Julian Klaus

Julian Klaus
University of Bonn | Uni Bonn ·  Department of Geography

PhD

About

96
Publications
31,113
Reads
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2,266
Citations
Additional affiliations
January 2020 - March 2020
University of Birmingham
Position
  • Researcher
February 2017 - April 2017
University of Western Australia
Position
  • Fellow
October 2013 - August 2021
Luxembourg Institute of Science and Technology (LIST)
Position
  • Senior Researcher
Education
April 2008 - July 2011
Technische Universität München
Field of study
  • Environmental Engineering
October 2001 - September 2006
University of Freiburg
Field of study
  • Hydrology

Publications

Publications (96)
Preprint
Catchment-scale transpiration is commonly determined by the use of sap-flow sensors, and its quantification, which is critical for water and forest management, relies crucially on the total catchment’s sapwood area (A s ). Species-specific allometric relationships between the trees A s and the trees diameter at breast height (DBH) are widely used f...
Article
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Emerging drought stress on vegetation over western Eurasia is linked to varying teleconnection patterns. The North-Sea Caspian pattern (NCP) is a relatively less studied Eurasian teleconnection pattern which has a role on drought conditions and the consequence of changing conditions on vegetation. Between 1981 and 2015, we found that the Standardiz...
Conference Paper
Full-text available
Precipitation extremes are commonly linked with land use types. The UKCP18 Convection-Permitting Model (CPM) Projections at 5km high resolution simulation provide opportunities to investigate probable relationships between precipitation extremes and land use types. Changes in the duration and severity of extreme precipitation events can be linked t...
Preprint
The transport of solutes in river networks is controlled by the interplay of processes such as in-stream solute transport and the exchange of water between the stream channel and dead zones, in-stream sediments, and the hyporheic zone. Transient storage models (TSMs) are a powerful tool for testing hypotheses related to solute transport in streams....
Article
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In river systems, headwater networks contain the vast majority of the stream length. Thus, climate and land‐use change in headwaters have disproportionate impacts on downstream ecosystems and societies that rely on them. Despite decades of hydrological research, difficulties in observing hydrological properties across scales means that scientific k...
Article
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Knowledge of the sources of surface water in riparian zones and floodplains is critical to understanding its role in runoff generation and impact on biogeochemical and ecological processes. In this study, we demonstrate the potential of integrated surface‐subsurface hydrologic modeling (HydroGeoSphere) in combination with a hydraulic mixing‐cell ap...
Article
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The role of landscape topography in mediating subsurface water availability and ultimately tree transpiration is still poorly understood. To assess how hillslope position affects tree water use, we coupled sap velocity with xylem isotope measurements in a temperate beech‐oak forest along a hillslope transect in Luxembourg. We generally observed gre...
Article
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The substantial tree-to-tree variability of transpiration poses a major challenge to a reliable stand-scale quantification of transpiration. The diameter at breast height (DBH) and landscape characteristics have been identified as drivers of tree-to-tree variability, but it remains unclear if their control on sap velocity varies between species-spe...
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Ocean-atmosphere modes of climate variability in the Pacific and Indian oceans, as well as monsoons, regulate the regional wet and dry episodes in tropical regions. However, how those modes of climate variability, and their interactions, lead to spatial differences in drought patterns over tropical Asia at seasonal- to interannual time scales remai...
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Understanding near-stream groundwater dynamics and flow directions is important for predicting hillslope-stream connectivity, streamflow generation, and hydrologic controls of streamwater quality. To determine the drivers of groundwater flow in the stream corridor (i.e., the stream channel and the adjacent groundwater in footslopes and riparian are...
Article
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West Africa exhibits decadal patterns in the behaviour of droughts and floods, creating challenges for effective water resources management. Proposed drivers of prolonged shifts in hydrological extremes include the impacts of land-cover change and climate variability in the region. However, while future land-degradation or land-use are highly unpre...
Article
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Widespread observations of ecohydrological separation are interpreted by suggesting that water flowing through highly conductive soil pores resists mixing with matrix storage over periods of days to months (i.e., two “water worlds” exist). These interpretations imply that heterogenous flow can produce ecohydrological separation in soils, yet little...
Conference Paper
Full-text available
Drought conditions of Southeast China are associated with the sea surface temperature warm pool in the tropical Western Pacific, which is related to low-frequency hydroclimatic patterns and their teleconnections. Empirically, the moisture influx to the region is linked to the interannual and decadal teleconnections, including the Pacific Decadal Os...
Article
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We present a method to simulate fluid flow with reactive solute transport in structured, partially saturated soils using a Lagrangian perspective. In this context, we extend the scope of the Lagrangian Soil Water and Solute Transport Model (LAST) (Sternagel et al., 2019) by implementing vertically variable, non-linear sorption and first-order degra...
Article
The Weierbach experimental catchment (0.45 km²) is the most instrumented and studied sub‐catchment in the Alzette River basin in Luxembourg. Within the last decade, it has matured towards an interdisciplinary critical zone observatory focusing on a better understanding of hydrological and hydro‐geochemical processes. The Weierbach catchment is embe...
Article
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Catchment travel time distributions (TTDs) are an efficient concept for summarizing the time-varying 3D transport of water and solutes towards an outlet in a single function of a water age and for estimating catchment storage by leveraging information contained in tracer data (e.g., deuterium 2H and tritium 3H). It is argued that the preferential u...
Preprint
Full-text available
Submitted for publication in Hydrological Processes: Widespread observations of ecohydrological separation are interpreted by suggesting that water flowing through highly conductive soil pores resists mixing with matrix storage over periods of days to months (i.e., two water worlds). We quantified the separation between mobile water moving through...
Preprint
Full-text available
We present an approach to simulate reactive solute transport within the Lagrangian Soil Water and Solute Transport Model framework (LAST). The LAST-Model is based on a Lagrangian perspective describing the (1-D) movement of discrete water particles, which travel at different velocities and carry solutes through a heterogeneous, partially saturated...
Poster
Full-text available
Ecohydrological separation has been observed across climates and biomes, and at a fundamental level suggests that water in mobile versus immobile domains may resist mixing over varying periods of time; however little mechanistic evidence exists to explain this separation at a process scale. Non-equilibrium flow in the vadose zone may partially acco...
Article
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Travel time distributions (TTDs) are concise descriptions of transport processes in catchments based on water ages, and they are particularly efficient as lumped hydrological models to simulate tracers in outflows. Past studies have approximated catchment TTDs with unimodal probability distribution functions (pdf) and have successfully simulated tr...
Article
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The occurrence of preferential flow in the subsurface has often been shown in field experiments. However, preferential flow is rarely included in models simulating the hydrological response at the catchment scale. If it is considered, preferential flow parameters are typically determined at the plot scale and then transferred to larger‐scale simula...
Article
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Surface saturated areas are key features in generating runoff. A detailed characterisation of the expansion and contraction of surface saturation in riparian zones and its connectivity to the stream is fundamental to improve our understanding of the spatial and temporal variability of streamflow generation processes. In this first contribution of a...
Article
Full-text available
The occurrence of preferential flow in the subsurface has often been shown in field experiments. However, preferential flow is rarely included in models simulating the hydrological response at the catchment scale. If it is considered, preferential flow parameters are typically determined at the plot scale and then transferred to larger‐scale simula...
Article
Full-text available
Catchment travel times integrate the multitude of hydrological flow processes and provide insights into catchment functioning. StorAge Selection (SAS) functions describe how residence times of water in storage are related to travel times of water in catchment outflows. As such, SAS functions are useful to summarize transport processes in catchments...
Preprint
Full-text available
Catchment travel time distributions (TTDs) are an efficient concept to summarize the time-varying 3-dimensional transport of water and solutes to an outlet in a single function of water age and to estimate catchment storage by leveraging information contained in tracer data (e.g. ²H and ³H). It is argued that the increasing use of the stable isotop...
Article
Full-text available
Investigating the spatio‐temporal variability of streamflow generation is fundamental to interpret the hydrological and bio‐chemical functioning of catchments. In humid temperate environments, streamflow generation is often linked to the occurrence of near stream surface saturated areas, which mediate hydrological connectivity between hillslope and...
Article
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The inundation of flood-prone areas varies in space and time and can have crucial impacts on runoff generation and water quality when the surface saturated areas become connected to the stream. In this study, we aimed to investigate and explain the variability of surface saturation patterns and dynamics within a forested headwater catchment. On the...
Article
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Despite ubiquitous field observations of nonuniform flow processes, preferential flow paths are rarely considered in hydrological models, especially at catchment scale. In this study, we investigated the extent to which plot-scale observations of preferential flow paths are informative for rainfall–runoff simulations at larger scales. We used data...
Article
Full-text available
Catchment storage controls most eco-hydrological processes by modulating, among other things, the hydrological connectivity between landscape units. However, little is known about the internal dynamics of storage and its feedback with hydraulic connectivity. Here, we evaluate the capability of a combined lumped approach (i.e. combining catchment wa...
Conference Paper
Full-text available
Monsoons affect millions of lives in West Africa. Regional and decadal droughts and floods are proposed to be related to the anomalies of the monsoon strength, timing and duration. In multiple scales, causes and effects of interannual monsoon variability are valuable in predicting extreme regional hydroclimatic conditions. Driven by climate indices...
Article
Full-text available
Surface saturation can have a critical impact on runoff generation and water quality. Saturation patterns are dynamic, thus their potential control on discharge and water quality is also variable in time. In this study, we assess the practicability of applying thermal infrared (TIR) imagery for mapping surface-saturation dynamics. The advantages of...
Article
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In this commentary, we summarize and build upon discussions that emerged during the workshop "Isotope-based studies of water partitioning and plant-soil interactions in forested and agricultural environments" held in San Casciano in Val di Pesa, Italy, in September 2017. Quantifying and understanding how water cycles through the Earth's critical zo...
Article
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In this study we assess the practicability of applying thermal infrared (TIR) imagery for mapping surface saturation dynamics. The advantage of TIR imagery compared to other surface saturation mapping methods is its large spatial and temporal flexibility combined with a non-invasive and intuitive character. Based on an 18-month field campaign, we r...
Article
Full-text available
In this commentary, we build on discussions that emerged during the workshop "Isotope-based studies of water partitioning and plant-soil interactions in forested and agricultural environments" held in San Casciano Val di Pesa, Italy, in September 2017. Quantifying and understanding how water cycles through the Earth's critical zone is important to...
Article
Full-text available
Diel fluctuations of stream water DOC concentrations are generally explained by a complex interplay of different instream processes. We measured the light absorption spectrum of water and DOC concentrations in situ and with high frequency by means of a UV–Vis spectrometer during 18 months at the outlet of a forested headwater catchment in Luxembour...
Article
Full-text available
Recent advancements in analytical solutions to quantify water and solute travel time distributions (TTDs) and the related StorAge Selection (SAS) functions synthesize catchment complexity into a simplified, lumped representation. While these analytical approaches are efficient in application, they require rarely available long-term and high-frequen...
Article
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The cover image, by Laurent Pfister et al, is based on Advanced Review Terrestrial diatoms as tracers in catchment hydrology: a review, DOI: 10.1002/wat2.1241.
Article
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Diatoms are remarkable organisms. They are present in almost all habitats containing water (e.g., lakes, streams, soils, bark) and rank among the most common algal groups in both freshwaters and marine ecosystems. The ubiquitous character of aquatic diatoms has triggered countless applications as environmental tracers for studies in water quality,...
Article
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We monitored dissolved organic carbon (DOC) and nitrate concentrations and fluxes in situ with a UV-Vis spectrometer for two years at a high temporal resolution of 15 minutes in the forested Weierbach headwater catchment. The catchment exhibits a characteristic double peak runoff response to incident rainfall during periods with wet initial conditi...
Article
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Quantifying the travel times, pathways, and dispersion of solutes moving through stream environments is critical for understanding the biogeochemical cycling processes that control ecosystem functioning. Validation of stream solute transport and exchange process models requires data obtained from in-stream measurement of chemical concentration chan...
Article
Full-text available
Diel fluctuations of streamwater DOC concentrations are generally explained by a complex interplay of different instream processes. We measured the light absorption spectrum of water and DOC concentrations in-situ and with high-frequency by means of a UV-Vis spectrometer during 18 months at the outlet of a forested headwater catchment in Luxembourg...
Article
Full-text available
Stream confluences are important hotspots of aquatic ecological processes. Water mixing dynamics at stream confluences influence physio-chemical characteristics of the stream as well as sediment mobilisation and pollutant dispersal. In this study, we investigated the potential for handheld thermal infrared (TIR) imagery to provide rapid information...
Article
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The bedrock controls on catchment mixing, storage, and release have been actively studied in recent years. However, it has been difficult to find neighboring catchments with sufficiently different and clean expressions of geology to do comparative analysis. Here, we present new data for 16 nested catchments (0.45 to 410 km2) in the Alzette River ba...
Article
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The movement of water, matter, organisms, and energy can be altered substantially at ecohydrological interfaces, the dynamic transition zones that often develop within ecotones or boundaries between adjacent ecosystems. Interdisciplinary research over the last two decades has indicated that ecohydrological interfaces are often “hotspots” of ecologi...
Article
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Double peak hydrographs are widespread phenomena but poorly understood mechanistically. In many cases, saturation-excess overland flow in the near-stream areas is assumed to control the initial peak, while the delayed peak is explained by subsurface flow in the soil or sediment cover or groundwater flow on fractured bedrock. Here we explore the mec...
Article
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The highly dynamic processes within a hillslope-riparian-stream (HRS) continuum are known to affect streamflow generation, but are yet not fully understood. Within this study, we simulated a headwater HRS continuum in western Luxembourg with an integrated hydrologic surface subsurface model (HydroGeoSphere). The model was set up with thorough consi...
Article
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Diel (also called diurnal) discharge patterns with minima in the afternoon are generally explained by the daily cycle of evapotranspiration, while maxima in the afternoon are often linked to freeze-thaw cycles. In a schistose and forested headwater catchment in Luxembourg, we observed daily discharge maxima in the afternoon, although temperatures r...
Article
Earthworms play a key role in regulating soil ecosystem functions and services. The small scale variability in earthworm abundance is often found to be very high, which is a problem for representative sampling of earthworm abundance at larger scales. In agricultural fields, soil tillage may influence both the average earthworm abundance as well as...
Article
Full-text available
Interactions among hydraulic conductivity distributions, subsurface topography, and lateral flow are poorly understood. We applied 407 mm of water and a suite of tracers over 51 hours to a 12 by 16.5 m forested hillslope segment to determine interflow thresholds, preferential pathway pore velocities, large-scale conductivities, the time series of e...
Conference Paper
Full-text available
A double peak hydrograph features two peaks as a response to a unique rainfall pulse. The first peak occurs at the same time or shortly after the precipitation has started and it corresponds to a fast catchment response to precipitation. The delayed peak normally starts during the recession of the first peak, when the precipitation has already ceas...
Article
It is well known that sediment properties, including sediment-associated chemical constituents and sediment physical properties, can exhibit significant variations within and between storm runoff events. However, the number of samples included in suspended sediment studies is often limited by time consuming and expensive laboratory procedures after...
Article
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Nitrogen (N) is an important nutrient as it often limits productivity, but in excess can impair water quality. Most studies on watershed N cycling have occurred in upland forested catchments where snowmelt dominates N export; fewer studies have focused on low-relief watersheds that lack snow. We examined watershed N cycling in three adjacent, low-r...
Article
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We evaluated the occurrence of perching and interflow over and within a sandy clay loam argillic horizon within first-order, low-relief, forested catchments at the Savannah River Site (SRS) in the Upper Coastal Plain of South Carolina. We measured soil hydraulic properties, depths to the argillic layer, soil moisture, shallow groundwater behavior,...
Article
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Connectivity between different landscape units and flow paths to the stream has gained much attention in hydrological science. Recent work has focused on the threshold sequencing of spatial sources in upland forested watersheds, connectivity and its spatial patterns in the hillslope-riparian-stream (HRS) continuum. Fast flow path connectivity in th...
Article
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Hydrological processes research remains a field that is severely measurement limited. While conventional tracers (geochemicals, isotopes) have brought extremely valuable insights into water source and flowpaths, they nonetheless have limitations that clearly constrain their range of application. Integrating hydrology and ecology in catchment scienc...