Urban heat island (UHI) is a major anthropogenic alteration on Earth environments and its geospatial pattern remains poorly understood over large areas. Using MODIS data from 2003 to 2011, we ...quantified the diurnal and seasonal surface UHI intensity (SUHII, urban–suburban temperature difference) in China's 32 major cities, and analyzed their spatial variations and possible underlying mechanisms. Results show that the annual mean SUHII varied markedly from 0.01 to 1.87°C in the day and 0.35 to 1.95°C at night, with a great deal of spatial heterogeneities. Higher SUHIIs for the day and night were observed in the southeastern and northern regions, respectively. Moreover, the SUHII differed greatly by season, characterized by a higher intensity in summer than in winter during the day, and the opposite during the night for most cities. Consequently, whether the daytime SUHII was higher or lower than the nighttime SUHII for a city depends strongly on the geographic location and research period. The SUHII's distribution in the day related closely to vegetation activity and anthropogenic heat releases in summer, and to climate (temperature and precipitation) in winter, while that at night linked tightly to albedo, anthropogenic heat releases, built-up intensity, and climate in both seasons. Overall, we found the overwhelming control of climate on the SUHII's spatial variability, yet the factors included in this study explained a much smaller fraction of the SUHII variations in the day compared to night and in summer relative to winter (day vs. night: 57% vs. 72% in summer, and 61% vs. 90% in winter, respectively), indicating more complicated mechanisms underlying the distribution of daytime SUHII, particularly in summer. Our results highlight the different diurnal (day and night) and seasonal (summer and winter) SUHII's spatial patterns and driving forces, suggesting various strategies are needed for an effective UHI effect mitigation.
•Mapped surface urban heat island intensity (SUHII) in 32 cities•SUHII showed distinct diurnal and seasonal spatial patterns with varying drivers•Climate was the dominant control on cross-city SUHII variability•More complicated mechanisms underlying the SUHII in the day than at night
•Litter peaks of tropical forests occurred at the dry spring or winter.•Litter peaks of evergreen forests occurred at various seasons.•Precipitation and radiation dominate the litterfall seasonality ...at tropical forests.•Radiation and temperature dominate the seasonality at temperate and boreal forests.•Ecosystem models need to consider litterfall seasonal patterns.
The seasonal litterfall plays an important role in the process of forest carbon and nutrient cycles. The current dynamic vegetation models use a simplified method to simulate seasonal patterns of litterfall, and assume that litterfall inputs distributed evenly through the year for deciduous trees or occur once during the start of year for evergreen trees. In this study, we collected more than 400 litterfall measurements for different forest ecosystems from existing literature and monographs, and analyzed the seasonal patterns of litterfall over the various forest types. The results showed that the total annual litterfall varied significantly by forest types in the range of 3–11Mgha−1y−1. The seasonal litterfall patterns had diverse forms and varied obviously among the forest types. For tropical forests, the litter peaks occurred mostly in spring or winter, corresponding to the drought season; for temperate broadleaved and needle-leaved evergreen forests, litter peaks could occur at various seasons; and for temperate deciduous broadleaved and boreal evergreen needle-leaved forests, litter peaks were observed in autumn. Global analyses showed that seasonal patterns of litterfall were determined by both the physiological mechanism and environmental variables.
Objective This study aims to evaluate the accuracy of virtual surgical planning in two-jaw orthognathic surgery via quantitative comparison of preoperative planned and postoperative actual skull ...models. Study Design Thirty consecutive patients who required two-jaw orthognathic surgery were included. A composite skull model was reconstructed by using Digital Imaging and Communications in Medicine (DICOM) data from spiral computed tomography (CT) and STL (stereolithography) data from surface scanning of the dental arch. LeFort I osteotomy of the maxilla and bilateral sagittal split ramus osteotomy (of the mandible were simulated by using Dolphin Imaging 11.7 Premium (Dolphin Imaging and Management Solutions, Chatsworth, CA). Genioplasty was performed, if indicated. The virtual plan was then transferred to the operation room by using three-dimensional (3-D)-printed surgical templates. Linear and angular differences between virtually simulated and postoperative skull models were evaluated. Results The virtual surgical planning was successfully transferred to actual surgery with the help of 3-D-printed surgical templates. All patients were satisfied with the postoperative facial profile and occlusion. The overall mean linear difference was 0.81 mm (0.71 mm for the maxilla and 0.91 mm for the mandible); and the overall mean angular difference was 0.95 degrees. Conclusions Virtual surgical planning and 3-D-printed surgical templates facilitated the diagnosis, treatment planning, and accurate repositioning of bony segments in two-jaw orthognathic surgery.
Corn stover as well as perennial grasses like switchgrass (
Panicum virgatum) and miscanthus are being considered as candidates for the second generation biofuel feedstocks. However, the challenges ...to biofuel development are its effects on the environment, especially water quality. This study evaluates the long-term impacts of biofuel production alternatives (e.g., elevated corn stover removal rates and the potential land cover change) on an ecosystem with a focus on biomass production, soil erosion, water quantity and quality, and soil nitrate nitrogen concentration at the watershed scale. The Soil and Water Assessment Tool (SWAT) was modified for setting land cover change scenarios and applied to the Iowa River Basin (a tributary of the Upper Mississippi River Basin). Results show that biomass production can be sustained with an increased stover removal rate as long as the crop demand for nutrients is met with appropriate fertilization. Although a drastic increase (4.7–70.6%) in sediment yield due to erosion and a slight decrease (1.2–3.2%) in water yield were estimated with the stover removal rate ranging between 40% and 100%, the nitrate nitrogen load declined about 6–10.1%. In comparison to growing corn, growing either switchgrass or miscanthus can reduce sediment erosion greatly. However, land cover changes from native grass to switchgrass or miscanthus would lead to a decrease in water yield and an increase in nitrate nitrogen load. In contrast to growing switchgrass, growing miscanthus is more productive in generating biomass, but its higher water demand may reduce water availability in the study area.
► We evaluate the impacts of biofuel production on water quantity and quality. ► Biomass production can be sustained under higher removal rates with fertilization. ► Sediment yield increased and N load decreased when more corn stover was removed. ► Conversion from grass to bioenergy crops could decrease water and raise N load. ► Miscanthus is more productive but it consumes more water and N than switchgrass.
Parameter optimization and uncertainty issues are a great challenge for the application of large environmental models like the Soil and Water Assessment Tool (SWAT), which is a physically-based ...hydrological model for simulating water and nutrient cycles at the watershed scale. In this study, we present a comprehensive modeling environment for SWAT, including automated calibration, and sensitivity and uncertainty analysis capabilities through integration with the R package Flexible Modeling Environment (FME). To address challenges (e.g., calling the model in R and transferring variables between Fortran and R) in developing such a two-language coupling framework, 1) we converted the Fortran-based SWAT model to an R function (R-SWAT) using the RFortran platform, and alternatively 2) we compiled SWAT as a Dynamic Link Library (DLL). We then wrapped SWAT (via R-SWAT) with FME to perform complex applications including parameter identifiability, inverse modeling, and sensitivity and uncertainty analysis in the R environment. The final R-SWAT-FME framework has the following key functionalities: automatic initialization of R, running Fortran-based SWAT and R commands in parallel, transferring parameters and model output between SWAT and R, and inverse modeling with visualization. To examine this framework and demonstrate how it works, a case study simulating streamflow in the Cedar River Basin in Iowa in the United Sates was used, and we compared it with the built-in auto-calibration tool of SWAT in parameter optimization. Results indicate that both methods performed well and similarly in searching a set of optimal parameters. Nonetheless, the R-SWAT-FME is more attractive due to its instant visualization, and potential to take advantage of other R packages (e.g., inverse modeling and statistical graphics). The methods presented in the paper are readily adaptable to other model applications that require capability for automated calibration, and sensitivity and uncertainty analysis.
•Dilatant crystals caused the internal structure of the concrete to undergo the process of loose damage after densification.•The corroded concrete specimens were divided into three parts from the ...outside to the inside.•The formula for calculate the internal expansion stress were given.•A constitutive model based on ion diffusion, chemical reaction and mechanical analysis was established.
Stress-strain constitutive relationship is one of the basic mechanical properties of concrete materials, and the stress-strain relationship of concrete subjected to salt corrosion has changed significantly. Saline soil in Western China has the characteristics of many kinds of salt and high concentration, which makes the damage to concrete more serious. In this paper, the uniaxial compressive stress-strain constitutive relation of corroded concrete in saline soil area of Western China is studied, and the constitutive model based on ion diffusion, chemical reaction and mechanical analysis was also given. Firstly, the causes and mechanisms of the change of stress-strain curve of corroded concrete were analyzed via the stress-strain curve, scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), and porosity. Then, the corroded concrete specimens were divided into three parts from the outside to the inside, namely, the corrosive damage part, the corrosive enhancement part and the non-corrosive part. Combined Fick's diffusion law and chemical reaction, the formulas for calculate the critical failure depth and the internal expansion stress were given. The corrosion effects of the corrosive damage part and the corrosive enhancement part were expressed by the critical failure depth and the internal expansion stress respectively. Finally, based on the meso-statistical parallel bar constitutive model of non-corroded concrete, a stress-strain constitutive model of corroded concrete in saline soil region of Western China was established considered the corrosion effect.
A new algorithm to detect contacts between three-dimensional (3-D) arbitrarily shaped polyhedral blocks for the discontinuous deformation analysis (DDA) method is presented in this paper. The new ...algorithm includes three main steps, i.e. neighbor search, contact type examination, and entrance candidate identification, all of which are performed using the general features and relations of geometric elements of polyhedra. First, contact detection begins with searching neighbor blocks and vertices potential to be in contact in order to improve the computation efficiency. Then, pairs of neighbor blocks are examined in more detail for four basic contact types. Finally, corresponding contact points and planes for each contact type are identified by general entrance formulas, which is prepared for the subsequent contact force calculations in the program. The new algorithm has been implemented in the original 3-D DDA program and the extended 3-D DDA program can display the results using OpenGL. Three typical contact examples including concave blocks, i.e. vertex-to-concave-edge, convex-edge-to-concave-edge and vertex-to-concave-vertex contacts are provided to verify the new algorithm. Additionally, a practical example in rock engineering, sliding of a tetrahedral wedge, is also presented, and the 3-DDA results are compared with the analytical solutions.
•A new contact detection algorithm of polyhedral blocks for 3-D DDA is proposed.•Neighbor search techniques are presented to improve contact detection efficiency.•Four basic contact types are examined based on the relation of geometric elements.•Entrance candidates are identified by the general entrance formulas.•The extended 3-D DDA program can be used for practical engineering applications.
Increased atmospheric CO
2
concentration and climate change may significantly impact the hydrological and meteorological processes of a watershed system. Quantifying and understanding hydrological ...responses to elevated ambient CO
2
and climate change is, therefore, critical for formulating adaptive strategies for an appropriate management of water resources. In this study, the Soil and Water Assessment Tool (SWAT) model was applied to assess the effects of increased CO
2
concentration and climate change in the Upper Mississippi River Basin (UMRB). The standard SWAT model was modified to represent more mechanistic vegetation type specific responses of stomatal conductance reduction and leaf area increase to elevated CO
2
based on physiological studies. For estimating the historical impacts of increased CO
2
in the recent past decades, the incremental (i.e., dynamic) rises of CO
2
concentration at a monthly time-scale were also introduced into the model. Our study results indicated that about 1–4% of the streamflow in the UMRB during 1986 through 2008 could be attributed to the elevated CO
2
concentration. In addition to evaluating a range of future climate sensitivity scenarios, the climate projections by four General Circulation Models (GCMs) under different greenhouse gas emission scenarios were used to predict the hydrological effects in the late twenty-first century (2071–2100). Our simulations demonstrated that the water yield would increase in spring and substantially decrease in summer, while soil moisture would rise in spring and decline in summer. Such an uneven distribution of water with higher variability compared to the baseline level (1961–1990) may cause an increased risk of both flooding and drought events in the basin.
Responses of hydrological processes to climate change are key components in the Intergovernmental Panel for Climate Change (IPCC) assessment. Understanding these responses is critical for developing ...appropriate mitigation and adaptation strategies for sustainable water resources management and protection of public safety. However, these responses are not well understood and little long‐term evidence exists. Herein, we show how climate change, specifically increased air temperature and storm intensity, can affect soil moisture dynamics and hydrological variables based on both long‐term observation and model simulations using the Soil and Water Assessment Tool (SWAT) in an intact forested watershed (the Dinghushan Biosphere Reserve) in Southern China. Our results show that, although total annual precipitation changed little from 1950 to 2009, soil moisture decreased significantly. A significant decline was also found in the monthly 7‐day low flow from 2000 to 2009. However, the maximum daily streamflow in the wet season and unconfined groundwater tables have significantly increased during the same 10‐year period. The significant decreasing trends on soil moisture and low flow variables suggest that the study watershed is moving towards drought‐like condition. Our analysis indicates that the intensification of rainfall storms and the increasing number of annual no‐rain days were responsible for the increasing chance of both droughts and floods. We conclude that climate change has indeed induced more extreme hydrological events (e.g. droughts and floods) in this watershed and perhaps other areas of Southern China. This study also demonstrated usefulness of our research methodology and its possible applications on quantifying the impacts of climate change on hydrology in any other watersheds where long‐term data are available and human disturbance is negligible.
Coastal wetland ecosystems, one of the most important ecosystems in the world, play an important role in regulating climate, sequestering blue carbon, and maintaining sustainable development of ...coastal zones. Wetland landscapes are notoriously difficult to map with satellite data, particularly in highly complex, dynamic coastal regions. The Liao River Estuary (LRE) wetland in Liaoning Province, China, has attracted major attention due to its status as Asia’s largest coastal wetland, with extensive Phragmites australis (reeds), Suaeda heteroptera (seepweed, red beach), and other natural resources that have been continuously encroached upon by anthropogenic land-use activities. Using the Continuous Change Detection and Classification (CCDC) algorithm and all available Landsat images, we mapped the spatial–temporal changes of LRE coastal wetlands (e.g., seepweed, reed, tidal flats, and shallow marine water) annually from 1986 to 2018 and analyzed the changes and driving forces. Results showed that the total area of coastal wetlands in the LRE shrank by 14.8% during the study period. The tidal flats were the most seriously affected type, with 45.7% of its total area lost. One of the main characteristics of wetland change was the concurrent disappearance and emergence of wetlands in different parts of the LRE, creating drastically different mixtures of wetland quality (e.g., wetland age composition) in addition to area change. The reduction and replacement/translocation of coastal wetlands were mainly caused by human activities related to urbanization, tourism, land reclamation, and expansion of aquaculture ponds. Our efforts in mapping annual changes of wetlands provide direct, specific, and spatially explicit information on rates, patterns, and causes of coastal wetland change, both in coverage and quality, so as to contribute to the effective plans and policies for coastal management, preservation, and restoration of coastal ecosystem services.
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