Hydrology

33 pages, 4849 KB

Open AccessArticle

Hydrochemical Variability in Karst Hypothermal Mineral Springs of Greece

by Nerantzis Kazakis, Vasiliki Stavropoulou, Maria Margarita Ntona, Christos Pouliaris, Maria Papailiopoulou, Eleni-Anna Nanou, Apostolis Tsoutanis, Dimitra Lambropoulou and Eleni Zagana

Hydrology 2025, 12(9), 237; https://doi.org/10.3390/hydrology12090237 - 13 Sep 2025

Abstract

In Greece, the geodynamics of karst hypothermal–mineral springs, in which often shallow fresh groundwater is intermixed, is not well known. This study aims to investigate the monthly hydrochemical variability of three karst hypothermal mineral springs in Greece named Kyllini (southern Greece), Agiasma (northern [...] Read more.

In Greece, the geodynamics of karst hypothermal–mineral springs, in which often shallow fresh groundwater is intermixed, is not well known. This study aims to investigate the monthly hydrochemical variability of three karst hypothermal mineral springs in Greece named Kyllini (southern Greece), Agiasma (northern Greece), and Voskina (northern Greece). Hence, monthly samples were collected and an analysis of major and trace elements, ion ratios, and saturation indices was performed, as well as statistical analysis and cross correlation. Elevated concentrations of Ca²⁺, Mg²⁺, and HCO₃⁻ are present in all springs, indicating that the dissolution of calcite and dolomite constitutes the main water–rock interaction process. Additionally, the mobilization and transport of Mn, Fe, and As are favored by the negative ORP values. However, there are also differences between the three springs. The Kyllini spring is characterized by high salinity and dominated by Na–Cl–HCO₃ water, while the Agiasma spring exhibits a mixed water type with moderate salinity. The Voskina spring reflects a fresher, bicarbonate-dominated aquifer system with modest trace element mobilization. This study provides the first comprehensive monthly assessment of the hydrochemical response of karst hypothermal–mineral springs in Greece, offering new insights into seasonal geochemical dynamics. Full article

(This article belongs to the Special Issue Groundwater Pollution: Sources, Mechanisms, and Prevention (Second Edition))

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26 pages, 730 KB

Open AccessReview

Nature-Based Approaches for Managing Bioavailable Phosphorus in Aquatic Ecosystems

by Marcela Pavlíková, Klára Odehnalová, Štěpán Zezulka, Eliška Maršálková, Adéla Lamaczová and Blahoslav Maršálek

Hydrology 2025, 12(9), 236; https://doi.org/10.3390/hydrology12090236 - 10 Sep 2025

Abstract

High levels of phosphorus cause eutrophication, leading to water blooms and making the water undesirable in aquatic environments. Surface water pollution by phosphorus (P) is caused by both point and diffuse sources. Despite the recent technological advancements in wastewater phosphorus removal, this element [...] Read more.

High levels of phosphorus cause eutrophication, leading to water blooms and making the water undesirable in aquatic environments. Surface water pollution by phosphorus (P) is caused by both point and diffuse sources. Despite the recent technological advancements in wastewater phosphorus removal, this element persists in aquatic ecosystems, particularly in sediments, often in non-bioavailable forms (in the case of precipitation by aluminum salts) or within biomass associated with high concentrations of heavy metals, rendering it unsuitable for reuse. In this paper, we review the measures and methods commonly used for reducing or removing bioavailable phosphorus, with a focus on the strategies and methods for direct in situ phosphorus removal or reuse, including the use of microbial biofilms and aquatic macrophytes, natural and constructed wetlands, and biotised (biologically enhanced) solid-phase sorbents or woodchip bioreactors. This paper also highlights the significance of bioavailable phosphorus from both the hydrochemical perspectives, examining phosphorus speciation, solubility, and the geochemical interactions influencing mobility in water and sediments, and the biological perspectives, which consider phosphorus uptake, bioaccumulation in aquatic organisms, and the role of microbial and plant communities in modulating phosphorus cycling. This overview presents sustainable phosphorus management approaches that are key to reducing eutrophication and supporting ecosystem health. Full article

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Graphical abstract

30 pages, 5345 KB

Open AccessArticle

Climate Change and Its Potential Impact on the Conservation of Wooden Pole Dwellings in Lake Bolsena: Insights from Climate Proxy Data and High-Frequency Water Monitoring

by Swati Tamantini, Maria Cristina Moscatelli, Francesco Cappelli, Barbara Barbaro, Egidio Severi, Federica Antonelli, Giulia Galotta, Marco Ciabattoni and Manuela Romagnoli

Hydrology 2025, 12(9), 235; https://doi.org/10.3390/hydrology12090235 - 10 Sep 2025

Abstract

This study examines the impact of recent climatic trends on the preservation of submerged wooden structures at the Gran Carro archaeological site in Lake Bolsena, Italy. Climatic data from the Bolsena Meteorological Station were analysed alongside in situ water quality measurements collected near [...] Read more.

This study examines the impact of recent climatic trends on the preservation of submerged wooden structures at the Gran Carro archaeological site in Lake Bolsena, Italy. Climatic data from the Bolsena Meteorological Station were analysed alongside in situ water quality measurements collected near the archaeological remains at a depth of 4 m. The key parameters included water temperature (Tw), redox potential (Eh), dissolved oxygen (DO), and total dissolved solids (TDS). Trend analyses using the Mann–Kendall test and Sen’s slope revealed significant increases in air and water temperatures, which were strongly correlated. Although precipitation exhibited an upward trend, its negative correlation with temperature suggests greater variability rather than a stable water supply. Despite increased rainfall, lake levels showed a significant decline, likely due to intensified evaporation and water extraction for irrigation. UAV surveys confirmed recent lowering of the lake’s water surface during drought periods. Among the limnological parameters, dissolved oxygen saturation declined significantly, while redox potential increased, indicating shifts toward more anaerobic conditions. These environmental changes could promote the activity of erosive bacteria that degrade submerged wood. Conversely, increased evaporation might also enhance oxygen penetration at depth, potentially activating decay agents such as soft rot fungi and wood-boring bacteria. Overall, the findings suggest that ongoing climatic changes are adversely affecting the preservation of submerged wooden structures, highlighting the need for adaptive management strategies to protect both the lake ecosystem and its archaeological heritage. Full article

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21 pages, 11249 KB

Open AccessArticle

Are Hydrological Geosites Related to High Hydrodiversity? A Study in the State of Rio Grande do Norte, Northeast Brazil

by Maria Luiza de Oliveira Terto, Paulo Pereira and Marco Túlio Mendonça Diniz

Hydrology 2025, 12(9), 234; https://doi.org/10.3390/hydrology12090234 - 8 Sep 2025

Abstract

This study presents an assessment of hydrological diversity (hydrodiversity) in Rio Grande do Norte, Brazil, aiming to identify potential correlations between hydrodiversity and hydrological features of geoheritage. The methodology applied a quantitative approach based on mean annual precipitation, river discharge, reservoir distribution, and [...] Read more.

This study presents an assessment of hydrological diversity (hydrodiversity) in Rio Grande do Norte, Brazil, aiming to identify potential correlations between hydrodiversity and hydrological features of geoheritage. The methodology applied a quantitative approach based on mean annual precipitation, river discharge, reservoir distribution, and stream order. These variables were analyzed within a 5.5 km grid using GIS tools. The four resulting sub-indices were normalized through the Maximum Possible Value method to ensure equal weighting in the final Hydrodiversity Index, which classifies areas into four levels: low, medium, high, and very high. Results show the highest hydrodiversity values in the eastern region and along the Apodi–Mossoró River, where rainfall and drainage density are greatest. The Hydrodiversity Index map was examined alongside land use data and the distribution of 22 previously identified hydrological sites (hydrosites). A greater concentration of anthropogenic land use was noted in areas with medium to high hydrodiversity, especially in the east and along the northern coast, emphasizing the role of water resources in territorial dynamics. The findings indicate that no hydrosites are located within areas of Very High Hydrodiversity; however, more than 50% of the hydrosites correspond to areas classified as High Hydrodiversity. While further research is required to better elucidate the relationship between geodiversity and geoheritage, these results underscore both the complexity of the link between hydrodiversity and water-related geoheritage, as well as the importance of employing an index to inform conservation and management strategies. Full article

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14 pages, 1459 KB

Open AccessArticle

Proposal for a Water Quality Index for Supplying Rural Communities in the Brazilian Federal District

by Eduardo C. Oliveira-Filho, Daphne H. F. Muniz, Elizabeth C. M. Gonçalves and Juaci V. Malaquias

Hydrology 2025, 12(9), 233; https://doi.org/10.3390/hydrology12090233 - 6 Sep 2025

Abstract

The environmental characterization of a given region is fundamental for decision-making by public administrators and, consequently, for sustainable development. Regarding water quality, establishing the use of this resource is a priority, as specific parameters must be defined for each type of usage, to [...] Read more.

The environmental characterization of a given region is fundamental for decision-making by public administrators and, consequently, for sustainable development. Regarding water quality, establishing the use of this resource is a priority, as specific parameters must be defined for each type of usage, to determine water quality in that region. The objective of this study was to propose a water quality index for supplying rural communities, given that the most commonly used indices relate to urban water after treatment. To construct the index, water samples were collected over 12 months from 29 sampling points across seven rural centers without the governmental service of treated water. Principal component analysis was used to identify the most representative parameters, and final weights were assigned considering Brazilian regulatory standards. The results obtained revealed a very simplified index with five variables and five usage classes, with scores ranging from simplified to advanced treatment. It is hoped that the proposed index will better guide rural communities and generate improved policies for water resource management in the Brazilian Federal District and support public policy development in rural areas with limited water treatment infrastructure. Full article

(This article belongs to the Section Surface Waters and Groundwaters)

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12 pages, 3541 KB

Open AccessArticle

Simulating the Porosity Reduction in a Permeable Reactive Barrier–Aquifer System Using THMC Software

by Thi-Tuyet-Han Nguyen, Heejun Suk, Ching-Ping Liang and Jui-Sheng Chen

Hydrology 2025, 12(9), 232; https://doi.org/10.3390/hydrology12090232 - 4 Sep 2025

Abstract

A permeable reactive barrier (PRB) containing zero-valent iron (ZVI) is an in situ groundwater remediation technology that passively intercepts and treats contaminated groundwater plumes. Over time, secondary mineral precipitation within the PRB diminishes porosity and hydraulic conductivity, altering flow paths, residence times, and [...] Read more.

A permeable reactive barrier (PRB) containing zero-valent iron (ZVI) is an in situ groundwater remediation technology that passively intercepts and treats contaminated groundwater plumes. Over time, secondary mineral precipitation within the PRB diminishes porosity and hydraulic conductivity, altering flow paths, residence times, and sometimes causing bypass of the reactive zone. This study utilizes the THMC software to simulate porosity reduction in a PRB, capturing the coupled effects of fluid flow and geochemical interactions. The simulation results indicate that porosity loss is most significant at the PRB entrance and stabilizes beyond 0.2 m. Porosity reduction is primarily caused by aragonite, siderite, and ferrous hydroxide precipitating in pore spaces. The model further elucidates the influence of groundwater chemistry, demonstrating that variations in bicarbonate concentrations significantly impact mineral precipitation processes, thereby leading to porosity reduction. Furthermore, the study highlights reaction kinetics, with anaerobic iron corrosion rates being critical in controlling porosity reduction via mineral precipitation. THMC software effectively simulates porosity reduction in PRBs, identifies key factors driving clogging, and informs design optimization for long-term remediation. Full article

(This article belongs to the Section Surface Waters and Groundwaters)

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17 pages, 5226 KB

Open AccessArticle

Impact of Grated Inlet Clogging on Urban Pluvial Flooding

by Beniamino Russo, Viviane Beiró, Pedro Luis Lopez-Julian and Alejandro Acero

Hydrology 2025, 12(9), 231; https://doi.org/10.3390/hydrology12090231 - 2 Sep 2025

Abstract

This study aims to analyse the effect of partially clogged inlets on the behaviour of urban drainage systems at the city scale, particularly regarding intercepted volumes and flood depths. The main challenges were to represent the inlet network in detail at a rather [...] Read more.

This study aims to analyse the effect of partially clogged inlets on the behaviour of urban drainage systems at the city scale, particularly regarding intercepted volumes and flood depths. The main challenges were to represent the inlet network in detail at a rather large scale and to avoid the effect of sewer network surcharging on the draining capacity of inlets. This goal has been achieved through a 1D/2D coupled hydraulic model of the whole urban drainage system in La Almunia de Doña Godina (Zaragoza, Spain). The model focuses on the interaction between grated drain inlets and the sewer network under partial clogging conditions. The model is fed with data obtained on field surveys. These surveys identified 948 inlets, classified into 43 types based on geometry and grouped into 7 categories for modelling purposes. Clogging patterns were derived from field observations or estimated using progressive clogging trends. The hydrological model combines a semi-distributed approach for micro-catchments (buildings and courtyards) and a distributed “rain-on-grid” approach for public spaces (streets, squares). The model assesses the impact of inlet clogging on network performance and surface flooding during four rainfall scenarios. Results include inlet interception volumes, flooded surface areas, and flow hydrographs intercepted by single inlets. Specifically, the reduction in intercepted volume ranged from approximately 7% under a mild inlet clogging condition to nearly 50% under severe clogging conditions. Also, the model results show the significant influence of the 2D mesh detail on flood depths. For instance, a mesh with high resolution and break lines representing streets curbs showed a 38% increase in urban areas with flood depths above 1 cm compared to a scenario with a lower-resolution 2D mesh and no curbs. The findings highlight how inlet clogging significantly affects the efficiency of urban drainage systems and increases the surface flood hazard. Further novelties of this work are the extent of the analysis (city scale) and the approach to improve the 2D mesh to assess flood depth. Full article

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22 pages, 3391 KB

Open AccessArticle

Assessing Stream Temperature Interactions with Physical and Environmental Variables Along the Longitudinal Profile of a First- to Fourth-Order Perennial Stream in a Multi-Land Use Watershed in Western Oregon, USA

by Derek C. Godwin and Carlos G. Ochoa

Hydrology 2025, 12(9), 230; https://doi.org/10.3390/hydrology12090230 - 1 Sep 2025

Abstract

Stream temperatures are expected to increase with warming air temperatures, yet the extent and aquatic health impacts vary significantly across heterogeneous landscapes. This study was conducted in a 3360-ha multi-land-use watershed in the Pacific Northwest region of the USA to assess and compare [...] Read more.

Stream temperatures are expected to increase with warming air temperatures, yet the extent and aquatic health impacts vary significantly across heterogeneous landscapes. This study was conducted in a 3360-ha multi-land-use watershed in the Pacific Northwest region of the USA to assess and compare the driving factors for stream temperature heating, cooling, and cool-water refugia along a 12-km mainstem stream longitudinal profile. Study objectives were to (1) determine yearlong stream temperature variability along the entire stream longitudinal profile, and (2) assess stream-environment relationships influencing stream temperature dynamics across forest, agriculture, and urban landscapes within the watershed. Stream and riparian air temperatures, solar radiation, shade, and related stream-riparian characteristics were measured over six years at 21 stations to determine changes, along the longitudinal profile, of thermal sensitivity, maximum and minimum stream temperatures, and correlation between solar radiation and temperature increases, and potential causal factors associated with these changes. Solar radiation was a primary heating factor for an exposed agricultural land use reach with 57% effective shade, while southern stream aspects and incoming tributary conditions were primary factors for forested reaches with greater than 84% effective shade. Potential primary cooling factors were streambank height, groundwater inflows, and hyporheic exchange in an urban reach with moderate effective shade (79%) and forest riparian width (16 m). Combining watershed-scale analysis with on-site stream-environmental data collection helps assess primary temperature heating factors, such as solar radiation and shade, and potential cooling factors, such as groundwater and cool tributary inflows, as conditions change along the longitudinal profile. Full article

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27 pages, 3098 KB

Open AccessArticle

Improving Operational Ensemble Streamflow Forecasting with Conditional Bias-Penalized Post-Processing of Precipitation Forecast and Assimilation of Streamflow Data

by Sunghee Kim and Dong-Jun Seo

Hydrology 2025, 12(9), 229; https://doi.org/10.3390/hydrology12090229 - 31 Aug 2025

Abstract

This work aims at improving the accuracy of ensemble streamflow forecasts at short-to-medium ranges with the conditional bias-penalized regression (CBPR)-aided Meteorological Ensemble Forecast Processor (MEFP) and streamflow data assimilation (DA). To assess the potential impact of the CBPR-aided MEFP and streamflow DA, or [...] Read more.

This work aims at improving the accuracy of ensemble streamflow forecasts at short-to-medium ranges with the conditional bias-penalized regression (CBPR)-aided Meteorological Ensemble Forecast Processor (MEFP) and streamflow data assimilation (DA). To assess the potential impact of the CBPR-aided MEFP and streamflow DA, or CBPR-DA, 20-yr hindcast experiments were carried out using the Global Ensemble Forecast System version 12 reforecast dataset for 46 locations in the service areas of 11 River Forecast Centers of the US NWS. The results show that, relative to the current practice of using the MEFP and no DA, or MEFP-NoDA, CBPR-DA improves the accuracy of ensemble forecasts of 3-day flow over lead times of 0 to 3 days by over 40% for 4 RFCs and by over 20% for 9 of the 11 RFCs. The margin of improvement is larger where the predictability of precipitation is larger and the hydrologic memory is stronger. As the lead time increases, the margin of improvement decreases but still exceeds 10% for the prediction of 14-day flow over lead times of 0 to 14 days for all but 3 RFCs. Full article

(This article belongs to the Special Issue New Perspectives in the Flood Forecasting Chain (Weather Prediction, Rainfall-Runoff Modeling, and Communication with Stakeholders), Second Edition)

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22 pages, 6496 KB

Open AccessArticle

High-Resolution Bathymetric Survey and Updated Morphometric Analysis of Lake Markakol (Kazakhstan)

by Askhat Zhadi, Azamat Madibekov, Serik Zhumatayev, Laura Ismukhanova, Botakoz Sultanbekova, Aidar Zhumalipov, Zhanar Raimbekova, María-Elena Rodrigo-Clavero and Javier Rodrigo-Ilarri

Hydrology 2025, 12(9), 228; https://doi.org/10.3390/hydrology12090228 - 29 Aug 2025

Abstract

Accurate and up-to-date morphometric data on lakes are crucial for hydrological modeling, ecosystem monitoring, and sustainable water resource management. This study presents the first centimeter-scale, high-resolution bathymetric model of Lake Markakol (eastern Kazakhstan), generated using advanced hydroacoustic and geospatial techniques. The primary objective [...] Read more.

Accurate and up-to-date morphometric data on lakes are crucial for hydrological modeling, ecosystem monitoring, and sustainable water resource management. This study presents the first centimeter-scale, high-resolution bathymetric model of Lake Markakol (eastern Kazakhstan), generated using advanced hydroacoustic and geospatial techniques. The primary objective was to reassess key morphometric parameters—surface area, depth, volume, and shoreline configuration—more than six decades after the only existing survey from 1962. High-density depth data were acquired with a Lowrance HDS-12 Live echo sounder, achieving vertical precision of ±0.17 m, and processed using ReefMaster and ArcGIS to produce a three-dimensional, hydrologically correct model of the lake basin. Compared with archival data, results show that while the surface area (455.365 ± 0.005 km²), length (38.304 ± 0.002 km), and width (19.138 ± 0.002 km) have remained stable, the maximum depth is lower (24.14 ± 0.17 m vs. 27 m), and the total water volume is slightly higher (6.667 ± 0.025 km³ vs. 6.37 km³). These differences highlight both the limitations of historical lead-line surveys and the enhanced accuracy of modern hydroacoustic and GIS-based methods. The workflow developed here is transferable to other remote alpine lakes, providing an invaluable baseline for limnological research, ecological assessment, hydrodynamic modeling, and long-term water resource management strategies in data-scarce mountain regions. Full article

(This article belongs to the Special Issue Lakes as Sensitive Indicators of Hydrology, Environment, and Climate)

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16 pages, 4224 KB

Open AccessArticle

Zoning of the Territory of Southern Kazakhstan Based on the Conditions of Groundwater Availability for Watering Pasture Lands

by Vladimir Smolyar, Dinara Adenova, Timur Rakhimov, Rakhmatulla Ayazbayev, Gulnura Nyssanbayeva and Almagul Kerimkulova

Hydrology 2025, 12(9), 227; https://doi.org/10.3390/hydrology12090227 - 28 Aug 2025

Abstract

In the arid and semi-arid climate of Southern Kazakhstan, groundwater is the primary and most resilient source of water for pasture irrigation. This study provides an integrated assessment of the predicted, natural, and operational groundwater resources across five administrative regions—Almaty, Zhetysu, Zhambyl, Kyzylorda, [...] Read more.

In the arid and semi-arid climate of Southern Kazakhstan, groundwater is the primary and most resilient source of water for pasture irrigation. This study provides an integrated assessment of the predicted, natural, and operational groundwater resources across five administrative regions—Almaty, Zhetysu, Zhambyl, Kyzylorda, and Turkestan—considering water quality (total dissolved solids, TDS), potential well yield, and aquifer depth. Hydrogeological maps at 1:200,000 and 1:1,000,000 scales, a regional well inventory, and GIS-based spatial analysis were combined to classify resource availability and identify surplus and deficit zones. Results show that 92.5% of predicted exploitable resources (totaling 1155.2 m³/s) have TDS ≤ 3 g/L, making them suitable for domestic and livestock use. Regional disparities are pronounced: Zhetysu, Almaty, and Zhambyl exhibit resource surpluses, Kyzylorda approaches balance, while Turkestan faces a marked deficit. The developed groundwater availability map integrates mineralization, well productivity, and recommended drilling depth, enabling the design of water intake systems without costly field exploration. This decision-support tool has practical value for optimizing water allocation, reducing operational costs, and improving the sustainability of pasture management under the constraints of limited surface water resources. Full article

(This article belongs to the Section Soil and Hydrology)

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14 pages, 915 KB

Open AccessArticle

Evaluation of Analytical Solutions Based on the Assumption of One-Dimensional Groundwater Flow Using Numerical Solutions for Two-Dimensional Flows

by Konstantinos L. Katsifarakis, Yiannis N. Kontos and Odysseas Keremidis

Hydrology 2025, 12(9), 226; https://doi.org/10.3390/hydrology12090226 - 28 Aug 2025

Abstract

The proper development of groundwater resources is very important in many parts of the world. Its planning requires mathematical simulation of groundwater flows. Simulation can be either analytical or numerical. Analytical tools, when available, require fewer computational resources, but they are usually based [...] Read more.

The proper development of groundwater resources is very important in many parts of the world. Its planning requires mathematical simulation of groundwater flows. Simulation can be either analytical or numerical. Analytical tools, when available, require fewer computational resources, but they are usually based on more assumptions, at the conceptual level, which restrict their applicability. In this paper, we aim to check the applicability of one-dimensional analytical solutions for groundwater flows through non-homogeneous aquifers, which are bound by two constant head and two impermeable boundaries and bear many zones of different transmissivities. These solutions are based on the stepwise inclusion of neighboring zones to larger ones, with equivalent transmissivity coefficients. We compare analytical results with numerical ones, obtained from a two-dimensional numerical model. We have selected the boundary element method (BEM) for this task. BEM is very versatile in solving steady-state groundwater flow problems, since discretization is restricted to external and internal field boundaries only. This feature fits perfectly with our research, which requires flow velocities at the boundaries only. Our research shows that analytical results can serve as upper and lower limits of total inflow. If the differences between the transmissivities of adjacent zones are small, they can be used in preliminary calculations too. Full article

(This article belongs to the Section Surface Waters and Groundwaters)

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19 pages, 2239 KB

Open AccessArticle

Assessment of Satellite Precipitation Products in an Andean Catchment: Ambato River Basin, Ecuador

by Pablo Arechúa-Mazón, César Cisneros-Vaca, Julia Calahorrano-González and Mery Manzano-Cepeda

Hydrology 2025, 12(9), 225; https://doi.org/10.3390/hydrology12090225 - 28 Aug 2025

Abstract

Accurate precipitation data are essential for hydrological planning in mountainous regions with sparse opportunities for observation, such as the Ambato River basin in Ecuador. In this study, CHIRPS and IMERG satellite precipitation products were compared against six automatic rain gauges from 2014 to [...] Read more.

Accurate precipitation data are essential for hydrological planning in mountainous regions with sparse opportunities for observation, such as the Ambato River basin in Ecuador. In this study, CHIRPS and IMERG satellite precipitation products were compared against six automatic rain gauges from 2014 to 2023, using both categorical metrics (to assess daily rainfall detection skill) and continuous validation (to evaluate rainfall amount), complemented by bias decomposition and spatiotemporal analysis. Our results show that IMERG demonstrated higher skill in detecting daily rainfall, while CHIRPS delivered a more stable performance during dry conditions, with fewer false alarms. Both products capture the main seasonal precipitation patterns but differ in bias behavior: CHIRPS tends to under-estimate daily rainfall less, whereas IMERG provides more reliable volumetric estimates overall. These findings suggest that IMERG may be best suited for flood risk and hydrological modelling, while CHIRPS could be preferred for drought monitoring and climatological studies in Andean catchments. Full article

(This article belongs to the Special Issue Advances in the Measurement, Utility and Evaluation of Precipitation Observations)

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23 pages, 4474 KB

Open AccessArticle

Anthropogenic River Segmentation Case Study: Bahlui River from Romania

by Nicolae Marcoie, Ionuț Ovidiu Toma, Șerban Chihaia, Tomi Alexandrel Hrăniciuc, Daniel Toma, Cătălin Dumitrel Balan, Elena Niculina Drăgoi and Mircea-Teodor Nechita

Hydrology 2025, 12(9), 224; https://doi.org/10.3390/hydrology12090224 - 25 Aug 2025

Abstract

This manuscript introduces a river segmentation method and explores the impact of human interventions through a long-term study of total nitrogen, total phosphorus, chemical oxygen demand, and biochemical oxygen demand. An indicator linking parameter concentrations to the river’s flow rate was used to [...] Read more.

This manuscript introduces a river segmentation method and explores the impact of human interventions through a long-term study of total nitrogen, total phosphorus, chemical oxygen demand, and biochemical oxygen demand. An indicator linking parameter concentrations to the river’s flow rate was used to assess the development of the examined parameters. The analysis spanned from 2011 to 2022, considering both seasonal and yearly variations. Normal probability plots served as statistical tools to evaluate whether the data followed normal distributions and identify outliers. The proposed segmentation divided the Bahlui River into four segments, each defined by anthropogenic stressors. It was found that, due to human activity, each river segment could be viewed as an “independent” river. This supports the idea that river segments can be analyzed separately as distinct components. The proposed segmentation approach represents an alternative approach in river water quality research, moving from traditional continuous system models to fragmented system analysis, which better reflects the reality of heavily modified river systems. The study’s findings are important for understanding how anthropogenic modifications affect river ecosystem functioning in the long term. Full article

(This article belongs to the Topic Climate Change and Human Impact on Freshwater Water Resources: Rivers and Lakes)

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28 pages, 2147 KB

Open AccessArticle

Generalized Methodology for Two-Dimensional Flood Depth Prediction Using ML-Based Models

by Mohamed Soliman, Mohamed M. Morsy and Hany G. Radwan

Hydrology 2025, 12(9), 223; https://doi.org/10.3390/hydrology12090223 - 24 Aug 2025

Abstract

Floods are among the most devastating natural disasters; predicting their depth and extent remains a global challenge. Machine Learning (ML) models have demonstrated improved accuracy over traditional probabilistic flood mapping approaches. While previous studies have developed ML-based models for specific local regions, this [...] Read more.

Floods are among the most devastating natural disasters; predicting their depth and extent remains a global challenge. Machine Learning (ML) models have demonstrated improved accuracy over traditional probabilistic flood mapping approaches. While previous studies have developed ML-based models for specific local regions, this study aims to establish a methodology for estimating flood depth on a global scale using ML algorithms and freely available datasets—a challenging yet critical task. To support model generalization, 45 catchments from diverse geographic regions were selected based on elevation, land use, land cover, and soil type variations. The datasets were meticulously preprocessed, ensuring normality, eliminating outliers, and scaling. These preprocessed data were then split into subgroups: 75% for training and 25% for testing, with six additional unseen catchments from the USA reserved for validation. A sensitivity analysis was performed across several ML models (ANN, CNN, RNN, LSTM, Random Forest, XGBoost), leading to the selection of the Random Forest (RF) algorithm for both flood inundation classification and flood depth regression models. Three regression models were assessed for flood depth prediction. The pixel-based regression model achieved an R² of 91% for training and 69% for testing. Introducing a pixel clustering regression model improved the testing R² to 75%, with an overall validation (for unseen catchments) R² of 64%. The catchment-based clustering regression model yielded the most robust performance, with an R² of 83% for testing and 82% for validation. The developed ML model demonstrates breakthrough computational efficiency, generating complete flood depth predictions in just 6 min—a 225× speed improvement (90–95% time reduction) over conventional HEC-RAS 6.3 simulations. This rapid processing enables the practical implementation of flood early warning systems. Despite the dramatic speed gains, the solution maintains high predictive accuracy, evidenced by statistically robust 95% confidence intervals and strong spatial agreement with HEC-RAS benchmark maps. These findings highlight the critical role of the spatial variability of dependencies in enhancing model accuracy, representing a meaningful approach forward in scalable modeling frameworks with potential for global generalization of flood depth. Full article

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22 pages, 4204 KB

Open AccessArticle

Integrative Runoff Infiltration Modeling of Mountainous Urban Karstic Terrain

by Yaakov Anker, Nitzan Ne’eman, Alexander Gimburg and Itzhak Benenson

Hydrology 2025, 12(9), 222; https://doi.org/10.3390/hydrology12090222 - 22 Aug 2025

Abstract

Global climate change, combined with the construction of impermeable urban elements, tends to increase runoff, which might cause flooding and reduce groundwater recharge. Moreover, the first flash of these areas might accumulate pollutants that might deteriorate groundwater quality. A digital elevation model (DEM) [...] Read more.

Global climate change, combined with the construction of impermeable urban elements, tends to increase runoff, which might cause flooding and reduce groundwater recharge. Moreover, the first flash of these areas might accumulate pollutants that might deteriorate groundwater quality. A digital elevation model (DEM) describes urban landscapes by representing the watershed relief at any given location. While, in concept, finer DEMs and land use classification (LUC) are yielding better hydrological models, it is suggested that over-accuracy overestimates minor tributaries that might be redundant. Optimal DEM resolution with integrated spectral and feature-based LUC was found to reflect the hydrological network’s significant tributaries. To cope with the karstic urban watershed complexity, ModClark Transform and SCS Curve Number methods were integrated over a GIS-HEC-HMS platform to a nominal urban watershed sub-basin analysis procedure, allowing for detailed urban runoff modeling. This precise urban karstic terrain modeling procedure can predict runoff volume and discharge in urban, mountainous karstic watersheds, and may be used for water-sensitive design or in such cities to control runoff and prevent its negative impacts. Full article

(This article belongs to the Special Issue The Influence of Landscape Disturbance on Catchment Processes)

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12 pages, 2068 KB

Open AccessArticle

Effect of Storm Event Duration on the Indices of Concentration Discharge Hysteresis

by Samer Majdalani

Hydrology 2025, 12(8), 221; https://doi.org/10.3390/hydrology12080221 - 20 Aug 2025

Abstract

The relationship between concentration and discharge (C/Q) is widely studied to understand the behavior of solute transport in complex natural media during storm events. The causes of C/Q hysteresis are due to the delay between the signals of [...] Read more.

The relationship between concentration and discharge (C/Q) is widely studied to understand the behavior of solute transport in complex natural media during storm events. The causes of C/Q hysteresis are due to the delay between the signals of C and Q at a given observation point. Many indices are used to characterize the C/Q hysteresis curve, like the hysteresis index (HI) and the flushing index (FI). The limitation of relating C/Q hysteresis relationships or indices to storm event parameters is because, in real-world situations, we ignore and do not control storm event parameters. This paper is the first attempt to study the variability of C/Q relationships under a well-known storm event on a controlled experimental channel. We tested nine scenarios where the storm event consisted of a triangular input signal with a constant peak and a variable duration. The main parameter of this study is the storm event duration. We calculated known indices, like the hysteresis index (HI) and the flushing index (FI), and we introduced the following two new indices: the saturation index (SI) and the bisector index (BI). Then we related all calculated indices to the storm duration parameter. The importance of our study is that it presents, for the first time, a quantitative description of how the magnitude of the hysteresis indices varies with the storm duration parameter. We found that the most popular HI index does not follow a monotonic behavior for increasing storm duration. Conversely, the FI index and the two newly introduced indices (SI and BI) follow a monotonic behavior for increasing storm duration according to a Fermi-type function. The SI varies between 0.11 and 0.93, while the BI varies between 1 and 0.32 for an increasing storm event duration. Full article

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33 pages, 12539 KB

Open AccessArticle

A Flood Forecasting Method in the Francolí River Basin (Spain) Using a Distributed Hydrological Model and an Analog-Based Precipitation Forecast

by Daniel Carril-Rojas, Carlo Guzzon, Luis Mediero, Javier Fernández-Fidalgo, Luis Garrote, Maria Carmen Llasat and Raul Marcos-Matamoros

Hydrology 2025, 12(8), 220; https://doi.org/10.3390/hydrology12080220 - 19 Aug 2025

Abstract

Recent flooding events in Spain have highlighted the need to develop real-time flood forecasts to estimate streamflows over the next few hours and days. Therefore, a meteorological forecast that provides possible precipitation for the upcoming hours combined with a hydrological model to simulate [...] Read more.

Recent flooding events in Spain have highlighted the need to develop real-time flood forecasts to estimate streamflows over the next few hours and days. Therefore, a meteorological forecast that provides possible precipitation for the upcoming hours combined with a hydrological model to simulate the rainfall-runoff processes in the basin and its flood response are needed. In this paper, a probabilistic flood forecasting tool is proposed for the Francolí river basin, located in Catalonia (Spain). For this purpose, the Real-time Interactive Basin Simulator (RIBS) distributed hydrological model was calibrated in this basin for a set of flood events. Then, a series of rainfall field forecasts based on the analog method have been used as input data in the hydrological model, obtaining a set of hydrographs for given flood events as output. Finally, a probabilistic forecast that supplies the probability distribution of the possible response flows of the Francolí river is provided for a set of episodes. Full article

(This article belongs to the Section Water Resources and Risk Management)

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19 pages, 1347 KB

Open AccessArticle

Enhancing MUSIC’s Capability for Performance Evaluation and Optimization of Established Urban Constructed Wetlands

by Fujia Yang, Shirley Gato-Trinidad and Iqbal Hossain

Hydrology 2025, 12(8), 219; https://doi.org/10.3390/hydrology12080219 - 18 Aug 2025

Abstract

The Model for Urban Stormwater Improvement Conceptualization (MUSIC) serves as a key hydrological tool for simulating urban stormwater runoff pollution and evaluating the treatment performance in Water-Sensitive Urban Designs like constructed wetlands (CWs). However, a significant limitation exists in MUSIC’s current inability to [...] Read more.

The Model for Urban Stormwater Improvement Conceptualization (MUSIC) serves as a key hydrological tool for simulating urban stormwater runoff pollution and evaluating the treatment performance in Water-Sensitive Urban Designs like constructed wetlands (CWs). However, a significant limitation exists in MUSIC’s current inability to model heavy metal contaminants, even though they are commonly found in urban stormwater and pose significant environmental risks. This eventually affects the model’s utility during critical planning phases for urban developments. Thus, there is a need to address this limitation. Field investigations were conducted across established CWs in residential and industrial catchments throughout Greater Melbourne, Australia. Through systematic monitoring and calibration, an approach was developed to extend MUSIC’s predictive capabilities to include several prevalent heavy metals. The results indicate that the enhanced model can generate plausible estimates for targeted metals while differentiating catchment-specific pollutant generation and treatment patterns. This advancement enhances MUSIC’s functionality as a planning support tool, enabling the preliminary assessment of heavy metal dynamics alongside conventional pollutants during both design and operational stages. The findings underscore the value of incorporating metal-specific parameters into stormwater models, offering improved support for urban water management decisions and long-term water quality protection. Full article

(This article belongs to the Special Issue Advances in Urban Hydrology and Stormwater Management)

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