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Xinjiang, an arid region of China, has experienced a substantial warming–wetting trend over the past five decades. However, climate change has affected vegetation growth/greening in arid Central Asia in unexpected ways due to complex ecological effects. We found a significant greening trend (consistent increase in the normalized difference vegetation index or NDVI) from 1982 to 1996, during the growing season; however, the NDVI consequently decreased and plateaued from 1997 to 2015, especially in naturally vegetated regions. Atmospheric vapor pressure deficit (VPD) is a critical driver of vegetation growth, is a direct measure of atmospheric aridity, and has increased sharply in recent decades. A partial correlation analysis indicated a significant relationship between growing season NDVI and VPD from 1997 to 2015. This implies that decreased VPD corresponds to increasing NDVI, and increasing VPD corresponds to a decrease and plateauing in the NDVI trend. Using the partial derivative equation method, our results suggest that the trend in growing season NDVI was affected primarily by increasing VPD (contributing 87.57%) from 1997 to 2015, especially in the grassland and desert biomes. Rising temperatures lead to a greater VPD, resulting in exacerbated evaporative water loss. Soil drought and atmospheric aridity limit plant stomatal conductance and could effectively lead to a decrease in the greening trend and increased vegetation mortality in arid Xinjiang. Our results emphasize the importance of VPD as a limiting factor of greening trends in arid regions. The influence of VPD on vegetation growth should be considered when evaluating arid ecosystem functioning under global warming. [ABSTRACT FROM AUTHOR]

Vegetation is an indicator of changes in the ecological environment and a key source of feedback on the impact of drought. In this work we selected northern China as the study area and used the standardized precipitation evapotranspiration index (SPEI) and the normalized difference vegetation index (NDVI) to assess the relationship between drought and vegetation dynamics at annual and seasonal scales for the period 1982–2015. The results indicated that annual drought showed a slight increase in northern China during this time, and it was mainly attributed to the intensified summer drought; the percentages of areas where significant drying, drying, wetting, and significant wetting occurred accounted for 3.30%, 53.36%, 40.39%, and 2.95%, respectively. Annual NDVI showed a highly significant (p < 0.01) upward trend in northern China, suggesting that vegetation there is greening. However, there was still a significant decrease in the NDVI trend in 13.65% of the study area, and forest accounted for the greatest area among the three land cover types studied. A positive correlation between annual SPEI and annual NDVI was found in most of northern China, and 18.66% of the study area (p < 0.05) were mainly distributed in the central-eastern part of Inner Mongolia, the central part of the Loess Plateau, and northwestern part of Xinjiang Province. Residual analysis found that the percentages of vegetation dynamics affected by human-induced degradation, human-induced improvement, and drought accounted for 13.91%, 47.91%, and 38.18%, respectively; however, 54.15% of the areas affected by drought were located in arid and semi-arid regions and that about 54.61% of those were grassland. The work could provide guidance for vegetation construction and water resource management in northern China. [ABSTRACT FROM AUTHOR]

Global warming and human activities have posed a great threat to the climatic elements in drylands. The very fragile ecosystem is also highly sensitive to natural and anthropogenic disturbances. It is a serious risk to the evolutionary direction and habitability of oases in recent years. Among them, the Land Surface Temperature (LST) is one of the most important parameters to evaluate the interaction and energy exchange between the earth and the atmosphere. The spatial pattern of the surface temperature and the thermal environment in a region can be attributed to the combined effect of the regional small terrain factors and the properties of underlying surfaces. It is a high demand to explore the spatial distribution of the LST and the "source-sink" effect in the dryland oases, particularly for the local climate change patterns and the influencing factors in the arid regions. However, the oases cold island has put a great challenge on the temperature inversion and high-temperature center using remote sensing in the large-scale basins or open terrain regions. This study aims to analyze the spatial distribution of LST and the influencing factors in the Yanqi Basin in Xinjiang of China. The Mono-window algorithm was also utilized in this case. A quantitative analysis was performed to determine the contribution of the “source-sink” effect in the different land use/cover types to the LST change. The results showed that: 1) The land use/cover type was determined by the spatial distribution pattern of surface temperature and the “source-sink” effect. There was the strongest heat source in the unused lands. The strongest heat sink was observed in the water bodies. There was little influence of grasslands and construction lands on the land surface thermal environment. The intensity of the heat sink effect in the croplands depended mainly on the area of agricultural irrigation and crop growth conditions. 2) The Normalized Difference Vegetation Index (NDVI) was negatively correlated with the LST. The surface temperature decreased by about 1.98 to 2.66 for every 0.1 increase in NDVI. ℃ However, more effects of the vegetation were found on the surface temperature in the cultivated, grassland, and unused land. Less effect of the vegetation was observed in the wetlands. There was also a smaller cooling effect on the vegetation in the construction lands, due to the relatively small proportion of green space in the towns and cities. 3) The slope presented the most significant impact on the gentle slope areas less than 13° at the lower elevation in the basin. The LST increased rapidly with the increase of the slope. There was a weaker effect of slope on the LST at altitudes higher than 1 252 m. The LST decreased gently with the increase of slope. 4) The cold island effect also created a unique thermal structure of the near-surface atmosphere over the Yanqi Basin Oasis. Specifically, the surface temperature rose rapidly at first, with a high-temperature center at the height of 100 to 300 m from the ground, and then gradually decreased, as the altitude rose. The atmospheric temperature inversion layer was generated on June 22. The thickness then exceeded 1 000 m on July 1. The redistribution of the slope direction on the solar radiation disappeared within the height range of 100-300 m above the Yanqi Basin Oasis surface. This absence was attributed to the high-temperature center. This finding can fill the gap in the observation data in the Yanqi Basin in Xinjiang of China. [ABSTRACT FROM AUTHOR]

The ecological evolution and relevant factors in semi-arid and arid regions is a research focus on climate changes. One such region, the mountain-oasis-desert coupling system in Xinjiang, China, is sensitive to global climate changes because it has a fragile ecological environment. This study attempted to investigate the temporal-spatial variations of surface soil moisture, vegetation cover and their influencing factors of mountain-oasis-desert coupling system in Xinjiang from 1986 to 2015. The results showed that: (1) The surface soil moisture increased in most of the ecoregions of Xinjiang from 1986 to 2015 whereas the vegetation cover decreased in the same period. (2) The comparison of the correlations between soil moisture content (SMC) and the variables of precipitation and temperature revealed that precipitation is an important supplement source of SMC. The variation characteristics of surface soil moisture are closely related to the dry and wet soil conditions. (3) The comparison of the correlations between the normalized difference vegetation index (NDVI) and the variables of precipitation and temperature revealed that the different responses of vegetation to precipitation were related to the gradually decreased precipitation pattern in the mountain-oasis-desert system. Meanwhile, vegetation was found to be more sensitive to precipitation in deserts and oases and more sensitive to temperature in mountainous regions. In each ecoregion, the variation cycles of SMC and vegetation cover were slightly different, but it was found that SMC is more likely to be affected by temperature and precipitation rather than vegetation cover. Overall, surface soil moisture and vegetation cover products have a great potential to be effectively used in investigating landscape pattern variations, which is very important theoretically and practically for the mountain-desert-oasis system in arid areas. [ABSTRACT FROM AUTHOR]

In the process of agricultural development in arid and semi-arid areas, the carbon fixation capacity of vegetation can be affected to different degrees, but research on its driving factors is lacking. Consequently, this paper focuses on the Weiku Oasis in Xinjiang as its research area, in which the carbon fixation capacity of vegetation is estimated with the chemical equation of a photochemical reaction, using methods such as linear system models and Geodetector to analyze the relationship between cropland expansion characteristics and the carbon fixation capacity of vegetation from 1990 to 2020. The influence of land-use changes on the space differentiation of carbon fixation was elucidated through a time series relationship, and the synergistic effects of nine influencing factors on the carbon fixation capacity during the process of vegetation changes were discussed. The results were as follows: (1) In the process of agricultural development, the proportions of cultivated land area and spatial agglomeration had significant negative correlations with carbon sequestration, and the significance was rising, but the effect of cultivated land area proportion was more significant. (2) Through temporal sequential cooperativity analysis, when other land-use types were converted into cultivated land, the carbon fixation capacity of vegetation suddenly and significantly decreased in the initial year of the transformation, but the effect of cultivated land reclamation on the carbon fixation capacity of vegetation did not have a significant time lag. Moreover, after a certain period of time, cultivated land can gradually recover part of its lost carbon fixation capacity. (3) Among the nine driving factors, potential evapotranspiration is the most prominent in explaining the carbon fixation capacity of vegetation. This single-factor pairwise interaction presents the relationship between bivariate enhancement and nonlinear enhancement. When terrain factors interact with other factors, the enhancement effect of the influence on the carbon fixation capacity of vegetation has an obvious promotion effect. However, the change in the carbon fixation capacity of vegetation is more significantly influenced by potential evapotranspiration and the interaction between the normalized difference vegetation index (NDVI) and other factors. This research is helpful to understanding the basic theories related to the change in the carbon fixation capacity of vegetation during the process of agricultural development in arid and semi-arid areas, as well as providing theoretical reference for ecological environment construction and sustainable development. [ABSTRACT FROM AUTHOR]

Mountainous ecosystems provide humans with multiple ecosystem services (ESs), but global changes and anthropogenic activities threaten the supply of such services in arid regions. To maintain regional ecological security and achieve ecosystem sustainability, it is quite essential to understand the spatiotemporal characteristics of mountainous ESs in arid regions and clarify the main driving factors of different ESs. Using the integrated valuation of ecosystem services and tradeoffs (InVEST) and revised universal soil-loss equation (RUSLE) models, we evaluated the ESs provided by the Tianshan Mountains of Xinjiang from 2000 to 2020. The research showed that: (i) over the 20 years in question, habitat quality and carbon storage remained relatively stable, while soil retention and water yield fluctuated significantly. (ii) All ES pairs exhibited synergies. Spatial synergy areas were concentrated in the northwestern and southwestern areas; spatial trade-off areas alternated with spatial synergy areas. (iii) Hotspots with at least two ESs covered 73% of the study region. Middle- and high-altitude areas were the main supply areas of ES. (iv) Land-use types were the dominant driving factor of habitat quality and carbon storage, while mean annual precipitation had the strongest explanatory power for water yield. Soil retention was mainly affected by mean annual temperature and the normalized difference vegetation index. Our findings could provide guidance for policymakers when developing measures for ecosystem conservation and management. [ABSTRACT FROM AUTHOR]