The National Basic Resources Investigation Program "Integrated Scientific Investigation of the North-South Transitional Zone" introduced the concept of north-south transitional zone (Qinling-Daba Mountains). Variation of north-south series in vegetation of the Qinling-Daba Mountains is of great significance to reveal the transition, diversity and complexity of the regional structure of China's north-south transitional zone. Based on the survey data of plant communities, in this study, the eastern Qinling-Daba Mountains is divided into four geography units: north flank of eastern Qinling Mountains (EQMN), south flank of eastern Qinling Mountains (EQMS), north flank of eastern Daba Mountains (EBMN), south flank of eastern Daba Mountains (EBMS). The regional climate divisions on levels of plant species, plant community structure and species richness are explored. The results show that: (1) On plant species level, there are mainly north plants in EQMN, evergreen species and fewer north plants in EQMS. Then to the eastern Daba Mountains, there are mainly south plants which like wetness and heat. (2) On plant community structure level, there are 4 formations (3 northern formations, 0 southern formation, 1 widespread formation) in EQMN, 6 formations (3 northern formations, 1 southern formation, 2 widespread formations) in EQMS, 4 formations (0 northern formation, 2 southern formations, 2 widespread formations) in EBMN, 3 formations (0 northern formation, 3 southern formations, 0 widespread formation) in EBMS. In terms of the numbers and properties of formation, there is a mixture of northern and southern formations only in EQMS. On species richness level, the diversity of family, genus and species decreases with the increase of latitude, but the mixture of north and south plants occurred in the south flank of eastern Qinling Mountains. This paper studies the variation of series in vegetation, which increases the scientificity of determining north-south dividing line, and shows that the south flank of eastern Qinling Mountains is more suitable as the warm temperate-subtropical zones dividing line.

The Qinling Mountains, located at the junction of warm temperate and subtropical zones, serves as the boundary between North and South China. Exploring the sensitivity of vegetation response to hydrothermal dynamics can be conducive to understanding the pattern and dynamics of main vegetation types and the mechanism of their response to changes in temperature and moisture. Importance should be attached to the laws of vegetation change in different climate zones. To reveal the sensitivity and areal differentiation of vegetation responses to hydrothermal dynamics, the spatial and temporal variation characteristics of NDVI and SPEI on the southern and northern slopes of the Qinling Mountains from 2000 to 2018 are explored using the meteorological data from 32 meteorological stations and the MODIS NDVI datasets. The results show that: (1) The overall vegetation coverage of the Qinling Mountains improved significantly from 2000 to 2018. The NDVI rise rate and area ratio on the southern slope were higher than those on the northern slope, and the vegetation on the southern slope exhibited better improvement than that on the northern slope. The Qinling Mountains showed an insignificant humidification trend. The humidification rate and humidification area of the northern slope were greater than those on the southern slope. (2) Vegetation on the northern slope of the Qinling Mountains was more sensitive to hydrothermal dynamics than that on the southern slope. Vegetation was most sensitive to hydrothermal dynamics from March to June on the northern slope, and from March to May (spring) on the southern slope. The vegetation on the northern and southern slopes was mainly affected by hydrothermal dynamics on a scale of 3-7 months, and it responds weakly to hydrothermal dynamics on a scale of 11-12 months. (3) 90.34% of NDVI and SPEI were positively correlated in the Qinling Mountains. Spring humidification in most parts of the study area could promote the growth of vegetation all the year round. The sensitivity of vegetation responses to hydrothermal dynamics with increasing altitude increased first and then decreased. The altitude of 800 to 1200 m was the most sensitive altitude for vegetation response to hydrothermal dynamics. The sensitivity of vegetation response at the elevation of 1200-3000 m decreased with the increasing altitude. The grass was the most sensitive vegetation type to hydrothermal dynamics on the northern and southern slopes of the Qinling Mountains, but most of other vegetation types on the northern slope were more sensitive to hydrothermal dynamics than those on the southern slope.

Xinjiang, a unique natural unit, is sensitive to the global warming. Studies on the spatial-temporal variation and impacts of drought and wetness in Xinjiang have a significant effect on the adaptability of future climate change. Based on observations of monthly mean temperature, monthly precipitation, and calculated standardized precipitation evapotranspiration index (SPEI), this paper analyzes the drying trend and impacts of climate change on the water resources and vegetation dynamics over Xinjiang, China. The results can be shown as follows: (1) The climate experienced a significant shift from warm-wet to warm-dry over Xinjiang in 1997 based on the SPEI data, after which the frequency, trend, dry months and percentage of stations of drought increased sharply. (2) The increased meteorological drought severity had a direct effect on the normalized difference vegetation index (NDVI) and river discharge. The NDVI exhibited a significant decrease during the period 1998-2015 compared with 1982-1997, which was found to be caused by increased soil moisture loss. (3) The hydrological drought was very complicated and not entirely comparable to the SPEI droughts. Hydrological records indicate that runoff in most rivers in the Tianshan Mountains has increased, while it remained stable or even decreased slightly in the Kunlun Mountains over the past 20 years. The runoff in Xinjiang is strongly influenced by glacial melt, and it is getting worse due to global warming. The climatic shift and intensified climate extremes over Xinjiang have resulted in SPEI-drought severity. These changes also have possibly intensified the instability of water cycle system and ecosystem. The results provide valuable decision-making reference for the regional drought disaster prevention, reduction and emergency management over Xinjiang, China.

Based on the three dimensions of "hazard-formative factors, hazard-formative environments, hazard-affected bodies", we assessed the risk of sandstorm diffusion in the southern Xinjiang using the Spatial Principal Component Analysis (SPCA) method. A multi-level ecological network was built and components of key landscape patterns were optimized by the Minimum Cumulative Resistance (MCR) model. (1) The risk of hazard was high in this region by single dimension factor analysis. Under the action of wind, eight sandstorm source areas and Tarim Basin were prone to sandstorm diffusion because of the existence of abundant sand materials. The hazard-formative environment was relatively fragile. Hejing and Aheqi counties had relatively good ecological background. In the Tarim Basin and its southern counties, the sandstorm tends to spread, especially in Hotan Prefecture, and counties of Qiemo and Ruoqiang. Oasis population and agricultural production were highly concentrated and vulnerable to environmental factors. (2) Some 46.53% of the area had high risk of sand diffusion due to abundant sand sources and poor site conditions. The most important factors affecting the wind sand diffusion were vegetation coverage and soil types of the underlying surface. The main causes of regional sand source diffusion were the intensity of wind field. (3) Based on the MCR model, 20 ecological corridors were constructed to connect ecological source areas, including five river types, nine road types and six green belt types of corridors. Among them, corridors 1 and 4 connected via Taklimakan Desert, and the rest of the corridors presented a circular distribution pattern at the outer edge of Tarim Basin. At the same time, 30 ecological nodes were identified, including seven class-A ecological nodes and 23 class-B ecological nodes, which were mainly distributed in Hotan and Bayingolin prefectures. The risk of sandstorm diffusion can be reduced by constructing shelterbelts and improving vegetation coverage. Results provide technical support for the prevention and control of sandstorm diffusion and the optimization of landscape patterns in the arid and semi-arid areas of northern China.

Freeze-thaw erosion is the main erosion in the Qinghai-Tibet Plateau. In this study, both the failure process and the transport process of the soil on a slope are analyzed under a similar climatic condition in eastern Tibet. It reveals that the sensitivity factors should be divided into the latent factor and the dominant factor. The latent factors change gradually over time, which include the geological structures, the lithology, and the slope direction. The dominant factors with catastrophe include the climate, the sloping topography, and the vegetation cover. The driving forces of freeze-thaw erosion are the gravity force and hydrodynamic force, while the erosion resistance is controlled by the dual structure of soil and the anchoring force of vegetable roots. On a temporal scale, the freeze-thaw erosion is a cyclic evolution process. It begins with the weathering of bedrock and soil formation, goes through the freezing-thawing and the tensile failure process, and ends with the re-exposure of bedrock after the soil is transported. Generally, this cycle should last a long term, but it could only last several years or decades of the period due to the structure of the soil. Based on the failure mechanism of the limit equilibrium state of the soil, freeze-thaw erosion can be divided into trailed progressive disintegration and multi-level disintegration type, both of which have the characteristics of 'multi-pathogenesis and same symptoms'. The characteristic parameter of freeze-thaw erosion intensity is introduced to describe how those influence factors affect the mechanism of freeze-thaw erosion. The formula is established by the relationship between the intensity value and the factors including both latent factors and dominant factors. It can be used to forecast calculate the amount of soil erosion when there is a standard-value in the study. Although there are still a few discretization errors in the formula building because of the randomness of sensitivity factors, the fitting results can still explain more than 90% of the evolution trend. Moreover, a new model of freeze-thaw erosion intensity based on soil erosion observation is proposed. Therefore, different from previous research, in this paper, the new model of erosion intensity can effectively reduce the errors caused by regional suitability and provide a theoretical basis for formulating countermeasures under different conditions.