Runoff reduction in most river basins in China has become a hotpot in recent years. The Gushanchuan river, a primary tributary of the middle Yellow river, Northern China, showed a significant downward trend in the last century. Little is known regarding the relative contributions of changing environment to the observed hydrological trends and response on the runoff generation process in its watershed. On the basis of observed hydrological and meteorological data from 1965–2010, the Mann-Kendall trend test and climate elasticity method were used to distinguish the effects of climate change and human activities on runoff in the Gushanchuan basin. The results indicate that the runoff in the Gushanchuan Basin has experienced significant declines as large as 77% from 1965 to 2010, and a mutation point occurred around 1997; the contribution rate of climate change to runoff change is 12.9–15.1%, and the contribution rate of human activities to runoff change is 84.9–87.1%. Then we divided long-term data sequence into two stages around the mutation point, and analyzed runoff generation mechanisms based on land use and cover changes (LUCC). We found that the floods in the Gushanchuan Basin were still dominated by Excess-infiltration runoff, but the proportion in 1965–1997 and 1998–2010 decreased gradually (68.46% and 45.83% in turn). The proportion of Excess-storage runoff and Mixed runoff has increased, which means that the runoff is made up of more runoff components. The variation law of the LUCC indicates that the forest area increased by 49.61%, the confluence time increased by 50.42%, and the water storage capacity of the watershed increased by 30.35%. Full article

The Water Framework Directive (WFD) is typically a framework directive that tries to encourage integration of policies for water quality and agriculture. Nutrients (nitrates, phosphates) from agricultural sources remain a ‘wicked problem’ in realizing the aims of the WFD, partly because the directive has to rely on other, neighboring policies to tackle to problem pressure of nutrients; it seems to lack instruments and measures to directly intervene in relevant agricultural policies. This contribution describes the different governance approaches of five member states and regions (The Netherlands, Flanders in Belgium, Lower Saxony- in Germany, Denmark and Ireland) to the nutrients problem and specifically focuses on the relationship between the nature of governance and the nature of measures taken. On the one hand, countries can vary in terms of a more consensual or antagonistic approach to dealing with water quality and diffuse pollution by agriculture, and emphasize more integration or separation in organization and programs. On the other hand, they can vary in the ‘outcomes’ in terms of more source-based measures or effect-based measures and the emphasis in policy instruments used. This article is based on the screening of policy documents, 44 interviews and several (international) feedback workshops. We found a great variety in governance approaches, while the nature of measures, in terms of source-based and effect-based, is only slightly different. On closer inspection, there are interesting differences in the consensual or antagonist discourses and differences in the use of more mandatory instruments or area-based policies. In many countries, the major challenge is to strike a balance between taking source-based measures, where necessary, and accommodating the difficult situations farmers very often find themselves in, as the reduction of nutrients (as a source-based measure) use can lead to lower yields and higher costs for manure disposal. Full article

Biochemical methane potential (BMP) tests are commonly applied to evaluate the recoverable amount of methane from a substrate. Standardized protocols require inclusion of a positive control with a known BMP to check the experimental setup and execution, as well as the performance of the inoculum. Only if the BMP of the positive control is within the expected range is the entire test validated. Besides ignorance of this requirement, limited availability of the standard positive control microcrystalline cellulose might be the main reason for neglecting a positive control. To address this limitation, eight widely available grocery store products have been tested as alternative positive controls (APC) to demonstrate their suitability. Among them, Tic Tacs and gummi bears were very promising, although they are dominated by easily degradable sugars and so do not test for hydrolytic performance. Coffee filters exhibited a similar performance to microcrystalline cellulose, while whole milk might be chosen when a more balanced carbohydrate:protein:lipid ratio is important. Overall, the approach of predicting the BMP of a substrate based on the nutritional composition provided on the product packaging worked surprisingly well: BMP of the eight tested products was 81–91% of theoretical maximum BMP based on nutritional information and generic chemical formulas for carbohydrates, proteins, and lipids. Full article

The vadose zone is the main host of surface and subsurface water exchange and has important implications for ecosystems functioning, climate sciences, geotechnical engineering, and water availability issues. Geophysics provides a means for investigating the subsurface in a non-invasive way and at larger spatial scales than conventional hydrological sensors. Time-lapse hydrogeophysical applications are especially useful for monitoring flow and water content dynamics. Largely dominated by electrical and electromagnetic methods, such applications increasingly rely on seismic methods as a complementary approach to describe the structure and behavior of the vadose zone. To further explore the applicability of active seismics to retrieve quantitative information about dynamic processes in near-surface time-lapse settings, we designed a controlled water infiltration experiment at the Ploemeur Hydrological Observatory (France) during which successive periods of infiltration were followed by surface-based seismic and electrical resistivity acquisitions. Water content was monitored throughout the experiment by means of sensors at different depths to relate the derived seismic and electrical properties to water saturation changes. We observe comparable trends in the electrical and seismic responses during the experiment, highlighting the utility of the seismic method to monitor hydrological processes and unsaturated flow. Moreover, petrophysical relationships seem promising in providing quantitative results. Full article

Magdalena River surface water and shoreline sediments were sampled for microplastic particles at three locations in the city of Neiva, Colombia: upstream, city center, and downstream of the raw wastewater outflow. The absence of an industrial and manufacturing sector in Neiva provided an opportunity to assess the impact of upstream agricultural practices, as well as municipal activities such as wastewater outflow and laundry washing, on the quantity, polymer composition, and morphology of microplastic particles produced per capita and entering a river system. Microplastic particle concentrations increased with downstream distance, with microfiber concentrations ranging from 0.097 to 0.135 fibers/L in the river water and 25.5 to 102.4 fibers/kg in shoreline sediment. Microplastic fragment concentrations were 0.013–0.028 fragments/L in surface water and 10.4–12.7 fragments/kg of sediment. Raman microscope and scanning electron microscopy identified the relative composition of the polymers comprising the microplastic particles was similar regardless of sampling site or whether the sample was collected from the surface water or shoreline sediments, with polypropylene and polyethylene comprising at least 75% of the total polymers in all samples. Average fiber widths of < 20 µm in all but one sample, along with the lack of acrylic and polyester fibers used predominantly in woven synthetic textiles, indicated that the degradation of nonwoven synthetic textiles is the predominant origin of these microplastic fibers in the Magdalena River. Full article

Global change, that results from population growth, global warming and land use change (especially rapid urbanization), is directly affecting the complexity of water resources management problems and the uncertainty to which they are exposed. Both, the complexity and the uncertainty, are the result of dynamic interactions between multiple system elements within three major systems: (i) the physical environment; (ii) the social environment; and (iii) the constructed infrastructure environment including pipes, roads, bridges, buildings, and other components. Recent trends in dealing with complex water resources systems include consideration of the whole region being affected, explicit incorporation of all costs and benefits, development of a large number of alternative solutions, and the active (early) involvement of all stakeholders in the decision-making. Systems approaches based on simulation, optimization, and multi-objective analyses, in deterministic, stochastic and fuzzy forms, have demonstrated in the last half of last century, a great success in supporting effective water resources management. This paper explores the future opportunities that will utilize advancements in systems theory that might transform management of water resources on a broader scale. The paper presents performance-based water resources engineering as a methodological framework to extend the role of the systems approach in improved sustainable water resources management under changing conditions (with special consideration given to rapid climate destabilization). An illustrative example of a water supply network management under changing conditions is used to convey the basic principles of performance-based water resources engineering methodology. Full article

Climate change (CC) and land use/cover change (LUCC) are the main drivers of streamflow change. In this study, the effects of CC and LUCC on streamflow regime as well as their spatial variability were examined by using the Distributed Hydrology Soil Vegetation Model (DHSVM) for the Beichuan River Basin in the northeast Tibetan Plateau. The results showed that CC increased annual and maximum streamflow in the upstream but decreased them in the downstream. CC also enhanced minimum streamflow in the whole river basin and advanced the occurrence of daily minimum streamflow. Temperature change exerted greater influence on streamflow regime than wind speed change did in most situations, but the impact of wind speed on streamflow reflected the characteristics of accumulative effects, which may require more attention in future, especially in large river basins. As for LUCC, cropland expansion and reservoir operation were the primary reasons for streamflow reduction. Cropland expansion contributed more to annual mean streamflow change, whereas reservoir operation greatly altered monthly streamflow pattern and extreme streamflow. Reservoir regulation also postponed the timing of minimum streamflow and extended durations of average, high, and low streamflow. Spatially, CC and LUCC played predominant roles in the upstream and the downstream, respectively. Full article

Cyanobacterial blooms are considered a major threat to global water security with documented impacts on lake ecosystems and public health. Given that cyanobacteria possess highly adaptive traits that favor them to prevail under different and often complicated stressor regimes, predicting their abundance is challenging. A dataset from 822 Northern European lakes is used to determine which variables better explain the variation of cyanobacteria biomass (CBB) by means of stepwise multiple linear regression. Chlorophyll-a (Chl-a) and total nitrogen (TN) provided the best modelling structure for the entire dataset, while for subsets of shallow and deep lakes, Chl-a, mean depth, TN and TN/TP explained part of the variance in CBB. Path analysis was performed and corroborated these findings. Finally, CBB was translated to a categorical variable according to risk levels for human health associated with the use of lakes for recreational activities. Several machine learning methods, namely Decision Tree, K-Nearest Neighbors, Support-vector Machine and Random Forest, were applied showing a remarkable ability to predict the risk, while Random Forest parameters were tuned and optimized, achieving a 95.81% accuracy, exceeding the performance of all other machine learning methods tested. A confusion matrix analysis is performed for all machine learning methods, identifying the potential of each method to correctly predict CBB risk levels and assessing the extent of false alarms; random forest clearly outperforms the other methods with very promising results. Full article

Pollution of ground-and surface waters with nitrates from agricultural sources poses a risk to drinking water quality and has negative impacts on the environment. At the national scale, the gross nitrogen budget (GNB) is accepted as an indicator of pollution caused by nitrates. There is, however, little common EU-wide knowledge on the budget application and its comparability at the farm level for the detection of ground-and surface water pollution caused by nitrates and the monitoring of mitigation measures. Therefore, a survey was carried out among experts of various European countries in order to assess the practice and application of fertilization planning and nitrogen budgeting at the farm level and the differences between countries within Europe. While fertilization planning is practiced in all of the fourteen countries analyzed in this paper, according to current legislation, nitrogen budgets have to be calculated only in Switzerland, Germany and Romania. The survey revealed that methods of fertilization planning and nitrogen budgeting at the farm level are not unified throughout Europe. In most of the cases where budgets are used regularly (Germany, Romania, Switzerland), standard values for the chemical composition of feed, organic fertilizers, animal and plant products are used. The example of the Dutch Annual Nutrient Cycling Assessment (ANCA) tool (and partly of the Suisse Balance) shows that it is only by using farm-specific “real” data that budgeting can be successfully applied to optimize nutrient flows and increase N efficiencies at the farm level. However, this approach is more elaborate and requires centralized data processing under consideration of data protection concerns. This paper concludes that there is no unified indicator for nutrient management and water quality at the farm level. A comparison of regionally calculated nitrogen budgets across European countries needs to be interpreted carefully, as methods as well as data and emission factors vary across countries. For the implementation of EU nitrogen-related policies—notably, the Nitrates Directive—nutrient budgeting is currently ruled out as an entry point for legal requirements. In contrast, nutrient budgets are highlighted as an environment indicator by the OECD and EU institutions. Full article

Runoff from Arctic rivers constitutes a major freshwater influx to the Arctic Ocean. In these nival-dominated river systems, the majority of annual discharge is released during the spring snowmelt period. The circulation regime of the salinity-stratified Arctic Ocean is connected to global earth–ocean dynamics through thermohaline circulation; hence, variability in freshwater input from the Arctic flowing rivers has important implications for the global climate system. Daily discharge data from each of the four largest Arctic-draining river watersheds (Mackenzie, Ob, Lena and Yenisei; herein referred to as MOLY) are analyzed to identify historic changes in the magnitude and timing of freshwater input to the Arctic Ocean with emphasis on the spring freshet. Results show that the total freshwater influx to the Arctic Ocean increased by 89 km³/decade, amounting to a 14% increase during the 30-year period from 1980 to 2009. A distinct shift towards earlier melt timing is also indicated by proportional increases in fall, winter and spring discharges (by 2.5%, 1.3% and 2.5% respectively) followed by a decrease (by 5.8%) in summer discharge as a percentage of the mean annual flow. This seasonal increase in discharge and earlier pulse onset dates indicates a general shift towards a flatter, broad-based hydrograph with earlier peak discharges. The study also reveals that the increasing trend in freshwater discharge to the Arctic Ocean is not solely due to increased spring freshet discharge, but is a combination of increases in all seasons except that of the summer. Full article

Rainwater harvesting systems are often used as both an alternative water source and a stormwater management tool. Many studies have focused on the water-saving potential of these systems, but research into aspects that impact stormwater retention—such as demand patterns and climate change—is lacking. This paper investigates the short-term impact of demand on both water supply and stormwater management and examines future and potential performance over a longer time scale using climate change projections. To achieve this, data was collected from domestic rainwater harvesting systems in Broadhempston, UK, and used to create a yield-after-spillage model. The validation process showed that using constant demand as opposed to monitored data had little impact on accuracy. With regards to stormwater management, it was found that monitored households did not use all the non-potable available water, and that increasing their demand for this was the most effective way of increasing retention capacity based on the modelling study completed. Installing passive or active runoff control did not markedly improve performance. Passive systems reduced the outflow to greenfield runoff for the longest time, whereas active systems increased the outflow to a level substantially above roof runoff in the 30 largest events. Full article

Developing a general, predictive understanding of ecological systems requires knowing how much structural and functional relationships can cross scales and contexts. Here, we introduce the CROSSLINK project that investigates the role of forested riparian buffers in modified European landscapes by measuring a wide range of ecosystem attributes in stream-riparian networks. CROSSLINK involves replicated field measurements in four case-study basins with varying levels of human development: Norway (Oslo Fjord), Sweden (Lake Mälaren), Belgium (Zwalm River), and Romania (Argeş River). Nested within these case-study basins include multiple, independent stream-site pairs with a forested riparian buffer and unbuffered section located upstream, as well as headwater and downstream sites to show cumulative land-use impacts. CROSSLINK applies existing and bespoke methods to describe habitat conditions, biodiversity, and ecosystem functioning in aquatic and terrestrial habitats. Here, we summarize the approaches used, detail protocols in supplementary materials, and explain how data is applied in an optimization framework to better manage tradeoffs in multifunctional landscapes. We then present results demonstrating the range of riparian conditions present in our case-study basins and how these environmental states influence stream ecological integrity with the commonly used macroinvertebrate Average Score Per Taxon (ASPT) index. We demonstrate that a qualitative index of riparian integrity can be positively associated with stream ecological status. This introduction to the CROSSLINK project shows the potential for our replicated study with its panoply of ecosystem attributes to help guide management decisions regarding the use of forested riparian buffers in human-impacted landscapes. This knowledge is highly relevant in a time of rapid environmental change where freshwater biodiversity is increasingly under pressure from a range of human impacts that include habitat loss, pollution, and climate change. Full article

Climate change might potentially cause extreme weather events to become more frequent and intense. It could also enhance water scarcity and reduce food security. More efficient water management techniques are thus required to ensure a stable food supply and quality. Maintaining proper soil water content and soil temperature is necessary for efficient water management in agricultural practices. The usage of water and fertilizers can be significantly improved with a precise water content prediction tool. In this study, we proposed a new framework that combines weather forecast data, numerical models, and machine learning methods to simulate and predict the soil temperature and volumetric water content in a greenhouse. To test the framework, we performed greenhouse experiments with cherry tomatoes. The numerical models and machine learning methods we selected were Newton’s law of cooling, HYDRUS-1D, the random forest model, and the ICON (inferring connections of networks) model. The measured air temperature, soil temperature, and volumetric water content during the cultivation period were used for model calibration and validation. We compared the performances of the models for soil temperature and volumetric water content predictions. The results showed that the random forest model performed a more accurate prediction than other methods under the limited information provided from greenhouse experiments. This approach provides a framework that can potentially learn best water management practices from experienced farmers and provide intelligent information for smart greenhouse management. Full article

Against the background of global climate change and anthropogenic stresses, extreme climate events (ECEs) are projected to increase in both frequency and intensity. Precipitation is one of the main climate parameters for ECE analysis. However, accurate precipitation information for extreme climate events research from dense rain gauges is still difficult to obtain in mountainous or economically disadvantaged regions. Satellite precipitation products (SPPs) with high spatial and temporal resolution offer opportunities to monitor ECE intensities and trends on large spatial scales. In this study, the accuracies of seven SPPs on multiple spatiotemporal scales in the Yangtze River Basin (YRB) during the period of 2003–2017 are evaluated, along with their ability to capture ECE characteristics. The seven products are the Tropical Rainfall Measuring Mission, Climate Hazards Group InfraRed Precipitation with Station Data (CHIRPS) (25), CHIRPS (05), Climate Prediction Center Morphing (CMORPH), Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks (PERSIANN)-Climate Data Record, PERSIANN-Cloud Classification System, and Global Precipitation Measurement (GPM) IMERG. Rain gauge precipitation data provided by the China Meteorological Administration are adopted as reference data. Various statistical evaluation metrics and different ECE indexes are used to evaluate and compare the performances of the selected products. The results show that CMORPH has the best agreement with the reference data on the daily and annual scales, but GPM IMERG performs relatively well on the monthly scale. With regard to ECE monitoring in the YRB, in general, GPM IMERG and CMORPH provide higher precision. As regards the spatial heterogeneity of the SPP performance in the YRB, most of the examined SPPs have poor accuracy in the mountainous areas of the upper reach. Only CMORPH and GPM IMERG exhibit superior performance; this is because they feature an improved inversion precipitation algorithm for mountainous areas. Furthermore, most SPPs have poor ability to capture extreme precipitation in the estuaries of the lower reach and to monitor drought in the mountainous areas of the upper reach. This study can provide a reference for SPP selection for ECE analysis. Full article

This study reports the changes in glacier extent and streamflow similar to many Himalayan studies, but takes the unusual step of also linking these to downstream land use changes in Kashmir Valley. This study assessed changes in the area, snout, and equilibrium line altitude (ELA) of four parts of the Kolahoi Glacier using earth observation data from 1962 to 2018. Changes in the discharge of the two streams flowing out from Kolahoi Glacier into the Jhelum basin were also assessed between 1972 and 2018. Additionally, satellite data was used to track the downstream land system changes concerning agriculture, orchards, and built-up areas between 1980 and 2018. This analysis suggested a cumulative deglaciation of 23.6% at a rate of 0.42% per year from 1962 to 2018. The snout of two larger glaciers, G1 and G2, retreated at a rate of 18.3 m a⁻¹ and 16.4 m a⁻¹, respectively, from 1962 to 2018, although the rate of recession accelerated after 2000. Our analysis also suggested the upward shift of ELA by ≈120 m. The streamflows measured at five sites showed statistically significant depleting trends that have been a factor in forcing extensive land system changes downstream. Although the area under agriculture in Lidder watershed shrunk by 39%, there was a massive expansion of 176% and 476% in orchards and built-up areas, respectively, from 1980 to 2018. The conversion of irrigation-intensive agriculture lands (rice paddy) to less water-intensive orchards is attributed to economic considerations and depleting streamflow. Full article

Low-impact development (LID) has been widely used at both site-specific and local scales to try and mitigate the impact of urban stormwater runoff caused by increasing impervious urban areas. Recently, the concept of a “sponge city” was proposed by the Chinese government, which includes LID controls at the source, a pipe drainage system midway, and a drainage system for excess stormwater at the terminal. There is a need to evaluate the effectiveness of sponge city construction at the large urban catchment scale, particularly with different spatial distributions of LIDs that reduce directly connected impervious areas (DCIAs). In this paper, the performances of five design scenarios with different spatial distributions but same sizes of LID controls at the urban catchment scale were analyzed using a geographic information system (GIS) of the United States Environmental Systems Research Institute (ESRI)—based Storm Water Management Model (SWMM) of the United States Environmental Protection Agency (USEPA) and MIKE 11 of Danish Hydraulic Institute (DHI) in Xining City, China. Results confirmed the effectiveness of sponge city construction in reducing the urban stormwater runoff. The hydrological performance reduction was positively correlated and linearly dependent on DCIA reduction. Peak flow reduction was most sensitive to DCIA reduction, followed by runoff volume and peak time. As rainfall intensity increased, the hydrological performance was more sensitive to rainfall intensity than DCIA reduction. Results of this study provide new insights for stormwater managers to implement LID more effectively at the urban catchment scale. Full article

Urban flooding, caused by unusually intense rainfall and failure of storm water drainage, has become more frequent and severe in many cities around the world. Most of the earlier studies focused on overland flooding caused by intense rainfall, with little attention given to floods caused by failures of the drainage system. However, the drainage system contributions to flood vulnerability have increased over time as they aged and became inadequate to handle the design floods. Adaption of the drainages for such vulnerability requires a quantitative assessment of their contribution to flood levels and spatial extent during and after flooding events. Here, we couple the one-dimensional Storm Water Management Model (SWMM) to a new flood inundation and recession model (namely FIRM) to characterize the spatial extent and depth of manhole flooding and recession. The manhole overflow from the SWMM model and a fine-resolution elevation map are applied as inputs in FIRM to delineate the spatial extent and depth of flooding during and aftermath of a storm event. The model is tested for two manhole flooding events in the City of Edmonds in Washington, USA. Our two case studies show reasonable match between the observed and modeled flood spatial extents and highlight the importance of considering manholes in urban flood simulations. Full article

The water crisis has become increasingly serious, particularly in arid and semiarid areas. Agricultural water productivity (AWP) is an important indicator for evaluating water use efficiency and agricultural water management. This study uses water consumption derived from satellite data, combined with statistical survey information, to analyze the spatiotemporal variations and driving factors of AWP at the region and county scales over the past 15 years (2002–2015) in the Turpan region (China). The results showed the increasing change trends of AWP throughout Turpan and its three counties. A multiple regression analysis was applied to evaluate AWP, agricultural production and water consumption with driving factors. The contribution of agricultural factors (fertilizer amount, pesticide use and irrigation area) was 86.3% for change of production and 93.3% for change of water consumption in Turpan. The synchronous changes associated with the similar factor contributions resulted in a nonsignificant change in AWP for the whole region. However, the significant increase in AWP in Toksun County was caused by a weakened effect of synchronous changes due to the difference between the largest contributing factors (irrigation area for production at 29.3% and temperature for water consumption at 35.4%). The different change trends of the AWP at regional and county levels indicated that agricultural planting structure adjustment could be an effective way to improve water productivity. This paper provides objective and new information to understand the effects of AWP changes at regional and county scales, which is beneficial for irrigation agriculture development in Turpan. Full article

Rainfall runoff models are frequently used for design processes for urban infrastructure. The most sensitive input for these models is precipitation data. Therefore, it is crucial to account for temporal and spatial variability of rainfall events as accurately as possible to avoid misleading simulation results. This paper aims to show the significant errors that can occur by using rainfall measurement resolutions in urban environments that are too coarse. We analyzed the spatial variability of rainfall events from two years with the validated data of 22 rain gauges spread out over an urban catchment of 125 km². By looking at the interstation correlation of the rain gauges for different classes of rainfall intensities, we found that rainfall events with low and intermediate intensities show a good interstation correlation. However, the correlation drops significantly for heavy rainfall events suggesting higher spatial variability for more intense rainstorms. Further, we analyzed the possible deviation from the spatial rainfall interpolation that uses all available rain gauges when reducing the number of rain gauges to interpolate the spatial rainfall for 24 chosen events. With these analyses we found that reducing the available information by half results in deviations of up to 25% for events with return periods shorter than one year and 45% for events with longer return periods. Assuming uniformly distributed rainfall over the entire catchment resulted in deviations of up to 75% and 125%, respectively. These findings are supported by the work of past research projects and underline the necessity of a high spatial measurement density in order to account for spatial variability of intense rainstorms. Full article

This study aims to evaluate the sorption characteristics of ${\mathrm{NH}}_4^{+}$ -N and ${\mathrm{PO}}_4^{3-}$ -P onto the surface of natural zeolites coming from Chile and their potential application in the subsurface-flow treatment wetlands for wastewater treatment in rural areas. For this purpose, adsorption experiments onto the zeolite were developed in batch assays. The effects of the adsorbent quantity (20 g and 50 g) and particle size (0.2–1.0 mm; 1.5–3.0 mm, and 5.0–8.0 mm) were evaluated in terms of adsorption capacity at different NH₄⁺-N and PO₄⁻³-P concentrations. Then, the obtained laboratory results were adjusted to theoretical models: Saturation-growth-rate and Langmuir. The saturation adsorption of NH₄⁺-N on the zeolite increases at the same time that the initial concentration increases for the same zeolite quantity; however, the saturation values were similar between the different zeolite sizes tested. For PO₄⁻³-P, the adsorption did not have a direct relationship with the initial concentration nor zeolite quantity and better results were only achieved for zeolite sizes of 1.5–3.0 mm. Regarding the Langmuir model, sizes of 1.5–3.0 mm had the best adsorption characteristics, with the maximum adsorption capacity of up to 1.58 mg/g for NH₄⁺-N and up to 0.08 mg/g for PO₄⁻³-P. Therefore, a new material—a natural zeolite from the Maule Region of Chile—is described as a potential support medium for treatment wetlands. Full article

The application of statistical and Machine Learning models plays a critical role in planning and decision support processes for efficient and reliable Water Distribution Network (WDN) management. Failure models can provide valuable information for prioritizing system rehabilitation even in data scarcity scenarios, such as developing countries. Few studies have analyzed the performance of more than two models, and examples of case studies in developing countries are insufficient. This study compares various statistical and Machine Learning models to provide useful information to practitioners for the selection of a suitable pipe failure model according to information availability and network characteristics. Three statistical models (i.e., Linear, Poisson, and Evolutionary Polynomial Regressions) were used for failure prediction in groups of pipes. Machine Learning approaches, particularly Gradient-Boosted Tree (GBT), Bayes, Support Vector Machines and Artificial Neuronal Networks (ANNs), were compared in predicting individual pipe failure rates. The proposed approach was applied to a WDN in Bogotá (Colombia). The statistical models showed an acceptable performance (R² between 0.695 and 0.927), but the Poisson Regression was the most suitable for predicting failures in pipes with lower failure rates. Regarding Machine Learning models, Bayes and ANNs exhibited low performance in the prediction of pipe failure condition. The GBT approach had the best performing classifier. Full article

To simulate the dynamics of two-dimensional dam-break flow on a dry horizontal bed, we use a smoothed particle hydrodynamics model implementing two advanced boundary treatment techniques: (i) a semi-analytical approach, based on the computation of volume integrals within the truncated portions of the kernel supports at boundaries and (ii) an extension of the ghost-particle boundary method for mobile boundaries, adapted to free-slip conditions. The trends of the free surface along the channel, and of the impact wave pressures on the downstream vertical wall, were first validated against an experimental case study and then compared with other numerical solutions. The two boundary treatment schemes accurately predicted the overall shape of the primary wave front advancing along the dry bed until its impact with the downstream vertical wall. Compared to data from numerical models in the literature, the present results showed a closer fit to an experimental secondary wave, reflected by the downstream wall and characterized by complex vortex structures. The results showed the reliability of both the proposed boundary condition schemes in resolving violent wave breaking and impact events of a practical dam-break application, producing smooth pressure fields and accurately predicting pressure and water level peaks. Full article

For countries in Southeast Asia that mainly rely on surface water as their water resource, changes in weather patterns and hydrological systems due to climate change will cause severely decreased water resource availability. Warm weather triggers more water use and exacerbates the extraction of water resources, which will change the operation patterns of water usage and increase demand, resulting in water scarcity. The occurrence of prolonged drought upsets the balance between water supply and demand, significantly increasing the vulnerability of regions to damaging impacts. The objectives of this study are to identify trends and determine the impacts of extreme drought events on water levels for the major important water dams in the northern part of Borneo, and to assess the risk of water insecurity for the dams. In this context, remote sensing images are used to determine the degree of risk of water insecurity in the regions. Statistical methods are used in the analysis of daily water levels and rainfall data. The findings show that water levels in dams on the North and Northeast Coasts of Borneo are greatly affected by the extreme drought climate caused by the Northeast Monsoon, with mild to the high risk recorded in terms of water insecurity, with only two of the water dams being water-secure. This study shows how climate change has affected water availability throughout the regions. Full article

Dam-break wave propagation usually occurs over irregular topography, due for example to natural contraction-expansion of the river bed and to the presence of natural or artificial obstacles. Due to limited available dam-break real-case data, laboratory and numerical modeling studies are significant for understanding this type of complex flow problems. To contribute to the related field, a dam-break flow over a channel with a contracting reach was investigated experimentally and numerically. Laboratory tests were carried out in a smooth rectangular channel with a horizontal dry bed for three different lateral contraction geometries. A non-intrusive digital imaging technique was utilized to analyze the dam-break wave propagation. Free surface profiles and time variation of water levels in selected sections were obtained directly from three synchronized CCD video camera records through a virtual wave probe. The experimental results were compared against the numerical solution of VOF (Volume of Fluid)-based Shallow Water Equations (SWEs) and Reynolds-Averaged Navier-Stokes (RANS) equations with the k-ε turbulence model. Good agreements were obtained between computed and measured results. However, the RANS solution shows a better correspondence with the experimental results compared with the SWEs one. The presented new experimental data can be used to validate numerical models for the simulation of dam-break flows over irregular topography. Full article

Groundwater is a major source of drinking and agricultural water supply in arid and semiarid regions. Poor groundwater quality can be a threat to human health especially when it is combined with hazardous pollutants like heavy metals. In this study, an innovative method involving entropy weighted groundwater quality index for both physicochemical and heavy metal content was used for a semiarid region. The entropy weighted index was used to assess the groundwater’s suitability for drinking and irrigation purposes. Thus, groundwater from 19 sampling sites was used for analyses of physicochemical properties (electrical conductivity—EC, pH, K⁺, Ca²⁺, Na⁺, SO₄²⁻, Cl⁻, HCO₃⁻, TDS, NO₃⁻, F⁻, biochemical oxygen demand—BOD, dissolved oxygen—DO, and chemical oxygen demand—COD) and heavy metal content (As, Ca, Sb, Se, Zn, Cu, Ba, Mn, and Cr). To evaluate the overall pollution status in the region, heavy metal indices such as the modified heavy metal pollution index (m-HPI), heavy metal evaluation index (HEI), Nemerow index (NeI), and ecological risks of heavy metals (ERI) were calculated and compared. The results showed that Cd concentration plays a significant role in negatively affecting the groundwater quality. Thus, three wells were classified as poor water quality and not acceptable for drinking water supply. The maximum concentration of heavy metals such as Cd, Se, and Sb was higher than permissible limits by the World Health Organization (WHO) standards. However, all wells except one were suitable for agricultural purposes. The advantage of the innovative entropy weighted groundwater quality index for both physicochemical and heavy metal content, is that it permits objectivity when selecting the weights and reduces the error that may be caused by subjectivity. Thus, the new index can be used by groundwater managers and policymakers to better decide the water’s suitability for consumption. Full article

The end clearance of the impeller is one of the most important structural parameters in the hydraulic design of a high-speed electrical submersible pump (ESP). In this paper, an ESP with a rotating speed of 6000 r/min was taken as the research object. Numerical calculations were carried out for five different end clearance conditions of 0.1 mm, 0.3 mm, 0.6 mm, 0.9 mm, and 1.2 mm, respectively, to obtain the performance and internal flow field under different situation. The simulation results were verified by the pump performance experiment. It showed that the increase of the end clearance led to a decrease of the head and efficiency of the electrical submersible pump. Through the analysis of the internal flow field, it was found that the existence of the end clearance reduced the flow rate and caused free pre-whirl. With the increase of the end clearance, the phenomenon of de-flow in the diffuser passage was aggravated, which further reduced the performance of the electrical submersible pump. Finally, the reasonable recommended value of the end clearance was given, which facilitated the optimization design and engineering application of the high-speed ESP. Full article

Sludge is a by-product of municipal wastewater treatment plants (WWTPs) and its management contributes significantly to the operating costs. Large WWTPs usually have anaerobic sludge digesters to valorize sludge as methane and to reduce its mass. However, the low methane market price opens the possibility for generating other high value-added products from the organic matter in sludge, such as polyhydroxyalkanoates (PHAs). In this work, the economic feasibility of retrofitting two types of WWTPs to convert them into biofactories of crude PHAs was studied. Two cases were analyzed: (a) a large WWTP with anaerobic sludge digestion; and (b) a small WWTP where sludge is only dewatered. In a two-stage PHA-production system (biomass enrichment plus PHAs accumulation), the minimum PHAs cost would be 1.26 and 2.26 US$/kg PHA-crude for the large and small WWTPs, respectively. In a single-stage process, where a fraction of the secondary sludge (25%) is directly used to accumulate PHAs, the production costs would decrease by around 15.9% (small WWTPs) and 19.0% (large WWTPs), since capital costs associated with bioreactors decrease. Sensitivity analysis showed that the PHA/COD (Chemical Oxygen Demand) yield is the most crucial parameter affecting the production costs. The energy, methane, and sludge management prices also have an essential effect on the production costs, and their effect depends on the WWTP’s size. Full article

In terms of evident climate change and human activities, investigating changes in lakes and reservoirs is critical for sustainable protection of water resources and ecosystem management over the Nenjiang watershed (NJW), an eco-sensitive semi-arid region and the third-largest inland waterbody cluster in China. In this study, we established a multi-temporal dataset documenting lake and reservoir (area ≥ 1 km²) changes in this region using an object-oriented image classification method and Landsat series images from 1980 to 2015. Using the structural equation model (SEM), we analyzed the diverse impacts of climatic and anthropogenic variables on lake changes. Results indicated that lakes experienced significant changes with fluctuations over the past 35 years including obvious declines in the total area (by 42%) and number (by 51%) from 1980 to 2010 and a slight increase in the total lake area and number from 2010 to 2015. More than 235 lakes in the size class of 1–10 km² decreased to small lakes (area < 1 km²), while 59 lakes covering 243.75 km² disappeared. Total reservoir area and number had continuous increases during the investigated 35 years, with an areal expansion of 54.9% from 919 km² to 1422 km², and a number increase by 65.3% from 78 to 129. The SEM revealed that the lake area in the NJW had a significant correlation with the mean annual precipitation (MAP), suggesting that the MAP decline clarified most of the lake shrinkage in the NJW. Furthermore, agricultural consumption of water had potential impacts on lake changes, suggested by the significant relationship between cropland area and lake area. Full article

This study addresses the visible light-induced bacterial inactivation kinetics over a Bi₂WO₆ synthesized catalyst. The systematic investigation was undertaken with Bi₂WO₆ prepared by the complexation of Bi with acetic acid (carboxylate) leading to a flower-like morphology. The characterization of the as-prepared Bi₂WO₆ was carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), specific surface area (SSA), and photoluminescence (PL). Under low intensity solar light (<48 mW/cm²), complete bacterial inactivation was achieved within two hours in the presence of the flower-like Bi₂WO₆, while under visible light, the synthesized catalyst performed better than commercial TiO₂. The in situ interfacial charge transfer and local pH changes between Bi₂WO₆ and bacteria were monitored during the bacterial inactivation. Furthermore, the reactive oxygen species (ROS) were identified during Escherichia coli inactivation mediated by appropriate scavengers. The ROS tests alongside the morphological characteristics allowed the proposition of the mechanism for bacterial inactivation. Finally, recycling of the catalyst confirmed the stable nature of the catalyst presented in this study. Full article

Floods are the most destructive natural phenomenon, by the total number of casualties, and value of property damage, compared to any other type of natural disaster. However, some of the most destructive flash floods are related to dam breaches or complete collapses, that release the large amounts of water, affecting inhabited areas. Worldwide, numerous dams have almost reached or surpassed the estimated construction life span, and pose an increasing risk to structure stability. Considering their continuous degrading state, increasing rainfall aggressiveness, due to climatic changes, technical error, or even human error, there are numerous, potential causes, for which dams could develop breaches and completely fail. This study aims to portray a comparative perspective of flood impact, with real-life consequences, measured by quantifiable parameters, generated from computer simulations of different breach sizes. These parameters include the total flooded surface, water velocity, maximum water depth, number of affected buildings, etc. The analysis was undergone by means of HEC-RAS based 2D hydraulic modeling and GIS, depending on high-accuracy Lidar terrain data and historical hydrological data. As a case study, Drăcșani Lake with the associated Sulița earthfill embankment dam was chosen, being one of the largest and oldest artificial lakes in Romania. Full article

Anthropogenic changes in tidal estuaries have significantly altered bathymetry and topography over the past half century. The geomorphic-driven changes in estuarine hydrodynamics and salt transport remain unclear. To explore this issue, a SELFE (Semi-implicit Eulaerian-Lagrangian Finite Element) -based model was developed and utilized in a case study in the Danshui River, Taiwan. The model was calibrated and validated using observed water level, current, and salinity data from 2015, 2016, and 2017. The performance of the SELFE model corresponded well to the measured data. Furthermore, the validated model was utilized to analyze the hydrodynamics, residual current, limit of salt intrusion, and residence time under the predevelopment (1981) and present (2015) conditions. The predicted results revealed that the time lag of water surface elevation at both high tide and low tide under the present condition was approximately 0.5–2 h shorter under the predevelopment condition. The residual circulation under the predevelopment condition was stronger than under the present condition for low flow, causing the limit of salt intrusion to extend further upstream under the predevelopment condition compared to the limit of salt intrusion under the present condition. The calculated residence time under the predevelopment condition was longer than the residence time under the present condition. The freshwater discharge input is a dominating factor affecting the salt intrusion and residence time in a tidal estuary. A regression correlation between the maximum distance of salt intrusion and freshwater discharge and a correlation between residence time and freshwater discharge were established to predict the limit of salt intrusion and residence time under the predevelopment and present conditions with different scenarios of freshwater discharge input. Full article

Understanding the temporal variability of the nutrient transport from catchments is essential for planning nutrient loss reduction measures related to land use and climate change. Moreover, observations and analysis of nutrient dynamics in streams draining undisturbed catchments are known to represent a reference point by which human-influenced catchments can be compared. In this paper, temporal dynamics of nitrate-nitrogen (NO₃-N) flux are investigated on an event basis by analysing observed lag times between data series. More specifically, we studied lag times between the centres of mass of six hydrological and biogeochemical variables, namely discharge, soil moisture at three depths, NO₃-N flux, and the precipitation hyetograph centre of mass. Data obtained by high-frequency measurements (20 min time step) from 29 events were analysed. Linear regression and multiple linear regression (MLR) were used to identify relationships between lag times of the above-mentioned processes. We found that discharge lag time (LAG_Q) and NO₃-N flux lag time (LAG_N) are highly correlated indicating similar temporal response to rainfall. Moreover, relatively high correlation between LAG_N and soil moisture lag times was also detected. The MLR model showed that the most descriptive variable for both LAG_N and LAG_Q is amount of precipitation. For LAG_N, the change of the soil moisture in the upper two layers was also significant, suggesting that the lag times indicate the primarily role of the forest soils as the main source of the NO₃-N flux, whereas the precipitation amount and the runoff formation through the forest soils are the main controlling mechanisms. Full article

The deteriorating water environment demands new approaches and technologies to achieve sustainable and smart management of urban water systems. Wireless sensor networks represent a promising technology for water quality monitoring and management. The use of wireless sensor networks facilitates the improvement of current centralized systems and traditional manual methods, leading to decentralized smart water quality monitoring systems adaptable to the dynamic and heterogeneous water distribution infrastructure of cities. However, there is a need for a low-cost wireless sensor node solution on the market that enables a cost-effective deployment of this new generation of systems. This paper presents the integration to a wireless sensor network and a preliminary validation in a wastewater treatment plant scenario of a low-cost water quality monitoring device in the close-to-market stage. This device consists of a nitrate and nitrite analyzer based on a novel ion chromatography detection method. The analytical device is integrated using an Internet of Things software platform and tested under real conditions. By doing so, a decentralized smart water quality monitoring system that is conceived and developed for water quality monitoring and management is accomplished. In the presented scenario, such a system allows online near-real-time communication with several devices deployed in multiple water treatment plants and provides preventive and data analytics mechanisms to support decision making. The results obtained comparing laboratory and device measured data demonstrate the reliability of the system and the analytical method implemented in the device. Full article

Microplastic (MP) pollution is a global environmental issue, and traditionally treated wastewater has been identified as a source of land-based microplastics into the aquatic environment. This study evaluated the performance of a pilot-scale biofilter to polish wastewater treatment plant (WWTP) effluent before it enters the environment. The filter was divided into four zones, allowing the concentration of microplastics to be followed through the filter. It was fed with secondary effluent from a conventional WWTP in Denmark. The raw effluent from the WWTP contained 917 items m⁻³ which corresponded to a mass concentration of 24.8 µg m⁻³. After the top layer of the biofilter, the concentration had decreased to a median value of 197 item m⁻³ and 2.8 µg m⁻³, indicating an overall removal efficiency of 79% in terms of particle number and 89% in terms of particle mass. We also observed a tendency that MP of larger size and higher particle mass were more likely to be retained. After the last filtration zone, all MP larger than 100 µm had been removed. The results of this study demonstrate that biofilters are able to lower the MP abundance in treated wastewater significantly, but a complete removal is not ensured, hence some MP, particularly small-sized ones, can still be discharged into the receiving environment. Full article

In geotechnical engineering, the seepage phenomena, especially regarding the hydraulic heave, is one of the most dangerous failure mechanisms related to infrastructural stability. Hence, a fundamental understanding of this occurrence is important for the design and construction of water-retaining structures. In this study, a computational fluid dynamics (CFD) solver was developed and coupled with discrete element method (DEM) software to simulate the seepage failure process for the three phases of soil, water, and air. Specimens were constructed with two layers of gap-graded particles to give different permeability properties in the vertical direction. More significant heave failure was observed for the sample with higher permeability in the upper layer. Special attention was drawn to the particle-scale observations of the internal structure and drag force to study the erosion mechanism. The soil filled with air bubbles produced a higher drag force in the region below the retaining wall and showed a larger loss of fine particles than the saturated soil, particularly in the initial stages. The results indicate that the impact of air bubbles would accelerate the development of the heave or boiling phenomenon and influence the stability of the system at an early stage. Full article

As part of the Sustainable Development Goal (SDG) for ensuring clean water and sanitation worldwide by 2030, SDG target 6.4 seeks to attain sustainable withdrawals of freshwater through efficiency gains with a view to relieving water stress in vulnerable populated areas. The water footprint (WF) is a key metric to measure this concept, although the dynamics of the drivers of the WF through space and time remain relatively under-researched, whilst in foresight studies, the WF is often subject to simplistic assumptions. Thus, constructing a panel dataset of 130 countries and 156 crops for the period 2002–2016, this paper empirically assesses the sign and magnitude of WF drivers of agricultural crop activities, employing a careful selection of demographic, economic and climatic drivers. The study uncovers evidence of significant deviations in WF drivers across regions segmented by relative wealth, relating specifically to the stage of economic development and the presence (absence) of economies of scale, whilst we confirm that geographical coordinates have a major bearing on the climatic WF driver. Moreover, examining the temporal dimension, there is compelling evidence supporting a structural break in the role that technical progress exerted on the WF prior to, and in the wake of, the 2008 financial crisis. Full article

Ozonation followed by a polishing moving bed biofilm reactor (MBBR) was implemented in pilot and laboratory to remove the residual pharmaceuticals and toxicity from wastewater effluent, which was from a pilot hybrid system of MBBR and activated sludge, receiving municipal wastewater. The delivered ozone dosages achieving 90% pharmaceutical removal were determined both in pilot and laboratory experiments and they were normalised to dissolved organic carbon (DOC), illustrating our findings were comparable with previously published literature. During wastewater ozonation, the intensity of natural fluorescence was found to be greatly associated with the concentrations of the studied pharmaceuticals. In pilot experiments, toxicity, measured by Vibrio fischeri, increased after ozonation at delivered ozone dosages at 0.38–0.47 mg O₃/mg DOC and was completely removed by the subsequent polishing MBBR. Laboratory experiments verified that the polishing MBBR was able to remove the toxicity produced by the ozonation. Full article

This article investigates Qatar’s sustainability crisis of the high levels of water, electricity and food use. The high levels of consumption have been enabled by Qatar’s significant hydrocarbons wealth, a generous rentier state’s redistributive water governance, and structural dependence on imported food and food production subsidies. The water crisis is silent because it does not generate supply disruptions nor any public discontentment. The geopolitical blockade Qatar is experiencing sparked discussions in policy circles on the best ways to ensure food security, but has only exacerbated its water insecurity. The blockade makes more urgent than ever the necessity to maximize and increase synergies among different sectors. Full article

One of the keys to science and environmental literacy is systems thinking. Learning how to think about the interactions between systems, the far-reaching effects of a system, and the dynamic nature of systems are all critical outcomes of science learning. However, students need support to develop systems thinking skills in undergraduate geoscience classrooms. While systems thinking-focused instruction has the potential to benefit student learning, gaps exist in our understanding of students’ use of systems thinking to operationalize and model SHS, as well as their metacognitive evaluation of systems thinking. To address this need, we have designed, implemented, refined, and studied an introductory-level, interdisciplinary course focused on coupled human-water, or sociohydrologic, systems. Data for this study comes from three consecutive iterations of the course and involves student models and explanations for a socio-hydrologic issue (n = 163). To analyze this data, we counted themed features of the drawn models and applied an operationalization rubric to the written responses. Analyses of the written explanations reveal statistically-significant differences between underlying categories of systems thinking (F(5, 768) = 401.6, p < 0.05). Students were best able to operationalize their systems thinking about problem identification (M = 2.22, SD = 0.73) as compared to unintended consequences (M = 1.43, SD = 1.11). Student-generated systems thinking models revealed statistically significant differences between system components, patterns, and mechanisms, F(2, 132) = 3.06, p < 0.05. Students focused most strongly on system components (M = 13.54, SD = 7.15) as compared to related processes or mechanisms. Qualitative data demonstrated three types of model limitation including scope/scale, temporal, and specific components/mechanisms/patterns excluded. These findings have implications for supporting systems thinking in undergraduate geoscience classrooms, as well as insight into links between these two skills. Full article

Climate change is progressing and is now one of the most important global challenges for humanities. Water resources management is one of the key challenges to reduce disaster risk. In Northern Thailand, flood and drought have always occurred because of the climate change impact and non-systematic management in the conjunctive use of both sources of water. Therefore, this study aims to assess the climate change impact on surface water and groundwater of the Yom and Nan river basins, located in the upper part of Thailand. The surface water and groundwater regimes are generated by a fully coupled SWAT-MODFLOW model. The future climate scenarios are considered from the Representative Concentration Pathways (RCPs) 2.6 and 8.5, presented by the Coupled Model Intercomparison Project Phase 5 (CMIP5), in order to mainly focus on the minimum and maximum Green House Gas (GHG) emissions scenarios during the near future (2021–2045) periods. The results show that the average annual air temperature rises by approximately 0.5–0.6 °C and 0.9–1.0 °C under the minimum (RCP 2.6) and maximum (RCP 8.5) GHG emission scenarios, respectively. The annual rainfall, obtained from both scenarios, increased by the same range of 20–200 mm/year, on average. The summation of surface water (water yield) and groundwater recharge (water percolation) in the Yom river basin decreased by 443.98 and 316.77 million m³/year under the RCPs 2.6 and 8.5, respectively. While, in the Nan river basin, it is projected to increase by 355 million m³/year under RCP 2.6 but decrease by 20.79 million m³/year under RCP 8.5. These quantitative changes can directly impact water availability when evaluating the water demand for consumption, industry, and agriculture. Full article

Testing the homogeneity in extreme rainfall data series is an important step to be performed before applying the frequency analysis method to obtain quantile values. In this work, six homogeneity tests were applied in order to check the existence of break points in extreme annual 24-h rainfall data at eight stations located in the Umbria region (Central Italy). Two are parametric tests (the standard normal homogeneity test and Buishand test) whereas the other four are non-parametric (the Pettitt, Sequential Mann–Kendal, Mann–Whitney U, and Cumulative Sum tests). No break points were detected at four of the stations analyzed. Where inhomogeneities were found, the multifractal approach was applied in order to check if they were real or not by comparing the split and whole data series. The generalized fractal dimension functions D_q and the multifractal spectra f(α) were obtained, and their main parameters were used to decide whether or not a break point existed. Full article

The performance of four tree-based classification techniques—classification and regression trees (CART), multi-adaptive regression splines (MARS), random forests (RF) and gradient boosting trees (GBT) were compared against the commonly used logistic regression (LR) analysis to assess aquifer vulnerability in the Ogallala Aquifer of Texas. The results indicate that the tree-based models performed better than the logistic regression model, as they were able to locally refine nitrate exceedance probabilities. RF exhibited the best generalizable capabilities. The CART model did better in predicting non-exceedances. Nitrate exceedances were sensitive to well depths—an indicator of aquifer redox conditions, which, in turn, was controlled by alkalinity increases brought forth by the dissolution of calcium carbonate. The clay content of soils and soil organic matter, which serve as indicators of agriculture activities, were also noted to have significant influences on nitrate exceedances. Likely nitrogen releases from confined animal feedlot operations in the northeast portions of the study area also appeared to be locally important. Integrated soil, hydrogeological and geochemical datasets, in conjunction with tree-based methods, help elucidate processes controlling nitrate exceedances. Overall, tree-based models offer flexible, transparent approaches for mapping nitrate exceedances, identifying underlying mechanisms and prioritizing monitoring activities. Full article

Fluid–structure interaction (FSI) is a frequent and unstable inherent phenomenon in water conveyance systems. Especially in a system with a surge chamber, valve closing and the subsequent water level oscillation in the surge chamber are the excitation source of the hydraulic transient process. Water-hammer-induced FSI has not been considered in preceding research, and the results without FSI justify further investigations. In this study, an FSI eight-equation model is presented to capture its influence. Both the elbow pipe and surge chamber are treated as boundary conditions, and solved using the finite volume method (FVM). After verifying the feasibility of using FVM to solve FSI, friction, Poisson, and junction couplings are discussed in detail to separately reveal the influence of a surge chamber, tow elbows, and a valve on FSI. Results indicated that the major mechanisms of coupling are junction coupling and Poisson coupling. The former occurs in the surge chamber and elbows. Meanwhile, a stronger pressure pulsation is produced at the valve, resulting in a more complex FSI response in the water conveyance system. Poisson coupling and junction coupling are the main factors contributing to a large amount of local transilience emerging on the dynamic pressure curves. Moreover, frictional coupling leads to the lower amplitudes of transilience. These results indicate that the transilience is induced by the water hammer–structure interaction and plays important roles in the orifice optimization in the surge chamber. Full article

Human encroachment and development on coastlines have led to greater amounts of armoring of shorelines. Breakwaters are a common feature along coastlines, which are used to dampen wave energy and protect shorelines from flash floods or overwash events. Although common, their effects on sediment transport and marsh geomorphology are poorly understood. To address this gap, our study quantifies the effects of breakwaters on sediment transport and marsh evolution under different wave regimes using Delft3D-SWAN, a dynamic geomorphodynamic numerical model. Model configurations used the same numerical domain, but scenarios had different sediments, waves, tides, basin slopes and breakwater distances from the shoreline to explore how waves and tidal currents shape coastal margins. Model results suggested breakwaters were responsible for an average wave damping between 10–50%, proportional to the significant wave height across all modeled scenarios. Shear stress at the beginning of the marsh and the volume of sediment deposited at the end of the simulation (into the marsh behind the breakwater) increased on average between 20–40%, proportional to the slope and distance of the breakwater from the shoreline. Sediment trapping, defined as the ratio between the volume of sediment housed into the salt marsh behind and away from the breakwater, was found to be less than 1 from most model runs. Study results indicated that breakwaters are advantageous for wave breaking to protect shorelines from the wave’s energy, however, they might also be an obstacle for sediment transport, negatively affecting nourishment processes, and, consequently, impeded long-term salt marsh survival. Identifying a balance between waves dampening and shoreline nourishment should be considered in the design and implementation of these structures. Full article

The frequency responses of the transient wave propagating in a pump–pipe–valve system are studied with the system transfer matrix analysis (STMA) method. Being different to that in the reservoir–pipe–valve system, the transient wave is used as a long-distance communication technology in the pump–pipe–valve system, and very few works have been done on the model analysis and strategies to control the behavior of the oscillation signal of the pipe pressure. The theoretic solutions are studied with three internal friction models: frictionless, steady friction, and unsteady friction. The dimensionless parameter of the valve signal intensity (VSI) is proposed, and it is found to be a key factor affecting the quality of the wave propagation in the pipe. A larger pressure oscillation at the upstream side results when the VSI is smaller than one, whereas a more uniform amplitude for the resonances and anti-resonances is obtained when VSI approaches one. Some feasible suggestions are provided to obtain high quality wave signals. Full article

The aim of this study is to contribute to solving conflicts that arise in the operation of multipurpose reservoirs when determining maximum conservation levels (MCLs). The specification of MCLs in reservoirs that are operated for water supply and flood control may imply a reduction in the volume of water supplied with a pre-defined reliability in the system. The procedure presented in this study consists of the joint optimization of the reservoir yield with a specific reliability subject to constraints imposed by hydrological dam safety and downstream river safety. We analyzed two different scenarios by considering constant or variable initial reservoir level prior to extreme flood events. In order to achieve the global optimum configuration of MCLs for each season, we propose the joint optimization of three variables: minimize the maximum reservoir level (return period of 1000 years), minimize the maximum released outflow (return period of 500 years) and maximize the reservoir yield with 90% reliability. We applied the methodology to Riaño Dam, jointly operated for irrigation and flood control. Improvements in the maximum reservoir yield (with 90% reliability) increased up to 10.1% with respect to the currently supplied annual demand (545 hm³) for the same level of dam and downstream hydrological safety. The improvement could increase up to 26.8% when compared to deterministic procedures. Moreover, dam stakeholders can select from a set of Pareto-optimal configurations depending on if their main emphasis is to maintain/increase the hydrological safety, or rather to maintain/increase the reservoir yield. Full article

In a multi-layered groundwater model, achieving accurate spatiotemporal identification and solving the ill-posed problem is the vital topic for model calibration. This study proposes a symmetry rank three vectorized loading scores (SR3 VLS) quasi-Newton algorithm by modifying the Levenberg–Marquardt algorithm and importing a rank three structure from Broyden–Fletcher–Goldfarb–Shanno algorithm for identification of hydrogeological parameters and spatiotemporal recharge simultaneously. To accelerate directional convergence and approach a global optimum, this study uses a vectorized limited switchable step size in the transmissive groundwater inverse problem. The Hessian approximation rank three uses high and low-rank factor loading scores analyzed from simulated storage fluctuation between adjacent iterations for calculation and matrix correction. Two numerical experiments were designed to validate the proposing algorithm, showing the SR3 VLS quasi-Newton reduced the error percentages of the identified parameters by 1.63% and 9.65% compared to the Jacobian quasi-Newton. The proposing method is applied to the Chou-Shui River alluvial fan groundwater system in Taiwan. Results show that the simulated storage error decreased rapidly in six iterations, and has good head convergence as small as 0.11% with a root-mean-square-error (RMSE) of 0.134 m, indicating that the proposing algorithm reduces the computational cost to converge to the true solution. Full article

As the successor of Tropical Rainfall Measuring Mission, Global Precipitation Measurement (GPM) has released a range of satellite-based precipitation products (SPPs). This study conducts a comparative analysis on the quality of the integrated multisatellite retrievals for GPM (IMERG) and global satellite mapping of precipitation (GSMaP) SPPs in the Yellow River source region (YRSR). This research includes the eight latest GPM-era SPPs, namely, IMERG “Early,” “Late,” and “Final” run SPPs (IMERG-E, IMERG-L, and IMERG-F) and GSMaP gauge-adjusted product (GSMaP-Gauge), microwave-infrared reanalyzed product (GSMaP-MVK), near-real-time product (GSMaP-NRT), near-real-time product with gauge-based adjustment (GSMaP-Gauge-NRT), and real-time product (GSMaP-NOW). In addition, the IMERG SPPs were compared with GSMaP SPPs at multiple spatiotemporal scales. Results indicate that among the three IMERG SPPs, IMERG-F exhibited the lowest systematic errors and the best quality, followed by IMERG-E and IMERG-L. IMERG-E and IMERG-L underestimated the occurrences of light-rain events but overestimated the moderate and heavy rain events. For GSMaP SPPs, GSMaP-Gauge presented the best performance in terms of various statistical metrics, followed by GSMaP-Gauge-NRT. GSMaP-MVK and GSMaP-NRT remarkably overestimated total precipitation, and GSMaP-NOW showed an evident underestimation. By comparing the performances of IMERG and GSMaP SPPs, GSMaP-Gauge-NRT provided the best precipitation estimates among all real-time and near-real-time SPPs. For post-real-time SPPs, GSMaP-Gauge presented the highest capability at the daily scale, and IMERG-F slightly outperformed the other SPPs at the monthly scale. This study is one of the earliest studies focusing on the quality of the latest IMERG and GSMaP SPPs. The findings of this study provide SPP developers with valuable information on the quality of the latest GPM-era SPPs in YRSR and help SPP researchers to refine the precipitation retrieving algorithms to improve the applicability of SPPs. Full article

Recurring landslides in the Western Ghats have become an important concern for authorities, considering the recent disasters that occurred during the 2018 and 2019 monsoons. Wayanad is one of the highly affected districts in Kerala State (India), where landslides have become a threat to lives and properties. Rainfall is the major factor which triggers landslides in this region, and hence, an early warning system could be developed based on empirical rainfall thresholds considering the relationship between rainfall events and their potential to initiate landslides. As an initial step in achieving this goal, a detailed study was conducted to develop a regional scale rainfall threshold for the area using intensity and duration conditions, using the landslides that occurred during the years from 2010 to 2018. Detailed analyses were conducted in order to select the most effective method for choosing a reference rain gauge and rainfall event associated with the occurrence of landslides. The study ponders the effect of the selection of rainfall parameters for this data-sparse region by considering four different approaches. First, a regional scale threshold was defined using the nearest rain gauge. The second approach was achieved by selecting the most extreme rainfall event recorded in the area, irrespective of the location of landslide and rain gauge. Third, the classical definition of intensity was modified from average intensity to peak daily intensity measured by the nearest rain gauge. In the last approach, four different local scale thresholds were defined, exploring the possibility of developing a threshold for a uniform meteo-hydro-geological condition instead of merging the data and developing a regional scale threshold. All developed thresholds were then validated and empirically compared to find the best suited approach for the study area. From the analysis, it was observed that the approach selecting the rain gauge based on the most extreme rainfall parameters performed better than the other approaches. The results are useful in understanding the sensitivity of Intensity–Duration threshold models to some boundary conditions such as rain gauge selection, the intensity definition and the strategy of subdividing the area into independent alert zones. The results were discussed with perspective on a future application in a regional scale Landslide Early Warning System (LEWS) and on further improvements needed for this objective. Full article

Climate change implies changes in the frequency and magnitude of flood events. The influence of climate variability on flooding was evaluated by an analysis of sedimentary (palaeofloods) and documentary archives. A 500-year palaeoflood record at Montlleó River (657 km² in catchment area), eastern Spain, revealed up to 31 palaeofloods with a range of discharges of 20–950 m³ s⁻¹, and with at least five floods exceeding 740–950 m³ s⁻¹. This information contrasts with the available gauged flood registers (since year 1971) with an annual maximum daily discharge of 129 m³ s⁻¹. Our palaeoflood dataset indicates flood cluster episodes at (1) 1570–1620, (2) 1775–1795, (3) 1850–1890, and (4) 1920–1969. Flood rich periods 1 and 3 corresponded to cooler than usual (about 0.3 °C and 0.2 °C) climate oscillations, whereas 2 and 4 were characterised by higher inter-annual climatic variability (floods and droughts). This high inter-annual rainfall variability increased over the last 150 years, leading to a reduction of annual maximum flow. Flood quantiles (>50 years) calculated from palaeoflood+gauged data showed 30%–40% higher peak discharges than those using only instrumental records, whereas when increasing the catchment area (1500 km²) the discharge estimation variance decreased to ~15%. The results reflect the higher sensitivity of small catchments to changes on flood magnitude and frequency due to climate variability whereas a larger catchment buffers the response due to the limited extent of convective storms. Our findings show that extended flood records provide robust knowledge about hazardous flooding that can assist in the prioritization of low-regret actions for flood-risk adaptation to climate change. Full article