With global climate change and the rapid development of human society and economy, the contradiction between water supply and demand has become increasingly prominent in recent years, and the freshwater conflicts in international river basins have intensified, which has aroused widespread concern in academia. Here we analyzed the spatio-temporal dynamics of global freshwater conflicts (GFCs) over the last 70 years from the "event-relations" perspective, and establish a spatio-temporal database of GFCs from 1948 to 2018 based on data mining method and spatial analysis. The results show that: (1) The evolution of GFCs is a non-monotonic dynamic process with multi-dimensional characteristics of trend, mutation and volatility. The GFCs showed a general trend of fluctuating growth, with an obvious sudden change around 1987. (2) The GFCs are mainly composed of low-intensity conflicts, and the hydrological intervention and contention for resource ownership are the focus of conflicts. The number of conflicts caused by the construction of dams and other water conservancy projects increases significantly. South Asia, West Asia and East Africa are the leading forces driving the evolution of GFCs. (3) The pattern of GFCs has changed from single-center to multi-center, and there is a clear trend of spatial spread. However, the overall distribution pattern with more conflicts in the northern and eastern hemispheres and the pattern with less conflicts in the southern and western hemispheres is relatively stable. Along 30-degree north latitude, a dense zone of freshwater conflicts covering high water stress basins in South Asia, Central Asia, West Asia, and East Africa has formed. (4) International freshwater conflict has gradually become more ubiquitous, complicated and networked, and the basin communities of freshwater conflict network have increased significantly. But the "Matthew effect" of freshwater conflicts among countries are obvious, and its polarized distribution pattern is relatively stable. A "path-locking" effect has been formed among the major conflictive countries. There is a certain spatial mismatch between the quantity relationship and intensity relationship of GFCs.

Under the background of global climate change, drought has become more serious than before. Therefore strengthening drought risk governance is of great significance to the sustainable development of regional agriculture. The consensus of different stakeholders will affect drought risk governance, so quantifying consensus will help to deepen the understanding of cooperation and drought relief mechanism of multi-stakeholders. Starting from the "cognitive-emotional” dimension and considering the emotional positivity, this article constructed a consensus indicator system and a model based on "distance" to quantify the consensus of Dingcheng district government, township governments, village committees, households and agricultural enterprises in Hunan Province. The main conclusions are as follows: (1) In the "cognition" consensus, the average value of each group presents a trend of emergency understanding > preparedness understanding > recovery understanding. Cognition differences among households, village committees, and governments in preparedness and recovery measures are more obvious. (2) In the "emotion" consensus, the average of each group presents a trend of fairness perception < tolerance perception < constraint perception < sense of belonging. The attitudes of stakeholders towards fairness, consideration for others, and acceptance for resource constraints are not positive. The government, village committees, and enterprises have obvious differences. (3) In the integrated consensus, the average values of households with township governments, village committees with district government, township governments with district government are greater than 0.65, while those of the enterprises with other stakeholders do not exceed 0.6. The results reveal the differences in the perceptions, and open up a new quantifiable idea for the multi-stakeholders' "consilience" research on the integrated risk governance of drought, which provides references for further consideration of different stages, requirements of different stakeholders and resource allocation in the risk governance.

It is important to quantitatively analyze the effects of protecting important ecological spaces in China to ensure national ecological security. By considering changes in the ecological land, this study examines the effects of protecting three types of important natural ecological spaces in China. The results show that: (1) In 2018, the ratio of ecological land to important natural ecological spaces accounted for 92.64%. This land had a good ecological background that reflects the developmental orientation of important ecological spaces. (2) From 1980 to 2018, the area of ecological land in important ecological spaces shrank but the rate of reduction was lower than the national average, which shows the positive effect of regulating construction in natural ecological spaces. The restorative effects of ecological projects to convert farmland into forests and grasslands have been prominent. The expanded ecological land is mainly distributed in areas where such projects have been implemented, and the reduced area is concentrated in grain-producing regions of the Northeast China Plain and agricultural oases of Xinjiang. In the future, the government should focus on strengthening the management and control of these areas. (3) The area ratio of ecological land was the highest in national nature reserves. The rate of reduction in its area was the lowest and the trend of reduction was the smallest in national nature reserves, which reflects differences in the status of ecological protection among different spaces. (4) The ratio of ecological land to important ecological spaces was higher than that in the surrounding external space, and the rate of reduction in it was lower. Thus, the effects of internal and external protection had clear differences in terms of gradient.

Located in the southern part of the Mongolian Plateau, the Inner Mongolia grassland is an important ecological barrier in northern China. The ecological restoration is a tough task and poses a great pressure on the grassland. In this paper, we focus on the Ujumqin-Undurhan transect, a typical grassland of the Mongolian Plateau. We used Landsat TM data from 1988 to 2016 which was divided into five periods (of seven years), to reveal the characteristics of grassland utilization in the transect, a transboundary between Mongolia and Inner Mongolia autonomous region of China. In addition, we determined the main disturbance factors of grassland and explored effective restoration mitigation and an international experience for reference. Based on land-use type as of 2016, we found that grassland accounted for 95.05% of the transect, which was evenly distributed across the entire transect. Other land use types accounted for a small proportion, and were relatively concentrated in the localized areas. Among them, cultivated land was concentrated in the Mongolian section in the northwest of the transect, while mining and its industrial area, sandy land, and saline-alkali land were mainly located in the Inner Mongolian section in the southeast of the transect. In the past 30 years, the arable land in the transect decreased the most (35.71%), which was concentrated in the Mongolian section. The area of grassland and water mass suffered a continuous decline with a similar trend both on Chinese and Mongolian sides. However, the decrease in the area of grassland in Inner Mongolia, China was greater than that in Mongolia, and most of them were converted to unused land. The largest increase was found in mining and its industrial area in the transect, nearly 367 times of the initial period, which was concentrated in the Inner Mongolian section. The area of saline-alkali land and sandy land underwent a continuous increase and the changes within the two countries were comparable. Finally, we found the grassland was the predominant land use type on the plateau, which was mainly used for grazing. Mining was the chief disturbance factor of grassland in China, followed by grazing. Meanwhile, the reclamation was the main disturbance factor in Mongolia. The extent of grassland disturbance in Inner Mongolia, China was much greater than that in Mongolia. Overall, grassland degradation and drought were the main ecological and environmental challenges faced by the Mongolian Plateau, especially in Inner Mongolia.

By synthesizing the results from recent peer-reviewed publications on the agricultural history and the historical cropland cover reconstruction in China, we summarized the general characteristics of the agricultural area and fractional cropland cover changes in China for the past 2000 years. The conclusions are drawn as follows: (1) In the western Han Dynasty, the main agricultural areas expanded from the middle and lower reaches of the Yellow River to the northern China. During the Tang and Song dynasties, the expansion of the agricultural areas that mainly occurred in southern China featured from the plain to hill and to high-land. From the middle of Qing Dynasty, the expansion of the agricultural areas mainly occurred in the border areas including Northeast China, Southwest China, and Northwest China, as well as remote regions mountains. (2) In the past 2000 years, the total cropland area in China has been increased in general although there were fluctuations. The cropland area reached about 500, 600 and 800 million mu around beginning of the 1st century, the early 8th century and the late 11th century, respectively. It exceeded 1, 1.2, 1.6 and 2 billion mu around the late 16th century, the early 19th century, 1953 AD and 1980 AD, respectively. (3) In China, the pattern of cropland was formed in the 11th century. Around 1080 AD, the cropland cover fraction accounted for more than 30% in the Huang-Huai-Hai Plain and the Guanzhong Plain and about 30% in the Yangtze River Delta, the Jianghan-Dongting Plain, the Poyang Lake Basin and the Sichuan Basin. Around 1850 AD, the cropland cover fraction took up more than 30% in the North China Plain, the Weihe and Fenhe river basins and some parts of eastern Gansu Province, the Sichuan Basin, the Jianghan-Dongting Plain, the Poyang Lake Basin and the Yangtze River Delta. Around 2000 AD, in the agricultural areas including the Northeast China Plain, the North China Plain, the Weihe and Fenhe river basins and some parts of eastern Gansu, the Sichuan Basin and the middle and lower reaches of the Yangtze River, more than two-thirds of which had a cropland cover fraction of more than 50%. The cropland cover fraction was more than 15% in the Western Liaoning hills, the Bashang Plateau, the Loess Plateau, as well as the hilly and mountainous areas of southern China. The highest cropland cover fraction also exceeded 50% in some oasis agricultural areas and the valley agricultural areas on the Qinghai-Tibet Plateau.

The changes in the scale and structure of built-up land is the basis for spatial development and planning of the national territory. Previous studies mainly focused on the characteristics and patterns of the horizontal expansion of built-up land, but little attention has been given to the "three-dimensional" gradient characteristics and effects of built-up land (such as slope-climbing). Therefore, based on Google Earth Engine, this study, for the first time as far as we know, uses DEM and land use data to draw built-up land slope spectrums and calculates the average built-up land climbing index (ABCI). The gradient characteristics and laws of the slope climbing of China's built-up land from 1990 to 2018 at the national, regional, provincial, and urban scales are systematically analyzed and the various spatial effects are explored. The results show that: (1) From 1990 to 2018, the area of built-up land with slope angle above 5° in China increased by 1.43 times, and the proportion of the total built-up land area rose from 10.25% to 14.81%. Particularly, the 2010-2015 period witnessed the fastest and largest slope-climbing development of built-up land in China. Moreover, the slope-climbing intensities in the central and western regions are higher than that in other regions. (2) According to the average built-up land climbing index (ABCI) and the upper limited slope angle change (ULSC), the 34 provinces (autonomous regions and municipalities) in China can be divided into three types: high-climbing, low-climbing, and horizontally expanding. Among them, the number of high-climbing provinces accounts for more than 50% of the total. And seven horizontally-expanding provinces present the distribution characteristics of "southeast-northwest" in space. (3) Before 2010, the cities with slope-climbing phenomenon were mainly mountainous cities. However, ethnic minority settlements and low-hill and gentle slope development pilot cities became the main force for the slope-climbing of built-up land after 2010. (4) The slope-climbing of built-up land can reduce the occupation of plain arable land and ecological land by built-up land expansion to a certain extent, and thus alleviate the contradiction between supply and demand of build-up land. However, it is worth noting that development and construction without reasonable plans and bulldozing mountains to build cities driven by real estate can also lead to increased geological disasters and ecological risks.

Land use sustainability evaluation is vital in the cross-disciplinary study of land system science and sustainable development, which is of great significance to the identification of regional land-use problems and the decision making in sustainable land management. With the connotation analysis of land use sustainability (LUS), this study proposes a new framework for LUS evaluation based on the perspective of land system conflict and adaptation, which is suitable for different regions and periods. Taking the Yangtze River Delta (YRD) region from 2000 to 2015 as an example, the following conclusions are obtained: (1) Based on the external development pressure and the internal support of land system, the "M"-shaped land system structure consisting of "resource subsystem conflict", "function subsystem conflict", "capacity subsystem conflict", "resource-function adaptation" and "function-capacity adaptation" can be constructed. Further, land use sustainability is obtained by calculating the structural support and balance based on the static balance equation. (2) Among the land conflict-adaptation indicators in the study region, the improvement degree of FC is the highest and the degree of F-C is the lowest. All indicators have significant spatial differentiation characteristics of urban-rural areas, latitude, and land-sea. (3) The YRD region contains 17 types of land system configuration, showing the characteristics of the stable and unstable polarization and the small number of intermediate structures. The LUS results in the YRD region range from 0.20 to 1.58, among which the LUS of Zhejiang > Anhui > average of the whole region > Jiangsu > Shanghai. The LUS in areas implementing green development strategies like Zhuji City and Anji County in Zhejiang Province is significantly higher than that in areas implementing traditional economy-led development strategies such as Lianyungang City and Rudong County in Jiangsu Province. This study can provide a reference for analyzing the sustainability of the regional land system, setting the land sustainable development planning goal, and exploring the direction of land system transformation.