Landform is an important factor determining the spatial pattern of cropland through allocating surface water and heat. Therefore, it is of great significance to study the change of cropland distribution from the perspective of geomorphologic division. Based on China's multi-year land cover data (1990, 1995, 2000, 2005, 2010 and 2015) and geomorphologic regionalization data, we analyzed the change of cropland area and its distribution pattern in six geomorphologic regions of China over the period 1990-2015 with the aid of GIS techniques. Our results showed that the total cropland area increased from 177.1 to 178.5 million hectares with an average increase rate of 0.03%. Cropland acreage decreased in southern China and increased in northern China. Region I (eastern hilly plains) had the highest cropland increase rate, while the dynamic degree of Region IV (northwestern middle and high mountains, basins and plateaus) was significantly higher than that of other regions. The barycenter of China's land cultivation had shifted from North China to northwest over the 25 years. Regions IV and I were the two high-growth regions of cultivated land. Region II (southeastern low-middle mountains) and Region V (southwestern middle and low mountains, plateaus and basins) were the main decreasing regions of cultivated land. The area of cultivated land remained almost unchanged in Region III (north China and Inner Mongolia eastern-central mountains and plateaus) and Region VI (Tibetan Plateau). The loss of cropland occurred mostly in regions I and II as a result of growing industrialization and urbanization, while the increase of cropland occurred mainly in Region IV because of reclamation of grasslands and other wastelands.
The discussion on function transformation of agricultural utilization and its corresponding driving mechanism in the Three Gorges Reservoir Area (TGRA) can reflect the change of the relationship between people and environment in the transitional belt between central and western China, mountainous areas and reservoir area, and provide a scientific basis for the development of agricultural multi-function in typical mountainous areas. This paper, selected five counties from the hinterland of the TGRA as the study area, analyzed the change of scaling farmland and its corresponding mechanism by defining the concepts of "scaling farmland", with the aid of Arcgis10.2, SPSS, geodetectors and other technical means. Results show that the scaling farmland was mainly converted from cultivated land and shrubland. Apart from some land used for alpine off-season vegetables, the growth of scaling farmland generally occurred at low altitude, and was mainly found in the range with a slope of 30°. The spatial change of scaling farmland of different types was significantly different, which was closely related with road and township administrative center. At the patch level, natural factors such as elevation and slope contribute much to the scaling farmland. At the township level, the driving forces of socioeconomic and humanistic factors were attributed to road traffic, agricultural population density and so on. At the regional level, the influencing factors of each county were more significant than those of the study area. The change and development of scaling farmland was driven by many factors. But the agricultural policy had been one of the dominant factors. Behavior subjects at different levels would promote the scaling farmland development in different directions under the background of national agricultural development and policy implementation.
This paper pointed out that the alleged rapid increase of the information entropy of the land use structure in the urbanized areas should refer to the increase of the information entropy of the suburban land use structure in the urbanized areas. The obvious shift of the suburban land use structure towards the equilibrium direction during the period of urbanization leads to the increase of the information entropy of the suburban land use structure. Meanwhile the information entropy of the land use structure in urban built-up area has not increased. The proportion of various land use types in the urban built-up area during the period of urbanization is basically stable or enlarged on the residential areas, industrial and mining areas as well as the transportation land to some extent. This makes the information entropy of the land use structure in the urban built-up area basically remain unchanged or decrease somewhat. The local urbanized areas in the suburbs have made major contributions to the increase of the information entropy of the suburban land use structure. Data analysis shows that a great amount of suburban farmland is quickly transformed into urban construction land during the period of urbanization and the proportion of the urban construction land is highly and positively correlated with the information entropy of the suburban land use structure. It can be seen that the rapid increase of the urban construction land is the main reason for the increasing information entropy of the suburban land use structure. The analysis of entropy change indicates that the entropy of suburban system during the period of urbanization displays the same changing trend with the information entropy of the suburban land use structure, and both of them are greater than zero, which suggests that the suburban natural environments during the period of urbanization develop in a decline.
With the rapid development of urbanization and the continuous loss of the rural labor force, large areas of farmland have been abandoned in some regions of China. Remote sensing technology can indirectly help to detect the size and quantity of abandoned farmland, which is of great significance for the protection of farmland and food security. Using Qingyun and Wudi counties of Shandong Province as the study area, and based on the Landsat data and HJ-1A data, this paper uses the CART decision tree classification method to develop land use maps from 1990 to 2017, set down rules to identify abandoned farmland, and explore the spatial distribution, duration, and reclamation area of abandoned farmland. The results showed that the accuracy of the CART decision tree classification was higher than 85% from 1990 to 2017. The maximum abandoned farmland area was 5503.86 hm2 from 1992 to 2017, and the maximum abandonment rate was 5.37%. The rate of farmland abandonment reached the peak from 1996 to 1998, and the overall trend of abandonment has decreased year by year after 2006. The maximum duration of abandonment was 15 years during the period of 1992 to 2017. Most of the durations were within four years and a few durations were more than ten years. From 1993 to 2017, the maximum reclamation area of abandoned farmland was 2022.3 hm2, and the minimum reclamation area was about 20 hm2. The maximum reclamation rate was 67.44% and the annual average reclamation rate was 31.83%. The results from this paper not only help analyze the driving forces of farmland abandonment in the study area, but also provide references for the identification of abandoned farmland in other areas.
The formation mechanism and influencing factors identification of soil erosion are the core and frontier issues of current research. However, studies on the multifactor synthesis are still insufficient. In this study, the simulation of soil erosion and its quantitative attribution analysis have been conducted in different morphological types of geomorphology in a typical karst basin based on the RUSLE model and the geographical detector method. The influencing factors, such as land use type, slope, rainfall, elevation, lithology and vegetation cover, have been taken into consideration. Results show that the strength of association between the six influencing factors and soil erosion was notably different in various morphological types of geomorphology. Land use type and slope were the dominant factors of soil erosion in the Sancha River Basin, especially for land use type whose power of determinant (q value) for soil erosion was much higher than that of other factors. The q value of slope declined with the increase of relief in mountainous areas, namely it was ranked as follows: middle elevation hill > small relief mountain > middle relief mountain. Multi-factor interactions were proven to significantly strengthen soil erosion, particularly for the combination of land use type with slope, which can explain 70% of soil erosion distribution. It can be found that soil erosion in the same land use type with different slopes (such as dry land with a slope of 5°and dry land with slopes above 25°) or in the diverse land use types with the same slopes (such as dry land with a slope of 5° and forest with a slope of 5°), varied greatly. This indicates that prohibiting steep slope cultivation and the Grain for Green Project are reasonable measures to harness soil erosion in karst areas. Based on statistics of soil erosion difference between diverse stratifications of each influencing factor, results of risk detector suggest that the amount of stratification combinations with significant difference accounted for 55% at least in small and middle relief mountains. Therefore, the spatial heterogeneity of soil erosion and its influencing factors in different morphological types of geomorphology should be investigated to control karst soil loss more effectively.
The presence of CO2 in the caves affected by intense tourism activities has a significant impact on the drip hydrogeochemistry and sedimentation. In this investigation, a continuous monitoring on the indexes such as CO2, temperature, relative humidity, tourist number and drip hydrochemistry was conducted in Guizhou Suiyang Dafeng Cave from 30 September 2017 to 9 October 2017. Following the collection of data, different methods were applied systematically to analyze a number of elements comprehensively. The observed results show that, under the influence of factors such as tourist number and ventilation effect of cave, the partial pressure of CO2 in the cave (PCO2 (A)) presented obvious diurnal and interdiurnal variations in the time sequence, and showed a higher value in daytime whereas a lower value at nighttime, and also a higher value on days with many tourists and a lower value on days with few tourists. In space variation, due to different ventilation degrees and cavity volumes, the PCO2(A) of different monitoring points had obvious differences, from the deep cave to the entrance of cave as 3# (Magical Spring and Dewdrop) >1# (Time Tunnel)>2# (Legendary Luminous Pearl). Through the comparison of PCO2(A) and drip temperature, the former had more significant influence on the solubility of CO2 than the latter did. Moreover, the drip temperature and drip partial pressure of CO2 (PCO2(W)) of cave generally had the same trend of variation with that of PCO2(A), and also presented obvious diurnal and interdiurnal variations. The pH, SIc, and HCO3- generally had a trend of variation in the opposite way to that of PCO2 (A), EC and Ca2+ had no obvious diurnal variation but certain interdiurnal variation. With an increase in the strength of tourism activities, the variation amplitude of drip hydrochemistry gradually increased. Furthermore, the differences in the factors such as cavity structure, size and closeness caused differences in the diffusion speed of PCO2(A) and cave ventilation degree, and further influenced the hydrochemistry of the constituents of cave drip and sedimentation conditions of cave. Overall, this study will have a significant impact on the research on protection and management of cave environment as well as its karst cave carbon cycle.
The stream-power incision model shows that a bedrock channel longitudinal profile is characterized by a smooth, concave-up shape at the steady state, and its characteristics reflect the influences from external forces, such as tectonics, climate, and rock resistance. However, most of the natural rivers present a transient state characterized by knickpoints on longitudinal profiles, which can also infer the influences from external forces. Widespread knickpoints at high altitudes on river longitudinal profiles along the Zoulang Nan Shan (mountain), which is a part of northern Qilian Mountains, provide a particular case for studies on the factor affecting the disequilibrium profile. The analysis of the knickpoints indicates that the formation of the knickpoint at high altitudes is not influenced by lithology, climate and/or tectonics. By comparing the plaeo-glaicial evidences, we proposed that the high-altitude knickpoint reflects the boundary between residual glacier valleys and fluvial channels. The result suggests that we should pay more attention to the inheritance landform by ancient glaciation when analyzing the knickpoint located at high altitudes. This study would greatly increase the knowledge about the geomorphic evolution on high mountain ranges along orogenic belts.
At present, there is a lack of sufficient understanding of the evolution of floodplains and bars (FB) at the Jingjiang reach of Yangtze River after Three Gorges Reservoir impoundment. The erosion/accretion pattern and morphological evolution of FB at the Jingjiang reach were studied using remote sensing images acquired in low water periods before and after Gorges Reservoir impoundment. The results showed that the total area of FB at the Jingjiang reach shrank continually after the reservoir impoundment. By 2015 an area of 4.56 km2 had been scoured away, and most of the scour occurred within the first 6 years after the impoundment at an erosion rate of 0.55 km2/a. There were evident differences in erosion/accretion pattern and in morphological evolution between the upper and lower sections of Jingjiang reach. The total area of FB at the upper Jingjiang has continually decreased due to scouring after the impoundment, and the scouring intensity was greater than that in the lower Jingjiang. In contrast, erosion of the lower Jingjiang took place in the early period after the impoundment (2002-2009), but accretion was observed in the later period (2009-2015). In erosion/accretion distribution, the floodplains of upper Jingjiang reach were continually scoured and shrunk while the bars at concave banks were scoured in the early period but were accreted slightly in the later period; the mid-channel bars of upper Jingjiang were accreted in the early period but were scoured in the later period. In contrast, erosion mainly occurred at the floodplains of lower Jingjiang, while the bars at its concave banks and mid-channel bars were accreted. The mid-channel bar evolution at the Jingjiang reach after the reservoir impoundment was classified into eight types according to their position movement and erosion/accretion dynamics. On morphological evolution, the protruding parts of floodplains and the bars at concave banks of the upper Jingjiang were visibly eroded, while the morphology changed little. At the lower Jingjiang, however, the floodplains evolution had a characteristic pattern that the upstream part was eroded back, with a shrinkage of the top, while the downstream part was accreted, resulting in the alteration of convex bank from a highly curved morphology to a flattening-curved morphology. This erosion-accretion process of floodplains at the upstream convex bank even extended to the adjacent downstream concave bank when there was no obvious straight section connecting the neighboring highly curved bends or when the upstream convex bank shared the same bank with the downstream concave bank. Extension of upstream floodplain accretion to the downstream concave bank was an important reason for the development of both the bars at concave banks and the mid-channel bars at the lower Jingjiang. Generally, the accretion at the concave bank did not span to the top of concave bank.
The Jinsha River has attracted considerable attention for nearly a century due to its unusual drainage basin morphology. Most models describing its evolution suggest that the modern Jinsha River, draining the Tibetan Plateau margin, was once a tributary to a single, southward river system called "Paleo-Red River", which drained into the South China Sea and then its flow direction changed to east to join the Yangtze River due to river capture. The Red River submarine fan, considered to have been primarily fed by the Paleo-Red River system, suddenly disappeared at 5.5 Ma provides an important chronological constraint on this reorganization of drainage lines and reversal event. However, no geomorphic evidence has been found to agree with this hypothesized timeframe. Here, we present electron spin resonance (ESR) ages from eight terraces preserved in the Jinjiangjie reach of the Jinsha River together with their GPS altimetry data. Their ages from old to young are 1.07 Ma, 0.70 Ma, 0.65 Ma, 0.51 Ma, 0.47 Ma, 0.44 Ma, 0.30 Ma and 0.18 Ma, with a calculated average river incision rate of 147 mm/ka since 1.0 Ma. The paleo-topography, reconstructed by filling the deeply incised river gorges with digital elevation model (DEM) data, shows that the upper reach of the Paleo-Red River was captured by the Yangtze River and changed its flow direction eastward at the time of disruption of the 2000 m asl paleo-topographic surface in the Jinsha River drainage basin. The age of the paleo-topographic surface formation would be approximately 5.5 Ma using the average river incision rate extrapolation, suggesting that the present Jinsha River system was born after 5.5 Ma. This data support the chronological constraint from the Red River submarine fan, and hypothesized evolution of the Jinsha River.
In the context of climate change and urbanization, increase of flood disasters has been a great challenge for Chinese cities and one of the hotspots in natural hazards research. This paper aims to develop a commonly used paradigm for urban flood emergency assessment at city scale. The city center (within outer ring) of Shanghai, China was selected as the study area because it exhibits enhanced consequences of flooding. A simplified hydrodynamic model (FloodMap) that tightly couples a 1D river flow model with a 2D floodplain flow model in urban environment, was used to predict 100-year and 1000-year flood inundation in the current state, the 2030s and the 2050s with relative sea level rise taken into account. Moreover, GIS-based network analysis (service area and closest facility) was employed to evaluate the transportation conditions and emergency responses accessibility of critical public service sectors (Medical Treatment) under normal conditions and multiple flood scenarios. The results show that the performance of the emergency medical services was largely dependent on flood magnitude (extent and depth), traffic conditions (travel speed) and emergency station positioning. In normal conditions, when no flood restrictions are in place, emergency medical services would be able to reach most parts of the study area within 15 minutes even under significant traffic congestion. As inundation would mainly occur within 2-3 km of Huangpu river banks, flood has a limited influence on emergency medical treatment for the entire region of central Shanghai. Even during 1000-year flood scenario in the 2050s, over half (51%) of the area is predicted to be accessible within 15 minutes. Floodwater may directly compromise a number of hospitals, leading to travel delays and obvious disruption of emergency services in riparian areas. This study suggests that the framework developed for coupling flood modeling with urban emergency response assessment, is proved to be effective and practical, and will provide a support to the decision making of urban flood emergency management.
The global warming hiatus during 1998-2012 has aroused a great public interest in past several years. Based on the air temperature at 622 meteorological stations in China, the response of temperature to global warming hiatus was analyzed on national and regional scales. The main results were as follows: (1) The trend magnitude of air temperature in China was -0.221 ℃/10 a during 1998-2012, which was lower than the long-term trend during 1960-1998 by 0.427 ℃/10 a. There was a warming hiatus in China that was more obvious than the global mean. Winter played a dominant role (contribution rate was 74.13%) in the nationwide warming hiatus, and the contribution of summer was the least among the four seasons. (2) The warming hiatus was spatial incoherent in different climate backgrounds in China. Among the three natural zones in China (the monsoon region of eastern China, the arid region of northwestern China and the high frigid region of Tibetan Plateau), there was a significant cooling in the eastern and northwestern China, especially the eastern China with a contribution rate of 53.79%. In the eastern China, the trend magnitudes were 0.896 ℃/10 a in winter and 0.134 ℃/10 a in summer, respectively. In the Tibetan Plateau, the air temperature has increased by 0.204 ℃/10 a without significant warming hiatus. (3) The warming hiatus in China may be associated with the negative phase of PDO as well as the reduction of sunspot numbers and total solar radiation. (4) Although warming hiatus occurred in China during 1998-2012, the air temperature has rapidly increased after 2012 and is likely to be continuously warming in the next few years.
Non-point source pollution is one of the most severe problems impacting water environments. Identifying potential risk areas and risk paths contributing to non-point source pollution is the soution to this problem. This study introduces the minimum cumulative resistance model of landscape ecology, which is based on land use and soil mapping at a scale of 1∶100000 and DEM data with a resolution of 30 m. The model takes high pollution-loaded cultivated land and construction land as the main sources and uses the Topographic Wetness Index and Runoff Curve Numbers, which can describe the underlying resistance surface runoff yield characteristics, to visually identify and analyze the risk areas and risk paths of the Wuhua River Basin. The results show that underlying surface runoff production results in low-yield flow areas that are mainly concentrated in the southwest of the basin, while high-yield flow areas herringbone throughout the study area. The minimum cumulative resistance model can effectively identify the risk areas and risk paths in this basin. The high-risk areas of non-point source pollution are mainly distributed in Jionglong, Tianxin, Longmu, Tiechang, Dengyun, Tongqu, Heshi, Zishi, Qiling, Huacheng, Zhuanshui, Tanxia and Shuizai, which are located along both sides of the river. The spatial distributions of the risk paths of cultivated land and construction land are significantly different. The effects of cultivated land on water quality of the river are greater than those of construction land on it, and the nutrients and sediments from cultivated land are more likely to run into the receiving water via surface runoff. Vegetation buffer zones should be set up on both sides of the river adjacent to cultivated land when we deal with non-point source pollution that originates from cultivated land, and the harnessment of non-point source pollution originating from construction land should be monitored around major source areas. This study provides a novel method for the identification of source areas and risk paths of non-point source pollution and a theoretical basis to formulate future management strategies.
Soil water is the key link between land surface and atmosphere in water-heat exchange and it is the key element of water cycle. It is also the key control factor affecting the process of surface runoff. The Himalayan-Tibetan Plateau (HTP), also known as the "Asian Water Tower", is the source region of many Asian rivers. Meanwhile, HTP has direct impacts on its surrounding climate via hydro-meteorological processes, and on establishment and maintenance of Asian monsoon. This study collected observed soil moisture data from 100 in-situ soil moisture observatory stations and evaluated applicability of the available remote sensing and reanalysis soil moisture datasets such as ECV, ERA-Interim, MERRA, and Noah at different spatial resolutions (0.25°×0.25°, 0.5°×0.5°, 1°×1°) during different time intervals such as non-freezing and freezing periods. Statistical indicators such as R, RMSE and Bias were used to evaluate the performances of these remote sensing and reanalysis soil moisture datasets. The results indicated that: (1) All remote sensing and reanalysis soil moisture datasets except ERA can well estimate soil moisture changes of the Tibetan Plateau and the soil moisture changes are in generally good line with precipitation changes. In the Naqu region, however, the remote sensing and reanalysis soil moisture datasets substantially underestimate observed soil moisture. In space, MERRA and Noah are mostly consistent with the change of vegetation index, and can well estimate spatial distribution of soil moisture changes. (2) Soil moisture changes across most parts of the Tibetan Plateau are greatly influenced by precipitation changes. In addition, soil moisture changes in the western flank of the Tibetan Plateau and Himalayas are the combined results of melting snow/glaciers and precipitation. (3) Except in the Ngari region, soil moisture during non-freezing period is usually higher than that during freezing period. In the Naqu region, all remote sensing and reanalysis soil moisture datasets overestimate soil moisture amount during freezing periods, while they underestimate it during non-freezing periods. Besides, from a spatial scale viewpoint, at medium and large scales, remote sensing and reanalysis soil moisture datasets can better evaluate soil moisture availability compared with at small scale. This study provides a theoretical basis for selection of the right remote sensing and reanalysis soil moisture datasets for evaluation and analysis of soil moisture of the Tibetan Plateau.
Rice is the staple food in China and its production is impacted jointly by natural environment and human activities. In this process, terrain condition not only determines the spatial pattern of environmental factors, such as water, heat and radiation, but also affects the agricultural management measures. Although many studies focused on the impact of one or several specific factors on crop production, few studies investigated the direct influence of terrain condition on rice production. Therefore, we selected Hunan Province, one of major rice producing areas in China with complex terrain conditions, as the study area. Based on the remote sensing data and statistical data, we applied the spatial statistical analysis to explore the effects of terrain factors on the rice production from the following three aspects: spatial pattern of paddy field, rice production process and the final yield. We found that: (1) Terrain has a significant impact on the spatial distribution of paddy filed at both regional and county scales. Most paddy fields are located on the northern plain and central hills where the elevation is generally below 300 meters with the slope less than 9° and relief degree less than 140 meters. Also, the spatial pattern of paddy fields in Hunan is sensitive to surface roughness and slope position. (2) Terrain does determine the distribution of temperature, sunlight and soil, and these three environmental factors consequently have direct impact on rice growth. Additionally, several terrain factors (elevation, slope and surface roughness) are related with the phenological stage of double-cropping rice, especially for elevation, which is closely associated with the planting stage for early rice and harvesting stage for late rice. (3) However, compared with the pattern of paddy field and rice production process, the influences of terrain factors on the rice yield are not so evident except for elevation. (4) There is a spatial mismatch between spatial distribution of paddy field and production resources due to terrain factors: although paddy fields are widespread in the northern plain, the yield in this region is lower than that in the hilly area of central Hunan due to limited heat. Our results highly imply that the managers should guide farmers to choose suitable variety and planting system and allocate rice production resources in the northern plain so as to ensure food security.
This study, taking the Weihe River Basin in the Guanzhong-Tianshui Economic Region of China as a case, establishes a water conservation ecosystem service network model. Based on Bayesian belief networks, the model forecasts the distribution probability of water conservation ecosystem services projected under different land-use scenarios for the year 2050 with a CA-Marcov model. A key variable subset method is proposed to optimize the spatial pattern of the water conservation ecosystem service. There were three key study findings. First, under the protection scenario, the area of woodland increased by 18.12%, mainly from the conversion of cultivated land. The grassland and cities increased by 0.73% and 0.38%, respectively. The water and unused land were reduced by 5.08% and 0.92%, respectively. The probability of high water conservation value under this scenario is the largest in the three scenarios, and the design of protection scenario is conducive to the formulation of future land use policies. Second, the key factors influencing water conservation ecosystem service include precipitation, evapotranspiration and land use. The state set corresponding to the highest state of water conservation ecosystem service is {precipitation = Highest, evapotranspiration = High, land use = High}, mainly distributed in areas with high annual average rainfall and evapotranspiration and high vegetation coverage. Third, the regions suitable for optimizing water conservation ecosystem service are mainly distributed in the southern part of Maiji District in Tianshui, southwest of Longxian and south of Weibin District in Baoji, northeast of Xunyi County and northwest of Yongshou County in Xianyang, and west of Yaozhou District in Tongchuan. Identifying the optimization regions of water conservation ecosystem service based on Bayesian belief networks, not only helps to develop a better understanding of the water conservation ecosystem services processes, but also increases the rationality of the scenario design and pattern optimization. On this basis, the key variable subset method is crucial to sound eco-environment construction and policy formulation in the study area.
