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To provide scientific guidance for the use of foamed concrete (FC) in construction engineering, a thermal conductivity calculation method, based on the fractal model of FC, has been developed. The thermal conductivity (TC) of FC has been tested by the transient planar heat source method in order to verify the reliability of the proposed calculation model. The FC was made of cement, fly ash, and ore powder, and cured under natural conditions for 7 d, 14 d, 28 d, and 42 d, respectively. The TC of FC gradually decreases with the increase in age. The fractal dimension of FC can be determined by both the box-counting method and compressive strength test, and the dimensions determined by both methods are similar. The TC of FC at different porosities and curing ages can be calculated by the fractal dimension, and the estimated values are basically consistent with the test data.

Cropland abandonment is a widespread land-change process globally, which can stem from the accelerated outmigration of the population from rural to urban areas, socio-economic and political changes, catastrophes, and other trigger events. Clouds limit the utility of optical satellite data to monitor cropland abandonment in highly fragmented mountain agricultural landscapes of tropical and subtropical regions, including the south of China. Taking Nanjing County of China as an example, we developed a novel approach by utilizing multisource satellite (Landsat and Sentinel-2) imagery to map multiple trajectories of cropland abandonment (transitioning from cropland to grassland, shrubs and forest) in subtropical mountainous landscapes. Then, we employed a redundancy analysis (RDA) to identify the spatial association of cropland abandonment considering agricultural productivity, physiography, locational characteristics and economic factors. Results indicate the great suitability of harmonized Landsat 8 and Sentinel-2 images to distinguish multiple trajectories of cropland abandonment in subtropical mountainous areas. Our framework of mapping cropland abandonment resulted in good producer's (78.2%) and user's (81.3%) accuracies. The statistical analysis showed 31.85% of croplands cultivated in 2000 were abandoned by 2018, and more than a quarter of townships experienced cropland abandonment with high abandoned rates (>38%). Cropland abandonment mainly occurred in relatively unfavorable areas for agricultural production, for instance with a slope above 6°. Slope and the proximity to the nearest settlement explained 65.4% and 8.1% of the variation of cropland abandonment at the township level, respectively. The developed approaches on both mapping cropland abandonment and modeling determinants can be highly relevant to monitor multiple trajectories of cropland abandonment and ascribe their determinants not only in mountainous China but also elsewhere and thus promote the formulation of land-use policies that aim to steer cropland abandonment.

In order to dispose of high level nuclear waste during the operation of underground geological repositories, the buffer/backfill performance of bentonite–based material might be affected by the combined influence of temperature field and infiltrating groundwater thereby leading to uncertainties in the safe operation of repositories. In order to address this issue, bentonite–sand mixtures (BSM) were prepared by mixing GMZ01 bentonite with sand using ratios of 70:30 and 30:70 by weight. One-dimensional deformation experiments were conducted on the prepared BSM in NaCl solutions of varying concentrations (0, 0.1, and 1.0 mol/L) at three different temperatures (25, 60, and 90 °C). The experimental results on the BSM in NaCl solutions indicated that the swelling deformation increased as temperature rises, because osmotic swelling is the dominant swelling type under the experimental conditions. The swelling deformation of BSM could be represented by fractal em–pe relation (em is the montmorillonite void ratio, pe is the effective stress incorporating osmotic suction). At each temperature interval, the swelling of BSM with high bentonite content in different NaCl solutions can be expressed as a unique em–pe relation; however, the swelling coefficient of montmorillonite in the em–pe relationship increases at higher temperature. When the effective stress pe exceeds a threshold, sand–particle skeletons will be formed in BSM with low bentonite content, thus resulting in deviations in the value of em from the em–pe curve. The em–pe relation offers a simple and efficacious method to estimate the deformation of BSM under combined thermal–salt effects.

Forests play a central role in the global carbon cycle. China's forests have a high carbon sequestration potential owing to their wide distribution, young age and relatively low carbon density. Forest biomass is an essential variable for assessing carbon sequestration capacity, thus determining the spatio-temporal changes of forest biomass is critical to the national carbon budget and to contribute to sustainable forest management. Based on Chinese forest inventory data (1999–2013), this study explored spatial patterns of forest biomass at a grid resolution of 1 km by applying a downscaling method and further analyzed spatio-temporal changes of biomass at different spatial scales. The main findings are: (1) the regression relationship between forest biomass and the associated influencing factors at a provincial scale can be applied to estimate biomass at a pixel scale by employing a downscaling method; (2) forest biomass had a distinct spatial pattern with the greatest biomass occurring in the major mountain ranges; (3) forest biomass changes had a notable spatial distribution pattern; increase (i.e., carbon sinks) occurred in east and southeast China, decreases (i.e., carbon sources) were observed in the northeast to southwest, with the largest biomass losses in the Hengduan Mountains, Southern Hainan and Northern Da Hinggan Mountains; and, (4) forest vegetation functioned as a carbon sink during 1999–2013 with a net increase in biomass of 3.71 Pg.

Karst-related geo-disasters often occur in karst regions during underground construction. In recent years, a number of shallow buried karst features have been discovered in eastern China. Survey boreholes show that karst caves exist at depths of 26–30 m and 33–36 m, which are typical of shallow buried karst. Using cross-hole seismic computed tomographic techniques, 36 geological anomalies consisting of 26 mud-filled caves, three empty caves, and seven fissure zones/loose lens bodies were detected. Most of the karst caves were oblate or oval. After determining the scale of and the connection between the caves, the study area was divided into two areas to provide advice on the treatment of caves during construction. An analysis of the development characteristics of the karst suggests that karst is controlled by several key factors, including topography, structural features, groundwater conditions, and human activities. Following an analysis of these factors and field studies of the process of formation of the shallow buried caves, solutions are proposed to prevent karst-related geo-hazards. The research results can be used in the design of foundations for buildings that are located in regions that include shallow buried karst in eastern China.

Land consolidation (LC) is regarded as a useful tool to improve agricultural production. Measuring the effect of LC on agricultural production (ELCAP) is helpful for the planning of LC activities. In the past, it is difficult to measure ELCAP at regional level due to the lack of field observation, the change of crop planting structure, and high cost of sample collection. Satellite data have large coverage and high spatiotemporal resolution for vegetation observation, which can provide a new idea for estimating ELCAP at regional level. This study aims to build a novel assessment framework to quantitatively investigate ELCAP by developing several satellite‐based metrics. In addition, this study also explored the characteristics of ELCAP using the method of spatial autocorrelation and the geographical detector method in 1,281 LC areas in China. Our results show that agricultural productivity in more than 90% of total LC areas shows an increasing trend during 2001–2016. LC could play the positive but limited effects on agricultural production, and its productivity‐boosting effect (64.87% of total LC areas) is greater than its stability‐improving effect (46.53% of total LC areas). The spatial agglomeration of ELCAP is weak (Moran's I < 0.06), which may be resulted from the differences in field conditions and natural‐social–economic situations across LC areas. The interaction between several factors has a greater effect on the ELCAP than each of these factors. Methodology in this study provides a new and useful framework for evaluating ELCAP, and results can be used to guide the planning of LC activities.

Long-term urban extent data are highly desirable for understanding urban land use patterns. However, urban observation data based on remote sensing are typically confined to recent decades. In this study, we advance in this arena by reconstructing the walled cities for China that extend from the 15th century to the 19th century based on multiple historical documents. Cities in late imperial China (the Ming and the Qing dynasties, 1368–1911) generally had city walls, and these walls were usually built around the built-up urban area. By restoring the extent of the city walls, it is helpful to explore the urban extent in this period. Firstly, we collected the years of construction or reconstruction of city walls from the historical data. Specifically, the period in which the size of the city wall remains unchanged is recorded as a lifetime of it. Secondly, a specialization on the extent of the city wall could be conducted based on the urban morphology method and a variety of documentation, including the historical literature materials, the military topographic maps of the first half of the 20th century, and the remote sensing images of the 1970s. The correlation and integration of the lifetime and the spatial data led to the creation of the China City Wall Areas Dataset (CCWAD) for the late imperial period. Based on the proximity to the time of most of the city walls, we selected six representative years (i.e., 1400, 1537, 1648, 1708, 1787, and 1866) from CCWAD to produce the China Urban Extent Dataset (CUED) for the 15th–19th centuries. These datasets are available at https://doi.org/10.6084/m9.figshare.14112968.v3 (Xue et al., 2021).

Forest wildfire is an important threat and disturbance facing natural forest ecosystems. Conducting wildfire risk assessments and zoning studies are of great practical significance in guiding wildfire prevention, curbing fire occurrence, and mitigating the environmental effects of wildfire. Taking Hunan Province, China as the case area, this study used remotely sensed high-temperature fire data as the wildfire sample. Twelve factors related to topography, climatic conditions, vegetation attributes, and human activities were used as environmental variables affecting wildfire occurrence. Then, a Maxent wildfire risk assessment model was constructed with GIS, which analyzed the contribution, importance, and response of environmental variables to wildfire in Hunan Province. The results show that (1) the Maxent model has high applicability and feasibility when applied to wildfire risk assessment after a test of wildfire sample sites, (2) the importance of meteorological conditions and vegetation status variables to wildfire are 54.64% and 25.40%, respectively, and their contribution to wildfire are 43.03% and 34.69%, respectively. The interaction between factors can enhance or weaken the contribution of factors on wildfire. (3) The mechanism for the effects of environmental variables on wildfire is not linear as generally believed, temperature, aridity, land use type, GDP, distance from the road, and population density have a nonlinear positive correlation with the probability of wildfire occurrence. Elevation, slope, precipitation, wind speed, and vegetation cover within the suitable interval positively contribute to the probability of wildfire, while the environmental conditions outside the suitable interval curb the occurrence of wildfire. The response of wildfire probability to forest density is U-shaped, which means either too high or too low will promote the occurrence of wildfire. (4) There is geographical variation of wildfire risk in Hunan Province. The areas at high risk and below account for 74.48% of the total area, while the areas at significantly high risk and above account for a relatively low proportion, 25.52%.

Food security, economic development, and ecological environment protection have become global strategic issues concerning the sustainable development of human society, accompanied by the rapid globalization and urbanization. Exploring land space utilization efficiency (LSUE) quantitatively in agricultural production, economic development and ecological maintenance can help deepen regional understanding, tap the potential of land space, and implement strategies to optimize land space utilization. In this study, we established a new conceptual index system using system science, potential efficiency contribution analysis method, and least square error model for LSUE (i.e., state efficiency, potential efficiency) assessment as well as an analysis of the spatial coupling differentiation and development zoning trade-off of LSUE in Jiangsu Province of eastern China. Our results show that a large potential for sustainable land space utilization of Jiangsu exists with significant spatial difference. The high-value areas of agricultural production potential efficiency demonstrate a ring spatial pattern around the urban built-up areas, which may be explained by the occupation of arable land and the abandoned farmland induced by urbanization. The socio-economic development potential efficiency presents a south-to-north increasing pattern, indicating a prominent imbalance and greater polarization of regional development. The significant differences of ecological safety maintenance potential efficiency suggest that the northern and southern regions have played important roles in maintaining regional ecological security, while the central region leaves a great potential for improvement. Finally, we optimize the land space utilization and land use planning by proposing a framework of regional development trade-off zoning that targets balanced coordination among agriculture, economy and ecology in Jiangsu. Our overarching goal is to integrate local spatial differentiation and coupling relationship of LSUE into land use planning process and inform the policy-makers of more locally-adaptive decisions.

International audience; The effect of water distribution on heat conduction in unsaturated structural clayey soils with double porosity system is investigated in the present study. A dual-porosity model consisting of intra-aggregate and inter-aggregate pores is developed to describe the water distribution within intra-aggregate and inter-aggregate pores. Heat transfer using this model is then numerically simulated to determine the soil effective thermal conductivity. The obtained values are compared with available experimental data. The results show that the model can predict the accurate soil thermal conductivity values at various water contents and densities. On one hand, the model shows a higher soil thermal conductivity when water content and/or dry density are higher. On the other hand, the model shows an effect of water distribution on the soil thermal conductivity; this later is higher when water is preferentially distributed within aggregates than between aggregates. In addition, the model can give a direct visualization of heat transfer mechanisms in unsaturated clayey soils with double porosity system. In fact, heat conduction is dominant in the wet region of the dual-porosity space. This study provides both a useful predictive model of thermal conductivity and a better understanding on the physical mechanism of heat conduction in unsaturated structural clayey soils or other multiphase media with double porosity system.

Land consolidation (LC) is an innovative way to improve agricultural production. Spatiotemporal pattern of agricultural production in land consolidation area (LCA) is difficult to quantify with limited field observations and survey data. Satellite data has advantages on recording vegetation status changes frequently, which is very supportive of estimating variation of agricultural production. In this paper, we used Net Primary Productivity (NPP), Normal Difference Vegetation Index (NDVI), and Multiple Band Drought Index (MBDI) from satellite data, to examine five attributes (irrigation capacity, multiple cropping index, crop phenology, farmland productivity, and production stability) of agricultural production after land consolidation (LC) at a site in China. Results show that there were no significant spatial differences in irrigation capacity for farmland in few years after LC due to consistent climatic conditions and uniform irrigation and drainage system. Multiple cropping index shows a pattern of “first reducing, then growing, last reducing”, which may result from the disturbed “water-soil” environment and weak farmers' intention. Interannual variation of spatial distribution of phenology for the second-season crop is larger than that for the first-season crop since LC implementation adjusts short-term land use and management. With the improvement of production conditions and balanced distribution of production elements, farmland productivity has been improved and its differences among various farmland patches imply a reducing trend. Production in LCA is slightly less stable than that in the control area (TCA) where LC is not carried out because of limited and short-term effect from LC. We concluded that satellite data presents variation of agricultural production in LCA from different dimensions of time, space and attributes. Multidimensional variation of agricultural production is decided by several factors, including climate condition, LC activity, and farmers' intention.

Long-term urban extent data are highly desirable for understanding urban land use patterns and achieving sustainable development goals. However, urban observation data based on remote sensing are typically confined to recent decades. In this study, we advance in this arena by reconstructing the urban extents for China that extend back from 15th century to 19th century based on multiple historical documents. Cities in late imperial China (the Ming and the Qing Dynasties, 1368–1911) generally had city walls, and these walls were usually built around the urban built-up area. By restoring the scope of the city walls, the urban extend in this period could be restored. Firstly, we collected the years of construction or reconstruction of city walls from the historical data. Specifically, the period in which the scope of the city wall keeps unchanged is recorded as a lifetime of it. Secondly, specialization of the scope of the city wall could be conducted based on the urban morphology method, and variety of documentation, including the historical literature materials, the military topographic maps of the first half of the 20th century, and the remote sensing images of the 1970s. Correlation and integration of the lifetime and the spatial data would produce China City Wall Areas Dataset (CCWAD) in late imperial. Based on the proximity to the time of most of the city walls, we generated China Urban Extent Dataset (CUED) in the 15th–19th centuries in six representative years (i.e., 1400, 1537, 1648, 1708, 1787, and 1866). These datasets are available at https://doi.org/10.6084/m9.figshare.14112968.v1

Ecological restoration is important to mitigate global ecological degradation. However, previous restoration, mainly targeting a single ecosystem or ecological problem at a single scale, couldn’t effectively solve systemic ecological problems, especially in rapidly developing areas. Land-Space Ecological Restoration (LSER) policy was proposed to change the situation that traditional ecological restoration was lack of overall planning and united goals. To integrate ecological restoration measures in different departments and scales in LSER practice and management, a multi-scale evaluation framework for LSER planning strategy making based on “P-S-R” perspective and landscape, ecological, GIS methods was proposed, and applied in Jiangsu Yangtze River Economic Belt in China. We took fishnet scale as data calculation unit, and town, county, regional scales as decision scale to formulate a hierarchical evaluation and decision making system. In study area, ecological engineering type (including 7 kinds of protection or restoration, and artificial or natural measures) at town level was identified, guided by county-level LSER zoning and grading obtained by normal cloud model evaluation method. At regional scale, an ecological network including 53 ecological sources, 95 corridors, 674 restoration points, and 80 footstones was constructed to determine regional restoration priority. Based on the research results, a decision-making system could be formed, with the regional ecological network as the decision-making basis for the overall restoration pattern, the county-level LSER classification as the standard for planning goals and task decomposition, and the township LSER project classification as the basis for the site selection of diverse ecological restoration projects. The proposed evaluation framework could integrate the data and decision-making process of ecological restoration measures at different scales, and assist regional ecological goal setting and space strategy making of LSER planning to achieve sustainable development goals.

The clarification of land use management in areas of potential land use conflict plays an important role in maintaining ecosystem services. However, the relationship between land use strategies and ecosystem services in potential conflict zones remains uncertain, lacking quantitative evidence. Therefore, to construct a healthy territorial space system, a spatial classification model for land use was built based on land sparing and sharing. In addition, the inherent characteristics of different modes in the landscape structure and functional heterogeneity were also resolved. Then, an empirical analysis was carried out with the coastal agricultural production area of Maoming City, Guangdong Province. Focusing on the potential area of land use conflicts in Maoming City, that is, the suitable area for agricultural production, this study determined the differences in ecosystem services under multiple land use patterns at the pixel level, explored the trade-offs of ecosystem services in the entire suitable area and a single model, and examined the gradient effect of ecosystem services with the intensity of cultivated land use. According to the results, ecosystem services significantly differed in land use patterns, and the comprehensive ecosystem service was the highest in the land sharing model. Ecosystem services exert a synergistic effect in the entire suitable area for agricultural production, whereas there exists no correlation within a single model. When the arable land area of intensive agriculture exceeds 84.84%, food supply and other ecosystem services will be reduced to varying degrees. The study bridges the gap in research on the relationship between land sparing and sharing and ecosystem services in Chinese regions, and proposes clear land remediation strategies in potential conflict zones, which can thus provide some guidance for achieving sustainable regional development.

The maintenance of sustainable development in light of climate change is presenting society with a serious challenge. This study analyzes the spatial environment and its coupled relationship with socio-economic and food security in the Chaohu Lake Basin in central Anhui Province, China. Previous studies have shown that this study area has good environmental conditions. However, the ecological security, economic development, and food security in the Chaohu Lake Basin was generally poor and poorly coordinated in 2018, especially in the center of local cities and surrounding areas. Nevertheless, many towns are in a well-organized state, meaning sustainable and coordinated regional development can be achieved through resource optimization. Generally, the economic conditions in the Chaohu Lake Basin should be improved in a way that ensures that the environment is not significantly degraded. The main functional zoning requirements of the counties&rsquo, land management planning designate most of the counties as parts of ecological conservation areas. The present study provides monitoring of important basin ecosystems and serves as a guide to future sustainable regional development by providing directions and paths to follow, it can also provide a reference for eco-functional zoning that is applicable to various natural basins worldwide.

Under the premise of facing land-use sustainable development goals, clarifying the process and trend of regional land-use transition (LUT) is of considerable significance to the direction of national land-use optimization in the future. Suzhou City is not only an economically developed area in China but also a leading area of economic transformation and development, which embodies the changing process of regional development path since China's reform and opening up. This paper constructed an integrated research framework of micro-individual land use structure and macro-mixed landscape multifunctionality. It used spatial analysis technology to deeply analyze the LUT process of Suzhou, and quantified change characteristics of land use structure and function in Suzhou from 2000 to 2015. For structure, Suzhou has undergone a large-scale transition during the study period, mainly from farmland to construction land, in which transition speed and degree are at a high level until the trend slows down after 2010. For function, the number of high values of landscape multifunctionality gradually increases. Still, the scope of high-value areas progressively reduces by urban expansion constraints; the multifunctionality around urban expansion area gradually weakens. Besides, forest land, grassland, and other ecological land have the most significant number of land use functions. The comprehensive transition of land use structure and function can give a summary as a circle-layer dynamic change process of urban development. Transition hotspots can be divided into five specific regions of land management and finally realize comprehensive development zoning of urban and rural areas at the township level. LUT research framework based on structure-function coupling will provide ideas for land management mode transformation and contribute to sustainable land spatial planning strategy formulation.

A sustainable development system involves resource limitation, environmental stress and policy regulation, and the flow and integration of resources and factors on a multi-level spatial scale. However, it is difficult to meet the actual needs of local development through traditional single-scale and macro-scale evaluation of the comprehensive level. Taking Suzhou City as an example, based on the United Nations (UN) sustainable development goals (SDGs) framework, the entropy method and fuzzy comprehensive evaluation (FCE) were used to construct an evaluation index system of the municipal sustainable development level. Growth and obstacles of the sustainable development system and its subsystems were systematically analyzed on a multi-level spatial scale. Results show that during the study period (2000-2016), the sustainable development system in Suzhou was relatively low at the beginning of the study. With the passage of time, it generally developed in a stable, continuous, and balanced direction. The levels of development, deficiencies, and obstacle factors of sustainable development systems and their subsystems are significantly different between levels, especially during the study period, the order change between towns is significantly higher than the order change between districts. Within an evaluation unit, there is a process of rising and continuing growth among certain subsystems, but some subsystems have been developing slowly due to resource constraints, environmental load, etc., or their contribution to the level of sustainable development has remained low. The city sustainable development evaluation index system based on the SDGs framework can meet the requirements of regional assessment and has the potential for further promotion and use. The evaluation results can provide a necessary reference for the subsystem coordination, scale linkage, and resource space allocation of the sustainable development system in Suzhou.

Scientific assessment of the accounting over carbon in the terrestrial ecosystem in the process land use/land cover changes caused by human activities will help reduce the uncertainty in estimating carbon emissions from the terrestrial ecosystem. This study employs a bookkeeping model to estimate the carbon emissions from farmland reclamation in China during the past 300 years based on the annual rate of land use changes (derived from historical natural vegetation, farmland data), preset carbon density and coefficients of disturbance curves. We find out that: (1) there was a net increase of 79.30×104 km2 in national farmland; about 65% of reclaimed farmland had been forest land and 26% of that had been grass land previously; (2) the total amount of carbon emissions from farmland expansion in China had been between 2.94 and 5.61 Pg with the median 3.78 Pg during the past 300 years; specifically, carbon emissions of vegetation were 1.58 Pg while those of soil ranged from 1.35 Pg to 4.03 Pg with the median 2.20 Pg; (3) carbon emissions vary greatly across various ecosystems: the emissions were most from forest land, and then grass land and swamps, and the least from shrubs; deserts functioned more likely to be carbon stock in the process of land reclamation; (4) along the time line, carbon emissions had decreased first and then increased while the peak emissions occurred in the first half of 20th century; and spatially, carbon emissions were most released in Northeast and Southwest China; Northwest China was of the minimum carbon emissions.

Land use function (LUF) is a valuable concept that allows for more integrated assessments of land system change. Identifying the changes and relationships of multiple LUFs is pertinent to land use planning and management. Selection and quantification of LUF indicators are critical for LUFs assessment. However, past studies have mostly assessed LUFs using socioeconomic data, which are not suitable for spatial variable quantification. In this study, we proposed a new LUFs classification system based on spatial planning goals, and we applied the system to assess 12 LUFs across 63 counties in Jiangsu Province of eastern China based on multi-source data using geospatial modeling tools combined with statistical analysis of socioeconomic data. We also analyzed the change in LUFs between 2000 and 2015, as well as the interactions among multiple functions. Finally, we identified distinct function zones based on the LUFs assessment in 2000 and 2015 using k-means clustering. The result showed that 12 LUFs displayed significant changes and interactions between 2000 and 2015, which can be explained by differing topography and social-ecological characteristics among counties. Additionally, we found four distinct LUF zones that are spatially agglomerated in similar landscapes and characterize specific LUF relationships in each cluster. In the future, local LUFs and their changes over time should be taken into consideration for land use planning and management, which provide a reference for policy-makers to make decisions that better match local development realities.