Waterlogging is one of the major water issues in most cities of China and directly restricts their urbanization processes.The construction of Sponge City is an effective approach to solving the urban ...water issues,particularly for the waterlogging.In this study,both the urban issues emerged at the stage of rapid urbanization in China and the demands as well as problems of Sponge City construction related with the water issues were investigated,and the opportunities and challenges for the Sponge City construction in the future were also proposed.It was found that the current stormwater management focused on the construction of gray infrastructures（e.g.,drainage network and water tank） based on the fast discharge idea,which was costly and hard to catch up with the rapid expansion of city and its impervious surface,while green infrastructures（e.g.,river,lake and wetland）were ignored.Moreover,the current construction of Sponge City was still limited to low impacted development（LID） approach which was concentrated on source control measures without consideration of the critical functions of surrounding landscapes（i.e.,mountain,river,wetland,forest,farmland and lake）,while application of the integrated urban water system approach and its supported technologies including municipal engineering,urban hydrology,environmental science,social science and ecoscape were relatively weak and needed to be improved.Besides,the lack of special Sponge City plan and demonstration area was also a considerable problem.In this paper,some perspectives on Good Sponge City Construction were proposed such as the point that idea of urban plan and construction should conform to the integral and systematic view of sustainable urban development.Therefore,both the basic theoretical research and the basic infrastructure construction such as monitoring system,drainage facility and demonstration area should be strengthened,meanwhile,the reformation and innovation in the urban water management system and the education system should also be urgently performed.The study was expected to provide a deeper thinking for the current Sponge City construction in China and to give some of suggestions for the future directions to urban plan and construction,as well as urban hydrology discipline.
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•Module uncertainty and its propagation are estimated for integrated model.•Final distributions of both water quantity and quality parameters are skew.•Major simulation uncertainties ...of runoff and water quality are from model structure.•Hydrological parameter uncertainty propagates to water quality simulation.
Multiple uncertainty sources directly cause inaccurate simulations for water related processes in complicated integrated models, as such models include many interactive modules. A majority of existing studies focus on the uncertainties of parameter and model structure, and their effects on the model performance for a single process (e.g., hydrological cycle or water quality). However, comprehensive uncertainties of different modules and their propagations are poorly understood, particularly for the integrated water system model. This study proposes a framework of uncertainty and its propagation estimation for integrated water system model (HEQM) by coupling the Bootstrap resampling method and SCE-UA auto-calibration technique. Parameter and structure uncertainties of both hydrological cycle and water quality modules are estimated, including final distributions of parameters and simulation uncertainty intervals. Additionally, the effect of uncertainty propagation of hydrological parameters is investigated. Results show that: (1) HEQM simulates daily hydrograph very well with the coefficient of efficiency of 0.81, and also simulates the daily concentrations of ammonia nitrogen satisfactorily with the coefficient of efficiency of 0.50 by auto-calibration in the case study area; (2) The final ranges of all interested hydrological parameters are reduced obviously, and all the parameter distributions are well-defined and show skew. The uncertainty intervals of runoff simulation at the 95% confidence level bracket 18.7% of all the runoff observations due to uncertainties of parameter, and 86.0% due to both parameter and module structure, respectively; (3) The uncertainty propagation of hydrological parameters changes the optimal values of 37.5% of interested water quality parameters, but does not obviously change the water quality simulations which match well with the prior simulations throughout the period and bracket only 1.7% of observations at the 95% confidence level. Due to the further introduction of module structure uncertainties, 94.8% of observations are bracketed, only except the extreme high and low water quality concentrations; (4) The uncertainty of water quality parameters contributes 12.1% of total water quality simulations at the 95% confidence level. The figure increases to 21.0% and 92.0% if the uncertainty propagation of hydrological parameters, structure uncertainties of water quality module are considered, respectively. Therefore, although the parameter uncertainty and its propagation contribute a certain proportion of the whole simulation uncertainties, the module structure itself is the primary uncertainty source for the integrated water system model (HEQM), particular for the water quality modules.
Reference evapotranspiration (ET0) is important for agricultural, environmental and other studies, and understanding the attribution of its change is helpful to provide information for irrigation ...scheduling and water resources management. The present study investigates the attribution of the change of ET0 at 49 meteorological stations in the middle reaches of Yellow River basin (MRYRB) of China from 1960 to 2012. Results show that annual ET0 increases from the northwest to the southeast of MRYRB in space. We find that annual ET0 clearly presents a zigzag change pattern rather than a monotonically change during the whole period. The detected three breakpoints at 1972, 1988 and 1997 divide the whole period into four subperiods. The sensitivity analysis indicates that the ET0 is the most sensitive to surface solar radiation (Rs), followed by relative humidity (RH) and mean air temperature (T), and the least sensitive to wind speed (u) in our study area. Furthermore, we find that ET0 is becoming less sensitive to RH and more sensitive to T during 1960–2012. The attributions of the change in ET0 vary largely at different regions and subperiods. The declined wind speed is the dominant factor, followed by Rs to the ET0 reduction during 1960–2012. Further analysis shows that Rs and u are the two major contributing factors that control the change of ET0 at most stations and during most subperiods. Our study confirms that the change of ET0 is influenced by the complex interactions of climatic factors, and the dominant factor to the change of ET0 is different in various regions and time periods. The results presented here can provide a reference for agricultural production and water resources management in MRYRB as well as other semi-arid and semi-humid regions.
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•The annual ET0 series exhibits a zigzag change pattern rather than a monotonically change.•The ET0 is the most sensitive to Rs, and least sensitive to wind speed during 1960 to 2012.•The decline in Rs and u is the two major driver to the decreased ET0 during the whole period.
Overgrazing has caused serious soil degradation, vegetation destruction, and wind erosion in temperate desert areas of northwestern China. To address this, the Livestock Enclosure Scheme was ...implemented in 2004 to allow for self-recovery of the overgrazed desert. The aim of this study was to investigate the effect of livestock enclosure on the restoration process by examining changes in the ecological environment of a temperate desert recovering from overgrazing. Vegetation parameters and soil properties under grazing site, 5-year fenced site, and 9-year fenced site were examined in the degraded desert in the Hexi Corridor of China. The results showed that vegetation coverage, height, plant density, richness, diversity, and litter biomass all improved after 5years of fencing, demonstrating that short-time fencing had a positive effect on vegetation restoration in the temperate desert. Furthermore, 9years of fencing significantly increased soil organic C (SOC), total N (TN), and total P (TP) in the 0–20cm soil profile, while available N (AN) and available P (AP) showed the reverse trend. The values of soil C and N storage after 9years of fencing were almost 5.55Mgha−1 and 0.69Mgha−1, respectively. Enhanced vegetation caused reductions in soil water near the soil surface (0–30cm) where vegetation uptake mainly occurred. These findings could offer insight into the development of effective strategies for protecting and enhancing the resilience of a livestock-disturbed temperate desert.
•Vegetation and soil property response of short-time fencing in temperate desert were studied.•5years of fencing had a positive effect on vegetation restoration.•9years of fencing significantly increased soil nutrients.•The values of soil C and N storage after 9years of fencing were 5.55Mgha−1 and 0.69Mgha−1 in the temperate desert.
Flash floods present significant heterogeneity over both space and time due to diverse topographic, geomorphologic, and hydro-meteorological conditions of catchments. Accurate identification and ...simulation of typical flash flood types are of great significance for the mitigation of flash flood disasters at the national scale. Three flood peak indices and dynamic indices were adopted to characterize the behavioral variability of flash floods. The typical flash flood types and corresponding behavior indices were identified and simulated using statistical analysis (i.e., principal component analysis, dynamic
K
-means clustering, and analysis of similarity) and hydrological modelling (i.e., HEC and XAJ models). There were 177 flash flood events at the hourly scale being selected for case study from eight catchments with various climatic and geographic characteristics. Results showed that all the flash flood events were clustered into three types (named Types 1, 2, and 3). Type 1 was characterized by low peak flow intensity, early flood peak occurrence time, and thin flood process with short duration. Type 2 was characterized by low peak flow intensity, late flood peak occurrence time, and flat flood process with long duration. Type 3 was characterized by high peak flow intensity and late flood peak occurrence time. Flash flood types showed high consistency with their influencing factors (e.g., catchment forest ratio and drainage area, occurrence time and magnitude of maximum storm intensity, and concentration of a storm event). The simulation performances were basically the same for HEC and XAJ models. As for flash flood event simulations, the average relative error varied from 23.25% to 27.98%, from 11.95% to 18.19%, and from 8.30% to 18.25% for Types 1, 2 and 3, respectively. The average Nash-Sutcliffe efficiency coefficient varied from 0.39 to 0.54, from 0.76 to 0.85, and from 0.86 to 0.91, respectively. As for the six flash flood behavior indices simulations, the average relative root-mean-square error (
RMSEr
) varied from 0.37 to 0.69, from 0.37 to 0.41, and from 0.18 to 0.25 for Types 1, 2, and 3, respectively. The average correlation coefficient (
r
) varied from 0.52 to 0.68, from 0.78 to 0.85, and from 0.88 to 0.94, respectively. The flood peak indices were the best simulated for Types 2 and 3 with
RMSEr
varying from 0.18 to 0.28 and
r
varying from 0.86 to 0.91. The flood dynamic indices were the best simulated for Type 3 with
RMSEr
varying from 0.19 to 0.21 and
r
varying from 0.91 to 0.97. The study provided detailed flood information supports for flood management at catchment scale, and also provided new insights into flash flood simulations in small and medium-sized catchments from perspective of flood behavioral processes.
•Flow regime metrics were used to capture detailed signatures of hydrograph changes.•Multicollinearity of metrics was reduced by principal component and classification.•Interannual variation of ...impact patterns was identified in a comprehensive manner.•Impacts of Miyun Reservoir were gradually attenuated due to continuous drought.
Assessing the impact of human intervention on flow regimes is important in policy making and resource management. Previous impact assessments of dam regulation on flow regimes have focused on long-term average patterns, but interannual variations, which are important characteristics to be considered, have been ignored. In this study, the entire signatures of hydrograph variations of Miyun Reservoir in northern China were described by forty flow regime metrics that incorporate magnitude, variability and frequency, duration, timing, and rate of change for flow events based on a long-term synchronous observation series of inflow and outflow. Principal component analysis and cluster analysis were used to reduce the multidimensionality of the metrics and time and to determine impact patterns and their interannual shifts. Statistically significant driving factors of impact pattern variations were identified. We found that dam regulation resulted in four main impact classes on the flow regimes and that the regulated capacity was interannually attenuated from 1973 to 2010. The impact patterns alternated between the highly regulated class with extremely decreasing flow magnitude, slight variability, and extreme intermittency and the slightly regulated class with extremely increasing flow magnitude, slight variability, and extreme intermittency from 1973 to 1987 and then stabilized in the latter class from 1988 to 2001. After 2001, the pattern gradually changed from the moderately regulated class with moderately decreasing flow magnitude, extreme variability, and extreme intermittency to the slightly regulated class with slightly decreasing flow magnitude, slight variability, and no intermittency. Decreasing precipitation and increasing drought were the primary drivers for the interannual variations of the impact patterns, and inflow variability was the most significant factor affecting the patterns, followed by flow event frequency and duration, magnitude, and timing. This study shows that the use of interannual characteristics can help to gain more insight into the impact of dam regulation on flow regimes and will provide important information to scientifically guide the multi-purpose regulation of dams.
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•Three NDVI vegetation correction schemes with CRNS were provided.•The ratio of parameter N0 between different landscapes reached 1.42.•N0 was negatively correlated with NDVI ...(y = 373.9 (x + 0.015)−0.136, R2 = 0.77)•Three methods reduced RMSE from 0.093 to 0.063, 0.054, and 0.032 g g−1, respectively.
Cosmic-ray neutron sensors (CRNS) are a powerful tool for measuring soil moisture on a hectometer scale, and mobile cosmic-ray neutron technology holds significant importance for upscaling soil moisture. However, vegetation strongly affects with CRNS soil moisture measurements. Variations in vegetation over time change how the CRNS is affected, which is more challenging than a stable vegetation cover, particularly during CRNS roving, where one crosses many vegetation covers. To correct vegetation, we hypothesized that Normalized Difference Vegetation Index (NDVI) can representvegetation hydrogen pools. From 2020 to 2023, at the 74 plots with varying vegetation cover near the Qilian Mountains, the experiments for soil moisture measurements were conducted in shrubs, forests, deserts, farmlands, and grasslands using a Cosmic-ray Neutron Rover. The measured neutron intensity clearly varied across different landscapes, and the calibrated parameter N0 differed among 74 plots. The variations in vegetation cover resulted in low measurement accuracy for CRNS. All three NDVI vegetation correction methods (NDVI-θNDVI method, NDVI-NDVIave method, and NDVI-N0 method) offered by the study could improve accuracy of soil moisture measurements. In the optimal NDVI-N0 method, the relationship between NDVI and N0 was established using a power function y = 373.9 (x + 0.015)−0.136 (R2 = 0.77), which had the capability to decrease the root mean square error between oven-dried and measured soil moisture from 0.093 to 0.032 g g−1 in our study area. Employing NDVI instead of biomass for CRNS vegetation correction can substantially reduce workload and effectively enhance CRNS soil moisture measurements, showing the potential for upscaling soil moisture.
•Infiltration is directly affected by soil moisture, rather than rainfall duration.•Horton infiltration equation is improved by adopting soil moisture variation.•Improved equation is better in ...simulation performance and uncertainty intervals.
Soil water infiltration simulation is a subject receiving great interest in hydrological cycle modelling. The traditional Horton equation is based on the curve of infiltration capacity-rainfall duration time. However, the infiltration process is directly affected by soil moisture content, rather than rainfall duration. The objective of this study was to determine a relationship between infiltration capacity and soil moisture content in order to improve the Horton infiltration equation. Artificial rainfall-infiltration experiments were used to determine a series of power functions. The improved equation was cross-validated with observations from 32 experiments of multiple rainfall intensities and antecedent soil moisture. The simulation performance and uncertainty of the improved equation were compared with those of the original Horton equation to verify its accuracy. The results showed that infiltration rate decreases nonlinearly as soil moisture increases, and finally approaches a stable infiltration rate when the soil is saturated. Overland flow simulations by the improved Horton equation closely matched the observations from all 32 experiments over a soil moisture range of 0.222–0.349 m3/m3. The simulation performance was rated as good for most of the experiments for both the calibration and validation data sets. Compared with the original Horton equation, the simulation performance of the improved equation clearly improved estimation of infiltration, particularly as quantified by the Nash-Sutcliffe efficiency coefficient (NSE) and the coefficient of determination (R2). The number of simulations with NSE values greater than 0.65 increased 11.59% and 2.50% for the calibration and validation data sets, respectively. The number of simulations with R2 values greater than 0.90 increased 31.14% and 22.50%, respectively. The uncertainty intervals of the improved Horton equation became a little greater than those of the original Horton equation. For all 32 experimental simulations, the average relative length of the uncertainty interval at the 95% confidence level increased from 40.52% with the original Horton equation to 49.17% with the improved Horton equation. The number of observations falling within the 95% confidence interval increased from 92.13% to 95.94% with the improved Horton equation. Most of the observations were accurately simulated using the improved Horton equation. The greatest improvements in simulating overland flow were seen for the experiments with low flow simulations. The study results provide insights into soil infiltration mechanisms, and also provide references to support improved infiltration simulation by considering soil moisture variation.
Macropore flow not only provides a fast pathway for water and solute transport and increases the risks of water and nutrient loss but also enhances soil aeration and groundwater recharge. However, ...macropore flow characteristics in irrigated oasis soils subject to continuous crop cultivation are poorly understood. This study was to investigate the effect of continuous cultivation on soil properties and macropore flow and to quantify the changes in macropore flow characteristics in an old oasis field (>50 years of cultivation, OOF), young oasis field (20 years, YOF), and adjacent uncultivated sandy area (0 year, USL) in Northwest China. Triplicate soil samples were collected from each site to investigate soil properties. Dye tracer experiments with also three replicates were conducted at each site. The degree of macropore flow (i.e., parameters of macropore flow) was highest at the OOF, intermediate at the YOF, and minimal at the USL. The macropore flow fraction (i.e., fraction of total infiltration flows through macropore flow pathways) at the OOF was 3.4 times greater than at the USL. The heterogeneous infiltration pattern at the OOF was dominated by macropore flow, while funnel flow was predominant at the USL. Long‐term irrigation with silt‐laden river water has increased silt + clay contents of the oasis soils. Irrigation and high‐input crop cultivation also increased organic matter. These changes in soil properties contributed to the interaggregate voids formation. The conversion of native desert soils to irrigated croplands increases the degree of macropore flow, which might enhance groundwater recharge in the desert‐oasis ecotone.
Key Points
Continuous cultivation with river water irrigation enhanced soil properties and the degree of preferential flow
Preferential flow was dominated at old oasis field and young oasis field, while funnel flow was predominant at uncultivated sandy area
Silt and clay content, soil organic carbon, and macroporosity had positive influence on preferential flow occurrence
Epilithic algal community structure and function are important indicators of stream ecosystem health and are sensitive to ambient environmental changes. In this study, we examined the impact of light ...and nutrients on epilithic algal community structure and function by an in situ nutrient addition and shaded canopy experiment in subtropical streams in China. Epilithic algae structure, dominated by diatoms, was significantly different with nutrient addition and light reduction. Nutrient addition increased the epilithic algae and diatom density, colonial life-forms, planktonic diatoms, and high-profile diatoms but decreased the low-profile diatoms. The shaded canopy increased the low-profile diatoms but decreased the adnate life-forms, planktonic diatoms, and high-profile diatoms. Epilithic metabolism, including gross primary production (GPP), net daily metabolism (NDM), and production/respiration (P/R) increased with nutrient addition, while respiration (R) only increased when the canopy was open with nutrient addition. Epilithic GPP had a significant positive correlation with diatom density (
P
< 0.01, R
2
= 0.9425). Our results indicated that changes in epilithic algae structure due to changes in riparian canopy coverage and nutrients could affect epilithic algal community function. Quantifying the impacts of such drivers on community structure and function is vital to effective river management.
