Hydrology

28 pages, 3426 KiB

Open AccessArticle

The Utilization of a 3D Groundwater Flow and Transport Model for a Qualitative Investigation of Groundwater Salinization in the Ca Mau Peninsula (Mekong Delta, Vietnam)

by Tran Viet Hoan, Karl-Gerd Richter, Felix Dörr, Jonas Bauer, Nicolas Börsig, Anke Steinel, Van Thi Mai Le, Van Cam Pham, Don Van Than and Stefan Norra

Hydrology 2025, 12(5), 126; https://doi.org/10.3390/hydrology12050126 - 20 May 2025

Abstract

The Ca Mau Peninsula (CMP), the southernmost region of the Mekong Delta, is increasingly threatened by groundwater salinization, posing severe risks to both the freshwater supply and land sustainability. This study develops a three-dimensional, density-dependent groundwater flow and salinity transport model to investigate [...] Read more.

The Ca Mau Peninsula (CMP), the southernmost region of the Mekong Delta, is increasingly threatened by groundwater salinization, posing severe risks to both the freshwater supply and land sustainability. This study develops a three-dimensional, density-dependent groundwater flow and salinity transport model to investigate salinization dynamics across the CMP’s complex multi-aquifer system. Unlike previous studies that largely rely on model calibration, this research introduces a novel approach by systematically deriving the spatial distribution of longitudinal dispersivity based on sediment characteristics. Moreover, detailed land use mapping is integrated to assign spatially and temporally variable Total Dissolved Solids (TDS) values to the uppermost layers, thereby enhancing the model realism in areas where monitoring data are limited. The model was utilized not only to simulate the regional salinity evolution, but also to critically evaluate conceptual hypotheses related to the mechanisms driving groundwater salinization. Results reveal a strong influence of seasonal and land use factors on salinity variability in the upper aquifers, while deeper aquifers remain largely stable, affected primarily by paleosalinity and localized pumping. This integrated modeling approach contributes to a better understanding of regional-scale groundwater salinization and highlights both the potential and the limitations of numerical modeling under data-scarce conditions. The findings provide a valuable scientific basis for adaptive water resource management in vulnerable coastal zones. Full article

(This article belongs to the Topic Advances in Hydrogeological Research)

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24 pages, 3815 KiB

Open AccessArticle

Using High-Resolution Flood Hazard and Urban Heat Island Maps for High-Priority BGI Placement at the City Scale

by Stefan Reinstaller, Albert Wilhelm König and Dirk Muschalla

Hydrology 2025, 12(5), 125; https://doi.org/10.3390/hydrology12050125 - 20 May 2025

Abstract

This study presents a general workflow for creating a priority map for blue–green infrastructure (BGI) placement at the city scale, incorporating model-based benefit analysis. This workflow generates a BGI priority map, combining flood hazard and urban heat island maps, that guarantees multi-functional requirements [...] Read more.

This study presents a general workflow for creating a priority map for blue–green infrastructure (BGI) placement at the city scale, incorporating model-based benefit analysis. This workflow generates a BGI priority map, combining flood hazard and urban heat island maps, that guarantees multi-functional requirements are met. This approach was applied at a small study site in Feldbach, Austria. In the second part, we used the priority map generated to implement six BGI strategies in an integrated 1D-2D urban flood model and a semi-distributed hydrological model at high-priority and low-priority locations. The use of the efficiency index (EI_mod) enabled a multi-objective assessment. The results indicate that all the strategies led to a higher EI_mod when implemented in high-priority locations compared to low-priority locations. Our findings demonstrate that priority maps support decision making regarding where strategies should be implemented, providing remarkable benefits for water management objectives. Additionally, the findings highlight the importance of incorporating potential flooding areas to enhance prioritisation regarding flood hazard indicators. In future assessments, economic parameters, such as cost considerations, should also be integrated in order to optimise BGI placement efficiency. Full article

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

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26 pages, 27036 KiB

Open AccessArticle

Managed Aquifer Recharge (MAR) in Semiarid Regions: Water Quality Evaluation and Dynamics from the Akrotiri MAR System, Cyprus

by Maria Achilleos, Ourania Tzoraki and Evangelos Akylas

Hydrology 2025, 12(5), 123; https://doi.org/10.3390/hydrology12050123 - 19 May 2025

Abstract

Managed Aquifer Recharge (MAR) is increasingly being adopted across Europe to enhance water security in semiarid regions, with over 230 operational sites. The Akrotiri MAR system in Limassol, Cyprus, comprises 17 recharge ponds operating since 2016 to counteract saltwater intrusion. This study evaluates [...] Read more.

Managed Aquifer Recharge (MAR) is increasingly being adopted across Europe to enhance water security in semiarid regions, with over 230 operational sites. The Akrotiri MAR system in Limassol, Cyprus, comprises 17 recharge ponds operating since 2016 to counteract saltwater intrusion. This study evaluates MAR effectiveness by analyzing spatial and temporal variations in water quality from 2016 to 2020. Parameters analyzed include nutrients, metals, pesticides, pharmaceuticals, fecal indicators, physicochemical characteristics, recharge and pumping volumes, and groundwater levels. The results show that soil aquifer treatment (SAT) generally improves groundwater quality but certain boreholes exhibited elevated nitrate (range 12.70–31 mg/L), electrical conductivity (range 936–10,420 μs/cm), and chloride concentrations (range 117–1631 mg/L), attributed to recharge water quality, seawater intrusion, and nearby agricultural activities. Tertiary treated wastewater used for recharge occasionally exceeds permissible limits, particularly in E. coli (up to 2420/100 mL), chloride (up to 385 mg/L), and nitrogen (up to 41 mg/L). Supplementing recharge with dam-supplied freshwater improves groundwater quality and raises water levels. These findings underline the importance of continuous monitoring and effective management, adopting sustainable farming practices, and the strict control of recharge water quality. The study offers valuable insights for optimizing MAR systems and supports integrating MAR into circular water management frameworks to mitigate pollution and seawater intrusion, enhancing long-term aquifer sustainability. Full article

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

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20 pages, 6711 KiB

Open AccessArticle

Identification of Attribution of Runoff Variations in the Tumen River Basin Based on Budyko’s Hypothesis

by Dongqing Huo, Jiaqi Wu, Chunzi Zhao, Yongtao Yan, Weihong Zhu, Ri Jin and Jingya Zhou

Hydrology 2025, 12(5), 122; https://doi.org/10.3390/hydrology12050122 - 18 May 2025

Abstract

The Tumen River Basin (TRB), a critical China border region, has experienced a complex evolution of runoff due to climate change and human activities. This study aims to quantify the main drivers of runoff variations in the TRB based on the Budyko framework [...] Read more.

The Tumen River Basin (TRB), a critical China border region, has experienced a complex evolution of runoff due to climate change and human activities. This study aims to quantify the main drivers of runoff variations in the TRB based on the Budyko framework to assess the relative contributions of climate change and human activities to runoff fluctuations. Results indicate pronounced warming and increased precipitation in the TRB, while runoff exhibits a declining trend with temporal variability. Runoff decreased during 1956–1980 but increased post 1980. Overall, climate change is the dominant factor driving runoff fluctuations in the TRB. A comparison across different sub-basins shows that the contribution of climate change to runoff variations is higher in the middle and upper reaches of the Tumen River, reaching up to 93.8%. In the lower basin, human activities contribute significantly to runoff variations. Higher forest cover and reservoir construction help maintain the long-term stability of watershed runoff. This study provides a scientific basis and data support for water resources development and ecological protection in the basin. Full article

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23 pages, 3195 KiB

Open AccessArticle

The Impact of Expanding Eucalyptus Plantations on the Hydrology of a Humid Highland Watershed in Ethiopia

by Habtamu M. Fenta, Tammo S. Steenhuis, Teshager A. Negatu, Fasikaw A. Zimale, Wim Cornelis and Seifu A. Tilahun

Hydrology 2025, 12(5), 121; https://doi.org/10.3390/hydrology12050121 - 17 May 2025

Abstract

Changes in climate and land use significantly impact downstream water availability. Quantifying these effects in the Ethiopian Highlands is crucial, as 85% of the transboundary water in Egypt and Sudan originates from these highlands. While the impact of climate change on water availability [...] Read more.

Changes in climate and land use significantly impact downstream water availability. Quantifying these effects in the Ethiopian Highlands is crucial, as 85% of the transboundary water in Egypt and Sudan originates from these highlands. While the impact of climate change on water availability has been widely studied, few experimental studies have examined how it is affected by eucalyptus reforestation. Therefore, the objective was to investigate how eucalyptus expansion impairs water availability in the Ethiopian Highlands. The study was conducted in the 39 km² Amen watershed, located in the upper reaches of the Blue Nile. Rainfall data were collected from local agencies from 1990 to 2024, while streamflow data were available only for 2002–2009 and 2015–2018. Actual evapotranspiration was obtained using the WaPOR portal, and land use was derived from Landsat 5 TM and Landsat 8 OLI. The satellite images showed that the eucalyptus acreage increased from 238 ha in 2001 to 799 ha in 2024, or 24 ha y⁻¹. The actual evapotranspiration of eucalyptus was up to 30% greater than that of other land uses during the dry monsoon phase (January to March), resulting in decreased water storage in the watershed over a 23-year period. Since runoff is generated by saturation excess runoff, it takes longer for the valley bottoms to become saturated. In the 2002–2009 period, it took an average of around 160 mm of cumulative effective rain for significant runoff to start, and from 2015 to 2018, 274 mm was needed. Additionally, base flow decreased significantly. The annual runoff trended upward when the annual rainfall was more than the additional amount of water evaporated by eucalyptus, but decreased otherwise. Full article

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

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24 pages, 58090 KiB

Open AccessArticle

Flood Risk Assessment Under Climate Change Scenarios in the Wadi Ibrahim Watershed

by Asep Hidayatulloh and Jarbou Bahrawi

Hydrology 2025, 12(5), 120; https://doi.org/10.3390/hydrology12050120 - 14 May 2025

Abstract

Flooding poses a significant hazard to urban areas, particularly under the pressures of climate change and rapid urbanization. This study evaluates the flood risk in the Wadi Ibrahim watershed, located in Makkah Al-Mukarramah City, Kingdom of Saudi Arabia (KSA), by analyzing the impacts [...] Read more.

Flooding poses a significant hazard to urban areas, particularly under the pressures of climate change and rapid urbanization. This study evaluates the flood risk in the Wadi Ibrahim watershed, located in Makkah Al-Mukarramah City, Kingdom of Saudi Arabia (KSA), by analyzing the impacts of climate change on flood hazards. The analysis incorporates projections from the Coordinated Regional Climate Downscaling Experiment (CORDEX) regional climate model (RCM) for three climate scenarios: representative concentration pathway (RCP) 2.6, RCP 4.5 and RCP 8.5. A novel aspect of this study is the integration of 2D HEC-RAS rain-on-grid (RoG) hydrodynamic modeling with climate change projection analysis, which has not been previously applied in this watershed. Flood risk maps are generated for each scenario at three return periods: 50, 100, and 200 years. The results indicate an increasing flood volume and depth under future climate scenarios. The flood risk mapping shows an expansion of medium- and high-risk zones compared to current conditions. Under the current climate, the low-risk areas (0–0.5 m) slightly decrease from 13.9 km² (50 years) to 13.8 km² (200 years), while the medium- (0.5–2 m) and high-risk areas (>2 m) increase from 6.5 km² to 7.0 km² and from 7.2 km² to 9.8 km², respectively. Under RCP 2.6, the low-risk zones decline from 13.6 km² to 13.0 km², the medium-risk zones grow from 14.5 km² to 16.2 km², and the high-risk zones rise from 4.3 km² to 6.5 km². The higher emissions scenarios show greater risk increases, with the high-risk areas expanding from 5.3 km² to 12.0 km² under RCP 4.5, and from 9.5 km² to 16.6 km² under RCP 8.5. These findings underscore the escalating flood risks due to climate change and highlight the need for mitigation in the Wadi Ibrahim watershed. Full article

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43 pages, 8825 KiB

Open AccessArticle

Regional Analysis of the Dependence of Peak-Flow Quantiles on Climate with Application to Adjustment to Climate Trends

by Thomas Over, Mackenzie Marti and Hannah Podzorski

Hydrology 2025, 12(5), 119; https://doi.org/10.3390/hydrology12050119 - 14 May 2025

Abstract

Standard flood-frequency analysis methods rely on an assumption of stationarity, but because of growing understanding of climatic persistence and concern regarding the effects of climate change, the need for methods to detect and model nonstationary flood frequency has become widely recognized. In this [...] Read more.

Standard flood-frequency analysis methods rely on an assumption of stationarity, but because of growing understanding of climatic persistence and concern regarding the effects of climate change, the need for methods to detect and model nonstationary flood frequency has become widely recognized. In this study, a regional statistical method for estimating the effects of climate variations on annual maximum (peak) flows that allows for the effect to vary by quantile is presented and applied. The method uses a panel–quantile regression framework based on a location-scale model with two fixed effects per basin. The model was fitted to 330 selected gauged basins in the midwestern United States, filtered to remove basins affected by reservoir regulation and urbanization. Precipitation and discharge simulated using a water-balance model at daily and annual time scales were tested as climate variables. Annual maximum daily discharge was found to be the best predictor of peak flows, and the quantile regression coefficients were found to depend monotonically on annual exceedance probability. Application of the models to gauged basins is demonstrated by estimating the peak-flow distributions at the end of the study period (2018) and, using the panel model, to the study basins as-if-ungauged by using leave-one-out cross validation, estimating the fixed effects using static basin characteristics, and parameterizing the water-balance model discharge using median parameters. The errors of the quantiles predicted as-if-ungauged approximately doubled compared to the errors of the fitted panel model. Full article

(This article belongs to the Special Issue Runoff Modelling under Climate Change)

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29 pages, 8155 KiB

Open AccessArticle

Time-Series Analysis of Monitoring Data from Springs to Assess the Hydrodynamic Characteristics of a Coastal Discharge Zone: Example of Jurjevska Žrnovnica Springs in Croatia

by Andrej Stroj, Jasmina Lukač Reberski, Louise D. Maurice and Ben P. Marchant

Hydrology 2025, 12(5), 118; https://doi.org/10.3390/hydrology12050118 - 13 May 2025

Abstract

This study assesses the functioning of the karst aquifer system located on the Croatian coast of the Adriatic Sea, where saltwater intrusion often presents a major problem for freshwater supply. We use two years of sensor data collected from two coastal springs to [...] Read more.

This study assesses the functioning of the karst aquifer system located on the Croatian coast of the Adriatic Sea, where saltwater intrusion often presents a major problem for freshwater supply. We use two years of sensor data collected from two coastal springs to conduct a range of time-invariant and time-variant statistical analyses over various timescales. We perform separate analyses of the within-day and longer-term variation in the data as well as the interactions between the spring levels, salinity, rainfall, and sea levels. Such comprehensive analyses provide a greater understanding into the inner functioning of the intricate, heavily karstified aquifers. Time-invariant time-series analyses of the hourly data indicate that the spring levels and salinity are strongly controlled by sea levels. Furthermore, time-variant wavelet analyses demonstrate that the variation in spring levels in both springs has two modes defined by flow regime. Increases in the delay of the spring response to sea level indicate that aquifer diffusivity decreases in low flow conditions. Analyses facilitated the development of a conceptual model of the karst subsurface in the discharge zone. Using daily data, we constructed a linear mixed model of the spring levels. This model identified long-term sea level changes, rainfall from previous weeks, and seasonal recharge patterns as the primary factors influencing longer-term spring dynamics. Full article

(This article belongs to the Special Issue Characterization and Monitoring of Coastal Hydrological Environment for Assessing the Impact of Seawater Intrusion on Coastal Aquifers)

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29 pages, 23090 KiB

Open AccessArticle

Comparison of Flood Scenarios in the Cunas River Under the Influence of Climate Change

by Carlos-Enrique Torres-Mercado, Jhordan-Anderson Villafuerte-Jeremias, Giancarlo-Paul Guerreros-Ollero and Giovene Perez-Campomanes

Hydrology 2025, 12(5), 117; https://doi.org/10.3390/hydrology12050117 - 12 May 2025

Abstract

Climate change has a significant impact on river flows, leading to overflows and floods that affect populations, especially in Andean regions. This study examines flood scenarios in the Cunas River Basin (Junín, Peru) through hydrological and hydraulic simulations under various climate projections. A [...] Read more.

Climate change has a significant impact on river flows, leading to overflows and floods that affect populations, especially in Andean regions. This study examines flood scenarios in the Cunas River Basin (Junín, Peru) through hydrological and hydraulic simulations under various climate projections. A Reliability Ensemble Averaging (REA) approach was employed using CMIP6 climate models. In this analysis, precipitation data were processed, basin parameters were calculated, and peak flows and the extent of flood-prone areas were estimated. HEC-HMS software was used to simulate peak flows corresponding to return periods of 25, 50, 100, 139, and 200 years, while HEC-RAS was employed to determine flood zones. Model calibration and validation relied on historical precipitation data from nearby stations. The results indicate a considerable increase in peak flows and flood-prone areas due to climate change. A 3.32% increase in peak flow, a 55.35% expansion in flood-prone areas, and a 34.12% rise in flood depth are observed. These findings highlight the importance of implementing riverine protection structures. This study provides key information for flood risk management in the Peruvian highlands, using widely accepted tools to understand the hydrological response to climate change. Full article

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

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27 pages, 7434 KiB

Open AccessArticle

Baseflow Index Trends in Iowa Rivers and the Relationships to Other Hydrologic Metrics

by Elliot S. Anderson and Keith E. Schilling

Hydrology 2025, 12(5), 116; https://doi.org/10.3390/hydrology12050116 - 10 May 2025

Abstract

The US state of Iowa has experienced profound historical changes in its streamflow and baseflow. While several studies have noted increasing baseflow and baseflow index (BFI) values throughout the 20th century, analyses quantifying BFI trends in recent years or exploring spatial differences in [...] Read more.

The US state of Iowa has experienced profound historical changes in its streamflow and baseflow. While several studies have noted increasing baseflow and baseflow index (BFI) values throughout the 20th century, analyses quantifying BFI trends in recent years or exploring spatial differences in watersheds marked by varying land use and geologic properties have not been conducted. This study calculated annual values for BFI (and several other hydrologic metrics) using flow records from 42 Iowa stream gauges containing at least 50 years of uninterrupted measurements. While BFI overwhelmingly rose throughout the mid-1900s, circa 1990 it began to level off. In some areas of Iowa (e.g., the southwest), BFI has continued to rise over the past 30 years—albeit at a slower rate; in other regions, it has become stationary or declined. One site failed to follow this trend (Walnut Cr), the only basin to experience large-scale urbanization. Furthermore, BFI demonstrated a strong negative correlation to streamflow flashiness, indicating that rising baseflow has also made Iowa streams less dynamic. BFI was largely independent of overall streamflow. These results may suggest the increased influence of conservation practices and the diminishing impacts of tile drainage on the delivery of water to Iowa’s rivers. Full article

(This article belongs to the Special Issue Hydrological Processes in Agricultural Watersheds)

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24 pages, 4060 KiB

Open AccessArticle

River Stage Variability and Extremes in the Itacaiúnas Basin in the Eastern Amazon: Machine Learning-Based Modeling

by Luiz Rodolfo Reis Costa, Douglas Batista da Silva Ferreira, Renato Cruz Senna, Adriano Marlisom Leão de Sousa, Alexandre Melo Casseb do Carmo, João de Athaydes Silva, Jr., Felipe Gouvea de Souza and Everaldo Barreiros de Souza

Hydrology 2025, 12(5), 115; https://doi.org/10.3390/hydrology12050115 - 8 May 2025

Abstract

This study fosters tropical hydroclimatology research by implementing a computational modeling framework based on artificial neural networks and machine learning techniques. We evaluated two models, Multilayer Perceptron (MLP) and Support Vector Machine (SVM), in their ability to simulate 20-year monthly time series (2001–2021) [...] Read more.

This study fosters tropical hydroclimatology research by implementing a computational modeling framework based on artificial neural networks and machine learning techniques. We evaluated two models, Multilayer Perceptron (MLP) and Support Vector Machine (SVM), in their ability to simulate 20-year monthly time series (2001–2021) of minimum and maximum river stage in the Itacaiúnas River Basin (BHRI), located in the eastern Brazilian Amazon. The models were configured using explanatory variables spanning meteorological, climatological, and environmental dimensions, ensuring representation of key local and regional hydrological drivers. Both models exhibited robust performance in capturing fluviometric variability, with a comprehensive multimetric statistical evaluation indicating MLP’s superior accuracy over SVM. Notably, the MLP model reproduced the maximum river level during a sequence of extreme hydrological events linked to natural disasters (floods) across BHRI municipalities. These findings underscore the computational model’s potential for refining hydrometeorological products, thus supporting water resource management and decision-making processes in the Amazon region. Full article

(This article belongs to the Section Hydrology–Climate Interactions)

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22 pages, 7460 KiB

Open AccessArticle

Surface and Subsurface Heatwaves in the Hypersaline Dead Sea Caused by Severe Dust Intrusion

by Pavel Kishcha, Isaac Gertman and Boris Starobinets

Hydrology 2025, 12(5), 114; https://doi.org/10.3390/hydrology12050114 - 6 May 2025

Abstract

The relationship between global warming and heatwaves contributes to environmental risks. We investigate lake heatwaves (LHWs) in the Eastern Mediterranean, where dust intrusions are frequently observed. The dust intrusions are characterized by the arrival of warm air masses containing dust pollution from the [...] Read more.

The relationship between global warming and heatwaves contributes to environmental risks. We investigate lake heatwaves (LHWs) in the Eastern Mediterranean, where dust intrusions are frequently observed. The dust intrusions are characterized by the arrival of warm air masses containing dust pollution from the desert. In saline lakes, LHWs caused by dust intrusions have not been investigated in previous studies. In our study we focus on this point. It was found for the first time that, in the hypersaline Dead Sea, a severe dust intrusion (aerosol optical depth of over 3) caused the formation of LHWs, as appeared in September 2015. At the water surface, the LHWs were represented by abnormally high daily maximal and minimal surface water temperature (SWT) in comparison with their seasonally varied 90th percentile thresholds for 10 consecutive days (7–17 September). The surface LHWs’ intensity was up to 3 °C. Satellite (MODIS-Terra and METEOSAT) SWT did not detect the LHWs. Surface LHWs were accompanied by subsurface LHWs down to a depth of 20 m. The subsurface LHWs lasted longer (16 days) than the surface LHWs (10 days). There was a 4-day delay between the first date of the surface LHWs (7 September) and the start date of the subsurface LHWs (11 September). The maximal intensity of the subsurface LHWs decreased with depth from 1 m (0.6 °C) down to 5 m (0.3 °C), followed by an increase (up to 0.6 °C) at the deeper layers (from 10 m to 20 m). Taking into account that, over the Eastern Mediterranean, desert dust has increased during the past several decades, one can expect frequent occurrence of dust-related intense persistent heatwaves in the Dead Sea in the coming years. This will contribute to additional water heating and further drying up of the Dead Sea. Full article

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

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36 pages, 5817 KiB

Open AccessArticle

Evaluating Bias Correction Methods Using Annual Maximum Series Rainfall Data from Observed and Remotely Sensed Sources in Gauged and Ungauged Catchments in Uganda

by Martin Okirya and JA Du Plessis

Hydrology 2025, 12(5), 113; https://doi.org/10.3390/hydrology12050113 - 6 May 2025

Abstract

This research addresses the challenge of bias in Remotely Sensed Rainfall (RSR) datasets used for hydrological planning in Uganda’s data-scarce, ungauged catchments. Four bias correction methods, Quantile Mapping (QM), Linear Transformation (LT), Delta Multiplicative (DM), and Polynomial Regression (PR), were evaluated using daily [...] Read more.

This research addresses the challenge of bias in Remotely Sensed Rainfall (RSR) datasets used for hydrological planning in Uganda’s data-scarce, ungauged catchments. Four bias correction methods, Quantile Mapping (QM), Linear Transformation (LT), Delta Multiplicative (DM), and Polynomial Regression (PR), were evaluated using daily rainfall data from four gauged stations (Gulu, Soroti, Jinja, Mbarara). QM consistently outperformed other methods based on statistical metrics, e.g., for National Oceanic and Atmospheric Administration Climate Prediction Center (NOAA_CPC) RSR data at Gulu, Root-Mean-Square Error (RMSE) was reduced from 29.20 mm to 19.00 mm, Mean Absolute Error (MAE) reduced from 22.44 mm to 12.84 mm, and Percent Bias (PBIAS) reduced from −19.23% to 1.05%, and improved performance goodness-of-fit tests (KS = 0.03, p = 1.00), while PR, though statistically strong, failed due to overfitting. A bias correction framework was developed for ungauged catchments, using predetermined bias factors derived from observed station data. Validation at Arua (tropical savannah) and Fort Portal (tropical monsoon) demonstrated significant improvements in RSR data when the bias correction framework was applied. At Arua, bias correction of Climate Hazards Group InfraRed Precipitation with Station (CHIRPS) data reduced RMSE from 49.14 mm to 21.41 mm, MAE from 45.74 mm to 17.38 mm, and PBIAS from −59.83% to −8.18%, while at Fort Portal, bias correction of the CHIRPS dataset reduced RMSE from 28.35 mm to 15.02 mm, MAE from 25.28 mm to 11.35 mm, and PBIAS from −46.2% to 4.74%. Our research concludes that QM is the most effective method, and that the framework is a tool for improving RSR data in ungauged catchments. Recommendations for future work includes machine learning integration and broader regional validation. Full article

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32 pages, 3423 KiB

Open AccessArticle

Investigation of Sediment Characteristics and Nutrient Content in Relation to Pilot Dredging at Kis-Balaton Water Protection System (Hungary)

by Hilda Hernádi, András Makó, Zsófia Lovász, Sándor Szoboszlay, Péter Harkai, Judit Háhn, Mihály Kocsis, Eszter Schöphen, Zoltán Tóth, András Bidló, Márk Rékási, Árpád Ferincz, Gábor Csitári and Gyöngyi Barna

Hydrology 2025, 12(5), 112; https://doi.org/10.3390/hydrology12050112 - 6 May 2025

Abstract

The internal nutrient load of natural and artificial lakes is a worldwide problem. To minimize its potential risks, the dredging of the highly eutrophic shallow first reservoir of Kis-Balaton (Lake Hídvégi) is planned in the near future. Our study aimed to evaluate the [...] Read more.

The internal nutrient load of natural and artificial lakes is a worldwide problem. To minimize its potential risks, the dredging of the highly eutrophic shallow first reservoir of Kis-Balaton (Lake Hídvégi) is planned in the near future. Our study aimed to evaluate the potential effects of dredging and desiccation on water and sediment quality. Experimental dredging was carried out in the northernmost part of Lake Hídvégi (2023). The physical and chemical characteristics of the sediment and nutrient loss during desiccation were examined in a column experiment. The relationships between the properties of leachate and sediment were identified using principal component analysis (SPSS). Spatial variations in sediment particle size distribution, nutrient content, and other chemical parameters (e.g., organic matter) suggest that deeper core sampling than the depth of preliminary dredging is necessary for a more comprehensive assessment of potential impacts. We found that spatiotemporally varying the dominance of chemical and biological processes affects the amount of and changes in phosphorus fractions under lake-/sediment-specific conditions. The readily available calcium- and iron-bound phosphorus, texture, and organic matter content of the sediment play an important role in phosphorus fixation/release. Based on our results, dredging and desiccation are feasible within the intended operating parameters. The sediment’s composition does not preclude potential agricultural disposal. Full article

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

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20 pages, 10040 KiB

Open AccessArticle

Challenges and Future Opportunities of Groundwater Resources for Drinking Water Use: A Case Study of Slatina nad Bebravou (Slovakia)

by Marek Illes, Peter Lukac, Peter Halaj, Andrej Valek, Vera Hubacikova and Tatiana Kaletova

Hydrology 2025, 12(5), 111; https://doi.org/10.3390/hydrology12050111 - 6 May 2025

Abstract

The interlinked issues of climate change and increasing water demand are creating high pressure on water resources. In Slovakia, groundwater is a principal resource for human consumption. Consequently, an analysis was conducted of the current water yields of three springs, river discharges and [...] Read more.

The interlinked issues of climate change and increasing water demand are creating high pressure on water resources. In Slovakia, groundwater is a principal resource for human consumption. Consequently, an analysis was conducted of the current water yields of three springs, river discharges and precipitation trends, from several points of view. As a case study, we selected the area around Slatina nad Bebravou (Slovakia), which has the most relevant database. Descriptive statistics, the Mann–Kendall test and Sen’s slope were used for the trend analysis. The findings indicate that the current capacity of springs is sufficient to meet the present needs of water users. However, the downward trend in abundance, the increasing trend in water withdrawal, and the current poor state of infrastructure point to an early tipping point. Data analysis revealed a problem with the yield of springs, especially in the summer and autumn months. Full article

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

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15 pages, 2759 KiB

Open AccessArticle

Quantitative Approach to the Early Evaluation of Agricultural Reservoir Overflow Risk

by Kyuhyun Shim, Youngkyu Jin, Dongwoo Ko and Joon Heo

Hydrology 2025, 12(5), 110; https://doi.org/10.3390/hydrology12050110 - 5 May 2025

Abstract

Climate change has intensified extreme rainfall events, increasing the risk of overflow in agricultural reservoirs originally designed without flood control. This study presents a practical approach for assessing the overflow risk by incorporating both hydrological and structural factors. The key evaluation indicators used [...] Read more.

Climate change has intensified extreme rainfall events, increasing the risk of overflow in agricultural reservoirs originally designed without flood control. This study presents a practical approach for assessing the overflow risk by incorporating both hydrological and structural factors. The key evaluation indicators used for analysis were freeboard (height from the flood level to the embankment level), height from the full water level to the embankment level, inflow–outflow relationship, and flood management capacity relative to the watershed area. Based on the design standards, reservoirs in Jeollanam-do were selected for assessment, and those with a high overflow risk were identified. Rainfall runoff simulations were conducted to evaluate the reservoirs, and the results indicated that considering all four indicators allowed an effective assessment of overflow risk. Multiple regression analysis yielded an R² value of 0.79, suggesting that the relationships among the selected indicators were suitable and had high explanatory power. The findings of this study are expected to provide a practical method for rapidly assessing reservoir overflow risks and developing effective flood response strategies. Full article

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23 pages, 5043 KiB

Open AccessArticle

Assessing Hydrological Alterations and Environmental Flow Components in the Beht River Basin, Morocco, Using Integrated SWAT and IHA Models

by Fatima Daide, Thomas Hasiotis, Soumaya Nabih, Soufiane Taia, Abderrahim Lahrach, Eleni-Ioanna Koutsovili and Ourania Tzoraki

Hydrology 2025, 12(5), 109; https://doi.org/10.3390/hydrology12050109 - 2 May 2025

Abstract

This study presents a comprehensive analysis of hydrological alterations and environmental flow components in the Beht River basin in northwest Morocco, using a coupled approach involving the Soil and Water Assessment Tool (SWAT) for hydrological modeling, the Indicators of Hydrologic Alteration (IHA) for [...] Read more.

This study presents a comprehensive analysis of hydrological alterations and environmental flow components in the Beht River basin in northwest Morocco, using a coupled approach involving the Soil and Water Assessment Tool (SWAT) for hydrological modeling, the Indicators of Hydrologic Alteration (IHA) for flow regime assessment, and the Standardized Precipitation Index (SPI) for drought characterization. The SWAT model, run on a daily time step, showed satisfactory performance in terms of statistical criteria for both calibration and validation periods, despite encountering limitations, and proved its ability to simulate and reproduce the hydrological behavior of the basin. Using the IHA, we investigated changes in the hydrological regime over two distinct periods, revealing significant hydrological alteration. The SPI analysis supported these findings by highlighting the variable impacts of dry and wet periods on the hydrological regime, thus validating the observed changes in river flow indicators. As a preliminary step toward establishing environmental flows in the Beht River, this study provides foundational insights into the temporal evolution of its hydrology. These findings offer a valuable basis for better water resource management and conservation in the region. Full article

(This article belongs to the Special Issue Hydrological Modelling for the Sustainable Management of Water Resources in River Basins)

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3 pages, 119 KiB

Open AccessOpinion

Some Human Dimensions of Understanding Flood Risk Management

by Edmund C. Penning-Rowsell

Hydrology 2025, 12(5), 108; https://doi.org/10.3390/hydrology12050108 - 30 Apr 2025

Abstract

Flood risk management involves managing the consequences of flooding as well at its hazard characteristics. This means attending to the human effects of floods and flood risk reduction. These effects are many and varied and are often poorly understood by those who make [...] Read more.

Flood risk management involves managing the consequences of flooding as well at its hazard characteristics. This means attending to the human effects of floods and flood risk reduction. These effects are many and varied and are often poorly understood by those who make the relevant decisions. This short piece addresses this issue and calls for a greater awareness of what measures those at risk are motivated likely to undertake to reduce the risks that they personally face. Full article

(This article belongs to the Special Issue Understanding, Forecasting and Control of Flooding and Pollution in the Urban Environment: The 10th Anniversary of Hydrology)

22 pages, 7273 KiB

Open AccessArticle

Hydrological Modelling and Remote Sensing for Assessing the Impact of Vegetation Cover Changes

by Ángela M. Moreno-Pájaro, Aldhair Osorio-Gastelbondo, Dalia A. Moreno-Egel, Oscar E. Coronado-Hernández, María A. Narváez-Cuadro, Manuel Saba and Alfonso Arrieta-Pastrana

Hydrology 2025, 12(5), 107; https://doi.org/10.3390/hydrology12050107 - 29 Apr 2025

Abstract

This study presents a multi-temporal analysis of vegetation cover changes in the Guayepo stream watershed (Cartagena de Indias, Colombia) for 2000, 2010, and 2020 and their impact on surface runoff generation. Hydrological data from 1974 to 2019 were processed to model intensity–duration–frequency (IDF) [...] Read more.

This study presents a multi-temporal analysis of vegetation cover changes in the Guayepo stream watershed (Cartagena de Indias, Colombia) for 2000, 2010, and 2020 and their impact on surface runoff generation. Hydrological data from 1974 to 2019 were processed to model intensity–duration–frequency (IDF) curves and simulate heavy rainfall events using six storms of nine-hour duration. Following the Soil Conservation Service guidelines, these were used to estimate runoff flows for return periods of 25, 50, and 100 years via the curve number method in HEC-HMS. Vegetation cover was assessed using the CORINE land cover methodology applied to official land use maps. The analysis revealed a significant loss of natural vegetation: dense forest cover declined dramatically from 14.38% in 2000 to 0% in 2020, and clean pastures were reduced by 46%. In contrast, weedy pastures and pasture mosaics with natural areas increased by 299% and 136%, respectively, reflecting a shift towards more degraded land cover types. As a result of these changes, total runoff flows of the model increased by 9.7% and 4.3% under antecedent moisture conditions I and II, respectively, for the 100-year return period. These findings reveal ongoing degradation of the watershed’s natural cover, linked to expanding agricultural uses and changes in vegetation structure. The decline in forested areas has increased surface runoff, elevating flood risk and compromising the watershed’s hydrological regulation. The study suggests that integrated land management and ecological restoration strategies could be key in preserving hydrological ecosystem services and reducing the negative impacts of land use change. Full article

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