Hydrological impacts of climate change at catchment scale : a case study in the Grand-Duchy of Luxembourg

As a consequence of an increase of days with westerly atmospheric fluxes, bringing humid air masses from the Atlantic Ocean to Western Europe, important changes in the annual and seasonal distribution of rainfall have been observed over the past 150 years. Annual rainfall totals observed during the second half of the 19th century were less important than those observed during the second half of the 20th century. Moreover, during the past 50 years winter rainfall totals have significantly increased, while summer rainfall totals have been decreasing. Streamflow observations through the second half of the 20th century have shown a significant increase of winter maximum daily streamflow, in reaction to the winter rainfall increase. The modelling of the streamflow under the 19th century climatological conditions suggests that since then, the number of winter flood days has increased, while the occurrence of summer flood days has decreased. Moreover, high floods appear to have been more frequent in the second half of the 20th century

Comparing hydrological responses across catchments using a new soil water content metric

Soil water content (SWC) is a fundamental variable involved in several hydrological processes governing catchment functioning. Comparative analysis of hydrological processes in different catchments based on SWC data is therefore beneficial to infer driving factors of catchment response. Here, we explored the use of high-temporal resolution SWC data in three forested catchments (2.4–60 ha) in different European climates to characterize hydrological responses during wet and dry conditions. The investigated systems include Ressi, Italy, with a humid temperate climate, Weierbach, Luxembourg, with a semi-oceanic climate, and Can Vila, Spain, with a Mediterranean climate. We introduced a new SWC metric defined as the difference between seasonal mean SWC at a relatively shallow and a deep soil layer. The difference is classified in three distinct states: similar SWC between the two layers, higher SWC in the deeper layer, and higher SWC in the shallow layer. In the most humid site, Ressi, we frequently found similar SWC at the two soil depths which was associated with high runoff ratios. Despite similar precipitation amounts in Can Vila and Weierbach, SWC patterns were very different in both catchments. In Weierbach, SWC was similar across the entire soil profile during wet conditions, whereas evaporation of shallow water resulted in higher SWC in the deep soil layer during dry conditions. This led to high runoff ratios during wet conditions and low runoff ratios during dry conditions. In Can Vila, SWC was consistently higher in the deeper layer compared to the shallow layer, irrespective of the season, suggesting an important role of hydraulic redistribution and vertical water movement in this site. Our approach provides an easy and useful method to assess differences in hydrological behaviour solely based on SWC data. As similar datasets are increasingly collected and available, this opens the possibility for further analyses and comparisons in sites around the globe with contrasted physiographic and climate characteristics.C. Segura acknowledges a Fulbright Fellowship that supported her stay at the University of Florence, Italy and the National Science Foundation Award No. 1943574. The Weierbach datasets have been collected in the framework of the Doctoral Training Unit HYDRO-CSI (Innovative methodologies for unravelling hydrological, chemical, and biological interactions across multiple scales), funded by the National Research Fund of Luxembourg (grant PRIDE15/10623093). Data collection in Ressi catchment was supported by the projects “Ecohydrological Dynamics and Water Pathways in Forested Catchments” (Bando Starting Grants 2015, Fondazione Cassa di Risparmio di Padova e Rovigo), the project “SILVA-Water fluxes between soil, vegetation and atmosphere: a comparative analysis in two Italian forested catchments” (funded by Premio Florisa Melone 2018, assigned by the Italian Hydrological Society), the Italian MIUR Project (PRIN 2017) “WATer mixing in the critical ZONe: observations and predictions under environmental changes-WATZON” (code: 2017SL7ABC), and the RETURN Extended Partnership, receiving funding from the European Union Next-GenerationEU (National Recovery and Resilience Plan – NRRP, Mission 4, Component 2, Investment 1.3 – D.D. 1243 2/8/2022, PE0000005). J. Latron and L. Pfister contributions have been supported by the RHYSOTTO (PID2019-106583RB-I00) and WARMed (PID2022-141868NB-I00) projects, both funded by the Spanish Ministry of Science and Innovation (Ministerio de Ciencia e Inovación, Agencia Estatal de Investigación). J. Latron and L. Pfister also acknowledge the collaboration of Gisel Bertran and Elisenda Sánchez during field work and data collection. The results of this study were discussed within the COST Action: “WATSON” CA19120. We also thank the constructive reviews from Nitin Singh and an anonymous reviewer.Peer reviewe

A Standardized Morpho-Functional Classification of the Planet’s Humipedons

It was time to take stock. We modified the humipedon classification key published in 2018 to make it easier and more practical. This morpho-functional taxonomy of the topsoil (humipedon) was only available in English; we also translated it into French and Italian. A standardized morphofunctional classification of humipedons (roughly the top 30–40 cm of soil: organic and organomineral surface horizons) would allow for a better understanding of the functioning of the soil ecosystem. This paper provides the founding principles of the classification of humipedon into humus systems and forms. With the recognition of a few diagnostic horizons, all humus systems can be determined. The humus forms that make up these humus systems are revealed by measuring the thicknesses of the diagnostic horizons. In the final part of the article, several figures represent the screenshots of a mobile phone or tablet application that allows for a fast recall of the diagnostic elements of the classification in the field. The article attempts to promote a standardized classification of humipedons for a global and shared management of soil at planet level

A standardized morpho-functional classification of the planet’s humipedons

It was time to take stock. We modified the humipedon classification key published in 2018 to make it easier and more practical. This morpho-functional taxonomy of the topsoil (humipedon) was only available in English; we also translated it into French and Italian. A standardized morphofunctional classification of humipedons (roughly the top 30–40 cm of soil: organic and organomineral surface horizons) would allow for a better understanding of the functioning of the soil ecosystem. This paper provides the founding principles of the classification of humipedon into humus systems and forms. With the recognition of a few diagnostic horizons, all humus systems can be determined. The humus forms that make up these humus systems are revealed by measuring the thicknesses of the diagnostic horizons. In the final part of the article, several figures represent the screenshots of a mobile phone or tablet application that allows for a fast recall of the diagnostic elements of the classification in the field. The article attempts to promote a standardized classification of humipedons for a global and shared management of soil at planet level

Contrasting hydrologic response in the cuesta landscapes of Luxembourg

The Attert River basin in Luxembourg is characterised by a large variety of clean and mixed physiogeographical settings (i.e. topography, soil types, land use, bedrock geology, etc.). This in turn generates manifold configurations of rainfall-runoff transformation processes. Here, we provide experimental data from more than a decade of hydro-meteorological observations carried out in a nested catchment set-up, and develop on past and ongoing research on fundamental hydrological functions of catchments: water collection, storage and release. In a first section, we detail the characteristics of the Attert River basin and a set of 9 nested sub-catchments. The second section provides insights into the seasonal and spatial variability of hydrological responses along a wide range of landuse, soil and bedrock settings. The analysis of double-mass curves between precipitation and discharge provided insights into how certain physiogeographic characteristics control hydrological responses. In the third section, we develop on dynamic catchment storage and how it differs between catchments with contrasted landuse and lithology. The fourth section provides insights into the spatial and temporal variability of forest canopy and forest floor storage capacity. Given the considerable amount of precipitation that is intercepted at annual scale, the process is likely to have a substantial influence on catchment storage dynamics

A drifting GPS buoy for retrieving effective riverbed bathymetry

Spatially distributed riverbed bathymetry information are rarely available but mandatory for accurate hydrodynamic modeling. This study aims at evaluating the potential of the Global Navigation Satellite System (GNSS), like for instance Global Positioning System (GPS), for retrieving such data. Drifting buoys equipped with navigation systems such as GPS enable the quasi-continuous measurement of water surface elevation, from virtually any point in the world. The present study investigates the potential of assimilating GNSS-derived water surface elevation measurements into hydraulic models in order to retrieve effective riverbed bathymetry. First tests with a GPS dual-frequency receiver show that the root mean squared error (RMSE) on the elevation measurement equals 30 cm provided that a differential post processing is performed. Next, synthetic observations of a drifting buoy were generated assuming a 30 cm average error of Water Surface Elevation (WSE) measurements. By assimilating the synthetic observation into a 1D-Hydrodynamic model, we show that the riverbed bathymetry can be retrieved with an accuracy of 36 cm. Moreover, the WSEs simulated by the hydrodynamic model using the retrieved bathymetry are in good agreement with the synthetic ‘‘truth’’, exhibiting an RMSE of 27 cm

F-Specific RNA Bacteriophage Transport in Stream Water: Hydro-Meteorological Controls and Association with Suspended Solids

International audienceF-specific RNA bacteriophages (FRNAPHs) are commonly used as indicators of faecal and viral contamination in waters. Once they enter surface waters, the exact role of suspended solids, sediments and hydro-meteorological factors in their fluvial fate and transport is poorly understood, and long-term studies (e.g., over years) are lacking. In this study, FRNAPH concentrations and genogroup distribution were measured in the Orne River (France) during two years at weekly intervals, and during four storm runoff events. Hydro-meteorological driving factors were investigated at both time scales. FRNAPH concentrations and genogroups at different depths of a riverbank sediment core were also examined to better discriminate the origin of the faecal pollution. During low flows, the FRNAPH and the suspended solid transport were decoupled and the FRNAPH concentrations were mainly correlated with the air and water temperature. During storm runoff events, the FRNAPH concentrations only showed a significant correlation with conductivity, turbidity and water discharge. Despite the uncertainty of the predictions, multi parameter regression models using hydro-meteorological variables were suitable to predict log transformed FRNAPHs’ concentrations at low flows with a standard error of 0.46. Model performance using the storm runoff events dataset was low. This study highlights different driving factors at low flows and during storm runoff events, and the need to measure at both time scales to better understand phage transport dynamics in surface water