Urban green space (UGS) can be regarded as an effective approach to mitigate urban heat island (UHI) effects. Many studies have investigated the impacts of composition and configuration of UGS on ...land surface temperature (LST), while little attention has been paid to the impacts among different urban blocks. Thus, taking 1835 urban blocks in Beijing as samples, including low-rise point (LRP), low-rise street (LRS), low-rise block (LRB), mid-rise point (MRP), mid-rise street (MRS), mid-rise block (MRB), high-rise point (HRP), high-rise street (HRS) and high-rise block (HRB), this study investigated the impacts of UGS on LST among different urban blocks. The results showed that UGS serves as cold islands among different urban blocks. Percentage of landscape (PLAND) of UGS in all types of urban blocks, edge density (ED) of UGS in MRS, area-weighted fractal dimension index (FRAC_AM) of UGS in HRS and HRB show significantly negative impacts on LST, while aggregation index (AI) of UGS in LRP shows significantly positive impacts. The findings suggest that both composition and configuration of UGS can affect LST among different urban blocks and rational allocation of UGS would be effective for mitigating UHI effects.
Systematical downslope‐turbidity‐current experiments were performed to clarify the relationship between sediment‐transport modes and current propagation patterns caused by rigid vegetation, as well ...as adjustments in turbulence characteristics of current. The equations for predicting the front velocities of downslope turbidity currents with emergent vegetation were proposed and validated via experimental data. Experimental results reveal that sediment deposition causes the lower turbulent kinetic energy (TKE) peaks of turbidity currents to decrease or even disappear without affecting their upper TKE peaks, while the rigid vegetation has the opposite effect. Vegetation stems destroy the longitudinal low‐high speed streaks associated with the quasi‐streamwise eddies in the near‐bed region and increase the proportions of the outward and inward interactions. In addition, sediment deposition severely suppresses the turbulent bursting events within turbidity currents but does not influence the relative proportions of the four bursting types. Rigid vegetation and sediment deposition both degrade the absolute values of the third‐order moments of velocity fluctuations without changing their signs to reduce the generation frequency of sweep events. Emergent rigid vegetation accelerates the formation of the reflected bore to provide energy for the deposited sediment to move downstream continuously. On the other hand, the dense submerged vegetation makes turbidity currents easily form the two‐head propagating mode, which allows part of the sediments carried by the upper current head to be transported downstream rather than deposited within or upstream of the vegetation region. Furthermore, the sloping boundary provides favorable conditions to initiate these specific modes for sediment transport adjusted by rigid vegetation.
Key Points
Equations are developed and validated to predict the front velocities of turbidity currents flowing slopes with emergent rigid vegetation
Rigid vegetation and sediment gradation are key factors in controlling the turbulence characteristics of downslope turbidity currents
Rigid vegetation distinctly changes the sediment‐transport modes of downslope turbidity currents by adjusting their propagation patterns
The propagation and hydrodynamic processes of lock-exchange gravity current through vegetation regions were investigated experimentally. Experimental results show that the presence of vegetation can ...prominently advance the transition position of the gravity current from the slumping phase to the self-similar phase. The process of two-heads propagation can be divided into three stages: the coordinated advance stage (vegetation height controls), the overtaking stage (entrainment process and vegetation friction dominate), and the merge stage (vegetation density controls). After an adjustment period, the bulk slope angle
β
b
of the triangular gravity current converges to a constant terminal value. A modified empirical equation is fitted to better meet the stable convergence of the terminal bulk slope angle
β
b
. The mixing layer formed at the transverse boundary between the vegetation and no-vegetation part can promote fluid entrainment. For the submerged vegetation, the gravity current flows over a new “wall boundary”, i.e. the top of the vegetation region, and causes the negative vorticity. The changes in the vorticity field indicate the presence of vegetation can significantly affect the internal flow-field structure of gravity currents.
Article Highlights
The process of two-heads propagation for gravity current flowing within submerged vegetation can be divided into three stages: the coordinated advance stage (vegetation height controls), the overtaking stage (entrainment process and vegetation friction dominate), and the merge stage (vegetation density controls).
A modified empirical equation is fitted to better meet the stable convergence of the terminal slope angle
β
b
for lock-exchange gravity current within vegetation.
The vegetation exerts resistance on the gravity current and suppresses the K-H instability at the interface, which weakens the entrainment process, but the mixing layer formed at the transverse boundary of the vegetation region promotes fluid entrainment.
Crop classification is one of the most important agricultural applications of remote sensing. Many studies have investigated crop classification using SAR data, while few studies have focused on the ...classification of dryland crops by the new Gaofen-3 (GF3) SAR data. In this paper, taking Hengshui city as the study area, the performance of the Freeman–Durden, Sato4, Singh4 and multi-component decomposition methods for dryland crop type classification applications are evaluated, and the potential of full-polarimetric GF3 data in dryland crop type classification are also investigated. The results show that the multi-component decomposition method produces the most accurate overall classifications (88.37%). Compared with the typical polarization decomposition techniques, the accuracy of the classification results using the new decomposition method is improved. In addition, the Freeman method generally yields the third-most accurate results, and the Sato4 (87.40%) and Singh4 (87.34%) methods yield secondary results. The overall classification accuracy of the GF3 data is very positive. These results demonstrate the great promising potential of GF3 SAR data for dryland crop monitoring applications.
Abstract
Accelerated urbanization and frequent heatwave events pose significant threats to human health. Analyses of the differences in air and land surface temperature (LST) under extreme climates ...can aid in understanding human-nature ecosystem coupling and the required adaptations to climate change. In this study, we quantified differences in urban and rural temperatures in China under heatwave (CHW) and non-heatwave periods (NHW) conditions and the influence of meteorological factors on these differences. Based on impervious surface data, 2421 urban and rural stations were dynamically classified from 2008 to 2017. Heatwaves were identified using relative thresholds, and differences were explored using meteorological data and MODIS LST data. For LST, urban–rural temperature difference (U-R
Tempdiff
) was highest during the day, whereas air temperature peaks occurred at night, under both NHW and CHW conditions. During CHWs, the daytime U-R
Tempdiff
was greater for LST than for air temperature, reaching 4.24 ± 3.38 °C. At night, U-R
Tempdiff
was slightly lower (1.04 ± 1.41 °C). The proportion of air U-R
Tempdiff
contributed by rural air temperature was significantly higher during CHW nights than during NHW nights, whereas the proportion of land surface and air U-R
Tempdiff
remained relatively stable during daytime. Spatially, the daytime temperature difference in the north decreased with latitude, whereas the difference in the south was lower. Under CHWs, urbanization had a stronger effect on LST than on air temperature, with a slightly smaller difference (0.01 °C yr
−1
) during the day and a slightly larger difference (0.03 °C yr
−1
) at night. The contribution of urbanization to LST was higher than that to air temperature, particularly during the day (16.34%). The effects of wind speed and precipitation on the average air urban–rural temperature difference was greater than those of LST under CHW, accounting for 16.13%, with the effects of wind speed being more significant. These results show that a comprehensive perspective is needed to understand the risks associated with a temperature rise risk under extreme climate conditions and to formulate effective mitigation measures that will they improve human thermal comfort under climate change.
Detailed sowing and harvesting (S&H) information is crucial for climate-coupled crop models to accurately simulate dynamic crop growth. The timing of intra-annual crop growth not only reflects ...adaptation to climate change but also significantly influences terrestrial biophysical and biochemical processes, as well as the local climate. However, accurately providing sowing and harvesting dates in crop models is challenging due to the limited availability of S&H observations worldwide. In this study, we integrated a prognostic S&H scheme into the Noah-MP-Crop model to eliminate the need for prescribed S&H dates and optimised key crop-related parameters to better reproduce dynamic maize and soybean growth in the U.S. Corn Belt. Results indicated that the bias in estimating site-level S&H dates was within one week. The prognostic S&H schemes, along with optimised crop-related parameters, effectively captured maize and soybean growth at the site scale, as evidenced by leaf area index (LAI) and gross primary production (GPP) simulations. The determination coefficient (R2) for GPP ranged from 0.88 to 0.91 for maize and from 0.70 to 0.82 for soybean at two flux stations. Moreover, the prognostic schemes exhibited better regional LAI and GPP simulations at the beginning and end of the growing season compared to those using state-level median S&H dates, with significant improvements in correlation coefficients ranging from 0 to 0.6, particularly in maize-dominated regions. However, the accuracy in reproducing latent heat flux and sensible heat flux was less satisfactory and showed little association with crop growth status. This work provides an alternative approach to obtaining crop sowing and harvesting information in the Noah-MP-Crop model and facilitates studies on interactions between dynamic crop growth and the climate system, particularly when coupled with the widely used Weather Research and Forecasting (WRF) model.
•Addressing prescribed sowing-harvest dates constraints in the Noah-MP-Crop model.•Coupling temperature-based prognostic scheme to simulate sowing-harvest dates.•Biases of site-level sowing-harvest dates estimations are within 7 days.•Prognostic scheme improves simulations of regional crop growth.
Understanding the cooling effect (CE) of urban parks is vital to mitigate the urban heat islands. ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) land surface ...temperature data (LST) data were used to construct diurnal thermal variations to explore the CE of urban parks in the fifth ring regions of Beijing. Local climate zone (LCZ) classification was used to distinguish different parks for examining the internal CE of parks. New subclasses of LCZ (e.g., LCZAG, LCZBG, LCZCG) were created based on the basic subclasses, such as LCZA (mainly consist of dense trees), LCZB (scattered tress with dense bush), LCZC (scattered bush), and LCZG (water). The external CE of parks was evaluated in different directions, and the impacts of buildings around parks on the external CE were also analyzed. The results showed that urban parks tended to heat up slower than the whole urban regions during the daytime, and water releasing energy dominated the mean LST of parks at night. Large parks meeting the minimum area (40,000 m
2
) of LCZ had better CE inside each park during the daytime. Three hundred thirty four large parks were divided into six types of LCZ. The strength of the CE decrease with the increases of distance, and seemed to exist at a distance of up to 150–200 m. Such impacts of parks were insignificant at night. In addition, parks containing certain dense trees and water had better CE inside and out. The height and density of buildings had a relatively obvious impact on the CE of parks. This study can provide insight into the impacts of urban parks on the urban thermal environment and promote the CE of urban parks in future urban planning.
Land surface models (LSMs) have prominent advantages for exploring the best agricultural practices in terms of both economic and environmental benefits with regard to different climate scenarios. ...However, their applications to optimizing fertilization and irrigation have not been well discussed because of their relatively underdeveloped crop modules. We used a CLM5-Crop LSM to optimize fertilization and irrigation schedules that follow actual agricultural practices for the cultivation of maize and wheat, as well as to explore the most economic and environmental-friendly inputs of nitrogen fertilizer and irrigation (FI), in the North China Plain (NCP), which is a typical intensive farming area. The model used the indicators of crop yield, farm gross margin (FGM), nitrogen use efficiency (NUE), water use efficiency (WUE), and soil nitrogen leaching. The results showed that the total optimal FI inputs of FGM were the highest (230 ± 75.8 kg N ha−1 and 20 ± 44.7 mm for maize; 137.5 ± 25 kg N ha−1 and 362.5 ± 47.9 mm for wheat), followed by the FIs of yield, NUE, WUE, and soil nitrogen leaching. After multi-objective optimization, the optimal FIs were 230 ± 75.8 kg N ha−1 and 20 ± 44.7 mm for maize, and 137.5 ± 25 kg N ha−1 and 387.5 ± 85.4 mm for wheat. By comparing our model-based diagnostic results with the actual inputs of FIs in the NCP, we found excessive usage of nitrogen fertilizer and irrigation during the current cultivation period of maize and wheat. The scientific collocation of fertilizer and water resources should be seriously considered for economic and environmental benefits. Overall, the optimized inputs of the FIs were in reasonable ranges, as postulated by previous studies. This result hints at the potential applications of LSMs for guiding sustainable agricultural development.
A three-dimensional numerical model was established with OpenFOAM-5.x to investigate plume characteristics under windless and rainless weather conditions. The large eddy simulation was applied, ...combined with a modified solver for solving governing equations with the Boussinesq approximation in a single rotating frame. The relationship between plume characteristics (e.g., gradient Richardson number and maximum plume width) and quantified parameters (e.g., rotation period, shelf slope, and reduced gravity) was analyzed progressively. The results show the model can reproduce the change in plume types and instability found in the laboratory experiments. With the increase in the rotation period, river plumes change from a surface-advected type to a bottom-attached type. The outline of the plume bulge accurately delineates the external region where the gradient Richardson number is less than 0.25, as well as the region near the wall. When the shelf slope approaches 0, the offshore movement becomes stronger while the alongshore coastal current comes into being with a delay associated with the slope and the rotation period. Compared with the extremely gentle slope case and the steep slope case, the maximum width in the gentle slope case changes significantly at about 1.5 rotation periods. Greater reduced gravity does promote offshore propagation, especially near the surface.
Urban morphology significantly affects the urban thermal environment. Seasonal impacts of two-dimensional (2D) and three-dimensional (3D) urban morphology on land surface temperature (LST) remain ...uncertain, and the impacts exist scale effects. Thus, taking Beijing as the study area, boosted regression tree (BRT) model was used to investigate the seasonal contributions of urban morphology to the thermal environment. Building density (BD), building height (BH), floor area ratio (FAR), sky view factor (SVF), and frontal area index (FAI), were used to comprehensively characterize urban morphology, and 13 scales ranging from 30 m to 600 m were used to investigate scale effects. The results showed that there are obvious spatial differences in LST and urban morphology indicators in the study area. 270 m was determined as the optimal scale for modeling in the study area. BH and BD are the domain indicators, which together contribute more than 75% of the variance of LST among four seasons, while the relative influences of SVF, FAR, and FAI are relatively low. Relationships between urban morphology indicators and LST are nonlinear among four seasons. The findings provide a scientific understanding for urban planners on mitigating the UHI effects through optimizing buildings.
•BRT model was applied to explore seasonal contributions of 2D/3D urban morphology to the thermal environment.•Scale effects for urban morphology analysis were explored.•Relative contribution and marginal effect of urban morphology indicators to LST across seasons were analyzed.•Rational allocation of BH and BD should be carried out to mitigate UHI effects.
