Special Issue "Hillslope Hydrology: Towards Improved Process Understanding Using Modeling and/or Field Observations"

A special issue of Water (ISSN 2073-4441). This special issue belongs to the section "Hydrology and Hydrogeology".

Deadline for manuscript submissions: 31 August 2020.

Special Issue Editors

Dr. Jaromir Dusek
Website
Guest Editor
Department of Hydraulics and Hydrology, Faculty of Civil Engineering, Czech Technical University in Prague, Czech Republic
Interests: hillslope hydrology; transport in porous media; preferential flow; pesticides; soils; runoff processes
Dr. Ali Ameli
Website
Guest Editor
Department of Earth, Ocean and Atmospheric Sciences, The University of British Columbia, Canada
Interests: catchment hydrology; process understanding; hydrologic connectivity; transit time; residence time; hydrology & biogeochemistry interplay; watershed management
Dr. Matthias Sprenger
Website
Guest Editor
Institute of Environmental Assessment and Water Research (IDAEA-CSIC), Barcelona, Spain
Interests: isotope hydrology; ecohydrology; water ages; catchment hydrology; hillslope hydrology
Prof. Shiqin Wang
Website
Guest Editor
Key Laboratory of Agricultural Water Resources, Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, China
Interests: isotope hydrology; hydrogeology; water & nitrate cycle; vadose zone; groundwater modelling

Special Issue Information

Dear Colleagues,

The hillslope is a fundamental spatial unit of headwater catchments. It is recognized that hillslopes are of key importance for a reliable description of both catchment runoff generation and biogeochemical processes. However, understanding hillslope processes has been limited by problems posed by the presence of heterogeneity. Quantifying the threshold hydrological responses of hillslopes to rainfall as controlled by soil heterogeneity, preferential flow, and the spatiotemporal connectivity of soils’ saturated patches requires distinct and multi-scale monitoring procedures which are rare in most environments. The inability to measure or map heterogeneity has restricted the development of robust physically based models, critically required for getting the right answer for the right reason in hydrologic predictions as well as for understanding the interplay between hydrology, biogeochemistry, and ecohydrological feedbacks. To advance the current models, heterogeneity should be replaced by the ecosystem function that it performs, instead of characterizing and specifying its exact details. This would allow to move from a micro-scale Newtonian response to a hillslope-scale, functionally based response. The recent literature indicates that the residence times of water and the landscape transit time distribution are the crucial macro-scale descriptors of how catchment functions, providing a fundamental basis for studying hydrological and biogeochemical transformations in the subsurface. Flux partitioning of water and dissolved substances occurring along various flow pathways (e.g., above and on the soil surface, above the soil–bedrock interface, evaporation, and transpiration) with different residence times plays a major role in the overall hillslope water and material balance. The connectivity of hillslope soil water with the riparian zone and the underlying geological structures remain also poorly understood. To address the above-mentioned challenges, novel monitoring and observation techniques, as well as new modeling approaches, are needed to foster a better quantification of hillslope hydrologically functioning descriptors, including water transit time, residence time, and flow pathways.

Dr. Jaromir Dusek
Dr. Ali Ameli
Dr. Matthias Sprenger
Prof. Shiqin Wang
Guest Editors

Manuscript Submission Information

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Keywords

  • hillslope hydrology
  • stormflow
  • rainfall–runoff relationship
  • modeling
  • flux partitioning
  • threshold behavior
  • travel time of water
  • bedrock
  • preferential flow
  • soil heterogeneity
  • water residence time

Published Papers (4 papers)

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Research

Open AccessArticle
Soil Temperature Dynamics at Hillslope Scale—Field Observation and Machine Learning-Based Approach
Water 2020, 12(3), 713; https://doi.org/10.3390/w12030713 - 05 Mar 2020
Cited by 1
Abstract
Soil temperature plays an important role in understanding hydrological, ecological, meteorological, and land surface processes. However, studies related to soil temperature variability are very scarce in various parts of the world, especially in the Indian Himalayan Region (IHR). Thus, this study aims to [...] Read more.
Soil temperature plays an important role in understanding hydrological, ecological, meteorological, and land surface processes. However, studies related to soil temperature variability are very scarce in various parts of the world, especially in the Indian Himalayan Region (IHR). Thus, this study aims to analyze the spatio-temporal variability of soil temperature in two nested hillslopes of the lesser Himalaya and to check the efficiency of different machine learning algorithms to estimate soil temperature in the data-scarce region. To accomplish this goal, grassed (GA) and agro-forested (AgF) hillslopes were instrumented with Odyssey water level and decagon soil moisture and temperature sensors. The average soil temperature of the south aspect hillslope (i.e., GA hillslope) was higher than the north aspect hillslope (i.e., AgF hillslope). After analyzing 40 rainfall events from both hillslopes, it was observed that a rainfall duration of greater than 7.5 h or an event with an average rainfall intensity greater than 7.5 mm/h results in more than 2 °C soil temperature drop. Further, a drop in soil temperature less than 1 °C was also observed during very high-intensity rainfall which has a very short event duration. During the rainy season, the soil temperature drop of the GA hillslope is higher than the AgF hillslope as the former one infiltrates more water. This observation indicates the significant correlation between soil moisture rise and soil temperature drop. The potential of four machine learning algorithms was also explored in predicting soil temperature under data-scarce conditions. Among the four machine learning algorithms, an extreme gradient boosting system (XGBoost) performed better for both the hillslopes followed by random forests (RF), multilayer perceptron (MLP), and support vector machine (SVMs). The addition of rainfall to meteorological and meteorological + soil moisture datasets did not improve the models considerably. However, the addition of soil moisture to meteorological parameters improved the model significantly. Full article
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Open AccessArticle
Modeling Travel Time Distributions of Preferential Subsurface Runoff, Deep Percolation and Transpiration at A Montane Forest Hillslope Site
Water 2019, 11(11), 2396; https://doi.org/10.3390/w11112396 - 15 Nov 2019
Abstract
Residence and travel times of water in headwater catchments, or their smaller spatial units, such as individual hillslopes, represent important descriptors of catchments’ hydrological regime. In this study, travel time distributions and residence times were evaluated for a montane forest hillslope site. A [...] Read more.
Residence and travel times of water in headwater catchments, or their smaller spatial units, such as individual hillslopes, represent important descriptors of catchments’ hydrological regime. In this study, travel time distributions and residence times were evaluated for a montane forest hillslope site. A two-dimensional dual-continuum model, previously validated on water flow and oxygen-18 data, was used to simulate the seasonal soil water regime and selected major rainfall–runoff events observed at the hillslope site. The model was subsequently used to generate hillslope breakthrough curves of a fictitious conservative tracer applied at the hillslope surface in the form of the Dirac impulse. The simulated tracer breakthroughs allowed us to estimate the travel time distributions of soil water associated with the episodic subsurface stormflow, deep percolation and transpiration, thus yielding partial travel time distributions for the individual discharge processes. The travel time distributions determined for stormflow were dominated by the lateral component of preferential flow. The stormflow median travel times, calculated for nine selected rainfall–runoff events, varied considerably—ranging from 1 to 17 days. The estimated travel times were significantly affected by the temporal rainfall patterns and antecedent soil moisture distributions. The residence times of soil water, evaluated for three consecutive growing seasons, ranged from 29 to 37 days. The analysis reveals the interplay of soil water storage and discharge processes at the hillslope site of interest. The applied methodology can be used for the evaluation of runoff dynamics at the hillslope and catchment scales as well as for the quantification of biogeochemical transformations of dissolved chemicals. Full article
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Open AccessArticle
Performance of Conservation Techniques for Semiarid Environments: Field Observations with Caatinga, Mulch, and Cactus Forage Palma
Water 2019, 11(4), 792; https://doi.org/10.3390/w11040792 - 16 Apr 2019
Cited by 2
Abstract
Understanding small-scale hydrologic processes and the impact of soil conservation techniques are crucial in reducing runoff and sediment losses in semi-arid regions. This study was conducted in the Alto Ipanema River Basin, in Pernambuco State (Brazil). Soil and water dynamics were intensely monitored [...] Read more.
Understanding small-scale hydrologic processes and the impact of soil conservation techniques are crucial in reducing runoff and sediment losses in semi-arid regions. This study was conducted in the Alto Ipanema River Basin, in Pernambuco State (Brazil). Soil and water dynamics were intensely monitored in twelve experimental plots with different coverage conditions (plot with bare soil—Bare; plot with natural vegetation—Natur; plot with mulch—Mulch; plot with Cactus Palma—Palma). By far, bare soil conditions produced higher runoff and soil losses. Mulch cover was close to natural vegetation cover, but still presented higher runoff and sediment losses. Palma, which is a very popular spineless cactus for animal feed in the Brazilian semi-arid region, presented an intermediate hydrologic impact in controlling runoff, enhancing soil moisture, and also reducing soil losses. Experiments were conducted in one hydrologic year (2016/2017) at three different sites. They were intensely monitored and had the same number of plots. This enabled us to carry out a robust performance assessment of the two soil conservation practices adopted (Mulch and Palma), compared to natural vegetation cover and bare soil conditions. Such low-cost alternatives could be easily adopted by local farms in the region, and, hence, improve soil reclamation and regional resiliency in a water-scarce environment. Full article
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Open AccessArticle
Experimental Investigation of Lateral Subsurface Flow Depending on Land Use and Soil Cultivation
Water 2019, 11(4), 766; https://doi.org/10.3390/w11040766 - 13 Apr 2019
Abstract
The magnitude and timing of flood events are influenced by surface and subsurface flow generation as well as by present land use distribution. An integrated understanding of the interactions of soil properties, land use and flow generation is still missing. Therefore, field experiments [...] Read more.
The magnitude and timing of flood events are influenced by surface and subsurface flow generation as well as by present land use distribution. An integrated understanding of the interactions of soil properties, land use and flow generation is still missing. Therefore, field experiments are required to gain further knowledge about land use dependencies of discharge generation and concentration processes. In our research, we built an experimental setup consisting of three sites with similar soil and topographic conditions and different land use types (cropland, grassland, forest). The applied multimethod approach includes meteorological parameters, soil moisture, soil moisture tension, surface runoff, lateral subsurface flow, and stream discharge observations. The results show that low subsurface flow discharges more often occur at the cropland site, while large flow volumes were mainly observed at the grassland site. A correlation of the horizontal distribution of subsurface flow volumes and the accumulation areas of the surface topography has been found (r² = 0.76). The observed average response times for advective events increase from the forest site (6.0 h) to the grassland site (12.4 h) to the cropland site (20.9 h). Response times of convective events were shorter than 1 h at all sites. Full article
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