Hydrology

22 pages, 7092 KB

Open AccessArticle

A Water Budget Evaluation of a Tile-Drain-Fed Irrigation Pond in the Willamette Valley, Oregon, USA

by Noah Goodwin Bain, Carlos G. Ochoa, Derek C. Godwin, Abigail Tomasek and Arshdeep Singh

Hydrology 2026, 13(8), 211; https://doi.org/10.3390/hydrology13080211 - 4 Aug 2026

Agricultural systems face heightened risks from extreme weather events and water insecurity. Producers commonly use irrigation ponds to secure or improve crop yields. The hydrology and storage efficiency of irrigation ponds in the Willamette Valley, Oregon, USA, are not well understood. This study [...] Read more.

Agricultural systems face heightened risks from extreme weather events and water insecurity. Producers commonly use irrigation ponds to secure or improve crop yields. The hydrology and storage efficiency of irrigation ponds in the Willamette Valley, Oregon, USA, are not well understood. This study evaluated the hydrological interactions of a tile-drain-fed irrigation pond. A water balance approach was applied over the irrigation season using weather data, evaporation estimates, metered irrigation withdrawals, and bathymetry analysis for pond stage–volume estimates to quantify water budget components. Irrigation withdrawals were the largest output, with 75% of effective pond storage utilized, followed by evaporation (24.5%). Evaporation far exceeded precipitation over the same period. The unaccounted-for proportion of the water balance was negligible, indicating that net drain tile inflows and groundwater exchange had a minimal impact on seasonal irrigation water availability and seepage losses. This study provides an example for measuring water balance components and assessing water input–output relationships of an irrigation pond within a headwaters stream and catchment (<5 ha) of an important agricultural corridor in the Pacific Northwest region in the USA. The study methodology can be replicated in other similar agricultural areas with irrigation ponds worldwide. Findings from this study can be used by farmers, irrigation districts, and other stakeholders to better inform irrigation planning and water management decisions for similar site conditions. Full article

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24 pages, 17503 KB

Open AccessArticle

Dynamic Refinement of Temporally Static Land-Use Maps Using Satellite-Derived Moisture Signatures

by Nutchanart Sriwongsitanon, Chainarong Ophaphaibun, James Alexander Williams, Raj Mehrotra and Hubert H. G. Savenije

Hydrology 2026, 13(8), 210; https://doi.org/10.3390/hydrology13080210 - 4 Aug 2026

Abstract

Accurate land use/land cover (LULC) classification in monsoon-driven and heterogeneous landscapes is challenged by strong seasonal variability and inconsistencies between dynamic satellite observations and static reference datasets. This study proposes a time-series-based framework integrating MODIS-derived Normalized Difference Vegetation Index (NDVI) and Normalized Difference [...] Read more.

Accurate land use/land cover (LULC) classification in monsoon-driven and heterogeneous landscapes is challenged by strong seasonal variability and inconsistencies between dynamic satellite observations and static reference datasets. This study proposes a time-series-based framework integrating MODIS-derived Normalized Difference Vegetation Index (NDVI) and Normalized Difference Infrared Index (NDII) with unsupervised K-means clustering and a temporally consistent refinement strategy. Multi-temporal NDVI (23 composites year⁻¹) and NDII (46 composites year⁻¹) data from 2010–2021 were used to derive spectral clusters and aggregate them into five land use classes using percentile-based temporal signatures and RMSE-based similarity with Land Development Department (LDD) data. To reconcile discrepancies between dynamic satellite observations and static reference datasets, a refinement procedure combining spatial agreement and temporal similarity was applied to reassign misclassified pixels. Initial classifications achieved Overall Accuracies (OA) of 57.35% for NDII and 51.27% for NDVI, increasing to 87.28% and 86.24% after refinement, with Kappa coefficients of 0.82 and 0.81, respectively. NDII consistently outperformed NDVI, highlighting the value of moisture-sensitive indices for distinguishing vegetation classes in tropical environments. The modular Python-based version 3.11 implementation ensures reproducibility and transferability, providing a robust and scalable framework for LULC classification in dynamic landscapes. Full article

(This article belongs to the Topic Remote Sensing Research and Application of Agricultural Drought and Water Management)

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24 pages, 1583 KB

Open AccessArticle

Comparative Evaluation of Machine Learning Algorithms for Predicting Soil Wetting Front Dynamics Under Drip Irrigation System

by Oluwaseun Temitope Faloye, Oluwaseyi Matthew Abioye, Abiodun Afolabi Okunola, Olusegun K. Abass, Peter Pelumi Ikubanni, Natdanai Sinsamutpadung, Laemthong Laokhongthavorn and Viroon Kamchoom

Hydrology 2026, 13(8), 209; https://doi.org/10.3390/hydrology13080209 - 3 Aug 2026

Abstract

Accurate prediction of wetted width and wetted depth is essential for optimizing water use efficiency in drip irrigation systems. Existing empirical models are often restricted to specific soil textures and cannot adequately capture the complex nonlinear interactions among soil hydro-physical and chemical properties, [...] Read more.

Accurate prediction of wetted width and wetted depth is essential for optimizing water use efficiency in drip irrigation systems. Existing empirical models are often restricted to specific soil textures and cannot adequately capture the complex nonlinear interactions among soil hydro-physical and chemical properties, irrigation variables, and different soil textures. This study evaluated four machine learning algorithms—Linear Support Vector Machine (Linear SVM), Medium Gaussian Support Vector Machine (Medium Gaussian SVM), Matern 5/2 Gaussian Process Regression (GPR), and Boosted Tree Regression—for predicting wetted width and wetted depth in sand and sandy loam soils. Model inputs included emitter discharge, irrigation duration, and selected soil hydro-physical and chemical properties. Models were developed using a 70% training dataset and validated with the remaining 30%. The Matern 5/2 GPR achieved the highest training accuracy for wetted width (R² = 0.99; RMSE = 0.74) and wetted depth (R² = 0.98; RMSE = 0.90), but validation errors increased to RMSE values of 2.27 and 3.84, respectively. Medium Gaussian SVM yielded the lowest validation RMSE (2.11) for wetted width, whereas Boosted Tree Regression achieved the best wetted depth prediction (RMSE = 2.11; MAE = 1.69). These findings demonstrate the importance of model-specific selection for reliable irrigation management. Full article

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42 pages, 13504 KB

Open AccessArticle

Climate Change and Irrigation Effects on Hydrology and Crop Yield in the Geba Watershed, Tigray Region, Northern Ethiopia

by Adane Weldengus Meresa, Muuz Gebretsadik Gebremariam, Anthony Lehmann and Mostafa Jafari

Hydrology 2026, 13(8), 208; https://doi.org/10.3390/hydrology13080208 - 3 Aug 2026

Abstract

Climate change and irrigation expansion are expected to substantially alter hydrological processes and agricultural productivity in the semi-arid watersheds of northern Ethiopia; however, their combined impacts remain insufficiently quantified. This study evaluated the effects of future climate change and irrigation management on watershed [...] Read more.

Climate change and irrigation expansion are expected to substantially alter hydrological processes and agricultural productivity in the semi-arid watersheds of northern Ethiopia; however, their combined impacts remain insufficiently quantified. This study evaluated the effects of future climate change and irrigation management on watershed hydrology and crop yield in the Geba watershed using the Soil and Water Assessment Tool Plus (SWAT+). The model was calibrated and validated using observed daily streamflow data for the 2006–2020 period and driven by an ensemble of five bias-corrected CORDEX Africa regional climate models (RCMs) under the RCP 4.5 and RCP 8.5 scenarios for the mid-century (2046–2060) and late-century (2086–2100) periods. Two agricultural management systems, namely rainfed and irrigation-rainfed integrated management, were evaluated. Model performance was satisfactory for streamflow simulation, with NSE values of 0.56 and 0.50 and KGE values of 0.64 and 0.54 during calibration and validation, respectively. The results indicate a progressive shift toward an evapotranspiration-dominated hydrological regime under future climate conditions. Under rainfed management, surface runoff and evapotranspiration increased by up to 60% and 30%, respectively, whereas groundwater recharge and lateral flow declined substantially. Irrigation scenarios intensified hydrological stress by reducing percolation, lateral flow, and water yield by up to 80%, 60%, and 55%, respectively. Statistical analyses revealed that climate forcing, management type, and their interactions significantly affected hydrological responses (p < 0.001), with emission pathways representing the dominant driver of variability. Crop responses varied considerably among management systems and crop types. Rainfed maize and wheat exhibited moderate yield increases under mid-century conditions, whereas teff consistently showed negative responses under most climate scenarios, indicating high vulnerability to warming and moisture stress. Under irrigation management, most crops experienced substantial yield reductions during late-century periods, although tomatoes showed localized gains under high-emission scenarios. Overall, the findings demonstrate that irrigation expansion alone may not provide sustainable adaptation under increasing climate stress because it intensifies evapotranspiration and reduces groundwater recharge. Integrated watershed management, climate-resilient crop selection, efficient irrigation practices, and soil-moisture conservation strategies are therefore essential for sustaining agricultural productivity and water availability in semi-arid Ethiopian watersheds. Full article

(This article belongs to the Topic Linking Agricultural–Hydrological Processes and Extreme Events Under a Changing Climate)

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20 pages, 3271 KB

Open AccessArticle

Serendipity in Settings and Hydrologic Processes Helped People Survive Extreme Environments of the Sahara Desert

by Franklin Schwartz and Ganming Liu

Hydrology 2026, 13(8), 207; https://doi.org/10.3390/hydrology13080207 - 3 Aug 2026

Abstract

This paper explores the intricate relationship between novel paleo-hydrological settings and the sustainability of ancient human societies in the Sahara Desert, focusing on the sandstone massifs of Tassili n’Ajjer, Tadrart Acacus, and Messak Settafet. While this region is currently hyper-arid, archeological evidence reveals [...] Read more.

This paper explores the intricate relationship between novel paleo-hydrological settings and the sustainability of ancient human societies in the Sahara Desert, focusing on the sandstone massifs of Tassili n’Ajjer, Tadrart Acacus, and Messak Settafet. While this region is currently hyper-arid, archeological evidence reveals a history of significant human settlement facilitated by the African Humid Period (AHP). The core of the research is the idea that the natural geological and hydrogeological settings worked to magnify rainfall in a manner that is analogous to modern techniques in water systems engineering. Serendipitous features of geology, structural settings, and stream networks are presented, along with illustrative calculations to suggest how this system functioned as an accidental rainwater harvesting system, concentrating runoff into conveniently located lakes. On the Messak Settafet, the archaeologic evidence points to a rising water table and more robust groundwater flow as runoff infiltrated. We conceptualize this behavior as a managed aquifer recharge system. This natural system worked effectively by storing ephemeral surface water in a sandstone aquifer, shielded from the high evaporation rates of the Sahara. These “natural technologies” created perennial water sources such as lakes, ponds, and springs that supported hunter-gatherers and pastoralist societies. Long after the end of the Holocene AHP, the Garamantian Empire arose with the help of qanat technology that was able to produce the stored groundwater. This paper illustrates how an unlikely array of components worked to create natural technologies able to provide “livable niches.” These findings offer instructive lessons for modern sustainability, demonstrating how integrated landscape management can secure water resources in water-stressed environments. Full article

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

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40 pages, 38022 KB

Open AccessArticle

Validation of Downscaled and Bias-Corrected WorldClim 2.1– CRU-TS v4.09 Climate Dataset for Hydrological Modeling in a Semi-Arid Ecotonal Catchment of Central South Africa

by Kassaye Hussien and Yali E. Woyessa

Hydrology 2026, 13(8), 206; https://doi.org/10.3390/hydrology13080206 - 28 Jul 2026

Abstract

Reliable climate data are essential for hydroclimatic assessment and water-resources management in data-scarce regions. This study evaluated the performance of the WorldClim 2.1 historical weather dataset (WC2.1– CRU-TS v4.09), downscaled and bias-corrected from CRU-TS v4.0 using WorldClim 2.1 climatology, against observed meteorological records [...] Read more.

Reliable climate data are essential for hydroclimatic assessment and water-resources management in data-scarce regions. This study evaluated the performance of the WorldClim 2.1 historical weather dataset (WC2.1– CRU-TS v4.09), downscaled and bias-corrected from CRU-TS v4.0 using WorldClim 2.1 climatology, against observed meteorological records within the semi-arid C5 Secondary Drainage Region (C5 SDR; comprising the Riet and Modder River catchments) in central South Africa for the period 1950–2023. Precipitation, maximum temperature (TMAX), and minimum temperature (TMIN) were assessed using statistical performance evaluation metrics, scatter and residual analyses, Innovative Trend Analysis (ITA), Rescaled Adjusted Partial Sums (RAPS), and extreme-event evaluation based on the 95th-percentile threshold. The results showed strong agreement between observed and gridded precipitation records, with correlation coefficients ranging (R) from 0.78 to 0.90 and Nash–Sutcliffe Efficiency (NSE) values between 0.61 and 0.90. Temperature datasets exhibited similarly good performance, with TMAX showing stronger agreement than TMIN. ITA and RAPS analyses demonstrated that the dataset successfully reproduced long-term climatic trends, hydroclimatic regime shifts, and interannual variability observed in station records. Performance varied spatially, with the strongest agreement occurring at lower-elevation stations and comparatively lower performance at stations influenced by localized convective rainfall and topographic variability. Extreme-event analysis revealed that although the dataset effectively reproduced the timing and occurrence of high-rainfall years (R² = 0.974–0.997), it systematically underestimated the magnitude of extreme precipitation events, with percent bias values ranging from −5.5% to −21.0%. In contrast, extreme temperature events were reproduced with very high accuracy and minimal bias. Overall, the WC2.1– CRU-TS v4.09 dataset provides a reliable climatic baseline for hydroclimatic assessments in the C5 SDR. However, caution is required when applying the dataset to analyses sensitive to localized precipitation extremes. The results provide confidence in the use of this dataset for climate characterization, drought assessment, hydrological modeling, ecosystem service evaluation, and future climate-change impact investigations in data-scarce semi-arid environments. Full article

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16 pages, 7616 KB

Open AccessArticle

Spatiotemporal and Future Changes in Water Use Efficiency in the Agro-Pastoral Ecotone of Northern China Under Climate Warming and Vegetation Greening

by Yujiao Liu, Mengzhu Liu, Borui Li and Hongwei Pei

Hydrology 2026, 13(8), 205; https://doi.org/10.3390/hydrology13080205 - 28 Jul 2026

Abstract

The water use efficiency (WUE) in North China is undergoing rapid changes due to climate warming and vegetation “greening”, significantly impacting the ecosystem’s carbon and water cycles. Existing research lacks quantitative analysis of WUE or an understanding of future trends. This study selected [...] Read more.

The water use efficiency (WUE) in North China is undergoing rapid changes due to climate warming and vegetation “greening”, significantly impacting the ecosystem’s carbon and water cycles. Existing research lacks quantitative analysis of WUE or an understanding of future trends. This study selected the rapidly greening Agro-Pastoral Ecotone of Northern China (APENC) as a case study, utilizing linear regression, Hurst index analysis, and residual analysis to analyze the past and future changes and driving mechanisms of WUE. The results indicated that: (1) The multi-year (2001–2023) annual mean WUE in the APENC spatially ranged from 0.32 to 2.50 g C kg⁻¹ H₂O. (2) Gross primary productivity (GPP), evapotranspiration (ET), and WUE showed significant increasing trends of 10.22 g C m⁻² yr⁻², 5.62 kg H₂O m⁻² yr⁻², and 0.01 g C kg⁻¹ H₂O yr⁻¹, respectively. (3) Precipitation had highly positive impacts on GPP and ET, while non-climatic factors (land use, human activities, etc.) explained 62% of WUE variations in the APENC, and energy conditions (air temperature and solar radiation) were not the decisive factor of WUE. (4) The Hurst exponent of WUE indicates that WUE in the APENC region generally exhibits anti-persistent behavior. In terms of future trends, WUE is projected to shift from rising to declining in 58.9% of the region, while 28.5% is expected to continue increasing. Full article

(This article belongs to the Topic Ecohydrology and Water Resources Sustainability, 2nd Edition)

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14 pages, 2457 KB

Open AccessArticle

Multivariate Characterization of Hydrochemically Similar Groundwaters: Resolving Hydrochemical Structure and Process-Related Variability

by Riccardo Aigotti, Eugenio Alladio, Alberto Asteggiano and Claudio Medana

Hydrology 2026, 13(8), 204; https://doi.org/10.3390/hydrology13080204 - 28 Jul 2026

Abstract

Groundwater systems sharing similar major-ion facies may still differ in their hydrochemical organization and mineralization pathways, particularly in structurally complex aquifer settings. This study evaluated multivariate chemometric approaches for investigating two hydrochemically similar groundwater systems (MAJA and MAJA2) examined within the regulatory framework [...] Read more.

Groundwater systems sharing similar major-ion facies may still differ in their hydrochemical organization and mineralization pathways, particularly in structurally complex aquifer settings. This study evaluated multivariate chemometric approaches for investigating two hydrochemically similar groundwater systems (MAJA and MAJA2) examined within the regulatory framework for natural mineral water recognition. The dataset consisted of a 13-month monitoring campaign complemented by an independent multi-year validation dataset. Hydrochemical variables were organized into chemical and process-related blocks, including major ions, physicochemical parameters, D’Amore indices, and mineral saturation indices. SIMCA was applied to evaluate the intra-class hydrochemical structure, and OPLS-DA was used to investigate predictive and orthogonal sources of variability. Model robustness and parameter reproducibility were assessed using jackknife resampling, Leave-One-Month-Out cross-validation, repeated double cross-validation, and permutation testing. SIMCA identified PC1 as the only consistently reproducible latent component across resampling iterations. An exploratory Structural Response Coefficient (

R_{j}

) was introduced as a model-derived descriptor integrating explained and residual variance within the SIMCA model. OPLS-DA models showed stable class-related latent structures under nested validation conditions. Electrical conductivity, sulphate, potassium, SI_gypsum, SI_halite, and D’Amore index A were the variables most consistently associated with discriminant variability. Stable isotope data indicated a common meteoric origin and similar recharge conditions for both systems. The results illustrate how multivariate chemometric analysis, combined with stability-oriented validation procedures, may aid the interpretation of hydrochemical variability in compositionally similar groundwater systems. Full article

(This article belongs to the Topic Advances in Groundwater Science and Engineering)

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18 pages, 2297 KB

Open AccessArticle

Model Predictive Control-Based Hydrodynamic Regulation Framework for the Lower Ganjiang River

by Sufen Zhou, Xinming Zhang, Zhiwen Huang and Limo Tang

Hydrology 2026, 13(8), 203; https://doi.org/10.3390/hydrology13080203 - 27 Jul 2026

Abstract

The Lower Ganjiang River is a multi-branch delta with highly uneven spatial and temporal flow distribution, and conventional static diversion or threshold-based operation fails to stabilise the water level or optimise flow allocation under varying inflows. This study develops a hydrodynamic regulation framework [...] Read more.

The Lower Ganjiang River is a multi-branch delta with highly uneven spatial and temporal flow distribution, and conventional static diversion or threshold-based operation fails to stabilise the water level or optimise flow allocation under varying inflows. This study develops a hydrodynamic regulation framework that couples an improved integral time-delay model and model predictive control (MPC). A nonlinear state-space equation is constructed using a quadratic storage–water level relationship and rolling optimisation is solved with CasADi-IPOPT to minimise water-level tracking error, discharge deviation and control effort. The framework is validated offline against MIKE21 simulations for three historical flow scenarios (September 2016, February 2017 and March 2018). Under these scenarios, the Waizhou water level is maintained at 15.5 ± 0.2 m, daily water level variation is limited to ≤0.5 m/d, and the diversion ratio deviation is ≤5%. Compared with the natural state, water level fluctuation is reduced by 21.3% (September 2016 storage scenario). The proposed MPC framework effectively alleviates the spatiotemporal hydrodynamic imbalance of the Lower Ganjiang River, showing satisfactory model accuracy, constraint compliance, and engineering applicability, and offers a promising approach for advanced regulation of complex multi-branch river networks. Full article

(This article belongs to the Section Hydrological Measurements and Instrumentation)

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27 pages, 13001 KB

Open AccessArticle

Hydroclimatic Variability and Floodplain Wetland Dynamics in the Magdalena River: A Case Study of Zambrano, Colombia

by Ana Carolina Torregroza-Espinosa, Juan Camilo Restrepo, Rodney Correa-Solano, David Alejandro Blanco-Álvarez and Laura Salas Cantillo

Hydrology 2026, 13(8), 202; https://doi.org/10.3390/hydrology13080202 - 25 Jul 2026

Abstract

Understanding the interactions between vegetation dynamics and surface water availability is essential for assessing the resilience of tropical floodplain ecosystems under increasing hydroclimatic variability. This study analyzes the spatio-temporal dynamics of vegetation cover, surface water, and land use in Zambrano, a floodplain-dominated sector [...] Read more.

Understanding the interactions between vegetation dynamics and surface water availability is essential for assessing the resilience of tropical floodplain ecosystems under increasing hydroclimatic variability. This study analyzes the spatio-temporal dynamics of vegetation cover, surface water, and land use in Zambrano, a floodplain-dominated sector of the lower Magdalena River basin (Colombian Caribbean), over the period 1990–2025. Multi-temporal Landsat imagery was used to derive the Normalized Difference Vegetation Index (NDVI) and the Normalized Difference Water Index (NDWI), enabling the evaluation of seasonal and interannual ecohydrological variability under contrasting dry and rainy conditions. In addition, land-use classification was performed using a CORINE Land Cover methodology adapted for Colombia (CLC-C) to characterize the spatial organization of the landscape and its influence on vegetation–water interactions. Results show that vegetation dynamics are strongly controlled by hydroclimatic seasonality. Dense vegetation consistently expands during rainy periods, while dry seasons promote the expansion of open and sparse vegetation, reflecting seasonal vegetation stress rather than long-term degradation. NDWI patterns indicate that surface water and soil moisture are highly seasonal and spatially constrained, with open water largely confined to the Magdalena River channel and localized floodplain depressions. Extreme hydroclimatic events associated with the El Niño–Southern Oscillation (ENSO) produce abrupt but temporary changes in vegetation structure and surface moisture distribution. A strong inverse correlation between NDVI and NDWI reflects the contrasting spectral responses of vegetation and water surfaces resulting from the shared near-infrared (NIR) band in both indices. This spectral relationship is consistent with the observed seasonal variations in vegetation greenness and surface moisture across the floodplain. Land-use analysis reveals the progressive consolidation of the landscape, where the agropastoral matrix expanded from ~18,000 ha in 1990 to over 22,000 ha by 2025, driving a systematic reduction in natural and semi-natural forest structures. Forest conservation areas serve as critical ecological buffers, exhibiting lower seasonal variability in vegetation greenness. Overall, the results indicate that the Zambrano floodplain functions as a structurally stable yet highly responsive ecohydrological system, where vegetation dynamics and surface water availability are predominantly governed by interannual hydroclimatic pulses rather than long-term directional degradation. These findings demonstrate that while the structural matrix of the floodplain exhibits strong baseline resilience, its ecological functioning remains critically coupled with, and vulnerable to, the extreme phase shifts in ENSO cycles. Full article

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22 pages, 5169 KB

Open AccessArticle

Enhancing Daily Runoff Prediction via Uniform Design and Meta-Learning Integrated Hyperparameter Optimization Embedded in Transformer

by Wenxue Wang, Liuyang Li, Donghui Su, Xin Zhang, Haibin Tong, Tiantian Shao and Jiaxin Fan

Hydrology 2026, 13(8), 201; https://doi.org/10.3390/hydrology13080201 - 25 Jul 2026

Abstract

Accurate runoff prediction is an essential foundation for water resource management, flood prevention, and drought warning. Despite the superior performance of deep learning models in runoff prediction, the high-dimensional hyperparameter optimization limits their widespread application. To address this challenge, this study proposed a [...] Read more.

Accurate runoff prediction is an essential foundation for water resource management, flood prevention, and drought warning. Despite the superior performance of deep learning models in runoff prediction, the high-dimensional hyperparameter optimization limits their widespread application. To address this challenge, this study proposed a hyperparameter optimization strategy that integrated Uniform Design (UD) and Meta-Learning (ML) within the Transformer framework (UD-ML-Transformer) for daily runoff prediction. Performance of the proposed model was systematically evaluated against five benchmark models, including the UD-Transformer, Particle Swarm Optimization (PSO)-Transformer, and three Receptance Weighted Key Value (RWKV)-based models (PSO-RWKV, UD-RWKV, and UD-ML-RWKV), using hydroclimatic data spanning 1980 to 2014 from the Rio Pueblo de Taos watershed in USA. Results showed that the UD-ML-Transformer model performed the best in both prediction accuracy and peak flow, with the highest Nash-Sutcliffe Efficiency (NSE) of 0.906, and the lowest Mean Squared Error (MSE), Root Mean Squared Error (RMSE), and Mean Absolute Error (MAE) of 0.004, 0.062, and 0.034, respectively. The UD-Transformer ranked second in performance, followed by the PSO-Transformer. The integrated UD-ML hyperparameter optimization strategy also improved the performance of RWKV-based models. Compared with the PSO-RWKV and UD-RWKV models, the UD-ML-RWKV model exhibited an NSE improvement of 0.45–7.65% and an RMSE reduction of 1.47–21.18%, respectively. Moreover, cross-watershed validation conducted in the Ford River watershed, USA, also demonstrated the satisfactory performance of the proposed UD-ML-Transformer model, with the highest NSE of 0.890, and the lowest MSE, RMSE, and MAE of 0.088, 0.296, and 0.141, respectively. These findings highlight the superiority of integrating UD and ML for hyperparameter optimization in runoff forecasting. Full article

(This article belongs to the Special Issue Hydrological Modeling and Sustainable Water Resources Management, 2nd Edition)

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26 pages, 22497 KB

Open AccessArticle

Evaporative Water Consumption and Heat Redistribution Under Pumped-Storage Hydropower Operation in an Arid Region

by Jinhan Wang, Xinjun Yan, Shaolei Wang, Kewu Han, Kebin Shi and Dexin Zhao

Hydrology 2026, 13(8), 200; https://doi.org/10.3390/hydrology13080200 - 24 Jul 2026

Abstract

Pumped-storage hydropower (PSH) can modify reservoir evaporation in arid regions by altering water-level dynamics, surface-area exposure, and thermal exchange between reservoirs. This study quantifies operation-induced evaporation changes at the Fukang PSH station in Xinjiang, China, using a one-dimensional lumped hydrodynamic–thermal model driven by [...] Read more.

Pumped-storage hydropower (PSH) can modify reservoir evaporation in arid regions by altering water-level dynamics, surface-area exposure, and thermal exchange between reservoirs. This study quantifies operation-induced evaporation changes at the Fukang PSH station in Xinjiang, China, using a one-dimensional lumped hydrodynamic–thermal model driven by hourly station observations and ERA5 reanalysis for 2024. A four-scenario factorial design separates thermal, surface-area, and interaction effects within a unified water energy framework. Under station forcing, fully coupled operation reduces annual system-scale evaporation from 135.36 × 10⁴ m³ to 115.45 × 10⁴ m³, corresponding to a net reduction of 19.91 × 10⁴ m³ (14.7%). Energy-budget analysis identifies advective heat transport as the main pathway linking dispatch, reservoir thermal evolution, and evaporation response, with annual cumulative values of +205 TJ in the upper reservoir and −333 TJ in the lower reservoir. Dispatch-regime experiments further show that stronger exchange-flow operation does not necessarily increase evaporation reduction: the low, baseline, and enhanced schedules produce system-scale net changes of 37.70 × 10⁴ m³, 19.91 × 10⁴ m³, and −3.41 × 10⁴ m³, respectively. These results indicate that evaporation effects in arid-region PSH systems depend on the timing of surface-area exposure relative to local evaporative demand, rather than on exchange-flow magnitude or operating duration alone. Full article

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

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15 pages, 6783 KB

Open AccessArticle

Frequency-Dependent Groundwater Responses to Canal Regulation and Extreme Rainfall in the Huaibei Plain

by Zhaokai Wang, Hongwei Yuan, Jiwei Yang, Tao Shen and Youzhen Wang

Hydrology 2026, 13(8), 199; https://doi.org/10.3390/hydrology13080199 - 23 Jul 2026

Abstract

Groundwater levels in gated agricultural drainage networks respond to canal-stage changes, rainfall, antecedent storage, and changing operating conditions. We examined groundwater and surface-water records from the Chezegou Watershed, Huaibei Plain, China (2019–2024), using analytical solutions of the linearized Boussinesq equation. Groundwater was measured [...] Read more.

Groundwater levels in gated agricultural drainage networks respond to canal-stage changes, rainfall, antecedent storage, and changing operating conditions. We examined groundwater and surface-water records from the Chezegou Watershed, Huaibei Plain, China (2019–2024), using analytical solutions of the linearized Boussinesq equation. Groundwater was measured mostly at intervals of about five days, and analyses used the original observation dates. Using the half-power criterion |Z|² = 1/2 and hydraulic diffusivities of 5.27 × 10³–1.05 × 10⁴ m² d⁻¹, cutoff periods were 56.1–111.7 d at 150 m and 399.1–794.1 d at 400 m; the half-power distance for a 30 d cycle was 77.7–109.7 m. The record also includes a 106 mm storm on 12 July 2020. Groundwater depth at J5 (490 m from the canal) decreased from 2.23 to 0.54 m in 48 h, a 1.69 m water-level rise, while J9 (1020 m) rose by 1.79 m over five days. These observations show a rapid shallow-groundwater head response, although water-level records alone do not separate vertical recharge from hydraulic-pressure transmission. Canal influence depends on forcing duration and aquifer properties, while rainfall responses also reflect lateral boundaries and the shrink-swell behavior of Shajiang black soil. The calculated time-distance relations provide site-specific reference values for canal operation. Full article

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36 pages, 45114 KB

Open AccessArticle

Groundwater Vulnerability Assessment Using an Integrated GIS-Based DRASTIC, Land-Use, and Expert Elicitation Framework in Southern Egypt

by Mohamed El-Sayed El-Mahdy, Sally Sayed Saad, Ibraheem A. H. Yousif, Mohamed Ahmed Shahba and Abd-Alrahman S. Ahmed

Hydrology 2026, 13(8), 198; https://doi.org/10.3390/hydrology13080198 - 23 Jul 2026

Abstract

Groundwater vulnerability refers to an aquifer’s susceptibility to contamination based on natural hydrogeological properties, including geology, soil, topography, and unsaturated zone characteristics. In low-recharge arid systems, limited recharge reduces dilution and flushing, allowing contaminants introduced through anthropogenic activities to persist over time. This [...] Read more.

Groundwater vulnerability refers to an aquifer’s susceptibility to contamination based on natural hydrogeological properties, including geology, soil, topography, and unsaturated zone characteristics. In low-recharge arid systems, limited recharge reduces dilution and flushing, allowing contaminants introduced through anthropogenic activities to persist over time. This study assesses groundwater vulnerability in El-Farafra, El-Kharga, and Tushka using a GIS-based DRASTIC approach, enhanced with a Land-Use DRASTIC model to incorporate human activities. Parameters, including the depth-to-water table, net recharge, aquifer media, soil media, topography, the vadose zone, and hydraulic conductivity, were spatially analyzed to generate vulnerability indices. Sentinel-2 imagery was used for land-use classification. In addition, expert elicitation from twenty hydrogeology specialists provided alternative parameter weightings, which were compared with the standard DRASTIC weights. Results show that incorporating land use and expert-based weights refines vulnerability patterns, particularly in agricultural, urban, and industrial zones. El-Farafra exhibits the highest vulnerability due to intensive land use and hydrogeological conditions, El-Kharga shows moderate vulnerability, and Tushka shows lower vulnerability, where recharge from Lake Nasser enhances dilution and reduces contaminant persistence. The study highlights the importance of integrating land-use information and expert knowledge to improve vulnerability assessment in data-scarce arid environments and supports improved groundwater management strategies. Full article

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

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17 pages, 2522 KB

Open AccessArticle

Analysis of Soil Infiltration Characteristics and Their Influencing Factors Under Different Vegetation Based on a PLS-SEM Model

by Xuemin Tang, Yutong Peng, Jianli Zhang, Dandan Li, Yang Cao, Weiquan Zhao and Yunjie Wu

Hydrology 2026, 13(7), 197; https://doi.org/10.3390/hydrology13070197 - 22 Jul 2026

Abstract

Urban rocky desertification areas are characterized by shallow soils, rock–soil mosaics, and strong human disturbance, so infiltration processes may differ from those in homogeneous soils. However, interactions among multiple controlling factors remain insufficiently quantified. This study compared soil infiltration under artificially restored vegetation [...] Read more.

Urban rocky desertification areas are characterized by shallow soils, rock–soil mosaics, and strong human disturbance, so infiltration processes may differ from those in homogeneous soils. However, interactions among multiple controlling factors remain insufficiently quantified. This study compared soil infiltration under artificially restored vegetation (planted grassland (PG) and planted woodland (PW)), and natural secondary vegetation (secondary grassland (SG) and secondary woodland (SW)). Saturated hydraulic conductivity (Ks) and falling-head duration (T) were measured using falling-head tests on undisturbed soil columns. Soil physical properties were then integrated with partial least squares structural equation modeling (PLS-SEM) to assess the effects of rocky desertification, soil aggregates, and porosity. Soil bulk density was significantly lower under artificially restored vegetation, whereas capillary porosity, non-capillary porosity, and water-holding capacity were significantly higher (p < 0.05). Infiltration performance followed PW > PG > SW > SG. PLS-SEM indicated that rocky desertification (−0.78), porosity (0.51), and aggregates (−0.03) jointly regulated infiltration, with non-capillary porosity as the dominant positive factor. Higher infiltration in artificially restored plots was mainly associated with improved pore structure. These findings support vegetation configuration and soil–water management in urban rocky desertification areas. Full article

(This article belongs to the Section Soil and Hydrology)

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18 pages, 28063 KB

Open AccessArticle

Diagnostics of the Average Long-Term Water Discharge of Freely Meandering Rivers Based on Morphological Analysis of Their Channel Configurations

by Alexey Terekhov, Ravil Mukhamediev, Gulshat Sagatdinova and Igor Savin

Hydrology 2026, 13(7), 196; https://doi.org/10.3390/hydrology13070196 - 22 Jul 2026

Abstract

Freely meandering rivers flow through gently sloping plains composed of loess and fluvial sediments. Low-gradient alluvial plains are formed without the influence of landscape features such as rock outcrops or other features that distort the flow path. The channel configurations of such rivers, [...] Read more.

Freely meandering rivers flow through gently sloping plains composed of loess and fluvial sediments. Low-gradient alluvial plains are formed without the influence of landscape features such as rock outcrops or other features that distort the flow path. The channel configurations of such rivers, and in particular the size of meanders and oxbow lakes, depend on the average long-term water discharge. Large rivers form large meanders, while small rivers form correspondingly small ones. Morphological analysis of river channel configurations can offer a metric for estimating the average long-term water discharge of a river based solely on the sinuosity of its channel. The study examined six freely meandering rivers in Kazakhstan, with discharges ranging from 4.5 to 760 m³/s and channel slopes from 0.005 to 0.06%. The morphological analysis of river channels was based on the Relative Elevation Model, specifically its version based on the Copernicus Global Digital Elevation Model, with a spatial resolution of 30 m. River channel configurations were approximated using a set of inscribed circles, the diameters of which formed the basis for the river’s average long-term water discharge metric. The largest diameter circles, which could support the river channel with a sector of at least 135°, were expertly inscribed into river bends. The diameters of the inscribed circles within these sets varied from four times for small rivers to ten times for large rivers. These sets of circles, sorted by size, can characterize the average long-term water discharge of the analyzed rivers. For example, a sample of average median values of inscribed circle diameters has a high correlation with the average long-term water discharge, with a linear approximation reliability of R² = 0.997. The scope of the developed method for assessing the average long-term water discharge of freely meandering rivers includes retrospective analysis of changes in average long-term average long-term water discharge. This can provide significant historical depth of analysis, spanning centuries and millennia, since the analysis is based on describing the results of very slow processes of natural deformation of river channels. Thus, the method proposed in this study for assessing the average long-term water discharge of freely meandering rivers based on morphological analysis of their channel configurations expands the arsenal of tools for reconstructing certain paleoclimate elements related to the hydrology of territories. Full article

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

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23 pages, 4190 KB

Open AccessArticle

Prioritizing Small-Scale Water Retention Measures Through Spatial Differentiation of Dominant Runoff Processes

by Katharina Pilar von Pilchau, Christoph Mudersbach, Udo Nehren and Klaus Maas

Hydrology 2026, 13(7), 195; https://doi.org/10.3390/hydrology13070195 - 22 Jul 2026

Abstract

In order to mitigate the negative effects of heavy rainfall events, natural water retention measures (NWRM)—such as hedges, erosion control strips, vegetated drainage channels, wooded strips, retention basins and ditch pockets—have gained renewed attention as an effective climate adaptation strategy. To identify potential [...] Read more.

In order to mitigate the negative effects of heavy rainfall events, natural water retention measures (NWRM)—such as hedges, erosion control strips, vegetated drainage channels, wooded strips, retention basins and ditch pockets—have gained renewed attention as an effective climate adaptation strategy. To identify potential areas for NWRM, this study applied and methodologically expanded an existing approach for identifying dominant runoff processes (DRPs) to an agricultural sub-catchment in the Weserbergland region of Germany. The DRP were determined using a Geographic Information System (GIS) and validated through field surveys. Potential areas for water retention within the same runoff process classes were identified for three defined objectives: improving infiltration, extending flow paths, and redirecting runoff to surrounding areas. Spatial differentiation was achieved using accumulated catchment area and overland flow distance. The watershed is predominantly characterized by surface runoff (Hortonian Overland Flow). Field validation confirmed the DRP classification for around two-thirds of the study area, with deviations occurring predominantly on arable land. Supplementing the DRP approach with a topographic analysis allowed for further differentiation, focusing on small, topographically defined sub-watersheds. The identified areas offer significant potential for interventions. Combined with supplementary data, analyses of the water network and the involvement of local stakeholders, the resulting potential map provides a solid basis for planning smaller-scale water retention measures. Full article

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

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15 pages, 5184 KB

Open AccessArticle

Mechanical Load-Induced PFAS Transport in the Vadose Zone

by Zhi-He Jin

Hydrology 2026, 13(7), 194; https://doi.org/10.3390/hydrology13070194 - 22 Jul 2026

Abstract

PFAS-laden fluid-filled porous media may be subjected to various mechanical loads which induce solid deformation and fluid flow and hence PFAS transport. This work employs a poroelasticity theory for unsaturated porous media to address the coupled solid deformation, fluid flow and PFAS transport [...] Read more.

PFAS-laden fluid-filled porous media may be subjected to various mechanical loads which induce solid deformation and fluid flow and hence PFAS transport. This work employs a poroelasticity theory for unsaturated porous media to address the coupled solid deformation, fluid flow and PFAS transport in the vadose zone subjected to a mechanical load. The governing equation of the aqueous PFAS concentration is derived based on the PFAS mass balance that also considers the water content variation in the pores due to the solid deformation. Vertical PFAS transport in a finite soil layer under mechanical compression is studied using a finite difference method and the solutions of the pore fluid pressures and volumetric strain. Numerical results of the aqueous concentrations of perfluorooctane sulfonic (PFOS) in loamy sand and clay loam indicate that mechanical compression has pronounced effects on the spatial distribution of PFOS. In a loamy sand with relatively higher permeability, mechanical compression at the top drained surface leads to movement of PFOS from the topsoil to the surface thereby reducing the PFOS concentration in the topsoil especially at higher water saturations. The PFOS concentration in the subsoil, however, is not significantly influenced. The effect of mechanical compression on the PFOS concentration distribution in a clay loam can also be observed but is not as significant as in the loamy sand. The mechanical loading effects may be further explored to develop new technologies for PFAS risk assessment and remediation strategies. Full article

(This article belongs to the Topic Transport, Transformation and Cycling of Elements in Water and Soil and Their Response to Human Activities)

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25 pages, 5187 KB

Open AccessArticle

A Sensitivity Study of Vertical and Horizontal River–Aquifer Exchange and Implications for Flood Attenuation

by Gadadhara de Figueiredo Ferraz and Tamás Krámer

Hydrology 2026, 13(7), 193; https://doi.org/10.3390/hydrology13070193 - 18 Jul 2026

Abstract

River–aquifer exchange during floods controls groundwater recharge and bank storage, yet its sensitivity to floodplain geometry, flood duration, and subsurface permeability remains insufficiently quantified. A coupled model integrating one-dimensional surface-water flow, two-dimensional groundwater flow, and vertically resolved unsaturated floodplain infiltration was parameterized using [...] Read more.

River–aquifer exchange during floods controls groundwater recharge and bank storage, yet its sensitivity to floodplain geometry, flood duration, and subsurface permeability remains insufficiently quantified. A coupled model integrating one-dimensional surface-water flow, two-dimensional groundwater flow, and vertically resolved unsaturated floodplain infiltration was parameterized using observation-derived bank-storage estimates from Hungarian Danube floods. Idealized scenarios evaluated the effects of floodplain width, flood duration, and aquifer and soil permeability on river–aquifer exchange, bank storage, and flood attenuation. Simulations indicated that, under the investigated conditions, vertical floodplain infiltration dominates exchange processes, accounting for approximately 82–92% of total exchange and bank storage, whereas horizontal riverbed exchange remains secondary. Floodplain geometry and flood duration exerted influences on bank storage and flood attenuation comparable to those of subsurface permeability. Wider floodplains enhanced infiltration, storage capacity, and flood attenuation. Short floods produced high but transient infiltration and strong peak attenuation, whereas longer floods promoted sustained infiltration, larger bank storage, and delayed attenuation. Subsurface permeability regulated exchange efficiency but exhibited a nonlinear influence on bank storage. These results demonstrated that flood attenuation during overbank flooding depends not only on river–aquifer exchange magnitude, but also on its partitioning and the temporal evolution of subsurface storage. Full article

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

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