Water is the lifeline of socio-economic sustainable development in northwest China. The land area of northwestern region accounts for 35.9% of China's total, but it has only about 5% of water resources of the whole country. This study proposed the "Three Water Lines" (Heihe-Tengchong Line, Yangguan Line, and Qitai-Cele Line) of northwest China under the perspective of the evolution of hydro-meteorology, ecological landscapes and socio-economic development. The "Three Water Lines" were the optimal configuration lines of the rational development and utilization of water resources, the characteristic zoning lines of ecological civilization and environmental protection, the guiding lines of "the Belt and Road Initiative" strategic focus, and the national security lines of long-term stability of the border areas. Facing the existing problems and challenges in the development and utilization of water resources in northwest China, this study proposed the "Three Water Lines" strategy and its spatial pattern coupling with the analysis of scenarios of water diversion of northwest China. The west route of the South-North Water Transfer Project is a fundamental project for the implementation of the "Three Water Lines" strategy. It is essential to overcome the constraints of the socio-economic development through the new strategies: (1) breaking through the "Heihe-Tengchong Line" will promote balanced development between the eastern and western regions of China; (2) Breaking through the current "Yangguan Line" will boost social and economic development in the Hexi Corridor, (3) Breaking through the "Qitai-Cele Line" will enhance water resources and environmental carrying capacity. A new spatial pattern of water resources allocation along the gradient was formed by the "Three Water Lines" strategy. The new water resources allocation patterns will be able to support stable development of socio-economy and ecological civilization construction, optimize population distribution and the layout of socio-economic development, and provide a reliable guarantee of water resources for the implementation of "the Belt and Road Initiative".
Since the 20th century, geography came into being with distinctive disciplinary characteristics by sustained effort of geographers. This paper puts forward predicament from cognitive and thought in the new era, and depicts new geographic characteristics from five aspects: new technology, new orders, new data, new approaches and new driving factors. According to new content of geo-regionality and new approaches of geo-comprehensiveness, the paper proposes that complexity research would be a successful new path in geography, and the complexity would be the third characteristic of geography. Then, the paper details some complex spatial patterns, complex time processes and complex spatio-temporal mechanisms in geography research. Based on the concept of a geographic complex system, this paper presents core issues and corresponding complex research tools. Finally, the paper puts forward new challenges and new requirements for geography in the new era.
Construction of the Belt and Road, an advocacy of China to promote win-win international cooperation in the new era, aims at building green, healthy, intellectual and peaceful Silk Road and ensuring joint development with the people of the countries along the Belt and Road. Systematic analysis on environmental characteristics, evolutionary tendency and future risk pattern is a scientific fundamental of sustainable development for the construction. Based on remote sensing monitoring and statistical analysis, this paper studies spatial-temporal characteristics of climate, topography, soil, hydrology, vegetation cover and production of terrestrial ecosystems. Taking the methodology of the classical integrated natural regionalization, the region is delineated into 9 sub-regions: Central and Eastern Europe, Mongolia and Russia, Central and Western Asia, Southeastern Asia, Pakistan, Bangladesh-India-Myanmar, Eastern China, Northwestern China and Tibetan Plateau. By combining modeling simulation with scenario projections, natural disaster assessment methodology is used to assess the risk of abrupt extreme events such as heat waves, droughts and floods in the next 30 years. And trend-baseline comparison method is applied to assess the risk of gradual change events in macro-ecosystems, food production, etc. Results show that, on the basis of the regional framework, the western Eurasia would show a warming trend; both sides of Tibetan Plateau are in high temperature and heat waves risk; cold-wet region of central and eastern Europe in high drought risk; monsoon area of Bangladesh, India and Myanmar as well as eastern China in high risk of flooding; the desert margin areas in high ecological fragile risk; the middle and low latitude areas in high risk of grain production.
Currently, the "farmland red line" management has made major achievements in the quantitative protection of Chinese farmland. However, the increase of grain production as well as the improvement of peasants' incomes still calls for more researches concentrated on the recessive farmland transition based on the current resources endowment. The recessive farmland morphology has multi-properties referring different disciplines. So the study of farmland transition needs a multi-disciplinary comprehensive research framework. This paper drew an outline of the farmland transition in China since its founding, and made an in-depth literature review from multi-disciplinary perspectives of management, economics and sociology. Previous research shows an inefficient performance from the aspect of locality, integrity and systematicness. The shortcomings above may weaken its application due to lack of popularization and operability. So the authors argue that, geographical ideology and analytical method should be introduced into current researches on recessive farmland transition. And multi-disciplinary comprehensive researches should be constructed to make up the existing deficiencies. Ultimately, from the conceptual level, the overall design level, and the practical application level, this paper puts forward a multi-disciplinary comprehensive research framework for the recessive farmland transition, and illustrates a concrete application from the problem-oriented perspective.
How to obtain the greatest social and economic benefits with the least input of urban land resources is the center of regional ecological civilization construction. Based on municipal input-output data from 2005-2014, we introduce the SFA (stochastic frontier analysis) to measure the urban land use efficiency of 110 cities located in the Yangtze River Economic Zone, and then analyze the spatial association characteristics of the efficiency. The results show that: (1) Urban land use efficiency in the Yangtze River Economic Zone increases from 0.344 to 0.53 during 2005-2014, showing a significant growth trend with a cumulative growth rate of 54.07%. The efficiency growth rate of cities in the upper reaches of the Yangtze River is faster than that of cities in the middle and lower reaches. There is great growth potential across the whole area. (2) The urban land use efficiency shows a "bar-like" distribution across the whole area, which gradually decreases from the east to the west. Not only does it present great differences within each province, but also the inter-provincial differences and differences among the upper, middle and lower reaches are extremely evident. The total land use efficiency of cities in the lower reaches is the highest, followed by cities in the middle reaches and cities in the upper reaches. (3) The Moran's I of the study area is above 0 and increases year on year, which indicates that the land use efficiency among cities has positive spatial correlation, and the agglomeration level is enhanced. The LISA (local indicators of spatial association) reveals the characteristics of "small agglomeration and large dispersion". The High-High agglomeration area spreads outward along Zhejiang and Shanghai, while the areas with a Low-Low agglomeration pattern are mainly concentrated in northern Anhui province and northern Sichuan province. To sum up, the research framework and results are of great significance to sustainable land resource use and regional coordinated development.
Since the beginning of the 20th century, forest restoration, as the main theme of global forest development, has gradually replaced deforestation. It is of great significance to explore the transition path of China's forests, as China has abundant forest resources. Based on the MODIS land cover data, 14 contiguous destitute areas of China are chosen as study areas to analyze the characteristics of forest transition from 2002 to 2013. Using the method of cold/hot spot analysis, we investigate the forest change trend and its spatial heterogeneity. In addition, we explore factors affecting forest area change by a linear regression model and disclose the forest transition pathways in contiguous destitute areas. The results show that net forest area of the 14 contiguous destitute areas increases by 106554.75 km2, with a growth rate of 11.93%, which means that the forest transition may enter the last stage. The Qinling-Daba Mountains, Wuling Mountains, southeastern Tibet and the eastern part of Yanshan-Taihang Mountains are hot areas of forest area increase, while the cold areas of forest area increase are mainly distributed in the vast area north of the 800 mm isohyetal line, Dabie Mountains and the eastern part of Yunnan-Guizhou-Guangxi rocky desertification areas. Both the increase of non-agricultural population and the implementation of forestry projects play significant roles in promoting forest transition, thus forest transition of 14 contiguous destitute areas of China mainly follows the economic development pathway and the state forest policy pathway. Some policy implications are also put forward. The pace of construction of small towns in contiguous destitute areas should be speeded up to depopulate rural areas. At the same time, rural eco-tourism should be developed on the basis of rich natural resources to help promote targeted measures in poverty alleviation. As for state forest policies, contiguous destitute areas should be regarded as the key areas for ecological construction so as to protect natural resources effectively.
Runoff generation is an important part of water conservation service, and also plays a critical role in soil and water retention. Under the background of the ecosystem degradation, which was caused by the vulnerable karst ecosystem combined with human activity, it is necessary to understand the spatial pattern and impact factors of runoff services in the karst region. The typical karst peak-cluster depression was selected as the study area. And the calibrated and verified Soil and Water Assessment Tool (SWAT) was one of the main techniques to simulate the runoff services of typical karst basin. Further, the spatial variability of different services were analyzed with the assistance of the methods of gradient analysis and local regression. Results indicated that the law of spatial difference was obvious. And the surface runoff was at a low level, but the groundwater runoff was rich (about 2-3 times the surface runoff). The runoff coefficients of total and groundwater were 70.0% and 23.9%, respectively. Terrain is a significant factor contributing to macroscopic control effect on the runoff service in the Sanchahe River Basin, where the total and groundwater runoff increased significantly with the rising elevation and slope. Then, the distribution of vegetation has great effects on surface runoff. There were spatial differences between the forest land in the upstream and orchard land in the downstream, in turn the surface runoff presented a turning point due to the influence of vegetation. Moreover, the results of spatial overlay analysis showed that the highest value of total and groundwater runoff was observed in the forest land. It is not only owing to the stronger capacity of soil water conservation of forest ecosystem, and geologic feature of rapid infiltration in this region, but also reflected the combined effects on the land cover types and topographical features, that is, forest land was mostly distributed in the area with relatively great elevation and slope. Overall, this study will promote the development and innovation of ecosystem services fields in the karst region, and further provide a theoretical foundation for ecosystem restoration and reconstruction.
The climate-sensitive region is an important direction of climate change research, however most previous studies paid more attention to research on single index, instead of that on comprehensive indicators. Based on the spatial distribution and temporal variation of climate types defined by the K?ppen climate classification, this research presents a new definition method to classify the Chinese climate-sensitive regions, where climate types varied frequently. Here we selected Community Earth System Model (CESM) under the intermediate carbon emission scenario (RCP4.5) to simulate the change of climate types during 2006-2013, the 2040s and the 2090s, and predicted the variation of climate-sensitive regions in the next 30 to 80 years. The results indicate that the climate change sensitive regions were consistent with the precipitation sensitive regions. The most sensitive regions in China are located near the Heihe-Tengchong Line, the Qinling-Huaihe region, the western Qinghai-Tibet Plateau and the north of the Tianshan Mountains, while the most stable regions are distributed in the east-central Qinghai-Tibet Plateau, the Kunlun Mountains, the north of Qilian Mountains, the south of the Tianshan Mountains, the west of Helan Mountains and the Da Hinggan Mountains region. In the next 30 to 80 years, the climate change sensitive regions in the western part of China (the west of Helan Mountains and Hengduan Mountains) will be stable, while in the eastern they are shifting northward significantly. This study provides a new perspective for the research of climate change sensitivity and regional responses to climate change, and it is conducive to a timely and effective decision-making in tackling climate change.
Research on extreme temperature is of great significance to ecological and environmental protection and disaster warning in the context of climate change. Based on the daily temperature data observed from 32 meteorological stations from 1960 to 2013, we studied the spatial distributions of air temperature and extreme temperature in the Shaanxi section in Qinling Mountains by integrating the methods of Kriging interpolation, linearity estimation and correlation analysis and the RClimDex software. The results showed that: (1) The annual average temperature, maximum temperature and minimum temperature in the study area were 10.48℃, 16.44℃ and 6.18℃ during the last 54 years, respectively. The temperature on the southern slope of Qinling Mountains was higher than that on the northern slope in the middle-altitude area and high-altitude area, and lower than that in northern slope in the low-altitude area. The difference in air temperature between the northern and southern slopes was lower in the low-altitude area and greater in the middle-altitude area. (2) The frequency, intensity and duration of extreme temperature all tended to increase in the Qinling Mountains. The zones sensitive to extreme temperature change were Zhenan and Zhashui located on the southern slope as well as Zhouzhi and Huxian on the northern slope. (3) The variety of the extreme temperature change was more obvious in frequency on the northern slope while in intensity and duration on the southern slope. Moreover, warming occurred mainly in the night on the northern slope but in the daytime on the southern slope. (4) The warming rate of extreme temperature in the study area increased with the increase of altitude. The change of frequency and intensity of extreme temperature was more obvious in the high-altitude area, and the duration of extreme temperature more obvious in the middle-altitude area.
Strongly impacted by climate change, glacier and snow, as major parts of solid reservoirs in mountains, can regulate the local water sources. This study uses glacier and snow datasets to analyze the variations of glaciers, snow, water storage, and runoff in the Tianshan Mountains, and selects three typical river basins (Aksu River, Kaidu River, and Urumqi River) to interpret the impact of glacier and snow changes on regional water resources in this region. Results indicate that: (1) the functional relationship between glaciers retreat and glaciers area is f(x) = -0.53×x-0.15 (R2 = 0.42, RMSE = 0.086), and small glacier retreat is more sensitive under climate change. Meanwhile, glacier retreat rate at the low-middle elevation bands is faster than that of the high elevation band; (2) the decreasing rate of regional average total water storage (TWS) is -0.7±1.53 cm/a in the study area during 2003-2015. The maximum of TWS deficit region was mainly observed in the central part of the mountains, which is closely related with accelerated glacier retreats; (3) during the past half century, the increased melting of glacier and snow melt led to a runoff increase in the three typical river basins, especially in the Aksu river basin (0.4×108 m3/a). The area decreasing, thinning, and rising equilibrium line altitude (ELV) of glaciers are the major factor contributing to the decreasing trend of runoff in the three river basins since the mid-1990s. Therefore, results revealed that the mechanism of influence of solid water reserves reduction in mountains on regional water resources under climate change, and also provided references for water resources management in the mountainous river basin.
Due to the increasing effects of climate change, drought induced economic losses of agricultural production should no longer be ignored. It has become vital to better understand the causes of agricultural drought. This will help to ensure the security of agricultural production, especially in the major grain production regions of China. Few previous studies have focused on multi-year agricultural drought risk in the grain production of Northeast China. The three provinces are crucial to grain production in China. Increased understanding of drought in this agricultural region would benefit the management of agricultural production. This study focuses on the investigation of possible risks that contribute to agricultural drought in the region, based on the natural disaster system theory. A risk assessment model is developed, based on the region, to investigate the spatiotemporal features of agricultural drought and regionalize the potential risks at county and city levels. The contributing factors for agricultural drought potential risk are exposure, vulnerability, resistance capacity, and agricultural drought composite risk, and these factors have been explored separately. Results indicated two important ideas. First, at the province level, the risk of agricultural drought was the highest for Heilongjiang and the lowest for Liaoning, with Jilin falling in between. The disaster risk changed during the year when the fluctuation of exposure was comparatively stable. Drought vulnerability was gradually rising while agricultural drought resistance capacity remained stable from 2010 to 2014. Second, looking at the entire region, the risk of agricultural drought gradually increased from south to north. The severity level, which is the percentage of county and municipal agricultural drought composite risk within each province, was Heilongjiang (75.81%), Jilin (41.30%) and Liaoning (0%). The highest agricultural drought risks were concentrated in the Sanjiang Plain and Songnen Plain.
The Tongtian section of the Yangtze River is located in ??the central part of the Tibetan Plateau where the neotectonic activity is illustrated by frequent earthquakes, such as the Yushu earthquake (Ms 7.1) on April 14, 2010. The study area is situated in the upstream parts of the Yellow River Basin, the Yalong River and Lanchang River catchments. In this region the tributaries have developed an inverted drainage pattern with nearly right-angle intersection. Based on terrain and areal river system analysis, including geomorphic index calculation, this paper discusses the evolution of the drainage pattern related to the neotectonic movements in this area. Two groups of valleys are distinguished with NW-SE and SW-NE directions, respectively. The NW-trending rivers are unfit channels with gentle slope and large width, while most of the SW-trending rivers are canyons with steep slope and V-shaped transect. It turns out that the steepness index (ks) in the southeastern part of the Tongtian River is higher than that in the Duocai-Ningqia basin, Dengailong basin, Yequ basin and the southwestern part of the Batang basin. The stream length-gradient index (SL) is similar in the whole catchment, but the SL values in the inverted channels and nearly right-angle intersecting channels are abnormal. The value of the hypsometric integral (HI) is over 0.45 at both sides of the Tongtian River, while it is 0.15-0.45 in the Duocai-Ningqia basin, Dengailong basin, Yequ basin and Batang basin. The values and distribution of geomorphic indexes indicate that the pre-existing SE-trending parallel-drainage pattern turned to an inverted-drainage pattern as a result of strike-slip faulting. Dangjiang, Lixing, Longbao and the northeastern part of the Shanglaxiu regions became pull-apart basins, while the tributaries of the Tongtian River in the northeast eroded dramatically headward as a result of the uplift of the NE-trending thrust, and finally captured the former SE-trending channels.
The anastomosing river located at the First Great Bend of the Yellow River is different from other sand-bedded anastomosing rivers because of its gravel-bedded materials. So, it needs to be revealed whether its specific characteristics have a similarity with the sand-bedded anastomosing river, in terms of erosion and deposition, the stability of channel and interchannel wetlands, and so on. Based on four remote sensing images in 1990, 2001, 2013, and 2016 and two Google earth images in 2011 and 2013, combined with field sampling and observations, the Qihama anastomosing river reach with a main channel length of about 12 km was selected to analyze the variations of channel planforms and sedimentary characteristics in the period 1990-2016. The results show that the gravel-bedded anastomosing river has a high stability as a whole, and there is no obvious bank erosion and deposition for varied channels and wetlands. During the past 26 years, the anastomosing belt area increased by 2.43%, and the ratio of land to water area was close to 1:1. The number of wetlands increased gradually with the highest increasing rate of 62.16% due to the fragmentization of some small interchannel wetlands. Talweg migrated to the left or the right alternately in a long period of time, and the migration rate was relatively stable. Due to the influence of talweg migration, the change of islands in the main channel is large and the bank shift rate of the main channel was about 5 m/a. The network composed of secondary channels is very stable and the channel average migration rate was only about 1 m/a. The sediments in the bank columnar sections are mainly composed of fine sands or silts, and the clay content is relatively high. Besides, the grain-size distribution presents a multi-peak curve, which is little different from the muddy sediments in bank columnar sections of sand-bedded anastomosing rivers. However, the dense vegetation on the riparian and interchannel wetlands protects the anastomosing channels in the study river reach from being eroded, and maintains the stability of the channels, which is also an important factor contributing to high stability of the gravel-bedded anastomosing river system.
This study examines spatial and temporal changes in the continental coastline and the intertidal zone from the Xiuzhen estuary to the Lianxing estuary in Jiangsu province from 1984 to 2016. This work employed an improved water-line method based on 61 multi-source remote-sensing images, as well as tide and measured slope data. The coastline is a combination of the mean high-tide line and artificial coastline. The mean high-tide line was derived from elevation data contained in the waterlines through the improved water-line method. Water lines were extracted from remote sensing images using object-oriented classification, band operation, etc. Then, tides at the tide stations at image acquisition times were predicted using the T-Tide program. The predicted tides were assigned to water lines and intertidal slopes were calculated. Finally, mean high-tide and low-tide lines were determined from measured and calculated slopes. The quantitative analysis of the coastline, mean low tide line, and intertidal zone yielded the following main conclusions. From 1984 to 2016, Jiangsu's coastline advanced mainly towards the sea because of coastal development. The natural shoreline decreased from 458.24 to 166.74 km, while the artificial shoreline increased from 163.66 to 598.74 km. The length of Jiangsu’s continental coastline also increased from 621.90 to 765.48 km. During this period, the positions and lengths of different segments of the coastline changed. The deposited coast, which advanced toward the sea at an annual rate of 83.03 m, was 127.62 km long. The reclaimed coast, which advanced towards the sea at an annual rate of 87.63 m, was 401.21 km. The erosional coast, which receded at an annual rate of 10. 81 m, was 71.17 km long. The eroded reclaimed coast, which receded at an annual rate of 8.64 m, was 25.95 km long. The area of Jiangsu underwent a net increase of 104332 hm2, primarily due to reclamation, with reclaimed land representing 98520 hm2. Erosion mainly occurred in the abandoned Yellow River Delta, but during 2008-2016, it extended southward from the Xinyang to the Doulong harbor. The slopes of the intertidal zone became steeper due to reclamation and shoreline erosion, changing from 1.4‰ to 1.9‰. The abandoned Yellow River Delta experienced the most severe change in slope, with its mean slope in the range of 3‰-14‰. The mean slope of the radial sandbank of the onshore coast, which had the gentlest slope, increased from 0.9‰ to 1.5‰. The intertidal area decreased by 38% from 271747 to 168645 km2, while the mean width of the intertidal zone decreased by 39% from 5064 m to 3096 m.
Hydrological and biogeochemical cycles process in a watershed ecosystem are closely coupled by the physical function of the hydrological flux, of which the coupling process of the matter and energy in the spatial and temporal scales will provide important basis for matter balance in biogeochemical cycles. These cycles also influence ecosystem productivity and exchanges with the atmosphere and the downstream water bodies. Therefore, the research on biogeochemical cycle and hydrological coupling process in the watershed scale will reveal the coupling mechanism on the carbon-nitrogen coupling cycles between terrestrial and aquatic ecosystem under water cycle driving, and the interaction of human activities and associated biological, physical and chemical processes under climatic change. The aims of this study are to synthetically clarify the biogeochemical and hydrological coupling characteristics in temporal, spatial and spatio-temporal scales within a watershed ecosystem, reveal the coupling of nutrient cycling in spatio-temporal scales within a continuum of atmosphere-land-rivers-estuaries-marine systems, which are connected by water, gas and aerosol fluxes; disclose the biological regulation mechanism of the biogeochemical and hydrological coupling processes by the change of ecological stoichiometry characteristics within the watershed and the regulation of nutrient input and output by water-land interaction zone, and then finally enhance our understanding of ecohydrological and biogeochemical process and its ecological dynamics at watershed landscape scale.
