Danyang Di

Super-large-diameter caissons, serving as working wells for trenchless pipe jacking technology, are being extensively constructed alongside the increasing adoption of trenchless technology in urban areas. However, being regarded merely as ancillary structures, the structural stability of a caisson during both construction and operation phases are often neglected. This study, centered on the super-large-diameter caissons within the Jinshui River flood control project in Zhengzhou, China, systematically monitored the mechanical behavior of caisson structures and surface settlement during construction and operational phases. Utilizing a validated FE method, the influence of groundwater fluctuations on the structural stability of caissons during operational phases was examined. Furthermore, potential occurrences of loose soil, voids, and caisson tilting were considered. Subsequently, the applicability of permeable polymer, foam polymer, and anchor rod reinforcement techniques were evaluated, followed by an analysis of the structural stability of the caissons post reinforcement during long-term operations. The findings demonstrate the minimal horizontal displacement of and stress variation in caissons under seasonal groundwater fluctuations, without significant structural alterations. Nevertheless, the presence of loose soil, voids, and caisson inclinations may decline the caisson’s support force and bearing capacity. With the increase in non-compactness, void size, and inclination, the structural stability of caissons notably diminishes. Reinforcing loose soil with permeable polymers, filling voids with foam polymers, and utilizing anchor rods are all effective methods for strengthening caisson structures and enhancing their stability.

The growing concern surrounding climate change has gradually drawn attention to the influence of climate factors on drought occurrence. In order to effectively prevent the occurrence of drought and reasonably utilize water resources, the vegetation health index (VHI) was used to characterize drought in North China Plain (NCP) in this study. Furthermore, six climate factors: air temperature (AT), precipitation (P), evapotranspiration (ET), specific humidity (SH), soil moisture (SM), and soil temperature (ST) were selected. The pole symmetric mode decomposition (PSMD) and improved gridded trend test (IGT) were used to analyze the spatial–temporal characteristics of drought and climate factors in NCP from 1982 to 2020. By calculating the cumulative climatic factors of 0 months, 1 month, 2 months, and 3 months, the correlation between drought and the climatic factors with different cumulative scales was analyzed. The results showed that: (1) from 1982 to 2020, the drought in NCP showed a downward trend and the climate factors showed an upward trend; (2) with the increase in AT, P, ET, SH, SM, and ST, VHI showed an upward trend, and SM showed the strongest correlation with VHI; (3) the optimal cumulative lag time (CLT) for AT, P, ET, SH, SM, and ST were 1.67 months, 1.48 months, 1.95 months, 1.69 months, 0.89 months, and 1.81 months, respectively; and (4) AT was the main driving factor of drought in NCP. This study contributes to the early warning and prediction of drought events, providing a scientific basis for water management authorities in drought management and decision making, and mitigating the negative impacts of drought on socio-economic aspects.

In the article, on the basis of quantifying the emergy water ecological footprint, a sustainability evaluation system for the overall water ecological economic system of the basin and each province (region) was proposed. And using the subjective and objective combination of the Analytic Hierarchy Process (AHP) and Entropy Weight Method (EWM) to determine the weight of the indicator system, a TOPSIS model for sustainability evaluation was constructed. And taking the Yellow River Basin as an example, the results indicate that (1) Throughout the entire basin, the sustainability of the water ecological economic system showed a fluctuating upward trend year by year during the study period, from 0.37 to 0.51. (2) In each province (region), the sustainability of the water ecological economic system had gathered in space. The overall sustainability level of the upstream Sichuan, Qinghai and Gansu provinces is high, always at level (I). The overall sustainability level of the midstream Ningxia and Neimenggu was low, always at level (IV). The overall sustainability level of the downstream Shaanxi, Shanxi, Henan and Shandong provinces is high, rising gradually over time, from level (III) to level (II) or (I). Against the backdrop of the rapid development of the economy and society, the contradiction between economic and social development, ecological environment protection, and sustainable utilization of water resources is becoming increasingly severe, which has become a key factor restricting the sustainable development of the ecological economic system in Yellow River Basin. Multidimensional comprehensive evaluation of the sustainability level of the regional water ecological economic system is a prerequisite for identifying sustainable development issues in the Yellow River Basin, and also the basis for formulating targeted policies for sustainable utilization of regional water resources and high-quality economic development.

The vegetation drought phenomenon will reduce the amount of water available to the vegetation system, change the ecological and hydrological cycles of plants, and affect the aquatic and terrestrial ecosystem in various forms. Therefore, research on the dynamic variation and driving mechanism of vegetation drought will help us recognize and predict the response of vegetation under drought stress conditions, implement appropriate policy measures to deal with the drought crisis, and provide technical support for implementing vegetation protection and alleviating the increasing risk of vegetation drought. However, the dynamic variation of vegetation drought and its dynamic propagation mechanism are still undefined across China. In this study, the spatio-temporal evolutions and pixel-scaled trends of vegetation drought were analyzed during the period between 1999 and 2020. Additionally, the propagation features were investigated between vegetation drought and meteorological drought. Finally, the relationships between vegetation drought and atmospheric teleconnection were explicitly clarified using multivariate cross wavelet transform technology. The results highlighted five key findings: (1) the vegetation drought presented an overall decreasing trend across China in 1999–2020; (2) the most serious vegetation drought occurred in the year 2000, with the average vegetation condition index (VCI) values ranging from 0.36 to 0.46; (3) vegetation droughts were alleviating at the pixel scale for each season; (4) the propagation time from meteorological drought to vegetation drought was shorter in summer (1.26 months) and longer in winter (2.26 months); and (5) the three-factors combination of Pacific North American (PNA), El Niño-Southern Oscillation (ENSO), and Trans Polar Index (TPI) can satisfactorily explain the variations of vegetation drought. This study sheds new viewpoints into the identification of vegetation drought variation across China, which can also be applied in other areas.

To quantify and analyze the human demand for water resources and the available supply of water resource systems, this study combined emergy analysis and spatial autocorrelation analysis to establish a quantification and analysis system for water ecological footprint (WEF). First, the emergy theory of ecological economics and WEF were combined to propose an emergy quantification method for WEF and water ecological carrying capacity (WEC). Based on the spatial autocorrelation method, three-dimensional ecological footprint indicators (footprint size and depth) were introduced to analyze the spatial correlation and spatial aggregation of capital flow occupation and capital stock consumption in the water resource system. Using the Yellow River Basin (YRB) as the study area to verify the applicability of the WEF quantification and analysis system based on the emergy-spatial autocorrelation method, the following results were obtained. (1) From 2003 to 2018, the per capita WEF of the YRB generally showed a slow growth trend. (2) Compared to the upper and lower reaches of the YRB, the middle reaches had a higher WEF, and the WEC of the YRB was generally high in the west and low in the east. (3) Utilization of the water resources capital in the basin was generally unsustainable. It is necessary to take measures to promote rational allocation and efficient utilization of water resources for the coordinated development of society, the economy, and the environment in the YRB. (4) The emergy-spatial autocorrelation method is applied to basin/region water sustainability studies for decision makers.

To quantify and analyze the human demand for water resources and the available supply of water resource systems, this study combined emergy analysis and spatial autocorrelation analysis to establish a quantification and analysis system for water ecological footprint (WEF). First, the emergy theory of ecological economics and WEF were combined to propose an emergy quantification method for WEF and water ecological carrying capacity (WEC). Based on the spatial autocorrelation method, three-dimensional ecological footprint indicators (footprint size and depth) were introduced to analyze the spatial correlation and spatial aggregation of capital flow occupation and capital stock consumption in the water resource system. Using the Yellow River Basin (YRB) as the study area to verify the applicability of the WEF quantification and analysis system based on the emergy-spatial autocorrelation method, the following results were obtained. (1) From 2003 to 2018, the per capita WEF of the YRB generally showed a slow growth trend. The WEC was much lower than the WEF, and the water ecological deficit status remained unchanged. (2) Compared to the upper and lower reaches of the YRB, the middle reaches had a higher WEF, and the WEC of the YRB was generally high in the west and low in the east. (3) Except for Sichuan and Qinghai, the provinces (regions) in the YRB relied on water resource capital stock for social and economic development, and the sustainable development of the region was threatened. (4) Utilization of the water resources capital in the basin was generally unsustainable. It is necessary to take measures to promote rational allocation and efficient utilization of water resources for the coordinated development of society, the economy, and the environment in the YRB.