Earthquake, investigating the evolution of disaster science is worthwhile and can be used to improve the future execution of disaster risk management. Based on more than 55,786 articles on the relative topic of “Disaster” derived from the Web of Science Core Collection from 1999–2017, this study employs CiteSpace and Google Earth to identify and visualize the spatial distribution of publications, bursts of keywords and categories, highly cited references, and interdisciplinary levels and then identify the emerging trends of disaster research over the past 20 years. The results show that the earthquake indeed jumpstarted a massive wave of disaster research around the world and increased international cooperation over the last decade. However, in terms of both the quantity and quality of publications in disaster research fields, China is lagging behind the U.S. and European countries. Moreover, although designing disaster prevention and mitigation strategies is a new popular field of disaster science, geological environment changes and geologic hazards triggered by earthquakes are more popular research topics than disaster emergency and recovery. In addition, the transdisciplinary level of disaster science increased after the earthquake. This interdisciplinary characteristic of disaster science gradually increased in popularity, which demonstrates that people can learn from catastrophes. These emerging trends could serve as a scientific basis to clearly understand disaster science progress over the last 20 years and provide a reference for rapidly identifying frontier issues in disaster science.