Changes in surface temperature extremes have become a global concern. Based on the daily lowest temperature (TN) and daily highest temperature (TX) data from 2138 weather stations in China from 1961 to 2020, we calculated 14 extreme temperature indices to analyze the characteristics of extreme temperature events. The widespread changes observed in all extreme temperature indices suggest that China experienced significant warming during this period. Specifically, the cold extreme indices, such as cold nights, cold days, frost days, icing days, and the cold spell duration index, decreased significantly by −6.64, −2.67, −2.96, −0.97, and −1.01 days/decade, respectively. In contrast, we observed significant increases in warm extreme indices. The number of warm nights, warm days, summer days, tropical nights, and warm spell duration index increased by 8.44, 5.18, 2.81, 2.50, and 1.66 d/decade, respectively. In addition, the lowest TN, highest TN, lowest TX, and highest TX over the entire period rose by 0.47, 0.22, 0.26, and 0.16°C/decade, respectively. Furthermore, using Pearson’s correlation and wavelet coherence analyses, this study identified a strong association between extreme temperature indices and atmospheric circulation factors, with varying correlation strengths and resonance periods across different time-frequency domains.
Glaciers are considered to be ‘climate-sensitive indicators’ and ‘solid reservoirs’, and their changes significantly impact regional water security. The mass balance (MB) from 2011 to 2020 of the Qiyi Glacier in the northeast Tibetan Plateau is presented based on field observations. The glacier showed a persistent negative balance over 9 years of in-situ observations, with a mean MB of −0.51 m w.e. yr−1. The distributed energy-mass balance model was used for glacier MB reconstruction from 1980 to 2020. The daily meteorological data used in the model were from HAR v2 reanalysis data, with automatic weather stations located in the middle and upper parts of the glacier used for deviation correction. The average MB over the past 40 years of the Qiyi Glacier was −0.36 m w.e. yr−1 with the mass losses since the beginning of the 21st century, being greater than those in the past. The glacier runoff shows a significant increasing trend, contributing ~81% of the downstream river runoff. The albedo disparity indicates that the net shortwave radiation is much higher in the ablation zone than in the accumulation zone, accelerating ablation-area expansion and glacier mass depletion. The MB of the Qiyi Glacier is more sensitive to temperature and incoming shortwave radiation variation than precipitation. The MB presented a non-linear reaction to the temperature and incoming shortwave radiation. Under future climate warming, the Qiyi Glacier will be increasingly likely to deviate from the equilibrium state, thereby exacerbating regional water balance risks. It is found that the mass losses of eastern glaciers are higher than those of western glaciers, indicating significant spatial heterogeneity that may be attributable to the lower altitude and smaller area distribution of the eastern glaciers.
Since China’s reform and opening-up in 1978, rapid urbanization has coincided with a surge in carbon emissions. Statistical, geospatial, and time-series analysis methods were utilized to examine the dynamic relationship between urbanization and carbon emissions over the past 43 years; elucidate the mechanisms through which dimensions of urbanization, such as population, land, economy, and green development, impact carbon emissions at various stages; and further explore the heterogeneity among cities of different scales. The analysis reveals that 2001 and 2011 represent significant turning points in China’s carbon emission growth “S” curve. The phase of rapid carbon emissions growth is associated with an increase in the urbanization rate from 40% to 50%, a shift in industrial structure from being dominated by secondary industry to tertiary industry, and a decrease in urban population density from 19,600 to 16,000 people per square kilometer of built-up area. Regions northeast of the “Bayannur-Ningde Line” have experienced rapid increases in carbon emissions, with large and medium-sized cities being the primary contributors nationwide. The TVP-VAR results indicate that higher urbanization rates have short-term carbon and mid- to long-term carbon-reducing effects. Population concentration in large cities facilitates short- to mid-term carbon reduction, whereas intensive urban development, industrial upgrading, and the promotion of clean energy use have sustained carbon-reducing effects. Carbon emissions exhibit path dependence. Increased urbanization rates in mega-cities and super-cities result in carbon-increasing effects, whereas the optimization of industrial structures exerts an inhibitory effect on carbon emissions in medium-sized and large cities. The changes in impulse response values of various variables are influenced by the developmental trajectory of Chinese cities from “small to large and then to agglomerations.” These recommendations indicate the necessity for differentiated emission reduction strategies contingent on the specific regions and types of cities in question.
Urban sprawl has been a prevailing phenomenon in developing countries like China, potentially resulting in significant carbon dioxide (CO2) emissions from the transport sector. However, the impact of urban sprawl on transport CO2 emissions (TCEs) is still not fully understood and remains somewhat rudimentary. To systematically investigate how urban sprawl influences TCEs, we employ panel regression and panel threshold regression for 274 Chinese cities (2005-2020), and obtain some new findings. Our results affirm that the degree of urban sprawl is positively associated with TCEs, and this holds true in different groups of city size and geographical region, while significant heterogeneity is observed in terms of such impact. Interestingly, we find urban sprawl nonlinearly impacts TCEs—with an equal increase in urban sprawl degree, TCEs are even lower in cities with larger population size and better economic condition, particularly in East China. Furthermore, the low-carbon city pilot policy shows potential in mitigating sprawl’s impact on TCEs. Drawing on our findings, we argue that to achieve the target of TCEs reduction in China by curbing urban sprawl, more priority should be placed on relatively small, less developed, and geographically inferior cities for cost-efficiency reasons when formulating future urban development strategies.
The internal technological innovation (IT) and external technological cooperation (ET) of a city are crucial drivers for its green development (GD). Although previous studies have extensively explored the effect of IT on GD, IT, ET and GD have not been integrated into the same framework to explore their relationship. Using panel data of 13 cities in the Beijing-Tianjin-Hebei urban agglomeration, this study revealed the spatio-temporal evolution of GD and analyzed the effects of IT and ET on GD from the perspective of baseline impact, spatial effect and synergy effect. Empirical results demonstrate that the level of urban GD has upgraded and the difference in GD between cities has been narrowed though it decreases from the middle to both ends. IT significantly promotes the growth of GD while ET has an inverted U-shaped effect on GD. Under the influence of spatial spillover, IT has a U-shaped effect on the GD of neighboring cities while the effect of ET on neighboring GD is not significant. Additionally, the interaction between IT and ET has not been effective, leading to an insignificant synergy effect on GD. These findings will provide reference for taking rational advantage of IT and ET to facilitate urban GD.
Land-use and land-cover change (LUCC) simulations are powerful tools for evaluating and predicting future landscape dynamics amid rapid human‒nature interactions to support decision-making. However, existing models often overlook spatial heterogeneity and temporal dependencies when modeling LUCC at both the macro and microscales. In this paper, we propose a new model, a self-calibrated convolutional neural network-based cellular automata (SC-CNN-CA) model, which integrates macro- and microspatial characteristics to simulate complex interactions among land-use types. The SC-CNN-CA model incorporates a self-calibration module using Gaussian functions to capture macrotrend such as urban sprawl while accounting for microlevel land-use interactions such as neighborhood effects. The results indicated that (1) the neighborhood effect between agricultural land and urban land tended to “increase followed by a decrease.” (2) Urban sprawl in Wuhan was highly compact, with a relatively high intensity of urban expansion at distances between 11.96 km and 24.44 km. (3) Compared with the other CA models tested, the SC-CNN-CA model demonstrated superior performance, achieving an overall accuracy of 84.12% and a figure of merit of 20.20%. This new model can enhance our understanding of historical LUCC trajectories and improve predictions of spatially explicit information for efficient land resource and urban management.
High-level investment facilitation is crucial for China’s overseas free economic zones (COFEZs) to attract and retain investment, mitigate business interruption risks, and foster a virtuous cycle. While research on investment facilitation in COFEZs has mainly focused on summarizing and examining the investment facilitation measures adopted by typical national-level examples of COFEZs, relatively little attention has been paid to investigating the overall level and general problems of investment facilitation across COFEZs. This study expands the scope of case investigations by taking 60 COFEZs as samples. It constructs a comprehensive evaluation indicator system which includes four dimensions: industrial infrastructure, social infrastructure, business support services, and seamless administrative supervision. By employing content analysis and regression analysis, this study identifies the characteristics and influencing factors of investment facilitation level in COFEZs. The results show that the overall level of investment facilitation in COFEZs is currently low. Specifically, COFEZs exhibit higher levels of investment facilitation in processing and manufacturing types and in Europe, while those in trade and logistics types and in Africa are relatively poor. Industrial infrastructure and business support services contribute more significantly to the overall scores of investment facilitation in COFEZs compared to social infrastructure and seamless administrative supervision. The investment facilitation level in COFEZs is essentially the result of a series of behaviors by developers and host governments, and it is affected by a combination of developers’ perceptions of investment facilitation and the social environment in which developers and host governments promote investment facilitation. This study offers a new perspective on understanding COFEZs and contributes to the sustainable development of COFEZs.
Polder is a type of irrigation field unique to the lower Yangtze River of China. It is a product of long-term and ingenuous human modifications of wetland landscapes. In the pre-Qin Period, 3000 years ago, the poldered area of eastern Wuhu city was once a large lake called the ancient Danyang wetland. The introduction of agricultural civilization and polder technology to the area during the Wu and Yue Kingdoms period gradually transformed it into an agricultural area. With an accelerating rate of land reclamation under a changing late-Holocene regional climate, the ancient Danyang wetland became an aquatic system strongly influenced by intensifying anthropogenic activities. In this study, based on field survey data, historical documents, and remote-sensing and archaeological data, we reconstructed the spatial distribution of the polder landscape over the last 3000 years and identified their structural diversity. We found that polder landscapes began to emerge in the Spring and Autumn Period, land reclamation intensified in the Three Kingdoms and developed rapidly in the Song Dynasty before eventually reaching the peak from the Ming and Qing Dynasties. The relocation of historical sites to low-altitude areas also marked the expansion of poldered fields from the center of the wetland to the southeast and northwest. The development and evolution of the polder landscape are related to regional climate conditions, changing social and economic statuses, and the development of agricultural technology in the Song Dynasty and succeeding periods.
It is essential to map the cropping patterns when investigating the mechanisms and impacts of climate change. However, the long-term evolution of cropping patterns remains poorly understood. This study collected hundreds of records of cropping intensity and crop combinations from local gazetteers and other relevant articles for the North China Plain (NCP) over the past 300 years. Then, we analyzed the evolutionary characteristics and drivers in terms of climate change and advances in agricultural technology. From the Qing Dynasty to the 1950s, one harvest per year (1H1Y) was the dominant pattern in the northern NCP, and three harvests in two years (3H2Y) was the dominant pattern in Henan and Shandong provinces. The 1H1Y crops were cereals and sorghum. The 3H2Y crop combinations were spring maize, winter wheat, and beans. In the 1960s and 1970s, the cropping intensity in much of the NCP was two harvests per year (2H1Y) or a mix of the 2H1Y and 3H2Y patterns. In the 1980s, the cropping intensity in the NCP was dominated by 2H1Y. Since the 1960s, the 2H1Y crop compositions have been winter wheat−summer maize in Shandong, Henan, and Hebei provinces, while winter wheat−rice dominated north of the Huaihe River. The 3H2Y summer crop changed from beans to maize/cereals over time. Climate warming was not the dominant factor driving the evolution of cropping intensity in the NCP. Advances in agricultural production conditions and reforms in production relations have promoted the rapid development of multiple cropping since the 1950s.
