Hydrology

29 pages, 15893 KiB

Open AccessArticle

Application of Temporal Fusion Transformers to Run-Of-The-River Hydropower Scheduling

by Rafael Francisco, José Pedro Matos, Rui Marinheiro, Nuno Lopes, Maria Manuela Portela and Pedro Barros

Hydrology 2025, 12(4), 81; https://doi.org/10.3390/hydrology12040081 - 3 Apr 2025

Abstract

This study explores the application of Temporal Fusion Transformers (TFTs) to improve the predictability of hourly potential hydropower production for a small run–of–the–river hydropower plant in Portugal. Accurate hourly power forecasts are essential for optimizing participation in the spot electricity market, where deviations [...] Read more.

This study explores the application of Temporal Fusion Transformers (TFTs) to improve the predictability of hourly potential hydropower production for a small run–of–the–river hydropower plant in Portugal. Accurate hourly power forecasts are essential for optimizing participation in the spot electricity market, where deviations incur penalties. This research introduces the novel application of the TFT, a deep–learning model tailored for time series forecasting and uncovering complex patterns, to predict hydropower production based on meteorological data, historical production records, and plant capacity. Key challenges such as filtering observed hydropower outputs (to remove strong, and unpredictable human influence) and adapting the historical series to installed capacity increases are discussed. An analysis of meteorological information from several sources, including ground information, reanalysis, and forecasting models, was also undertaken. Regarding the latter, precipitation forecasts from the European Centre for Medium–Range Weather Forecasts (ECMWF) proved to be more accurate than those of the Global Forecast System (GFS). When combined with ECMWF data, the TFT model achieved significantly higher accuracy in potential hydropower production predictions. This work provides a framework for integrating advanced machine learning models into operational hydropower scheduling, aiming to reduce classical modeling efforts while maximizing energy production efficiency, reliability, and market performance. Full article

(This article belongs to the Special Issue Editorial Board Members’ Collection Series: The Flood Estimation and Forecasting Chain: Meteorological–Hydrological–Hydraulic Forecasts and Predictive Uncertainty towards Operational Decisions)

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19 pages, 4549 KiB

Open AccessArticle

Modeling the Impact of Water Hyacinth on Evapotranspiration in the Chongón Reservoir Using Remote Sensing Techniques: Implications for Aquatic Ecology and Invasive Species Management

by Carolina Cárdenas-Cuadrado, Luis Morocho, Juan Guevara, Manuel Cepeda, Tomás Hernández-Paredes, Diego Arcos-Jácome, Carlos Ortega and Diego Portalanza

Hydrology 2025, 12(4), 80; https://doi.org/10.3390/hydrology12040080 - 2 Apr 2025

Abstract

The proliferation of water hyacinth (Eichhornia crassipes) in the Chongón Reservoir, located within the Parque Lago National Recreation Area in Guayaquil, Ecuador, poses significant challenges to the local aquatic ecosystem and water resource management. This study assesses the impact of water [...] Read more.

The proliferation of water hyacinth (Eichhornia crassipes) in the Chongón Reservoir, located within the Parque Lago National Recreation Area in Guayaquil, Ecuador, poses significant challenges to the local aquatic ecosystem and water resource management. This study assesses the impact of water hyacinth coverage on evapotranspiration rates over a 20-year period from 2002 to 2022 using remote sensing data and geospatial analysis. The Normalized Difference Vegetation Index (NDVI), derived from Landsat satellite imagery, along with meteorological records, was utilized to model the spatial and temporal dynamics of water hyacinth coverage and its effects on evapotranspiration. Our results indicate that water hyacinth coverage fluctuates significantly between rainy and dry seasons, increasing from covering 10.42% of the reservoir area in 2002 to a peak of 42.33% in 2017 during the rainy seasons. A strong positive correlation (

r = 0.92

,

p < 0.001

) was found between water hyacinth coverage and net daily water loss due to evapotranspiration. The evapotranspiration rates associated with water hyacinth were significantly higher during the rainy season (mean of 2309.90 mm/year) compared to the dry season (mean of 1917.87 mm/year). These elevated evapotranspiration rates contribute to increased water loss from the reservoir, potentially impacting water availability for municipal and agricultural use. Controlling the spread of water hyacinth is therefore crucial for preserving the reservoir’s ecological integrity and ensuring sustainable water resource management. The findings of this study provide valuable insights for informing management strategies aimed at mitigating the effects of invasive species on freshwater resources and maintaining aquatic ecosystem health. Full article

(This article belongs to the Special Issue GIS Modelling of Evapotranspiration with Remote Sensing)

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19 pages, 8968 KiB

Open AccessArticle

Role of Hungry Water on Sediment Dynamics: Assessment of Valley Degradation, Bed Material Changes and Flood Inundation in Pamba River During Kerala Flood, 2018

by Sreelash Krishnan Kutty, Padmalal Damodaran, Jeenu Mathai, Micky Mathew, Asha Rani, Rajat Kumar Sharma and Maya Kesavan

Hydrology 2025, 12(4), 79; https://doi.org/10.3390/hydrology12040079 - 1 Apr 2025

Abstract

Flood frequencies, along with the associated loss of life and property, have risen significantly due to climate change and increasing human activities. While prior research has primarily focused on high-intensity rainfall events and reservoir management in flood management, the influence of sediment-starved water—termed [...] Read more.

Flood frequencies, along with the associated loss of life and property, have risen significantly due to climate change and increasing human activities. While prior research has primarily focused on high-intensity rainfall events and reservoir management in flood management, the influence of sediment-starved water—termed “hungry water”—released from dams in controlling flood dynamics has not gained much attention. The present study is aimed at exploring the potential role of sediment-starved water, or the “hungry water effect” on the valley degradation, bed material changes and flood inundation in the Pamba River during the Kerala Flood, 2018, through a detailed characterization of bed materials and their deposition in the channel bed. The release of sediment-starved water from the Kakki reservoir during the episodic precipitation event (15 to 17 August 2018) resulted in significant bed degradation and scouring of the valley slopes, leading to the deposition of large boulders and rock masses and the inundating of approximately 196 km² of floodplains. This study highlights the need for integrated sediment management strategies in reservoir operations by providing essential insights into sediment transport dynamics during extreme weather events. Understanding these processes is crucial for formulating effective flood mitigation strategies and improving the resilience of riverine ecosystems, particularly as the interaction between intense rainfall and sediment-depleted releases significantly exacerbated the flood’s severity. Full article

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6 pages, 533 KiB

Open AccessOpinion

Urban Flood Risk and Resilience: How Can We Protect Our Cities from Flooding?

by Dragan Savić

Hydrology 2025, 12(4), 78; https://doi.org/10.3390/hydrology12040078 - 31 Mar 2025

Abstract

This article draws on over 40 years of the author’s experience with hydroinformatics tools for water and sustainability challenges, including flooding. It aims to spark discussion on urban flood risk and resilience rather than provide a literature review or definitive answers. Assessing urban [...] Read more.

This article draws on over 40 years of the author’s experience with hydroinformatics tools for water and sustainability challenges, including flooding. It aims to spark discussion on urban flood risk and resilience rather than provide a literature review or definitive answers. Assessing urban flood risk and resilience is complex due to the spatio-temporal nature of rainfall, urban landscape features (e.g., buildings, roads, bridges and underpasses) and the interaction between aboveground and underground drainage systems. Flood simulation methods have evolved to analyse flood mitigation schemes, damage evaluation, flood risk mapping and green infrastructure impacts. Advances in terrain mapping technologies have improved flood analyses. Despite investments in flood management infrastructure, a residual flood risk remains, necessitating an understanding of the recovery and return to normality post-flood. Both risk and resilience approaches are essential for urban flood planning and management. Future challenges and opportunities include both technological and governance solutions, with artificial intelligence advancements offering the potential for digital twins to better protect urban communities and enhance the recovery from flood disasters. 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)

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22 pages, 4166 KiB

Open AccessArticle

Quantifying Mercury Use and Modeling Its Fate and Transport in Artisanal and Small-Scale Gold Mining in the Lom Basin

by Marie Sorella Bella Atangana, Pol Magermans, Jules Rémy Ndam Ngoupayou and Jean-François Deliege

Hydrology 2025, 12(4), 77; https://doi.org/10.3390/hydrology12040077 - 28 Mar 2025

Abstract

This research quantifies mercury use and models its transport in artisanal and small-scale gold mining (ASGM) in the Lom River during two key periods of intense mining activities and high water flow. Mercury concentrations from mining surfaces were estimated using a soil input [...] Read more.

This research quantifies mercury use and models its transport in artisanal and small-scale gold mining (ASGM) in the Lom River during two key periods of intense mining activities and high water flow. Mercury concentrations from mining surfaces were estimated using a soil input function approach. Industrial mercury releases were assessed with a ratio-based approach using official gold production data and the mercury-to-gold ratio. The PEGASE model was applied to simulate mercury transport and pollution in the Lom River and to analyze the pressure–impact relationships of ASGM activities on surface water. Field measurements of the mercury concentrations in the Lom River during the dry and rainy seasons of 2021 were used to validate modeling results. The results indicate that volatilization has a more significant impact on the predicted mercury concentrations than photodissociation. Three scenarios were modeled for mercury use: whole ore amalgamation (WOA), combined whole and concentrate ore amalgamation (WOA + COA), and concentrate ore amalgamation (COA). Mercury use estimates ranged from 2250–7500 kg during intense activity to 1260–4200 kg during high water for the gold production of 750 and 525 kg, respectively. Industrial discharges dominated mercury pollution during the dry season while leaching from mining surfaces was the primary contributor during the rainy season. Full article

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20 pages, 7282 KiB

Open AccessArticle

Stormwater Management and Late-Winter Chloride Runoff into an Urban Lake in Minnesota, USA

by Neal D. Mundahl and John Howard

Hydrology 2025, 12(4), 76; https://doi.org/10.3390/hydrology12040076 - 28 Mar 2025

Abstract

Stormwater runoff containing road deicing salts has led to the increasing salinization of surface waters in northern climates, and urban municipalities are increasingly being mandated to manage stormwater runoff to improve water quality. We assessed chloride concentrations in runoff from late-winter snowmelt and [...] Read more.

Stormwater runoff containing road deicing salts has led to the increasing salinization of surface waters in northern climates, and urban municipalities are increasingly being mandated to manage stormwater runoff to improve water quality. We assessed chloride concentrations in runoff from late-winter snowmelt and rainfall events flowing into an urban Minnesota, USA, lake during two different years, predicting that specific stormwater drainages with greater concentrations of roadways and parking lots would produce higher chloride loads during runoff than other drainages with fewer impervious surfaces. Chloride levels were measured in runoff draining into Lake Winona via 11 stormwater outfalls, a single channelized creek inlet, and two in-lake locations during each snowmelt or rainfall event from mid-February through early April in 2021 and 2023. In total, 33% of outfall runoff samples entering the lake collected over two years had chloride concentrations exceeding the 230 ppm chronic standard for aquatic life in USA surface waters, but no sample exceeded the 860 ppm acute standard. Chloride concentrations in outfall runoff (mean ± SD; 190 ± 191 ppm, n = 143) were significantly higher than in-lake concentrations (43 ± 14 ppm, n = 25), but chloride levels did not differ significantly between snowmelt and rainfall runoff events. Runoff from highway locations had higher chloride concentrations than runoff from residential areas. Site-specific chloride levels were highly variable both within and between years, with only a single monitored outfall displaying high chloride levels in both years. There are several possible avenues available within the city to reduce deicer use, capture and treat salt-laden runoff, and prevent or reduce the delivery of chlorides to the lake. Full article

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3 pages, 146 KiB

Open AccessOpinion

Challenges and Opportunities for Urban Water That Is Fit to Play in

by David Werner

Hydrology 2025, 12(4), 75; https://doi.org/10.3390/hydrology12040075 - 28 Mar 2025

Abstract

As cities in Europe and beyond recognize the flood protection, recreational, and biodiversity benefits of blue-green spaces, human interaction with urban water is increasing. This trend raises public health concerns that must be addressed by the scientific community, regulators, and the water industry. [...] Read more.

As cities in Europe and beyond recognize the flood protection, recreational, and biodiversity benefits of blue-green spaces, human interaction with urban water is increasing. This trend raises public health concerns that must be addressed by the scientific community, regulators, and the water industry. Advances in measurement and modelling have made continuous city-scale water quality monitoring for real-time risk communication a realistic goal. Achieving this goal requires quality-assured data on hydrology, water quality, drainage infrastructure, and land use, along with robust mechanistic models and a deeper understanding of human behaviour. 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)

23 pages, 13387 KiB

Open AccessArticle

Comparative Analysis of SPEI and WEI⁺ Indices: Drought and Water Scarcity in the Umbria Region, Central Italy

by Stefano Casadei, Sara Venturi and Silvia Di Francesco

Hydrology 2025, 12(4), 74; https://doi.org/10.3390/hydrology12040074 - 27 Mar 2025

Abstract

The purpose of this study is to assess the possibility of relating two phenomena: first, meteorological drought, which is exclusively dependent on climate; second, water scarcity and its uses, which are predominantly anthropogenic in nature. Sometimes these phenomena may overlap, with the former [...] Read more.

The purpose of this study is to assess the possibility of relating two phenomena: first, meteorological drought, which is exclusively dependent on climate; second, water scarcity and its uses, which are predominantly anthropogenic in nature. Sometimes these phenomena may overlap, with the former amplifying the latter, but direct correlation is not always highlightable due to the anthropogenic character of water shortage and the variability of water supply sources. In the literature, many papers evaluate these two phenomena separately: in particular, the SPEI (Standardized Precipitation-Evapotranspiration Index) is widely used for detecting meteorological drought, while the link between water shortage and its uses is assessed through an index of water resource exploitation, WEI⁺ (Water Exploitation Index Plus), which is based on the calculation of an anthropogenic factor, withdrawals net of restitutions. Specifically, this study examines the SPEI and WEI⁺, respectively, calculated for the July–August–September quarter (SPEI3 sept) and during the low-flow period (WEI⁺_EF low flow), according to the environmental flow constraint. These periods are considered seasonally overlapping in the study area of the Umbria region. The results analyzed by spatial method show the more critical areas, where SPEI3 sept and WEI⁺_EF overlap their critical values, respectively, <−1.0 and >100%. The proposed methodological approach provides stakeholders in the water sector with essential information to adopt a proactive approach to drought phenomena. Full article

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23 pages, 3999 KiB

Open AccessArticle

Water Resource Assessment and Management in Dalha Basalts Aquifer (SW Djibouti) Using Numerical Modeling

by Moumtaz Razack, Mohamed Jalludin and Behailu Birhanu

Hydrology 2025, 12(4), 73; https://doi.org/10.3390/hydrology12040073 - 27 Mar 2025

Abstract

In the Republic of Djibouti (Horn of Africa), fractured volcanic aquifers serve as the primary water resource. The country’s climatic characteristics (arid climate, average rainfall of 140 mm/year, and absence of surface water) have led to intensive groundwater exploitation to meet increasing water [...] Read more.

In the Republic of Djibouti (Horn of Africa), fractured volcanic aquifers serve as the primary water resource. The country’s climatic characteristics (arid climate, average rainfall of 140 mm/year, and absence of surface water) have led to intensive groundwater exploitation to meet increasing water demands. This study focuses on the Dalha basalts aquifer in the Dikhil region. The Dikhil region, located in the southwest of Djibouti and bordering Ethiopia, spans 7200 km². Its population is estimated at 112,000 inhabitants. The Dalha aquifer is intensively exploited to supply the region and its capital, the city of Dikhil (35,000 inhabitants). The primary objective of this work is to assess the current resources of this aquifer using numerical modeling and its capacity to meet future water demands under the impact of climate change. The RCP 2.6 (Representative Concentration Pathway) was used to simulate the climate scenario up to 2100. Superficial recharge is estimated at 3.86 × 10⁶ m³/year. The current wellfield abstraction amounts to 2.34 × 10⁶ m³/year, accounting for 60% of the aquifer’s recharge. The simulation under RCP 2.6 indicates a declining trend in the water table. These findings highlight the fragile state of the Dalha aquifer, which is critical for the socioeconomic stability of the region. Given its current vulnerability, any increase in exploitation is unsustainable, despite the growing water demand in the Dikhil region. To tackle this challenge, we recommend conducting further studies to deepen the understanding of this system and implementing a real-time monitoring network to track aquifer changes. Full article

(This article belongs to the Special Issue Hydrological Modeling and Sustainable Water Resources Management)

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23 pages, 2956 KiB

Open AccessArticle

Combining Hydro-Geochemistry and Environmental Isotope Methods to Evaluate Groundwater Quality and Health Risk (Middle Nile Delta, Egypt)

by Atef M. Abu Khatita, Robert van Geldern, Abdullah O. Bamousa, Dimitrios E. Alexakis, Esam Ismail, Wael R. Abdellah and Ibrahim A. A. Babikir

Hydrology 2025, 12(4), 72; https://doi.org/10.3390/hydrology12040072 - 27 Mar 2025

Abstract

This study aims to assess the vulnerability of groundwater in the Nile Delta to contamination and evaluate its suitability for drinking and irrigation. A total of 28 groundwater wells (ranging from 23 to 120 m in depth) and two Nile surface water samples [...] Read more.

This study aims to assess the vulnerability of groundwater in the Nile Delta to contamination and evaluate its suitability for drinking and irrigation. A total of 28 groundwater wells (ranging from 23 to 120 m in depth) and two Nile surface water samples were analyzed for total dissolved solids (TDS), heavy metals, groundwater quality index (GWQI), and hazard quotient (HQ). The findings reveal that deep groundwater (60–120 m) displays paleo-water characteristics, with low TDS, total hardness, and minimal heavy metal contamination. In contrast, shallow groundwater (<60 m) is categorized into three groups: paleo-water-like, recent Nile water with elevated TDS and heavy metals, and mixed water. Most groundwater samples (64%) are of the Ca-HCO₃ type, while 28% are Na-HCO₃, and 8% are Na-Cl, the latter associated with sewage infiltration. Most groundwater samples were deemed suitable for irrigation, but drinking water quality varied significantly—4% were classified as “excellent”, 64% as “good”, and 32% as “poor”. HQ analysis identified manganese as a significant health risk, with 56% of shallow groundwater samples exceeding safe levels. These findings highlight the varying groundwater quality in the Nile Delta, emphasizing concerns regarding health risks from heavy metals, particularly manganese, and the need for improved monitoring and management. Full article

(This article belongs to the Special Issue Novel Approaches in Contaminant Hydrology and Groundwater Remediation)

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25 pages, 4338 KiB

Open AccessArticle

Assessment of Satellite-Based Rainfall Products for Flood Modeling in the Ouémé River Basin in Benin (West Africa)

by Marleine Bodjrènou, Kaidi Peng, Dognon Jules Afféwé, Jean Hounkpè, Hagninou E. V. Donnou, Julien Adounkpè and Aristide B. Akpo

Hydrology 2025, 12(4), 71; https://doi.org/10.3390/hydrology12040071 - 27 Mar 2025

Abstract

Reliable rainfall data are critical for managing hydrometeorological hazards in West Africa, yet they are often sparse and temporally inconsistent. The current study assessed the accuracy of four near real-time satellite-based rainfall data, namely IMERGv7 Late, IMERGv6 Early, GSMAP-NRT and PERSIANN-DIR Now, for [...] Read more.

Reliable rainfall data are critical for managing hydrometeorological hazards in West Africa, yet they are often sparse and temporally inconsistent. The current study assessed the accuracy of four near real-time satellite-based rainfall data, namely IMERGv7 Late, IMERGv6 Early, GSMAP-NRT and PERSIANN-DIR Now, for rainfall estimation and hydrological modeling in the Ouémé basin. These datasets were compared with ground-based rainfall data, bias-corrected and used to calibrate and validate the hydrological model HBV light. While they demonstrated qualitative accuracy, their quantitative estimation shows obvious discrepancies on a daily scale, varying across subdomains. The original IMERGv7 product outperforms others in capturing the rainfall pattern and amount (KGE > 0.6), while GSMAP performs moderately (KGE ≈ 0.51) and IMERGv6 and PERSIANN show lower reliability with KGE < 0.5. Quantile mapping emerges as the most effective bias-correction method, improving the performance of all satellite products, with RMSE reductions ≤ 15%. The results of hydrological simulations demonstrate the potential of satellite-based rainfall, particularly IMERGv7 and corrected IMERGv6 (NSE > 0.75), for near real-time flood monitoring and water management in the study area. This study underscores their suitability as valuable alternatives to ground-based data for flood management decision making in the Ouémé basin. Full article

(This article belongs to the Section Hydrological and Hydrodynamic Processes and Modelling)

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18 pages, 3834 KiB

Open AccessArticle

Geogenic Contamination of Groundwater in a Highland Watershed: Hydrogeochemical Assessment, Source Apportionment, and Health Risk Evaluation of Fluoride and Nitrate

by Kashif Alam, Muhammad Nafees, Wajid Ali, Said Muhammad and Abdur Raziq

Hydrology 2025, 12(4), 70; https://doi.org/10.3390/hydrology12040070 - 26 Mar 2025

Abstract

Groundwater is one of the major sources of freshwater supply for drinking and domestic purposes. This study evaluates the hydrogeochemical processes, groundwater quality for human consumption, associated health risks from fluoride F⁻ and nitrate (NO₃⁻), and sources of dissolved [...] Read more.

Groundwater is one of the major sources of freshwater supply for drinking and domestic purposes. This study evaluates the hydrogeochemical processes, groundwater quality for human consumption, associated health risks from fluoride F⁻ and nitrate (NO₃⁻), and sources of dissolved solutes in a highland watershed in northern Pakistan. Groundwater samples (n = 51) were gathered and analyzed for a range of physicochemical parameters. To evaluate contamination, indices such as the nitrate pollution index (NPI) and fluoride pollution index (FPI) were applied, along with a composite groundwater pollution index to assess overall water quality. The findings revealed that total dissolved solid, turbidity, F⁻, and K⁺ levels exceeded health-based thresholds in 20%, 1%, 4%, and 2% of samples, respectively. Among the water sources, handpumps were identified as the most contaminated. According to the NPI and composite index, 96% and 92% of the samples did not show significant contamination, respectively. However, the FPI results highlighted that 59% of the samples exhibited low F⁻ pollution, while 41% fell under medium pollution levels. While NO₃⁻ ingestion posed no notable health risks,

F^{-}

exposure presented significant concerns, with 58.8% of the samples posing risks, particularly for children. The dominant hydrochemical facies were Ca-Mg-HCO₃, with the main influence on water chemistry by rock-water interactions and reverse ion exchange processes. Full article

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19 pages, 6743 KiB

Open AccessArticle

Comparative Analysis of Spatiotemporal Variability of Groundwater Storage in Iraq Using GRACE Satellite Data

by Hanan Kaduim Mohammed, Imzahim A. Alwan and Mahmoud Saleh Al-Khafaji

Hydrology 2025, 12(4), 69; https://doi.org/10.3390/hydrology12040069 - 26 Mar 2025

Abstract

Iraq and other semi-arid regions are facing severe climate change impacts, including increased temperatures and decreased rainfall. Changes to climate variables have posed a significant challenge to groundwater storage dynamics. In this regard, the Gravity Recovery and Climate Experiment (GRACE) mission permits novel [...] Read more.

Iraq and other semi-arid regions are facing severe climate change impacts, including increased temperatures and decreased rainfall. Changes to climate variables have posed a significant challenge to groundwater storage dynamics. In this regard, the Gravity Recovery and Climate Experiment (GRACE) mission permits novel originate groundwater storage variations. This study used the monthly GRACE satellite data for 2002–2023 to determine variations in groundwater storage (GWS). Changes in GWS were implied by extracting soil moisture, acquired from the Global Land Data Assimilation System (GLDAS), from the extracted Territorial Water Storage (TWS). The results demonstrated that an annual average ΔGWS trend ranged for the Goddard Space Flight Center (GSFC) mascon and Jet Propulsion Laboratory (JPL) mascon was from 0.94 to −1.14 cm/yr and 1.64 to −1.36 cm/yr, respectively. Also, the GSFC illustrated superior performance in estimating ΔGWS compared with the JPL in Iraq, achieving the lowest root mean square error at 0.28 mm and 0.60 mm and the highest coefficient of determination (R²) at 0.92 and 0.89, respectively. These data are critical for identifying areas of depletion, especially in areas where in situ data are lacking. These data allows us to fill the knowledge gaps; provide critical scientific information for monitoring and managing dynamic variations. Full article

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15 pages, 8054 KiB

Open AccessArticle

Seasonal and Spatial Dynamics of Surface Water Resources in the Tropical Semi-Arid Area of the Letaba Catchment: Insights from Google Earth Engine, Landscape Metrics, and Sentinel-2 Imagery

by Makgabo Johanna Mashala, Timothy Dube and Kingsley Kwabena Ayisi

Hydrology 2025, 12(4), 68; https://doi.org/10.3390/hydrology12040068 - 24 Mar 2025

Abstract

Understanding the spatial and seasonal dynamics of surface water bodies is imperative for addressing water security challenges in water-scarce regions. This study aimed to evaluate the efficacy of multi-date Sentinel-2-derived spectral indices, specifically the normalized difference water index (NDWI), modified normalized difference water [...] Read more.

Understanding the spatial and seasonal dynamics of surface water bodies is imperative for addressing water security challenges in water-scarce regions. This study aimed to evaluate the efficacy of multi-date Sentinel-2-derived spectral indices, specifically the normalized difference water index (NDWI), modified normalized difference water index (MNDWI), and Sentinel 2 Water Index (SWI), in conjunction with landscape metrics for mapping spatial and seasonal fluctuations in surface water bodies. Google Earth Engine (GEE) was employed for this assessment. The research achieved impressive overall accuracies, ranging from 96 to 100% for both dry and wet seasons, highlighting the robustness of the methodology. The study revealed significant differences in water bodies in terms of size and coverage between the dry and wet seasons. Surprisingly, the dry season exhibited a higher prevalence of water bodies when compared to the wet season, indicating unexpected patterns of water availability in the region and the substantial heterogeneity of water bodies. Meanwhile, the wet season was characterized by extensive coverage. These findings challenge conventional assumptions about water resource availability during different seasons. Based on the findings, the study recommends that water resource management strategies in semi-arid regions consider the observed seasonal variability in water bodies. Policymakers and stakeholders should adopt adaptive management approaches to address the unique challenges posed by differing water body dynamics in dry and wet seasons. Future research endeavors should explore the underlying factors driving these seasonal fluctuations and assess the potential long-term impacts on water availability. This can help to develop more resilient and sustainable water security strategies to cope with changing climate conditions in semi-arid tropical environments. Full article

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34 pages, 74461 KiB

Open AccessArticle

Comparing Depth-Integrated Models to Compute Overland Flow in Steep-Sloped Watersheds

by Gergely Ámon, Katalin Bene and Richard Ray

Hydrology 2025, 12(4), 67; https://doi.org/10.3390/hydrology12040067 - 22 Mar 2025

Abstract

On steep-sloped watersheds, high-intensity, short-duration rainfall events are the leading causes of flash floods. Typical overland flow analysis assumes sheet-like flow with a shallow water depth. However, the natural creek beds in steep watersheds produce complex and intense flows with a shallow depth [...] Read more.

On steep-sloped watersheds, high-intensity, short-duration rainfall events are the leading causes of flash floods. Typical overland flow analysis assumes sheet-like flow with a shallow water depth. However, the natural creek beds in steep watersheds produce complex and intense flows with a shallow depth and high velocity. According to the hydrodynamical modeling processes for open channel turbulent flow, calculating rainfall-induced overland flow becomes a complex task. Steep topography requires a highly refined numerical mesh, which demands a more complex simulation process. Depth-integrated models with distributed parameters provide useful methods to capture the behavior of steep watersheds. This study investigates the watershed’s overland flow behavior by varying turbulent flow parameters and monitoring possible model errors. The refined modeling places a heavy demand on numerical solvers used for simulating the overland flow motion. This paper examines different depth-integrated model solvers applied to artificial watersheds and compares results produced by the different solver types. This study found that the Shallow Water Equation solutions produced the most consistent and stable results, with the Local Inertia Approximation solutions performing adequately. Adding Large Eddy Simulation to these solutions tended to overcomplicate Shallow Water solutions but generally improved Large Eddy solutions. The Diffuse Wave Equation solutions produced erratic results, losing stability and accuracy as watershed slopes steepened and flow paths became complex. Full article

(This article belongs to the Special Issue Hydrodynamics and Water Quality of Rivers and Lakes)

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24 pages, 4146 KiB

Open AccessArticle

Assessing the Effects of Bioenergy Cropping Scenarios on the Surface Water and Groundwater of an Intensively Agricultural Basin in Central Greece

by Maria Sismanidi, Lamprini Kokkinaki, Sofia Kavalieratou, Haralampos Georgoussis, Kyriakos D. Giannoulis, Elias Dimitriou and Yiannis Panagopoulos

Hydrology 2025, 12(4), 66; https://doi.org/10.3390/hydrology12040066 - 22 Mar 2025

Abstract

Pinios river basin constitutes the most important agricultural production area in Greece but contributes to the degradation of the quality and quantity of surface water and groundwater bodies. Bioenergy crops implemented as part of the existing cropping systems could be a novel and [...] Read more.

Pinios river basin constitutes the most important agricultural production area in Greece but contributes to the degradation of the quality and quantity of surface water and groundwater bodies. Bioenergy crops implemented as part of the existing cropping systems could be a novel and efficient mitigation strategy against water degradation, contributing to the production of energy through renewable sources. This study uses the Soil and Water Assessment Tool (SWAT) to first develop a representative model of Pinios river basin and evaluate its current state with respect to water availability and nitrate water pollution. A low-input perennial bioenergy crop, switchgrass, is then simulated closely to the Greek conditions to investigate its potential effects on water in three implementation scenarios: the installation and growth of switchgrass in the entire irrigated cropland, exclusively in irrigated sloping (slopes > 1.5%) cropland, and exclusively in irrigated non-sloping cropland. The simulated results demonstrate that under all scenarios, the water quality improvements with respect to the nitrate loads entering surface water and groundwater bodies were significant, with their reduction being directly affected by the extent to which switchgrass replaced resource-demanding conventional crops. Specifically, the reduction in the annual nitrate loads in the surface water under these three scenarios varied from 7% to 18% at the river basin scale, while in certain cropland areas, the respective reduction even exceeded a level of 80%. The potential to improve the water status was also considerable, as the implementation of the bioenergy crop reduced the irrigation water used annually in the basin by 10% (64 Mm³) when switchgrass replaced the conventional crops only on the sloping land and by almost 30% (187 Mm³) when it replaced them throughout the irrigated land. At the same time, significant biomass production above 18 t/ha/y applied in all of the simulations. This study also highlights the contribution of the bioenergy crop to the rehabilitation of the groundwater levels across the basin, with the possibility of increasing them by >50% compared to the baseline, implying that the adoption of switchgrass could be a promising means against water scarcity. 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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21 pages, 46789 KiB

Open AccessArticle

Assessing Deep Learning Techniques for Remote Gauging and Water Quality Monitoring Using Webcam Images

by Ruichen Xu and Binbin Wang

Hydrology 2025, 12(4), 65; https://doi.org/10.3390/hydrology12040065 - 22 Mar 2025

Abstract

River and stream gauging and water quality monitoring are essential for understanding and managing freshwater resources. The U.S. Geological Survey (USGS) has been implementing and expanding the coverage of webcams across the U.S. stream gauges. A publicly available website has been established, known [...] Read more.

River and stream gauging and water quality monitoring are essential for understanding and managing freshwater resources. The U.S. Geological Survey (USGS) has been implementing and expanding the coverage of webcams across the U.S. stream gauges. A publicly available website has been established, known as the Hydrological Imagery Visualization and Information System (HIVIS). Motivated by routine webcam monitoring and recent advances in image-based machine learning research, in this technical paper, we evaluate three convolutional neural network (CNN) models including two deep neural network models (CNN3, VGG16, and ResNet50) in predicting river gauging, turbidity, dissolved oxygen, and dissolved organic matter in the Missouri River. We select the Missouri River due to the logistical challenges in field data collection. Our objective is to evaluate the predictability of the selected CNN and deep CNN models in inferring water surface elevation and water quality parameters from webcam images. The results show that the images can provide robust prediction for gauge height, a reasonable prediction for dissolved oxygen, and unsatisfactory prediction for turbidity or dissolved organic matter. The results demonstrate the potential use and limitation of using webcam images to remotely sense water quantity and quality data. Full article

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26 pages, 11207 KiB

Open AccessArticle

Glacier, Wetland, and Lagoon Dynamics in the Barroso Mountain Range, Atacama Desert: Past Trends and Future Projections Using CA-Markov

by German Huayna, Edwin Pino-Vargas, Jorge Espinoza-Molina, Carolina Cruz-Rodríguez, Fredy Cabrera-Olivera, Lía Ramos-Fernández, Bertha Vera-Barrios, Karina Acosta-Caipa and Eusebio Ingol-Blanco

Hydrology 2025, 12(3), 64; https://doi.org/10.3390/hydrology12030064 - 20 Mar 2025

Abstract

Glacial retreat is a major global challenge, particularly in arid and semi-arid regions where glaciers serve as critical water sources. This research focuses on glacial retreat and its impact on land cover and land use changes (LULC) in the Barroso Mountain range, Tacna, [...] Read more.

Glacial retreat is a major global challenge, particularly in arid and semi-arid regions where glaciers serve as critical water sources. This research focuses on glacial retreat and its impact on land cover and land use changes (LULC) in the Barroso Mountain range, Tacna, Peru, which is a critical area for water resources in the hyperarid Atacama Desert. Employing advanced remote sensing techniques through the Google Earth Engine (GEE) cloud computing platform, we analyzed historical trends (1985–2022) using Landsat satellite imagery. A normalized index classification was carried out to generate LULC maps for the years 1986, 2001, 2012, and 2022. Future projections until 2042 were developed using Cellular Automata–Markov (CA–Markov) modeling in QGIS, incorporating six predictive environmental variables. The resulting maps presented an overall accuracy (OA) greater than 83%. Historical analysis revealed a dramatic glacier reduction from 44.7 km² in 1986 to 7.4 km² in 2022. In contrast, wetlands expanded substantially from 5.70 km² to 12.14 km², indicating ecosystem shifts potentially driven by glacier meltwater availability. CA–Markov chain modeling projected further glacier loss to 3.07 km² by 2042, while wetlands are expected to expand to 18.8 km² and bodies of water will reach 4.63 km². These future projections (with accuracies above 84%) underline urgent implications for water management, environmental sustainability, and climate adaptation strategies, particularly with regard to downstream hydrological risks and ecosystem resilience. Full article

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15 pages, 1869 KiB

Open AccessArticle

Molecular Composition of Stream Dissolved Organic Matter in Cool-Temperate Forest Headwaters with Landslides, Northern Japan

by Jun’ichiro Ide, Kenta Hara, Yohei Arata, Izuki Endo, Mizue Ohashi, Hiroshi Nishimura and Takashi Gomi

Hydrology 2025, 12(3), 63; https://doi.org/10.3390/hydrology12030063 - 19 Mar 2025

Abstract

Vegetation and subsequent ecosystem services can recover over time in forest headwaters devastated by massive disasters. However, in cold regions, their recovery rates are typically slow and often imperceptible, which makes it difficult to evaluate how much ecosystem services have recovered. This study [...] Read more.

Vegetation and subsequent ecosystem services can recover over time in forest headwaters devastated by massive disasters. However, in cold regions, their recovery rates are typically slow and often imperceptible, which makes it difficult to evaluate how much ecosystem services have recovered. This study targeted dissolved organic matter (DOM), which plays a central role in biogeochemical processes in forest ecosystems, and aimed to examine whether vegetation conditions affect the quality of stream DOM from cool-temperate forest headwaters in northern Japan. To achieve this, hydrological observations and stream water sampling were conducted monthly from May to December 2021 in three small forest catchments with different landslide coverage. Dissolved organic carbon (DOC) concentration in stream water was measured, and the molecular composition of DOM was analyzed using ultrahigh-resolution mass spectrometry and compared among the three catchments. The peak-intensity-weighted average aromaticity index (AI_wa) increased with DOC concentration. We found that AI_wa was the highest in the undisturbed catchment, followed by the catchments with landslide coverages of 16% and 52% at a given DOC level. These results indicate that the quality of DOM could dramatically change depending not only on DOC concentration but also on vegetation disturbance in cool-temperate forest headwaters. Full article

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

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