•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.
Abstract
Land subsidence induced by groundwater level decline has spatiotemporal variations. Taking the Interferometric Synthetic Aperture Radar (InSAR) results and the groundwater subsidence data ...acquired by the monitoring stations as the source material, this paper aims to reveal the spatiotemporal heterogeneity of groundwater-land subsidence in Beijing plain by using the Wind Rose Map (WRM) method and the Change Point Analysis (CPA) method. The WRM results show that the amount and variation in subsidence differs in different directions. This method detected the formation of new subsidence centers and the slowdown of land subsidence in 2008. The CPA results show that obvious changes are detected in subsidence development at the Wangsiying (WSY), Tianzhu (TZ) and Wangjing (WJ) stations. However, there is a relatively stable trend of groundwater decline and land subsidence at the Tianzhu (TZ) station. The stages of land subsidence development show a significant response to groundwater. Moreover, changes in land subsidence also show delayed response behind the changes in groundwater level. The time-lag could be affected by the variation in amplitude of the groundwater level.
The usage of reclaimed water can efficiently mitigate water crises, but it may cause groundwater pollution. To clearly understand the potential influences of long-term reclaimed water usage, a total ...of 91 samples of shallow and deep groundwater were collected from a typical reclaimed water use area during the dry and rainy seasons. The results suggest both shallow and deep groundwater are mainly naturally alkaline freshwater, which are composed mainly of Ca-HCO3, followed by mixed types such as Ca-Na-HCO3 and Ca-Mg-HCO3. A seasonal desalination trend was observed in both shallow and deep aquifers due to dilution effects in the rainy season. Groundwater chemical compositions in both shallow and deep aquifers are still dominantly controlled by natural processes such as silicate weathering, minerals dissolution and cation exchange. Human activities are also the factors influencing groundwater chemistry. Urbanization has been found responsible for the deterioration of groundwater quality, especially in shallow aquifers, because of the relative thin aquitard. Reclaimed water usage for agricultural irrigation and landscape purposes has nearly no influences on groundwater quality in rural areas due to thick aquitards. Therefore, reclaimed water usage should be encouraged in arid and semiarid areas with proper hydrogeological condition.
Entropy indexes are widely used to measure the complexity of precipitation and its spatiotemporal variability, due to their advantages in quantifying the complex and nonlinear interactions of climate ...variables. However, different entropy indexes may provide different outcomes on the complexity of precipitation, thus causing difficulties in the assessment of actual complexity. In this study, we identified and chose the optimal entropy index from six entropy indexes based on the reliability and stability of entropy values, to assess the complexity of precipitation. The six entropy indexes considered are: information entropy (IE), fuzzy entropy (FE), approximate entropy (AE), sample entropy (SE), wavelet entropy (WE), and permutation entropy (PE). We implemented the approach on the monthly precipitation data observed over the period 1968–2017 at 58 meteorological stations in Beijing, China. The results indicated that the SE index was the optimal index with the best reliability and stability and, thus, was used to examine the complexity of the 58 monthly precipitation series in Beijing. The results also suggested that the complexity of precipitation can be viewed in terms of four sub-regions in Beijing. The precipitation in the ‘Northern Mountain Area’, with high complexity, was more affected by the interactions between the terrain and climate variability, compared with that in the ‘Southern Mountain Area’ with low complexity. The precipitation in the ‘Central Urban Area’ was more significantly impacted by the extensive urbanization than that in the ‘Northeast Suburban Area’, causing higher complexity in the former. At temporal scale, the complexity of precipitation in the ‘Southern Mountain Area’ exhibited the largest increasing rate due to the highest impacts of climate variability, followed by the ‘Central Urban Area’ with a moderate increasing rate of complexity of precipitation due to the impacts of human activities. However, the complexity of precipitation in the ‘Northern Mountain Area’ and ‘Northeast Suburban Area’ exhibited small changes due to relatively weak sensitivity to climate variability and human activities.
Combined sewer overflow pollution has gradually become the limiting factor for the further improvement of river water quality during rain events. Setting up a comprehensive regulation method based on ...synchronous monitoring is essential for combined sewer overflow management. However, current studies mainly focus on single monitoring and lack a correlation between control objectives and control effects. This study establishes a new aspect of a comprehensive regulation and control method based on overflow characteristic analysis, a calculation model, and control target determination. Through synchronous monitoring of the pipe network, the sewage treatment plant, and the river course in the Liangshui River basin of China, rainfall thresholds of outlets in a combined pipe network, pre-treatment overflow, and simple-treatment overflow were 14, 9, and 16 mm, respectively, and the overflow volume was positively correlated with the rainfall. The COD (chemical oxygen demand) concentration from the pre-treatment overflow was much higher than that from the combined pipe network, and the EMC (event mean concentration) in heavy rain was higher than in rainstorms. The shortest time exceeding the water quality by overflow pollution was 1 h, and the longest time was more than 7 days. Overflow load proportions of the three links were 43.4%, 32.8%, and 23.8%, accounting for 66.3% of the total pollutant load of the river, and the best scheme of input–output ratio was to regulate the first three outlets of overflow load. Our results provide comprehensive guidance and a systematic approach for the monitoring and control of combined sewer overflow.
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•Landuse dynamics and urban flow routing are considered in a hydrological model.•Urban flow routing process is simplified based on national drainage design standard.•Both water ...resource and flood metrics are adopted at station and catchment scales.
Urbanization-induced landuse changes alter runoff regimes in complex ways. In this study, a detailed investigation of the urbanization impacts on runoff regimes is provided by using multiple runoff metrics and with consideration of landuse dynamics. A catchment hydrological model is modified by coupling a simplified flow routing module of the urban drainage system and landuse dynamics to improve long-term urban runoff simulations. Moreover, multivariate statistical approach is adopted to mine the spatial variations of runoff metrics so as to further identify critical impact factors of landuse changes. The Qing River catchment as a peri-urban catchment in the Beijing metropolitan area is selected as our study region. Results show that: (1) the dryland agriculture is decreased from 13.9% to 1.5% of the total catchment area in the years 2000–2015, while the percentages of impervious surface, forest and grass are increased from 63.5% to 72.4%, 13.5% to 16.6% and 5.1% to 6.5%, respectively. The most dramatic landuse changes occur in the middle and downstream regions; (2) The combined landuse changes do not alter the average flow metrics obviously at the catchment outlet, but slightly increase the high flow metrics, particularly the extreme high flows; (3) The impacts on runoff metrics in the sub-catchments are more obvious than those at the catchment outlet. For the average flow metrics, the most impacted metric is the runoff depth in the dry season (October ∼ May) with a relative change from −10.9% to 11.6%, and the critical impact factors are the impervious surface and grass. For the high flow metrics, the extreme high flow depth is increased most significantly with a relative change from −0.6% to 10.5%, and the critical impact factors are the impervious surface and dryland agriculture; (4) The runoff depth metrics in the sub-catchments are increased because of the landuse changes from dryland agriculture to impervious surface, but are decreased because of the landuse changes from dryland agriculture or impervious surface to grass or forest. The results of this study provide useful information for urban planning such as Sponge City design.
Water transfer from agriculture to urban uses will likely become increasingly common worldwide. The objectives of this study were to evaluate the effects of converting paddy rice to dry land crops ...(PPRDC) on local farmers’ income in China’s Chaobai watershed and to analyze the responses of surface water quality to the change in cropping system. An on-site investigation of 485 households and water quality data from 1999 to 2008 are presented in this study. The cost of cultivation as a percentage of the total revenue was 22.3 % for rice and 30.1 % for corn, and the calculated compensation level (CCOM) should be 6172.3 Yuan ha
−1
. PPRDC provided farms with stable income without regard to drought and flood: thus, farmers responded positively to PPRDC, and 76.7 % of farmers expected to continue PPRDC. Inflow water quality was improved in terms of total nitrogen (TN) and nitrate (NO
3
–N) because of the reduction in fertilizer and pesticides after PPRDC, but there was no significant change in total phosphorus (TP). PPRDC not only reallocates water resource to different users but also improves water quality through crop adjustment. A dynamic compensation mechanism based on changing crop price is required for the future water transfer project.
The water consumption of green space in a large region is difficult to attain through traditional methods. In this article, a practical method is developed using different sources of remote-sensing ...data. The green space was first derived from a high spatial resolution RapidEye image using the stratified classification method. Then the primary vegetation types of green space were identified using the object-oriented classification method. Afterwards regional green space evapotranspiration was inversed based on multi-temporal Landsat 8 images using the Surface Energy Balance Algorithm for Land model. Finally, water consumption patterns for different types of vegetation were analysed, and regional water consumption was estimated. The method was applied to the northwest region of Beijing City with an area of 147.5 km 2 where the green space area was 56.87 km 2 , and the deciduous broadleaf forest area was the largest among six vegetation types. The total quantity of water consumption for green space in the growing period in the study region was 41.52 × 10 6 m 3 (Mm 3). The quantity of water consumed by different types of vegetation in an order from high to low were deciduous broadleaf forest, mixed green space, grassland, evergreen needleleaf forest, golf course, and aquatic vegetation, ranging from 17.43 to 0.79 Mm 3. The results are helpful for identifying vegetation types, monitoring vegetation growth status, managing green space, and optimizing green space ecological functions in the Beijing region. The method presented in this article, having higher accuracy and more convenience, has great potential to be applied to other areas across the world.
•Two key hydrology-related open issues on the “Sponge City” program in China are discussed.•The trade-off between the investment for the SCP and its potential benefits can be used to determine proper ...VCRAR.•Nonstationarity of rainfall data should be considered for estimating proper rainfall threshold, to achieve the VCRAR.
For managing the worsening urban water disasters in China, the Government of China proposed the concept of “Sponge City” in 2013 and initiated the strategy in 30 pilot cities from 2015. Despite the promise of the concept, there have been many challenges in implementing the “Sponge City” program (SCP). In this manuscript, we discuss the hydrology-related challenges in implementing the SCP. In particular, we consider two key challenges: (1) Determination of the “Volume Capture Ratio of Annual Rainfall” (VCRAR), as controlling urban stormwater runoff is one of the core targets of the SCP; and (2) Estimation of a proper rainfall threshold, which influences the layout of green-infrastructures in the SCP to achieve the core VCRAR target. To discuss these challenges, we consider the city of Beijing, the capital of China, as a case study. Our analysis shows that the trade-offs between the investment for the SCP and its potential economic benefits should be considered by undertaking a proper determination of VCRAR. The VCRAR estimated for Beijing from the present analysis is 0.73. This value is more reasonable than the empirical value of 0.80 that is presently used, as it can guarantee the positive rate of return on the investment. We also find that the nonstationary characteristics of rainfall data and their spatiotemporal differences are important for the estimation of the rainfall threshold in SCP. For instance, even using the daily rainfall data over a period of 30 years (1983–2012) in Beijing, as required by the National Assessment Standard, the estimated rainfall threshold of 27.3 mm underestimates the reasonable rainfall threshold that should at least be larger than 30.0 mm. Thus, the former cannot ensure the VCRAR target of 0.80. Based on these results, we offer proper approaches and key suggestions towards useful guidelines for delivering better SCP in the Chinese cities.
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