The history of dune landform changes and dust activity at mid-latitudes is a good archive for exploring environmental changes and related landscape response. In this study, the dynamic changes, material sources, dust activity history and the influencing factors of typical sand dunes in the Hexi Corridor were comprehensively analyzed from the aspects of aeolian geomorphology, grain-size sedimentology, geochemistry and climatology. The results show that in the past half century, the typical crescent-shaped dunes and chains of crescent-shaped dunes in the study area have moved or swayed greatly, with an average speed ranging from 0.8 m/a (Dunhuang) to 6.2 m/a (Minqin). The dynamic changes of sand dunes are mainly affected by annual precipitation, annual average wind speed and annual gale days, which indicates that climate is the primary influencing factor of dune landform changes. The three-stage grain-size curve model of dune sands is obviously different from that of gobi sediments (two-stage), revealing the "immaturity" of the latter in sedimentology, while the former has experienced efficiently aeolian differentiation and non-local origin. The comprehensive evidences of paleogeography, sedimentology and geochemistry reveal that the source materials of sand dunes are mainly alluvial/proluvial and palaeo-fluvial sediments, including clastic sediments in the denudation/erosion zones of the north and south piedmonts. Indicators such as the proportion of surface fine particles, the coverage of surface salt crusts, and the content of erodible sandy materials indicate that the western gobi areas are not the main source areas of wind-blown dust in the central and eastern parts of the Hexi Corridor. The spatial distribution of the movement direction of sand dunes is similar to that of the regional dominant wind direction, which indicates that the difference in the dynamic evolution of dune landforms between the east and west of the Hexi Corridor should be controlled by the regional-scale wind system, that is, controlled by the dynamic mechanism rather than the difference in material sources. The warming and humidification of the Hexi climate is a synchronous response to the global warming and the strengthening of the Asian Summer Monsoon. It is also the main reason for the reduction of dust storms in the study area, which means that a potential inverse desertification process exists in the Hexi Corridor during the same period and it is also controlled by climate change. However, the process of desertification in the oasis areas during the period is caused by groundwater fluctuation affected by human activities.

Debris-covered glaciers are widely distributed in western China. Supraglacial debris lying at the atmosphere-glacier interface plays an important role in the air-ice energy flux and thus influences the underneath ice melt rate. Varying glacier debris thickness will have influence on the mass balance gradient of the debris-covered glacier, the development of ice cliff, ponds and drainage systems, as well as on the downstream runoff process. Using Landsat TM/TIRS images between 1990 and 2019, this study extracted the debris coverage and estimated the thickness changes of the debris-covered glaciers in the Mount Gongga by using a physically-based thermal conductivity method. We found that: (1) The debris coverage of glaciers in the study area totally expanded by 43.824 km², among which the Hailuogou Glacier expanded 2.606 km², Mozigou Glacier 1.959 km², Yanzigou Glacier 1.243 km², Dagongba Glacier 0.896 km², Xiaogongba Glacier 0.509 km² and Nanmenguangou Glacier 2.264 km². Annual expansion rates of their debris covered area are 3.2%, 11.1%, 1.5%, 0.9%, 1.0% and 6.5%, respectively. (2) In addition to debris cover area expansion, we found thickening debris layers, with glacier wide average debris thickness increasing by 5.2 cm, 3.1 cm, 3.7 cm, 6.8 cm, 7.3 cm and 13.1 cm for the above six mentioned glaciers, respectively. (3) Compared with glaciers on the east slope, debris-covered glaciers on the west slope of the Mount Gongga generally have higher debris cover rate but experienced lower debris cover expansion and lower terminal retreat rate during the past decades.

Food security, one of key components of national security, is a top priority for human survival and social development. In this study, we first sought to determine the influencing factors of crop yields and the process of drought impacts on crop yields. We then systematically reviewed the effects of droughts on major global crop yields from four aspects: field control experiments, statistical models, crop growth models, and remote sensing inversion models. Recent progress in crop yield impact assessment reveals that the current research has changed from single-hazard to multi-hazard, from single target to multiple targets, and from statistical models to a comprehensive model. A bibliometric analysis shows that the volume of research on drought impacts on crop yields has increased exponentially, and the related research theme has undergone a transformation from traditional research on crop water stress to comprehensive research on crop drought impacts and adaptation, reflecting the continuous deepening and integration of research perspectives. Agriculture, plant sciences, and environmental sciences are the three main disciplines in research on drought impacts on crop yields. We need to strengthen the application of geographical thinking, that is, systematic thinking concerning multiple factors and multiple scales to study the coupling of crop yields and water resources in the future. Finally, we suggest the following four priority areas for future research in consideration of the problems and challenges of the existing research: establishing a multi-source database of drought impact on crop yield, revealing the key process and mechanism of drought impacts on crop yields, developing a coupled macro and micro process crop growth model, and establishing a comprehensive monitoring platform system for crop yields and food security. This will help ensure sustainable agricultural development and global food security by improving monitoring, early warning, and scientific management of the impacts of droughts on crop yields.

The determination of temperature changes in major countries since the 1980s is a key scientific method to reveal the spatial difference of global temperature change and to achieve a common global climate change. Based on seven sets of reanalysis data, this paper analyzed the spatio-temporal characteristics of global temperature change and the temperature change of major countries from 1981 to 2019 by using climate tendency rate and spatial interpolation. The results revealed that the global land air temperature in the stydy period varied at a rate of 0.320 °C/10a, exhibiting a significant increasing trend, with a cumulative increase of 0.835 °C. The mean annual land air temperature in the northern and southern hemispheres varied respectively at rates of 0.362 °C/10a and 0.147 °C/10a, displaying significant increasing trends, with cumulative increases of 0.828 °C and 0.874 °C,respectively. The global land surface air temperature displayed an increasing trend, with more than 80% of the land surfaces showing a significant temperature increase. Across the globe, the change rates of annual mean air temperature were higher at high latitudes than at middle and low latitudes, with the highest change rates in regions at latitudes of 80°N-90°N, followed by the second-highest rates in regions from 70°N-80°N, and the third-highest rates from 60°N-70°N. Greenland, Ukraine, and Russia had the highest increase rates of annual mean air temperature, especially Greenland, which experienced a temperature tendency rate of 0.654 °C/10a. The regions with the lowest increase rates of annual mean air temperature were mainly in New Zealand and areas on or near the equator including South America, Southeast Asia and Southern Africa, where the temperature tendency rates were < 0.15 °C/10a. Among the 146 countries surveyed in this paper, 136 countries (93%) showed a significant warming trend, 10 (6.849%) had no significant change in temperature, and only 3 countries showed a downward trend. Among them, since the 1980s, there are 4, 34, and 68 countries with global warming above 2.0 ℃, 1.5 ℃, and 1.0 ℃, respectively, accounting for 2.740%, 23.288% and 46.575% of the countries concerned in this study. This paper held that there had been no global warming hiatus since 1998.

Fluctuations of lake level are good indicators of broad-scale wetness and thus can reflect the changes in the moisture balance (precipitation minus evaporation), which has been an important index in reconstructing the paleoclimate of late Quaternary. Spatial and temporal patterns of humidity changes since Last Glacial Maximum (LGM, 18 cal. ka BP) have been reconstructed for central and northern Eurasia based on the compilation of 149 lake records from the database documentation of the Soviet Union and Mongolia as well as China. The study areas were divided into three regions according to the climate differences, geographic locations and existing research results, that are, the Eastern Europe lake region, the arid Central Asian lake region and the East Asian monsoon lake region of northern China. A three-category scheme (collapsed coding) was used here to reclassify different lake statuses in order to standardize the lake level data over the past 18000 years. Then we used five-scheme status anomaly within each 1000-yr interval and the present to map and analyze the spatial patterns of five levels, namely, much drier, drier, no change, wetter and much wetter than today. The results demonstrated that moisture conditions have experienced diverse changes since LGM in different lake regions. There were relatively few lake records in Eastern Europe before late glacial period and the records increased substantially since the Holocene. Arid climate prevailed during the early Holocene in Eastern Europe, and relatively wet conditions dominated the middle and late Holocene. The arid Central Asian lake region as a whole experienced a wet climate from the LGM to the middle Holocene and turned dry during the late Holocene. But the patterns of climate change differed from lake to lake. In the East Asian monsoon region of northern China, the wet period was mainly observed in the early and middle Holocene and then the climate became drier in the late Holocene. The comparative analysis revealed that the eastern part of Eastern Europe lake region presented a wet trend with the retreat of the Scandinavian ice sheet during the early Holocene and the humidity reached a maximum in the mid-Holocene associated with cyclone activity on the downstream limb of the summer anticyclone. However, the western part of Eastern Europe experienced drier conditions in the early Holocene due to the development of a strong thermal high-pressure cell over central and western Siberia, and then returned to wetter conditions in the mid-Holocene as the result of the penetration of the Asian monsoon. The relatively wet condition in the arid Central Asian lake region during the glacial period was mainly produced by the precipitation brought by the westerlies and the significant decrease in evaporation, while the wet mid-Holocene was probably related to the strengthening of summer monsoon precipitation. The regional climate may have been mainly controlled by East Asian monsoon in the monsoon region of northern China.

Variations of hydrological connectivity are regulated by sluices in a plain river network, which increases the difficulty of studying the variations of hydrological connectivity. To this end, a reasonable indicator (Sluice Longitudinal Connectivity Index, SLCI), composed of sluice passage probability, passage efficiency, and cumulative effects of sluices, is proposed to detect the changes in the longitudinal connectivity in flood and non-flood seasons. The indicator considers different scheduling rules of sluices and its calculation unit is grid. The results in a grid scale could reveal the hydrological connectivity at the micro scale, which can present a more detailed spatial heterogeneity of the connectivity relative to the units of river basin or water conservancy region. Based on this, the Wu-Cheng-Xi-Yu region (WCXY) in China was taken as a study region. And the spatial heterogeneity of the hydrological connectivity was detected by the Getis-Ord G_i^* method. In the WCXY region, the average SLCI for the non-flood season is 0.66, while the average SLCI for the flood season is 0.50. The spatial agglomeration of connectivity in the non-flood season has a 5% spatial range larger than that in the flood season. Specifically, the values of high connectivity agglomeration during non-flood and flood seasons are 0.93 and 0.87, respectively; and the values of low connectivity agglomeration during non-flood and flood seasons are 0.25 and 0.16, respectively. Our method would provide a theoretical support for relevant departments to take measures of the river system construction in the Yangtze River Delta and a new idea for the assessment of hydrological connectivity in the plain river network region.

The lack of high-resolution terrain and image data has become a major bottleneck for geoscientists to study surface phenomena, features and processes. In recent years, the development of low-cost UAV equipment and photogrammetric technology makes it possible to obtain high-resolution data in the field of geoscience, which has greatly improved the accuracy and efficiency of geological disaster field survey and disaster cataloging. In this study, a database including 307 loess landslides was constructed through field investigation of UAV and remote sensing image interpretation. On this basis, through digital terrain analysis (DTA) and mathematical statistics, we summarize the distribution rule of loess landslides sample data, discuss the influence of terrain on the distribution of loess landslides is discussed, describe the influence of the relative height difference of terrain on the longest sliding distance, landslide perimeter, and landslide area, and propose formulas for quickly estimating landslide scale based on traditional empirical formula fitting. The results show that: (1) There are obvious regularities in the scale-frequency distribution of landslides. The frequency of loess landslides with different maximum lengths, maximum widths and perimeters shows a positive skew distribution, while the frequency distribution of landslides with different areas presents a power function pattern. (2) Terrain plays a significant role in controlling the development of loess landslides. The quantity of landslides on slope units with different height differences, average slopes, slope forms varies greatly. (3) The fitting curves of the relative height difference and the longest slipping distance, or landslide's perimeter, or landslide's area follow the power law distribution well. However, the fitting effects of different terrain areas are different. The loess hilly area has the best fitting effect, followed by the whole Loess Plateau, and the loess tableland area is the worst. (4) The rapid prediction models of loess landslide scale established in this study provide empirical formula support for landslide investigation.

As the effects of climate change become more devastating, the changes of precipitation patterns and food supply are and will be major challenges facing mankind nowadays and in the future. But the interannual relationship between the precipitation patterns and the food yields is still unclear. Studying changes in food yields and precipitation in those areas where the southwest and southeast monsoons interact is significant to revealing the dynamic correlation of food and precipitation, achieving regional food security, ensuring the stability of the southwestern frontier, implementing regional ethnic policies, and building a harmonious well-off society. The paper takes Yunnan Province in Southwest China as an example to describe the pattern of precipitation changes from 1988 to 2018 and discusses its impact on food production. The results suggested that: (1) The precipitation patterns of Yunnan are classified into three periods: Ⅰ abundance period (1988-2004), Ⅱ shortage period (2005-2015), and Ⅲ recovery period (2016-2018). (2) Areas with significant changes account for 15.07% of the whole province in periods I-Ⅱ to 13.87% in periods II-Ⅲ and to 16.53% in periods I-Ⅲ. (3) There is a significant positive relationship between precipitation and food supply (p < 0.01) across the province. The correlation index between crops yields and precipitation of the three periods is higher than that between precipitation and meat-and-dairy products. (4) In three precipitation value (d) zones, food yields had different responses to changes in precipitation. When d ≥ 1500 mm, the precipitation plummets while the food yield remains stable. When 1500 > d > 700 mm, the two values will decrease simultaneously. When d < 700 mm, a small decrease in precipitation will cause a large decrease in food yields. All in all, the precipitation pattern in Yunnan has undergone significant changes in the past 30 years, which has an essential impact on the food yields in different regions. Therefore, sorting out the grain-precipitation spatial region of the province can help us combat the increasing precipitation pattern changes.

Glacier is a crucial freshwater resource for populations and socio-economies in arid and semiarid regions, and the vulnerability of glacier change is an issue concerning regional ecological services and sustainable socio-economic development. We took Chinese Tianshan Mountains as an example and constructed a basic framework of the vulnerability of glacier change covering factors such as physical geography, population status, socio-economic level, agricultural development and social services based on exposure, sensitivity and adaptability, and constituted a targeted evaluation index system accordingly. We examined the spatial structure and spatial autocorrelation of the vulnerability on glacier change using ArcGIS and GeoDa softwares. We discussed the influence and interaction of natural conditions, socio-economy, population and other factors on glacier change adaptability using the GeoDetector model. Our results suggest that: (1) The vulnerability level decreased from west to east with significant differences. The eastern part of Chinese Tianshan Mountains has the lowest vulnerability, followed by the central part, and the western part has the highest value. (2) There is a significant positive correlation between exposure and sensitivity and a significant negative correlation between exposure and adaptability, indicating that the areas with high exposure and high sensitivity to glacier changes tend to have low adaptive capacity, which leads to higher vulnerability; on the contrary, the vulnerability is low. (3) The spatial heterogeneity of the ability to cope with glacier change in the Tianshan Mountains is the result of the combined effects of natural, social, economic and demographic factors. Among them, factors such as the production value of secondary and tertiary industries, urban population, urban fixed-asset investment and employees at the end of the year play a leading role.

The Qinling-Daba Mountains form the main body of China's north-south transitional zone. However, because there is a controversy about the specific location of the geographical boundary in academic community, it is important to determine and improve the existing classification indices to construct the ecological geographical pattern in China. Soil is the core section of the transitional zone, the spatial distribution and variations in key soil indexes in the Qinling-Daba Mountains are important indicators for identifying the transition effect and regional characteristics of China's north-south transitional zone. This paper analyzes the spatial characteristics of soil organic carbon (SOC) and total nitrogen (TN), and their relationships with major geographical factors by means of spatial analysis and geostatistics, using data from the second national soil survey, as well as terrain, climate and vegetation data. Results show that spatial trends of SOC and TN contents are similar, and that there are three areas with high contents, one secondary area with high content and one area with low content. The high contents are found in the high-altitude regions of the Qinling-Daba Mountains and in the mountainous areas to the west of the Jialing River. Here, SOC and TN contents range from 15.03-71.04 g/kg and 1782.61-7710.00 mg/kg, respectively. The low-content areas spread from west to east across the Weihe Valley, to the southern Wutai and Funiu mountains, and along the north slope of the Qinling Mountains. Here, SOC and TN contents range from 0.64-6.50 g/kg and 110.00-885.96 mg/kg, respectively. The secondary high-content area is mainly located on the both sides of the Hanjiang River, in the Qinling-Daba Mountains where altitudes are less than 1000 m, in the Funiu Mountains at altitudes less than 1000 m and on both sides of Jialing River at altitudes slightly higher than 1000 m. Here, SOC and TN contents are between the above two ranges, with a gradual increase in content forming a "horn-shaped" pattern from west to east. In terms of the spatial characteristics and functions of vegetation, topography and climatic factors, it is found that the SOC/TN range in the secondary high-content area is consistent along the 1000 m contour line, at the upper limit of the warm temperate deciduous broadleaved forest belt (containing evergreen forest) and of the subtropical/warm temperate mixed evergreen-deciduous broadleaved forest belts, as well as along the 0 °C isotherm line in January and the 24 °C isotherm line in July. The temperature changes are stable in January, July, annually and during the four seasons, but the rainfall varies greatly in each season. This region is the main body area of the transtional zone between subtropical zone and warm temperate zone: the northern boundary is roughly distributed along the line of Dujiangyan-Maoxian-Pingwu-Wenxian to the west of the Jialing River and the 1000 m contour line on the southern slope of the Qinling Mountains. The southern boundary lies along the line of Dujiangyan-Beichuan-Qingchuan to the west of the Jialing River and the 1000 m contour line of the northern slope of the Daba Mountains. The results show that the spatial variation of SOC/TN content provides a reference for the demarcation of the subtropical-warm temperate zone. A further understanding of the soil processes and ecological effects in typical regions and typical mountains will help reveal the multi-dimensional transition characteristics and variation mechanism in the region.

In order to investigate the past 150-year history of atmospheric dust deposition and its effect on the Asian monsoon zone and marginal zone, ombrotrophic peats from the Changbai Mountians were used to reconstruct the past history of atmospheric dust deposition based on the grain-size, lithogenic elements and ²¹⁰Pb and¹³⁷Cs dating. The dust deposition sequences were compared with those from Motianling peat of Great Hinggan Mountains. The mountain peat ash in northeast China was mainly composed of clay and silt. The medium grain size and the lithogenic elemental fingerprints also preliminarily revealed that the mineral dust in the mountain peat of northeast China were mainly from the soil dust in Mongolian and northern China desert and sand land areas. The atmospheric soil dust deposition flux increased gradually from the 1800s to the 1960s, which was consistent with the increase of human activities such as regional modernization, industrialization and aggressive wars. There was a decreasing trend in the atmospheric soil dust deposition during the past 60 years in northeast China, as shown by the mountain peat records, which is in good agreement with the monitoring data of regional natural dust storms. The background baseline of the long-distance atmospheric soil dust deposition flux in northeast China is calculated as 5.2±2.6 g m^-2 a^-1. The mean atmospheric soil dust flux was 5-38 g m^-2 a^-1 in the Changbai Mountain area, and that value was 14-68 g m^-2 a^-1 in the Great Hinggan Mountain area. The atmospheric dust deposition rates derived from the Changbai Mountain peat were smaller than those derived from the Great Hinggan Mountian peat. This suggested a decreasing atmospheric dust deposition with the increasing distance from the dust source area, and thus the influence extent of atmospheric dust deposition on the western side was higher than that on the eastern side of northeast China.

The tidal creek is the main channel for the interaction of the land-sea ecosystem and has a high degree of spatiotemporal dynamics. Taking the old and new river courses in the Yellow River Delta as the boundary, the North Bank of the Yellow River (Area I), the East of the South Bank (Area II), and the West of the South Bank (Area III) are divided into comparative study areas. Remote-sensing images of five key time nodes from 1998 to 2018 are selected as the data source. Using the GIS spatial analysis function, the typical morphological characteristics of the tidal creek development degree are quantitatively characterized. The influence of factors such as the Yellow River diversion, wetland restoration project, and alien species invasion on the development process of tidal creeks is analyzed. Mining the temporal and spatial evolution of the tidal creek network through morphological parameters. Results are shown as follows. (1) The morphological characteristics of tidal creeks have obvious spatiotemporal heterogeneity. From the early stage of the Yellow River diversion in 1998 to the early stage of wetland restoration in 2004, the number of tidal creeks at all levels in Area I decreased significantly. Owing to the siltation of tidal flats and the effect of Spartina alterniflora, the number, density, and bifurcation ratio of tidal creeks in Area II showed an increasing trend. During the rapid expansion period of Spartina alterniflora in 2013, the curvature and bifurcation ratio of the tidal creek increased significantly. The level, length, and density of tidal creek development in Area III were the highest, as is the frequency of conversion between levels. The wetland restoration project has resulted in a significant reduction in the number and length of low-grade tidal creeks. Strong ocean dynamics inhibited the development of meanders in tidal creeks. (2) The diversion of the Yellow River and construction of side-curved spur dams have led to an increase in the overmarsh path length (OPL). This reduces the drainage density of the tidal creek network The rapid expansion of Spartina alterniflora increased the drainage density and the OPL continued to decrease. The degree of tidal creek development is Area III>Area II>Area I. (3) The tidal creek system changed rapidly from adolescence to middle age, and the development tended to be in dynamic equilibrium. The research results aid an understanding of the development process and evolution mechanism of large-scale tidal creeks, and provide scientific decision support for the development and utilization of coastal tidal flats.