J. Hydrol. Hydromech., Vol. 72, No. 4 - Early View, 2024, p. 1 - 9, doi: 10.2478/johh-2024-0024
Scientific Paper, English

Martinho A.S. Martins, Sergio A. Prats, Jan Jacob Keizer, Frank G.A. Verheijen: Post-fire soil water repellency under stones and forest residue mulch versus of bare soil

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• Soil water repellency (SWR) is commonly defined as a physical property of soil to resist wetting. Fire can induce, enhance, or reduce SWR and, consequently, lead to considerable changes in soil water infiltration and storage and increase soil erosion by water. The application of mulches to cover burned areas has been found to be an efficient emergency stabilization treatment. However, little is known about possible side effects on SWR, especially long-term effects. Under forests, SWR is known to be very heterogeneous, particularly in proximity to trees and shrubs, litter type and thickness, stones, cracks and roots. This study targeted the effects of post-fire mulching on SWR in a eucalypt plantation five years after a wildfire. The application of forest residue mulch did not significantly change SWR in bare soil patches or under stones, comparing the mulched and untreated plots. By contrast, SWR in the mulched plots was, significantly stronger under mulch than in bare soil. The same was true for both soil organic matter content (SOM) and soil moisture content (SMC), suggesting that SOM played a more important role than SMC. In turn, SWR under mulch was not significantly different from SWR under stone, while both SMC and SOM were significantly higher under mulch than stone. This could be explained by the differences in SMC overriding the effects of the differences SOM, or, alternatively, by possible differences in SOM quality, in particular of the “fresh” input from the mulch. Overall, the present results indicated that different mechanisms may drive SWR dynamics beneath mulch fragments, stones and bare soil patches. A better understanding of these mechanisms is important to improve the knowledge of post-fire overland flow generation and, thereby, to improve its prediction using hydrological models, especially during the early phases of the window-of-disturbance.
  
  KEY WORDS: Wildfire; Hydrophobicity; Mulching; Rock fragment; Stone lag.
  
  Address:
  - Martinho A.S. Martins, Centre for Environmental and Marine Studies (CESAM), Dept. Environment and Planning, University of Aveiro, 3810-193 Aveiro, Portugal. (Corresponding author. Tel.:+351 916499823. Fax.: Email: martinho.martins@ua.pt)
  - Sergio A. Prats, Mediterranean Institute for Agriculture, Environment and Development (MED-CHANGE), Institute for Advanced Studies and Research, University of Évora, Pólo da Mitra, Ap. 94, 7006-554 Évora, Portugal.
  - Jan Jacob Keizer, GeoBiociencias, Geotecnologias E Geoengenharias (GEOBIOTEC), Department Environment and Planning, University of Aveiro, 3810-193 Aveiro, Portugal.
  - Frank G.A. Verheijen, Centre for Environmental and Marine Studies (CESAM), Dept. Environment and Planning, University of Aveiro, 3810-193 Aveiro, Portugal.

J. Hydrol. Hydromech., Vol. 72, No. 4 - Early View, 2024, p. 1 - 9, doi: 10.2478/johh-2024-0023
Scientific Paper, English

Viera Rattayová, Marcel Garaj, Juraj Parajka, Kamila Hlavčová: Regional calibration of the Hargreaves model for estimation of reference evapotranspiration

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• Estimation of reference evapotranspiration values is crucial in climatological and hydrological research, agricultural engineering, and irrigation design. The Penman-Monteith method, endorsed by the Food and Agriculture Organization (FAO) of the United Nations and numerous research studies, is widely regarded as the gold standard. However, its extensive data requirements limit its applicability in regions with sparse meteorological networks or limited measurement capabilities. The Hargreaves method, which requires only basic air temperature inputs, offers an alternative solution. The aims of this study were to calibrate the Hargreaves model for Central European climate conditions, considering altitudinal dependence, and to evaluate the temporal stability of the model parameters. In the first part of the research, we regionalized the Hargreaves coefficients using a curve-fitting method to ensure the best accuracy across 60 climatological stations in Slovakia. The regionalization of the Hargreaves coefficient improved accuracy by 10.1%, reducing the weighted absolute percentage error (WAPE) to 17.9%. However, our results showed that the accuracy of the modified Hargreaves model decreased with the increasing altitude of a climatological station. Incorporating altitude into the Hargreaves equation significantly improved model accuracy in stations at higher altitudes, providing a consistent level of accuracy across all climatological stations, regardless of their location and altitude. The results also indicated that the optimal model coefficient values change over time, showing a decreasing trend of –0.5 for the B coefficient and –0.1 for the C coefficient between the periods 1981–2000 and 2001–2020. Although regionalizing the Hargreaves model coefficients for local conditions can achieve good model performance, the model's accuracy is not stable over time. Thus, periodic validation of the model is necessary for short-term applications.
  
  KEY WORDS: Reference evapotranspiration; Hargreaves equation; Temporal stability of model parameters.
  
  Address:
  - Viera Rattayová, Slovak Hydrometeorological Institute, Climatological Service Department, Jeséniova 17, 833 15 Bratislava, Slovakia. Department of Land and Water Resources Management, Faculty of Civil Engineering, Slovak University of Technology in Bratislava, Radlinského 11, 810 05 Bratislava, Slovakia.
  - Marcel Garaj, Slovak Hydrometeorological Institute, Climatological Service Department, Jeséniova 17, 833 15 Bratislava, Slovakia. (Corresponding author. Tel.: Fax.: Email: Marcel.Garaj@shmu.sk)
  - Juraj Parajka, Institute of Hydraulic Engineering and Water Resources Management, Technische Universität Wien, Vienna, 1040, Austria.
  - Kamila Hlavčová, Department of Land and Water Resources Management, Faculty of Civil Engineering, Slovak University of Technology in Bratislava, Radlinského 11, 810 05 Bratislava, Slovakia.

J. Hydrol. Hydromech., Vol. 72, No. 4 - Early View, 2024, p. 1 - 9, doi: 10.2478/johh-2024-0022
Scientific Paper, English

Romuald Szymkiewicz: A simplified approach for simulating pollutant transport in small rivers with dead zones using convolution

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• In the paper an alternative method to solve the one-dimensional advective-diffusive equation describing the pollutants transport in river with dead zones is presented. Because very often transport in a small river can be treated as a 1D issue, then instead of numerical solution of the advection-diffusion equation an equivalent approach based on the convolution technique can be used. Consequently, for a given impulse response function the numerical calculations are required to compute a convolution only. The impulse response function is obtained as an analytical solution of the linear advection-diffusion equation for the Dirac delta function imposed as the boundary condition at the upstream end. Therefore, it represents the Gauss distribution and consequently, this approach is unreliable when the dead zones occur. To reproduce an asymmetric distribution of concentration along the channel axis an approximation of analytical impulse response function using the asymmetric Gumbel distribution is proposed. This approach valid for solution of the transport equation with constant coefficients is extended for piecewise constant coefficients. Convolution approach does not produce any numerical dissipation and dispersion errors typically generated by the methods based on the finite difference technique. Validation of the method using the results of field measurements confirmed its effectiveness.
  
  KEY WORDS: 1D pollution transport; Dead zones; Convolution; Impulse response function.
  
  Address:
  - Romuald Szymkiewicz, Institute of Hydro-Engineering, Polish Academy of Sciences, ul. Kościerska 7, 80-328 Gdańsk, Poland. (Corresponding author. Tel.: Fax.: Email: r.szymkiewicz@ibwpan.gda.pl)

J. Hydrol. Hydromech., Vol. 72, No. 4 - Early View, 2024, p. 1 - 20, doi: 10.2478/johh-2024-0021
Scientific Paper, English

Jakub Jeřábek, Petr Kavka: Sensitivity and uncertainty analysis of a surface runoff model using ensemble of artificial rainfall experiments

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• Surface runoff models are essential for designing water and soil protection measures. However, they often exhibit uncertainty in both parameterization and results. Typically, uncertainty is evaluated by comparing model realizations with measured data. However, this approach is constrained by limited data availability, preventing comprehensive uncertainty assessment. To overcome this limitation, we employed the generalized likelihood uncertainty estimation (GLUE) methodology to conduct sensitivity and uncertainty analyses on a series of surface runoff models. These models were based on an ensemble of artificial rainfall experiments comprising 77 scenarios with similar settings. We utilized the rainfall-runoff-erosion model SMODERP2D to simulate the experiments and employed Differential Evolution, a heuristic optimization method, to generate sets of behavioural models for each experiment. Additionally, we evaluated the sensitivity and uncertainty with respect to two variables; water level and surface runoff. Our results indicate similar sensitivity of water level and surface runoff to most parameters, with a generally high equifinality. The ensemble of models revealed high uncertainty in bare soil models, especially under dry initial soil water conditions where the lag time for runoff onset was the largest (e.g. runoff coefficient ranged between 0–0.8). Conversely, models with wet initial soil water conditions exhibited lower uncertainty compared to those with dry initial soil water content (e.g. runoff coefficient ranged between 0.6 – 1). Models with crop cover showed a multimodal distribution in water flow and volume, possibly due to variations in crop type and growth stages. Therefore, distinguishing these crop properties could reduce uncertainty. Utilizing an ensemble of models for sensitivity and uncertainty analysis demonstrated its potential in identifying sources of uncertainty, thereby enhancing the robustness and generalizability of such analyses.
  
  KEY WORDS: Surface runoff model; Uncertainty analysis; Sensitivity analysis; GLUE; Model ensemble.
  
  Address:
  - Jakub Jeřábek, The Department of Landscape Water Conservation, Faculty of Civil Engineering, Czech Technical University in Prague, Thákurova 7/2077, 166 29 Praha 6 – Dejvice, Czech Republic. (Corresponding author. Tel.:+420224354570 Fax.: Email: jakub.jerabek@fsv.cvut.cz)
  - Petr Kavka, The Department of Landscape Water Conservation, Faculty of Civil Engineering, Czech Technical University in Prague, Thákurova 7/2077, 166 29 Praha 6 – Dejvice, Czech Republic.

J. Hydrol. Hydromech., Vol. 72, No. 4 - Early View, 2024, p. 1 - 14, doi: 10.2478/johh-2024-0020
Scientific Paper, English

Ikram Mahcer, Djelloul Baahmed, Ludovic Oudin, Cherifa Hanene Kamelia Chemirik: Multidimensional analysis of NDVI dynamics in response to climate and land use/land cover change in Northwest Algeria

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• Climate change has emerged as a major concern at both regional and global scales in recent decades. Northwestern Algeria is particularly vulnerable as a semi-arid zone, where changes in climate and land cover (LC) will have a significant impact on vegetation in the long term. This study analyses, through a multidimensional approach, the influence of climate change and LC on vegetation dynamics. Hierarchical partitioning (HP) analysis was conducted to determine the most influential climatic variables (precipitation, temperature) on the dynamics of NDVI. The results show that the annual NDVI shows a fluctuating spatial trend between decrease and increase in different regions. Trends in seasonal NDVI are spatially varied and less uniform. Variations in precipitation are stable, while temperatures show clear and consistent significant increases across the region, with a general tendency to increase (p<0.01) in spring and summer. In mountainous areas, NDVI shows an increasing trend both annually and seasonally. The correlation (r²) between NDVI, temperature and precipitation (0.75–1.0) over the different seasons reveals significant seasonal and regional variability. LC transition patterns also influence spatio-temporal trends in vegetation cover. They reveal that the rate of change of NDVI varies between LC types and regions, with resilience in forests and grasslands. These variations have significant implications for vegetation dynamics, as observed by NDVI.
  
  KEY WORDS: Climate change; NDVI; Climatic factors; Trend; LC; Northwest Algeria.
  
  Address:
  - Ikram Mahcer, Civil and Environmental Engineering Laboratory (LGCE), Hydraulic Department, Faculty of Technology, University of Djillali Liabes, 22000 Sidi Bel Abbes, Algeria.
  - Djelloul Baahmed, Civil and Environmental Engineering Laboratory (LGCE), Hydraulic Department, Faculty of Technology, University of Djillali Liabes, 22000 Sidi Bel Abbes, Algeria. (Corresponding author. Tel.:+213 6 61 61 45 77 Fax.: Email: baahmed78@yahoo.fr)
  - Ludovic Oudin, Sorbonne Université, CNRS, EPHE, UMR METIS, Case 105, 4 place Jussieu, F-75005Paris, France.
  - Cherifa Hanene Kamelia Chemirik, Civil and Environmental Engineering Laboratory (LGCE), Hydraulic Department, Faculty of Technology, University of Djillali Liabes, 22000 Sidi Bel Abbes, Algeria.