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The operational efficiency error of a pumping station unit is affected by several factors, resulting in a large error between the theoretical and actual pumping efficiencies. To solve the problem of accurately simulating the operating efficiency of the pumping station unit, this study conducted research on efficiency simulation models of pumping based on data-driven from three aspects: ①model algorithm, ②feature input and ③response output. In this study, eight machine learning models were introduced to establish pumping unit efficiency simulation models and they were compared with the traditional polynomial regression models, and the models with better performance were selected. Then the experiment proposed using “upstream water level + downstream water level” (UWL + DWL) instead of the traditional “head” (H) as feature input to train the models, and discussed the effects on efficiency simulation accuracy with direct fitting efficiency and fitting power then calculate the efficiency through formula. An example analysis was carried out using the historical data of eight units at Pizhou Station and Suining 2nd Station on the East Line of the South-to-North Water Diversion Project. The experimental results show that ① among all methods, the models based on Gaussian Process Regression (GPR) has the most accurate in ERMS, EMA, R², and EMIindicators, R²is close to 0.92. ②After UWL + DWL was used to train the models, all the test set indicators of the GPR models improved, and the EMAindicator decreased from an average of 0.39–0.26 %. ③ The study found that the fitting efficiency directly is better than the calculation efficiency after fitting the power, but the R²of fitting the power is better than the efficiency, which may provide another idea for the optimal goal of economic operation of pumping stations. ④ On the whole, trainning the GPR models with UWL + DWL to simulate efficiency has the highest precision, for example the EMAand EMIindicators of No.4 unit in Pizhou station can be reduced from 16.49 % and 20.40–0.18 % and 1.55 % respectively. The research results have practical significance and can provide strong support for the economical operation of pump stations.

Flood disaster has always been the key direction of urban governance and the real-time optimization of urban drainage system has become an important solution. At present, the control of gates in urban flood control system is dominated by rule-based control (RBC), while the research on real-time optimization control (RTC) based on gate opening is relatively few. This paper develops a real-time reservoir optimization model (RTROM) to solve the problem of urban flash flood control. The gate opening was discretized at an interval of 0.1 m as a decision variable, and the differential evolution algorithm (DE) was used to calculate the objective function of this study to obtain the optimal control strategy describing the operation of urban flood control system. The model was tested in the Jingdian Lake area in Fuzhou, China. The results show that in practice, the model can reduce the upstream flood flow by 48.2 m3/s, but also increase the discharge flow after a delay of 17 h. Jingdian Lake can store up to 126,000 m3of floodwater, and the storage capacity utilization rate has reached 68.5%. It shows that RTROM can maximize the effect of regional lake flood control. More importantly, it effectively lowered the water level of the downstream Qintin Lake by 0.53 m, reducing the flood risk faced by the Qintin Lake. Compared with rule-based control (RBC) model, RTROM is more effective in reducing urban flooding and can provide optimal operation strategies for the real-time operation of urban drainage systems.

Streamflow is controlled by multiple factors concurrently. However, the multivariate relationship between global streamflow and meteorological factors/ocean signals is rarely explored at different temporal scales. Determining a suite of factors that explain most of the variations in global streamflow at multiple scales will be of great significance for water‐resource management and prediction. Temporally dependent multivariate relationships between streamflow and meteorological factors/ocean signals in 16 of the world's large rivers were identified using wavelet transform coherence and multiple‐wavelet coherence. Prior to that, the continuous wavelet transform was used to detect temporal patterns in streamflow. The continuous wavelet transform results showed that significant annual oscillations occurred in all streamflow series over the study period, either with continuous annual periodicity or with intermittent breaks. Oscillations with periodicities of around 4 to 6 months were also found in many rivers. A comparison of the results from the wavelet transform coherence and multiple‐wavelet coherence analyses indicated that streamflow variation could be best explained by one, two, or three meteorological factors. The combination of factors that best explained streamflow variations differed among the rivers, although total precipitation (PRE) or the number of rainy days (WET) either alone or in combination was a dominant factor for all rivers. The most common best predictor was PRE or/and WET combined with potential evapotranspiration. The differences in best predictor were due to differences in latitude, radiation forcing, terrain, vegetation coverage, hydrological processes, and so forth. Significant annual streamflow oscillations occurred in 16 world's large riversWe identified the multivariate relationships between streamflow and predictorsThe combinations of factors that best explained streamflow variations are different

Baseflow is an all‐important replenishment feature of the hydrologic cycle for maintaining surface water in basins across the world. Understanding its dynamics and the influence of climate variability and human activities will be beneficial for developing sustainable water‐management strategies. In this study, we selected 11 basins within the Loess Plateau (a typical semiarid region in China) for assessment of the variations in baseflow and baseflow index (BFI; the ratio of baseflow volume to total streamflow volume) during the period 1961–2014. We compared eight baseflow separation methods and selected the median series in order to reduce the uncertainty. Results showed that values of the “Bflow” and Eckhardt filter methods were higher than values of the other six methods for the period of peak discharge. Annual baseflow exhibited a statistically significant downward trend (p< 0.01) in all 11 basins except Qingjian and Yanhe basins, while nine basins trended upward for BFI. All basins exhibited downward trends for seasonal baseflow in all seasons, with Yanhe and Qingjian showing the least significant trend. Variations in both baseflow and the BFIwere more sensitive to variations in potential evapotranspiration than to variations in precipitation. Across these 11 basins for both the conservation engineering period (1971–1999) and the reforestation period(2000–2014), human activities (73% and 76%, respectively) contributed more than climate variability (27% and 24%, respectively) to average baseflow decline. However, climate variability was the main factor altering the BFI, with the contribution accounting for about 54% and 76%, respectively, for the two periods. Eight baseflow separation methods were reviewed and applied to evaluate baseflow variations on the Loess PlateauAnnual baseflow showed a statistically significant downward trend on the Loess PlateauHuman activity contributed more than 73% to average baseflow decline

Constructing and operating a multi-reservoir system changes the natural flow regime of rivers, and thus imposes adverse impacts on riverine ecosystems. To balance human needs with ecosystem needs, this study proposes an ecologically oriented operation strategy for a multi-reservoir system that integrates environmental flow requirements into the joint operation of a multi-reservoir system in order to maintain different ecological functions throughout the river. This strategy is a combination of a regular optimal operation scheme and a series of real-time ecological operation schemes. During time periods when the incompatibilities between human water needs and ecosystem needs for environmental flows are relatively small, the regular optimal operation scheme is implemented in order to maximize multiple human water-use benefits under the constraints of a minimum water-release policy. During time periods when reservoir-induced hydrological alteration imposes significant negative impacts on the river’s key ecological functions, real-time ecological operation schemes are implemented in order to modify the outflow from reservoirs to meet the environmental flow requirements of these functions. The practical use of this strategy is demonstrated for the simulation operation of a large-scale multi-reservoir system which located in the middle and lower Han River Basin in China. The results indicate that the real-time ecological operation schemes ensure the environmental flow requirements of the river’s key ecological functions, and that adverse impacts on human water-use benefits can be compensated for by the regular optimal operation scheme. The ecologically oriented operation strategy for a multi-reservoir system that is proposed in this study enriches the theoretical application of the multi-reservoir system joint operation which considers environmental flow requirements.

Extreme climate events affect sustainable development in many parts of the world. Although several studies of local extreme climate events exist, such events need more thorough investigation. Detailed studies of climatic variations that assess changes on both spatial and temporal scales are becoming increasingly necessary. In this study, 14 indices for extreme temperature and 12 indices for extreme precipitation were used to analyze the spatial distribution and temporal trends of extreme climate events in the three‐rivers headwater region (TRHR), China, over the past five decades. We found that the frequency of high temperature extremes has increased, whereas the frequency of dry extremes has decreased. Statistically significant upward trends emerged for the number of warm nights (TN90p) and the number of warm days (TX90p) in the TRHR, which increased at a rate of 11.75 and 6.79 days/10 years (p< 0.05), respectively. We also found a highly significant downward trend in the number of consecutive dry days with a rate of −4.05 days/10 years across the whole region. Overall, the TRHR has become warmer and wetter over the past 50 years and the frequency of extreme events has increased. Wavelet analysis indicated that there are significant relationships between extreme climate events in the TRHR and large‐scale ocean‐atmosphere circulation patterns, for example, the Pacific Decadal Oscillation and the El Niño–Southern Oscillation. Our findings will help local water managers and stakeholders ensure that there are effective measures in place to adapt to and mitigate the effects of potential future climate change in the TRHR. The TRHR has become warmer and wetter over the past 50 yearsThe frequency of high temperature extremes in TRHR has increased, whereas the frequency of dry extremes has decreasedThere are significant relationships between extreme climate events and the large‐scale ocean‐atmosphere circulation patterns in the TRHR

A multi-scale assessment framework for assessing and comparing the water resource sustainability based on the ecological footprint (EF) is introduced. The study aims to manage the water resource from different views in Heilongjiang Province. First of all, from the scale of each city, the water ecological carrying capacity (ECC) was calculated from 2000 to 2011, and map the spatial distribution of the recent 3 years which show that, the water ecological carrying capacity (ECC) is uneven and has a downward trend year by year. Then, from the perspective of the five secondary partition basins in Heilongjiang Province, the paper calculated the ecological carrying capacity (ECC), the ecological footprint (EF) and ecological surplus and deficit (S&D) situation of water resources from 2000 to 2011, which show that the ecological deficit situation is more prominent in Nenjiang and Suifenhe basins which are in an unsustainable development state. Finally, from the perspective of the province, the paper calculated the ecological carrying capacity (ECC), the ecological footprint (EF) and ecological S&D of water resources from 2000 to 2011 in Heilongjiang Province, which show that the ecological footprint (EF) is in the rising trend, and the correlation coefficient between the ecological carrying capacity (ECC) and the precipitation is 0.8. There are 5 years of unsustainable development state in Heilongjiang. The proposed multi-scale assessment of WEF aims to evaluate the complex relationship between water resource supply and consumption in different spatial scales and time series. It also provides more reasonable assessment result which can be used by managers and regulators.

A novel Cu-Zn-TiO2 nanotube array (TNTA) polymetallic nanoelectrode, intended to improve the electrochemical nitrate removal efficiency, was fabricated. The nanoelectrode was fabricated by plating Cu onto a Ti nanoelectrode and then plating Zn onto the Cu/Ti bilayer electrode produced. The Ti nanostructures on the Cu-Zn-TNTA nanoelectrode surface gave the nanoelectrode a large specific surface area, and the Zn and Cu gave the nanoelectrode a high electrocatalytic activity for reducing nitrate. Scanning electron microscopy images showed that the Cu-Zn-TNTA polymetallic nanoelectrode had a honeycomb structure with spongy deposits. X-ray diffractometry results showed that the Cu-Zn-TNTA nanoelectrode predominantly contained Cu, O, Ti, and Zn. The nitrate removal efficiency of the Cu-Zn-TNTA nanoelectrode was 345.7% of the removal efficiency for a Ti nanoelectrode. The presence of NaCl allowed both the cathodic reduction of nitrate and the anodic oxidation of the ammonia and nitrite byproducts to be achieved with high removal efficiencies, especially using an IrO2 anode. In the present of NaCl, nitrate removal rate was 93.4% in current density of 30 mA/cm2 after 90 min. Nitrate was completely removed using the IrO2 anode, and little ammonia was detected in the treated solution. The reduction efficiency increased slightly as the initial nitrate concentration increased through the range 20-100 mg/L, and the pH had little effect on the nitrate reduction efficiency.

This study introduces a simulation method to identify large-scale land-use parameters that can be used to directly assess how changes in land use affect the generation of runoff. The study examined data during the flood seasons for the Second Songhua River basin, located in the northeast China. The Easy distributed hydrological model was modified to simulate the rainfall–runoff processes of different land-use types. Input data comprised land-use data during a period of minimal human activity and also under subsequent human interference. Time-scale validation and spatial validation both confirmed the suitability of the model for the study area and the feasibility of transferring land-use parameters. Runoff generation per unit area was calculated for each land-use type, and was found to descend in such order: water surface > residential area > unused land > cultivated land > woodland > grassland.

The North China Plain (NCP) has been subjected to groundwater overexploitation over the past decades as a result of rapid socioeconomic development and irrigation water demand with relatively limited renewable water resources. Operation of the middle route of the South‐to‐North Water Diversion Project (SNWD‐M) since December 2014 has provided an opportunity for groundwater sustainability in the NCP by increasing water supply and reducing groundwater abstraction. Water use changes have largely been driven by socioeconomic changes. However, impacts of water diversion, water use change, as well as climate variability in the future on groundwater storage (GWS) in the NCP have not been investigated. This study aims to simulate and project GWS in the NCP during 2005–2050 by incorporating effects of water diversion, water use, and climate variability. The high‐resolution Community Water Model with 30 arcsec spatial resolution was set up to assess interactions between water demand and availability by simulating surface water and groundwater abstraction dynamically. Results show that water diversion and reductions in water use may increase GWS over the NCP in 2050 by 144 mm (19 km3) and 573 mm (75 km3), respectively. Evaluation of GWS among different scenarios shows that combinations of factors, including water use reductions, water diversion, and precipitation variability can contribute up to 73%, 37%, and 32% to GWS stability, respectively. This study highlights the contributions of different management strategies toward sustainable GWS and the importance of water conservation along with diversions. Human intervention (including water use reductions and water diversions) can stabilize groundwater storage in the North China Plain, which is among the most stressed aquifers globally and of great importance to food security in China. We found that water conservation (e.g., water use reductions) plays a more prominent role in groundwater stabilization than water diversions and climate variability. This has important implications for groundwater sustainability of heavily stressed aquifers globally. Regions considering large water diversion programs might reconsider the value of water conservation to address water‐resource issues, which is less costly and more environmentally benign. The high‐resolution community water model coupled with a water diversion module was set up across the North China PlainGroundwater storage was simulated and projected until 2050 by incorporating effects of water use, water diversion, and climate variabilityWater use reductions, water diversion, and precipitation variability can contribute up to 73%, 37%, and 32% to groundwater storage stability The high‐resolution community water model coupled with a water diversion module was set up across the North China Plain Groundwater storage was simulated and projected until 2050 by incorporating effects of water use, water diversion, and climate variability Water use reductions, water diversion, and precipitation variability can contribute up to 73%, 37%, and 32% to groundwater storage stability

This study investigates the potential of hydraulic tomography (HT) in identifying the boundary conditions of groundwater basins using numerical experiments. The experiment mimics the scenario of groundwater exploitation reduction in a pilot area of groundwater overexploitation control in the North China Plain. In this study, we propose an approach that integrates the HT concept and readily available groundwater monitoring data to identify the constant head and impermeable boundaries by mapping anomalously high‐ and low‐permeability zones from HT surveys in a large‐scale domain that encompasses the true groundwater basin. The resulting boundaries and conditions were then used in inversion of steady‐state and transient‐state simultaneous pumping tests and HT surveys of heterogeneity within the groundwater basin. The inversion results demonstrated significant advantages of HT surveys over multiple simultaneous pumping tests to identify boundary conditions and heterogeneity in the groundwater basin. Moreover, steady HT inversion outperforms transient HT inversion in capturing the true boundary conditions, leading to the better Testimates from steady HT inversion than those from transient HT inversion. Additionally, the study shows that accurate geological zonation information can significantly improve HT parameter estimations. An innovative approach of identifying the unknown boundary conditions in groundwater basins is proposedBoundary conditions are captured by identifying anomalously high/low‐permeability areas in a larger domain than a groundwater basin shapeHydraulic tomography facilitates the accurate identification of boundary conditions in groundwater basins

The South‐to‐North Water Diversion Middle Route Project (MRP), which started its operation in December 2014, was designed to transfer water from Danjiangkou Reservoir (DR) in Hanjiang River Basin to North China Plain (NCP) to alleviate water shortage and long‐term groundwater depletion in the water‐receiving region. This study investigates the effectiveness of actual MRP operation during 2015–2018 using the observed water budget data collected from DR and the groundwater level data from 559 monitoring wells. Assuming that MRP was in operation during 2005–2014, ensemble water diversion simulations were performed to study the sensitivity of MRP effectiveness to two important factors: the downstream water demand of DR (Dwd) and the ratio (Ir) of water diversion volume (Qd) replacing groundwater pumping in NCP. Even though the observed and simulated mean annual Qdduring 2015–2018 (i.e., 4.3 and 7.0 km3/year, respectively) failed to meet the original water delivery target of 9.5 km3/year due to its short operation and the coincidence with a dry cycle, MRP is effective in groundwater recovery as an increasing trend (+0.3 km3/year) in groundwater storage (GWS) was observed in NCP during 2015–2018. MRP's effectiveness is sensitive to Dwdand Ir. Dwdshould not exceed 23.0 km3/year to guarantee Qdreaching the original target, and Irshould not be less than 33% to guarantee GWS recovery. Those findings suggest that a reasonable decrease of Dwdand an increase of Irare the recommended pathway to ensure the effectiveness of MRP in meeting both water delivery and groundwater recovery targets. MRP is shown to be effective in meeting water delivery target in North China PlainMRP contributes to the recovery of groundwater level in North China PlainSensitivity of MRP effectiveness in water delivery and groundwater recovery is examined

Drought is the most recurrent and destructive hazard in arid and semiarid regions and will only become more complex under climate change. It is vital to characterize the various types of drought, to investigate the potential factors affecting different types of drought, and to assess the relationship between drought types. In this study, the Standardized Precipitation Index and the Standardized Runoff Index were used to characterize meteorological and hydrological drought, respectively, to investigate drought characteristics and mechanisms in 17 catchments on the Loess Plateau from 1961 to 2013. Furthermore, the propagation time from meteorological to hydrological drought was explored and the potential factors influencing drought propagation time were investigated. The results indicate that the Loess Plateau has experienced an increased tendency toward both meteorological and hydrological droughts over the period 1961–2013, with hydrological drought more serious than meteorological drought at various drought assessment time scales. Moreover, average drought duration and severity were greater for hydrological drought than meteorological drought. Maximum 5‐day precipitation (Rx5day) was the dominant extreme climate index for explaining variance in meteorological drought at the annual time scale. Owing to the greater complexity underlying hydrological drought, Rx5day, the number of warm days (Tx90p), and the number of warm nights (Tn90p) all contribute to the variance in hydrological drought. Furthermore, the percentage of forested land had a significant positive association (p< 0.001) with propagation time, whereas the percentage of land given over to pasture had a significant negative association (p< 0.001) with propagation time. Loess Plateau has experienced an increased tendency toward both meteorological and hydrological droughts over the period 1961–2013Average drought duration and severity were greater for hydrological drought than meteorological droughtChanges in land use and land cover can alter the propagation time from meteorological to hydrological drought

In this study, we used a multiyear normalized difference vegetation index data set (1981–2015), and corresponding data sets for observed climatic factors, to investigate vegetation‐climate interactions on the Loess Plateau using an innovative nonlinear Granger causality approach. From eight selected local near‐surface climate factors, we found that the diurnal temperature range, precipitation, and relative humidity were the dominant climate factors influencing the variability of vegetation on the plateau, Granger causing changes in vegetation over 26%, 49%, and 23% of the plateau, respectively. The reverse causality analysis showed that all of the climate factors except precipitation and sunshine hours were sensitive to normalized difference vegetation index on the Loess Plateau. Taken together, these results suggest that there is indeed an interaction between the local climate and changes in vegetation on the Loess Plateau. An innovative nonlinear Granger causality approach was used to investigate vegetation‐climate interactions on the Loess PlateauThere is indeed an interaction between the local climate and changes in vegetation on the Loess PlateauStationarity and seasonal periodicity removing is the prerequisites for the Granger causality analysis

The middle route of the south-to-north water diversion projectgreatly ease the conflict between supply and demand of water resources in Beijing, as an important supporting engineering of that, the integrated scheduling of the Miyun reservoir regulation and storage engineering is of great significance. In order to strengthen the scheduling management of engineering and realize the safety and economic operation of the project, using state space analysis, mathematical optimization, automatic control technology and other technologies to establish a "simulation, scheduling and control" technology system, which includes the multi-process simulation technology, multi-dimensional optimal scheduling technology and operation control technology of free-surface-pressurized flow and ice-water coupling in the water delivery system of cascade pumping stations. Research results applied to dumped station operation of the Tundian pumping station and intelligent scheduling system platform, which have strong applicability, can provide technical support for the scheduling management of the Miyun reservoir regulation and storage engineering and realize the goal of engineering safety and economic operation.

A novel Cu-Zn-TiO2nanotube array (TNTA) polymetallic nanoelectrode, intended to improve the electrochemical nitrate removal efficiency, was fabricated. The nanoelectrode was fabricated by plating Cu onto a Ti nanoelectrode and then plating Zn onto the Cu/Ti bilayer electrode produced. The Ti nanostructures on the Cu-Zn-TNTA nanoelectrode surface gave the nanoelectrode a large specific surface area, and the Zn and Cu gave the nanoelectrode a high electrocatalytic activity for reducing nitrate. Scanning electron microscopy images showed that the Cu-Zn-TNTA polymetallic nanoelectrode had a honeycomb structure with spongy deposits. X-ray diffractometry results showed that the Cu-Zn-TNTA nanoelectrode predominantly contained Cu, O, Ti, and Zn. The nitrate removal efficiency of the Cu-Zn-TNTA nanoelectrode was 345.7% of the removal efficiency for a Ti nanoelectrode. The presence of NaCl allowed both the cathodic reduction of nitrate and the anodic oxidation of the ammonia and nitrite byproducts to be achieved with high removal efficiencies, especially using an IrO2anode. In the present of NaCl, nitrate removal rate was 93.4% in current density of 30 mA/cm2after 90 min. Nitrate was completely removed using the IrO2anode, and little ammonia was detected in the treated solution. The reduction efficiency increased slightly as the initial nitrate concentration increased through the range 20–100 mg/L, and the pH had little effect on the nitrate reduction efficiency.