This session solicitates any contributions that share new insights about forest ecohydrological processes, or demonstrate new ways of observing and modelling water fluxes in forest ecoystems, forest water stress, drought resistance and resilience, or the links between forest hydrological processes and the water, carbon and nutrient cycles.
Forest canopies exert strong and complex controls over snow accumulation and melt dynamics, particularly in snow-dominated environments. Given the importance of snow for recharging soil and groundwater and for runoff generation, furthering the process-based understanding of the interplay between forests and snowpack is critical across a range of snow-dominated ecosystems. Here, we compare results from two complementary field-based studies at sites with contrasting forest and snow dynamics – the Marcell Experimental Forest in northern Minnesota, USA, and the Chicken Creek Snowtography Study in southern Colorado, USA. We found that forest canopies exerted significant control over snow depth and SWE at the two sites, but with differing directionality. Snow depth was measured at both field sites in water years 2023 and 2024, while measurements at Chicken Creek, which began in water year 2022, also included snow-water equivalent. Forest structure metrics varied for the sites, but included quantifications for typical two-dimensional measurements (e.g., basal area, tree height, leaf-area-index), and three-dimensional complexity (e.g., canopy overlap, structural diversity, canopy light attenuation, etc.). Results from both studies demonstrate that 3-D canopy metrics are better predictors of snow depth and SWE than 2-D metrics, which are typically measured by field practitioners. At the ponderosa pine-dominated Chicken Creek site, which typically has a warmer and ephemeral snowpack, snow depth and SWE decreased as the canopy vertical complexity increased. At the sub-boreal Marcell site, which is colder and has a seasonal snowpack, peak snow depth increased with increasing canopy overlap. Our results demonstrate the importance of incorporating canopy metrics over basal areas in understanding forest-snow dynamics. The contrasting directionality in canopy complexity over snow metrics further shows that forest-snow interactions vary across ecosystems and climate gradients. Field-based studies across a range of forests, elevations, topographies, and latitudes are needed to inform forest management practices to preserve snowpack water storage in snow-dominated ecosystems.
How to cite: Dymond, S., Farwell, H., Jones, M., Biederman, J., Feng, X., Kurzweil, J., Sebestyen, S., and Sanchez Meador, A.: Forest Structure Controls on Snowpack Dynamics in Two Contrasting Forest Ecosystems, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8426, https://doi.org/10.5194/egusphere-egu26-8426, 2026.
Boreal forest hydrological processes can be strongly influenced by the pronounced seasonality of precipitation, yet the spatiotemporal redistribution of rainfall and snowfall within forest canopies remains insufficiently understood. We investigate precipitation redistribution in a northern boreal Scots pine forest at the Oulanka station, Finland, with a focus on characterizing and quantifying seasonal variability and the spatial distribution of water inputs at the forest level and stable water isotope characterization of forest and open-area precipitation. We monitored throughfall, stemflow, snowmelt, and snowpack dynamics within the forest stand from July 2024 to April 2025. This integrated forest observational framework allows us to assess how canopy interception, rain-snow redistribution, and snowpack processes jointly regulate water inputs and its isotope composition to the forest floor across seasons. Preliminary analyses reveal strong seasonal differences in precipitation redistribution. Initial isotope observations suggest limited modification of precipitation isotopic signatures by canopy processes, indicating that physical redistribution rather than isotopic fractionation plays a dominant role in canopy-precipitation interactions in this forest. Our study provides new insights into the seasonal water inputs of boreal forest ecohydrology and contributes to improving process-based representations of forest ecohydrology in cold-regions and tracer-aided models, with potential benefits for local water resource management and the forestry sector.
How to cite: Li, J., Ala-Aho, P., Marttila, H., Paavola, R., and Chen, Z.: Spatial-temporal redistribution of seasonal precipitation and stable water isotopes in a boreal coniferous forest, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19163, https://doi.org/10.5194/egusphere-egu26-19163, 2026.
Forest floor litter layers can temporarily store and evaporate substantial fractions of annual precipitation, thereby reducing the amount of water that infiltrates into soils and becomes available for plant uptake. Yet litter retention and evaporation are commonly omitted from forest water-balance assessments. Here we synthesize evidence for these litter-layer effects across elevation gradients and contrasting climates using two complementary datasets: (i) long-term observations from Waldlabor Zürich and (ii) a pan-Alpine sampling campaign (>400 plots) combined with laboratory measurements of litter water storage and drying dynamics. Climate-chamber drying experiments indicated mean litter water retention times of ~6 days for broadleaf litter and ~10 days for needle litter, consistent with field observations across the European Alps. We used these experiments to parameterize sensitivity tests (half-life storage decay) and to drive a simple daily bucket model. Across the Alps, the litter layer temporarily stored roughly ~10-20% of annual precipitation, while litter evaporation accounted for ~15-25% of annual evapotranspiration, with magnitudes varying by elevation and litter type. Together, these results show that the litter layer is a small but hydrologically relevant reservoir that shifts the timing and partitioning of water fluxes in mountain forests.
How to cite: Floriancic, M., Chen, Y., and Molnar, P.: Effects of litter layer water retention along an elevation gradient, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2090, https://doi.org/10.5194/egusphere-egu26-2090, 2026.
Consecutive dry periods (e.g., 2014–2016, 2018–2019, 2022) led to persistent long-term impairments in maintaining tree functions such as growth and canopy structure thereby exacerbating drought stress and mortality in temperate forests. Despite growing attention to compound drought impacts on forest ecosystems, the role of deep-water sources at varying positions on hillslopes remains unclear.
In this study, we investigated how hillslope position influences growth dynamics and water-use strategies of co-occurring tree species in an unmanaged, structurally diverse forest stand in Lower Saxony, Germany. The stand is composed of the broadleaf deciduous tree species Fagus sylvatica (L.), Carpinus betulus (L.), Fraxinus excelsior (L.), and Quercus robur (L.) which differ in their root structure, stomatal regulation and growth strategies. Over the three years (2023-2025) we employed continuous point-dendrometer, sap flow and soil moisture measurements to monitor growth, soil and stand water use and water potential. Further destructive samples for verifying water potential and stable carbon isotopes of phloem sap were measured.
We found that growth patterns were strongly species-specific and closely aligned with contrasting tree water-use strategies. Despite similar climatic conditions in 2023 and 2024, pronounced interannual differences in growth were observed. These differences suggest a delayed recovery from previous long-term drought events (2018-2022), particularly for the shallow-rooted species F. sylvatica, C. betulus and F. excelsior, compared to deep-rooted Q. robur, highlighting long-term effects of compound droughts on productivity. It was notable that the species were able to adapt their strategies according to their position. Additionally, we observed in F. excelsior and Q. robur that high growth rates can be supported by using water storage (e.g., via deep roots and access to deep water sources or via stem water use) or by maintaining high transpiration rates during drought at the risk of cavitation. In conclusion, we postulate that drought mitigation strategies not only depend on species traits, but also on tree positioning and climatic conditions.
How to cite: Rohde, C., Iraheta, A., Beyer, M., Marshall, J. D., Demir, G., and Dubbert, M.: Tree water-use strategies and growth performance along a hillslope transect in a diverse Central European Forest, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11986, https://doi.org/10.5194/egusphere-egu26-11986, 2026.
Coastal forests of the North American Great Lakes have long provided ecological, economic, and cultural resources. However, extensive logging and shoreline development have greatly reduced the number of well-preserved coastal forests, leaving ridge-and-swale complexes among the most intact examples remaining in the region. These freshwater coastal landscapes formed from ancient beaches, creating sandy, tree-covered ridges separated by low-lying interdunal swales that commonly support wetlands. Ridge-and-swale complexes serve as the transition between upland ecosystems and the Great Lakes along which interaction with groundwater directly controls vegetation composition and function. They are an excellent natural setting to study forest-groundwater interactions as variation in groundwater depth impacts water available to plants. In these systems, groundwater hydrology reflects the combined influence of upland derived regional groundwater flow, local hydrologic inputs (precipitation) and outputs (evapotranspiration), and variability in Great Lakes Water Levels (GLWL). As environmental conditions and GLWLs continue to shift the trajectory of these tightly coupled groundwater-ecosystems interaction remains uncertain.
The goal of this work is to document modern spatial and temporal variation in forest-groundwater interactions, establish the influence of depth to groundwater on historical tree growth, and map forest susceptibility to groundwater conditions in a ridge-and-swale complex at the Ridges Sanctuary in Bailey’s Harbor, WI (45.075163, -87.108379). To investigate modern forest water use and groundwater dynamics, we instrumented a ridge-and-swale complex situated along Lake Michigan with shallow groundwater wells. Over 18 months, analysis of daily fluctuations in groundwater revealed that evapotranspiration from groundwater differs in timing and magnitude between stands of trees. Throughout the ridge-and-swale complex groundwater levels respond differently throughout the year and especially during extended dry periods. This indicates a limit of tree water use based on depth to groundwater and differing influence of regional groundwater and GLWL sources. To investigate historical tree growth, we evaluated tree-ring metrics (basal area increment (BAI), ring widths, earlywood, and latewood) from Pinus strobes and Pinus resinosa to quantify tree growth variability across the ridge-and-swale complex. Chronologies for 120 trees were established with a majority spanning over 125 years from throughout the ridge-and-swale complex with limited trees documenting growth starting in the late 1700s. Comparison of BAI and relative elevation have revealed both tree species experience differing levels of anoxia and water stress based on position in the landscape and depth to groundwater, indicating that annual variability in groundwater is recorded in tree growth. To map future susceptibility to groundwater conditions, we used our established chronologies to decipher where trees showed resilience to the influence of GLWLs. Preliminary analyses suggest that stands situated in areas supported by regional groundwater flow have historically experienced optimal tree growth throughout the period of record. Conversely, the influence of GLWL supporting or hindering tree growth depends on position relative to the coast and the stage of Lake Michigan at the time. These findings not only shed light upon the previously unknown historical influence of GLWL on coastal ridge-and-swale ecosystems but help shape future management for coastal aquifers and forests.
How to cite: Kastelic, E. and Loheide II, S. P.: Ecohydrology of a Freshwater Coastal Forest Under Fluctuating Lake Levels, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8587, https://doi.org/10.5194/egusphere-egu26-8587, 2026.
Forests are experiencing increasing stress from the combined effect of atmospheric warming and the air's capacity to hold more moisture. Vapour pressure deficit (VPD), a key measure of atmospheric moisture demand, increases with warming due to the nonlinear rise in saturation vapour pressure, amplifying transpiration demand and drought stress and increasing mortality risk. VPD may cause large-scale physiological stress in trees and can lead to forest die-backs. The Pfynwald Research platform (Southern Switzerland) is located in a natural forest reserve dominated by (> 100-year-old) Scots pines growing on shallow soils with low water-holding capacity. The region has experienced pronounced drought stress and tree mortality in recent decades, making it a natural laboratory to investigate drought impacts on tree physiology, ecosystem functioning, and resilience. The Pfynwald research team, led by WSL, has initiated a long-term irrigation study in 2003 to quantify ecosystem responses to alleviation of chronic drought stress. A more recent experiment, inaugurated in 2024, studies the effect of soil and atmospheric drought by a unique setup that (1) intercepts rainfall through a throughfall exclusion and (2) manipulates atmospheric VPD by regulating air humidity in the forest canopy. In this contribution, we focus on the belowground by showcasing a time-lapse quasi-3D geoelectric experiment that we started in May 2025 including daily repeated subsurface electrical resistivity surveys to track belowground moisture variations in time and space. Our setup allows us to investigate deeper belowground effects of aboveground manipulations, namely the VPD, irrigation, and drought treatments. We present a multi-disciplinary investigation that integrates our geophysical findings with the dense, aboveground observations of the site. Our work stresses the importance of distributed and continuous monitoring of belowground states in natural manipulation experiments, for a holistic understanding of how climate change will affect forest ecosystems.
How to cite: Shakas, A., Meusburger, K., Gessler, A., and Schmelzbach, C.: Belowground responses to soil and atmospheric drought imaged with time-lapse geoelectrics, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10909, https://doi.org/10.5194/egusphere-egu26-10909, 2026.
Abstract:
Mediterranean dryland forests are critically dependent on rainfall regimes and are increasingly exposed to prolonged droughts that disrupt soil–water–vegetation interactions and elevate the risk of tree mortality. Continuous monitoring of inter-depth soil moisture dynamics offers real-time insight into these processes, yet such data is very scarce. Based on long-term ecohydrological monitoring in HaKedoshim Pinus halepensis Forest, Israel, we quantified how drought alters soil moisture dynamics, water availability, and vegetation responses on shallow soil, hard rock (lime) terrains with contrasting canopy structures: dense forest plots (~550 trees hectare⁻¹) and thinned plots (~100 trees hectare⁻¹), where thinning was implemented 15 years earlier.
Volumetric water content (VWC) was continuously monitored using time-domain reflectometry (TDR) sensors at 0.5, 1.0, and 1.5 m depths during two consecutive hydrological years: HY23-24 (normal, ~561 mm year-1 of rainfall) and HY24-25 (drought, ~251 mm year-1). We derived seasonal soil-water subsidy metrics as the area under the excess VWC curve above the summer baseline (AUC_excess). We analyzed drought impacts using vertically aligned sensor sequences.
Despite greater understory development in the thinned plots over the years (55% cover vs. 35% in the dense forest), thinning significantly reduced tree mortality rate (six-fold). Annual evapotranspiration (ET) was also affected, with dense plots exhibiting 1.5 times greater ET compared to thinned ones.
In the thinned plots, higher volumetric soil moisture was measured in the upper soil layer (0.5 m) than in the dense plots, due to reduced rainfall interception and water consumption by the forest vegetation. In contrast, in the deep soil (1.5 m), two interesting phenomena were observed: moisture in the dense plots was higher than in the thinned plots and, the deep layers in the dense forest responded earlier than the shallow layers to rainfall inputs.
Extreme drought (-55% rainfall) caused substantial reductions in soil water subsidy across depths. Dense plots experienced greater losses (-73% overall; -79% in topsoil) compared to thinned ones (-56% overall; -37% in topsoil). These moisture declines were associated with prolonged periods of limited water availability.
Our results show that canopy structure regulates not only interception and evapotranspiration but also the vertical coherence of soil moisture recharge, with dense forests promoting preferential deep flow and root-induced bypass flow via interception, stemflow and root flow while thinning enhances infiltration and shallow soil storage.
These findings demonstrate that 15 years after thinning, forest structure exerts a lasting control on water availability through depth-dependent hydrological pathways, providing mechanistic insight into drought-driven forest mortality under climate change.
Keywords: Drought, Soil moisture, Ecohydrology, Bypass flow, Thinning
How to cite: Muklada, H., Moshe, Y., Cohen, Z., and Osem, Y.: Vertical Soil Water Dynamics and Drought-Response are Affected by Stand density In a Mediterranean Dryland Forest, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18947, https://doi.org/10.5194/egusphere-egu26-18947, 2026.
The role and importance of deep roots for tree survival during drought is an intuitive expectation. Numerous studies have examined root distribution, rooting depth, and the use of deep water resources. However, the impact of deep roots systems on the amount of deep water uptake and their contribution to tree survival during drought is still understudied.
In this study, we first measured predawn leaf water potential and the isotopic signatures of sap water and potential water sources. These isotopic measurements allowed us to estimate the proportion of deep water contributing to the total volume of water transpired by trees. Measurements were conducted on three tree species (Quercus ilex, Fagus Sylvatica and Abies alba) over two summer seasons (2014 and 2015) at two study sites in Mediterranean regions of France. We then used the plant hydraulic model SurEau-Ecos to infer the mobilisation of deep water reserves by trees, fitting the model to observed leaf water potential . We used ecophysiological trait databases for initial model parameterisation. Finally, we adjusted a single parameter defining root distribution to fit the model to the observations.
We obtained a root distribution that satisfactorily reproduced both leaf water potential and deep water use. This allowed us to quantify temporal variations in deep water use for each species. During periods of water stress, trees uptaked 102 mm of water from the deep soil reservoir. Without this resource, trees would likely have experienced hydraulic failure. Over the study period, deep water contributed on average between 8.5 and 37 % of total tree water use, depending on species.
To further investigate the role of fine root distribution in survival under extreme drought, we analysed the model sensitivity to the root development parameter and to deep-water reserves in terms of hydraulic failure risk. These analyses showed that survival time could vary by up to 100 days depending on the proportion of the root system located in deep soil. We also identified an optimal degree of deep root development that maximised tree survival. Overall, the methodology we developed will help better quantify the role of deep water uptake. They appear essential for both groundwater recharge assessments and vegetation drought response analyses.
How to cite: Mondon, L., Martin-StPaul, N., Rickert, G., Druel, A., Özgen, I., Cochard, H., Chaffaut, Q., Pessel, M., Jougnot, D., and Carrière, S.: Modelling fine root distribution and its role to increase tree resilience to drought in two Mediterranean forests, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4064, https://doi.org/10.5194/egusphere-egu26-4064, 2026.
Forests govern exchanges of water, energy, and carbon between the land surface and atmosphere through interactions between aboveground structure and subsurface access to stored water. Canopy height and root-zone water storage capacity are therefore key controls on ecosystem function, yet they have rarely been assessed together at the global scale. Classical ecohydrological theory posits coordinated investment above and below ground, whereby enhanced access to deep water supports taller and more structurally complex canopies. However, it remains unclear whether such coordination holds across diverse climatic conditions. Here, we integrate global GEDI-derived canopy height observations, independent estimates of root-zone water storage capacity, and an integrated climatic gradient capturing water availability, atmospheric demand, and seasonality to evaluate this long-standing hypothesis at the global scale. By quantifying how above- and belowground traits co-vary across hydroclimatic regimes, we assess how access to deep water influences forest structure and identify where empirical patterns diverge from theoretical expectations. Our results reveal that the relationship between canopy height and root-zone water storage capacity is far more variable than classical theory suggests, with clear decoupling in both humid and strongly seasonal regions. These findings advance our understanding of vegetation–water interactions, highlight limitations of simplified assumptions about hydraulic constraints and structural investment, and provide a data-driven foundation for improving the representation of vegetation processes in land–atmosphere and Earth system models.
How to cite: Khorami, M., Lane, P., Sheridan, G., and Fowler, K.: Climate-dependent coupling and decoupling between canopy height and root-zone water storage in global forests , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10872, https://doi.org/10.5194/egusphere-egu26-10872, 2026.
Water stress shifts the partitioning of turbulent heat fluxes towards sensible heat and therefore leaves an imprint of higher temperatures in the near surface atmosphere during the day (Ghausi et al., 2025), specifically the diurnal temperature range and in relative humidity. This temperature range therefore carries the information of soil water stress, as has been confirmed in global analyses with eddy covarince data (Chauhan et al., in review). Here we investigate how the diurnal temperature range in turn relates to ecosystem indicators of soil water stress at the daily, seasonal and annual time scale at the temperate broadleaved forest site Hohes Holz in the ICOS network (DE-HoH). For this, we apply the same method as described byChauhan et al. and Ghausi et al. 2025, and derive a soil water limitation factor based on the difference between observedand theoretical (non-water limited) diurnal temperature range. We compare this atmospherically-derived soil water limitation factor to the observed ecosystem variables indicating short-term reaction to water stress (reduction in GPP) and long-term integrated water stress (tree growth, δ13C).
How to cite: Hildebrandt, A., Bastos Campos, F., Pohl, F., Solly, E., Rebmann, C., Kleidon, A., Chauhan, T., and Ghausi, S. A.: Signatures of plant water stress in the near surface air: How is the diurnal temperature range related to ecosystem drought response at a broadleaved forest site? , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21257, https://doi.org/10.5194/egusphere-egu26-21257, 2026.
Trees are thought to use internal water stored within the stem as a key buffer against short-term drought. Together with deep root water uptake and stomatal regulation, this mechanism helps trees to maintain critical physiological functions alive. Stem moisture content and water potential is generally observed using electrical conductivity (EC), moisture sensors, or microtensiometers installed in the sap wood of living trees. While these sensors offer precise information at the point scale, applying imaging techniques such as Electrical Resistivity Tomography (ERT) can help the investigation of spatial patterns and internal changes in electrical conductivity across larger portions of the trunk. Although ERT monitoring was mainly developed for hydrogeological applications to track soil moisture or groundwater dynamics at scales of tens to hundreds of meters, it has more recently been adopted in forest ecohydrological research for smaller-scale applications. ERT imaging of tree stems has proven its ability to inform on internal structures of trunks, while time-lapse ERT has shown promise to inform on stem water content variations.
Here, we present results from a field experiment conducted on a mature beech tree (Fagus sylvatica L.) at the Weierbach Experimental Catchment (WEC) in Luxembourg. The tree has been equipped with 4 rings of 30 stainless-steel screw electrodes each, with 5 cm electrode spacing and 50 cm vertical spacing between rings. ERT data was acquired during the growing season, from March to November, at a 4-hour temporal resolution. Additional tree sensors installed on the same tree, including sap flux, radial growth, moisture, water potential and temperature, provide complementary measurements for comparison with the ERT results.
At the seasonal scale, observations indicate spatially consistent changes in resistivity, with progressive resistivity decrease in the sap wood during the growing season. At the diel scale, pronounced daily variations in electrical resistivity are also observed, which seem to follow physiological processes also picked up by sap flow sensors and dendrometers. We will discuss challenges linked with the downscaling of the time-lapse ERT technique, both in time and space. These include: (i) accounting for strong temperature effects within the stem that influence reconstructed resistivity models and require advanced correction methods, and (ii) accurately determining electrode geometry at high resolution, including electrode orientation and seasonal changes in stem diameter. Finally, we address the interpretation of resistivity changes in terms of wood moisture dynamics and potential variations in sapwood chemical composition.
How to cite: Watlet, A., Gourdol, L., Schymanski, S., Hissler, C., Costantini, A., Tailliez, C., Iffly, J.-F., and Keim, R.: Seasonal and diel variations of electrical resistivity in a beech tree stem using time-lapse electrical resistivity imaging, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20808, https://doi.org/10.5194/egusphere-egu26-20808, 2026.
Sap flow is one of the best direct indicators of transpiration at the tree level, which is a major component of the water balance. Understanding daily sap flow variability is essential for interpreting tree water consumption and its response to environmental conditions. This study aimed to classify days according to the behaviour of daily sap flow and determine whether the resulting categories differ in terms of meteorological and precipitation conditions. We used sap flow measurements from a birch tree located in a small urban park in Ljubljana, Slovenia. Along with meteorological variables such as solar radiation (SR), air temperature (T), vapor pressure deficit (VPD), wind speed (WS), and amount of precipitation, we analyzed the shape of daily sap flow curves for the fully leafed birch tree in 2025. For each day, we smoothed the daily sap flow curves and analyzed them using principal component analysis (PCA) and obtained daily PC1-PC3 values to compactly describe the curve shape. Based on these values, we grouped the curves and selected the number of clusters using information criteria (BIC). We tested for differences between clusters using nonparametric tests and interpreted the clusters in terms of meteorological conditions and precipitation amount. Five characteristic clusters of daily sap flow curves were defined, differing in curve shape, peak time and magnitude, and midday depression intensity. The clusters differed most significantly in terms of SR, while cluster 4 stood out from the others in terms of precipitation. This is also reflected in the greater variability of daily curve shapes within cluster 4. Despite the known positive correlation between VPD and sap flow, the days in cluster 5 showed a weak negative correlation, which is consistent with their pronounced midday depression. In contrast, cluster 1, which is characterized by the lowest values of SR, T, and VPD, exhibits the flattest average daily sap flow curve and is the only cluster without a pronounced midday depression. This is consistent with the known physiological regulation of transpiration at higher VPD values, when plants limit water flow by closing their stomata.
Acknowledgment: This work was supported by the research program P2-0180 through the Ph.D. grant of the first author that is financed by the Slovenian Research and Innovation Agency (ARIS). It is also part of the ongoing research project entitled “Evaluation of the impact of rainfall interception on soil erosion” supported by the Slovenian Research and Innovation Agency (J2-4489) and the Austrian Science Fund (FWF) I 6254-N.
How to cite: Radulović, L., Zabret, K., and Šraj, M.: Linking sap flow dynamics of birch tree to atmospheric and rainfall conditions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5106, https://doi.org/10.5194/egusphere-egu26-5106, 2026.
Hydraulic redistribution (HR) occurs in temperate ecosystems and may increase forest resilience to drought. However, its magnitude and influence on the stand-level water budget remain poorly understood. One major challenge in field studies is to distinguish HR from other processes that lead to real or apparent increases in soil water content at night. In this study, we aimed to identify and quantify upward water fluxes due to HR by combining multiple methodological approaches in a mixed broad-leaved forest in Germany. During three consecutive growing seasons, we monitored soil water dynamics using continuous soil water content and soil water potential sensors installed at multiple locations in the tree stand and in root-exclusion control plots, where roots were cut to prevent HR. Additionally, several infiltration events were performed by inducing 200–800 L of deuterium-enriched water at 1.8–3.5 m depth, and its movement was traced with continuous in situ and destructive isotope analyses plus geoelectrical monitoring. We hypothesized that (1) nocturnal increases in soil water content and soil water potential would be larger in the stand plots than in the control plots due to HR, and (2) we would detect the tracer in upper soil layers if water moved from the irrigation depth to the topsoil through HR. Our multi-method analysis confirmed the occurrence of HR in this temperate forest, although its magnitude was low. Initial results showed that nocturnal increases in soil water potential were more frequent in the stand plots than in the controls, but the associated changes in water content remained below 1 vol. %. The tracer rarely appeared in observed trees and was not detectable in the topsoil. Geophysical monitoring results showed the injected tracer was rapidly distributed (approximately 10 m within only a few hours) along preferential flow paths below 2 m depth. The reason no tracer uptake was observed in the trees could be that they either primarily rely on shallower water sources, or that the clayey soil prevented the infiltrated water from reaching more distant trees during our observation windows. Future spatially and temporally high-resolution geoelectrical monitoring experiments are planned to noninvasively map and upscale these HR fluxes, link them to nutrient and carbon cycling, and improve predictions of forest resilience to drought.
How to cite: Riedel, R., Iraheta, A., Gerchow, M., Rohde, C., Hoppenbrock, J., Gildemeister, A., Dubbert, M., Bückner, M., and Beyer, M.: A multi-method approach to quantify hydraulic redistribution, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20559, https://doi.org/10.5194/egusphere-egu26-20559, 2026.
One proposed approach for reducing downstream flood hazards is the implementation of runoff attenuation facilities upstream. These facilities are often based on natural floodplains and may be located adjacent to agricultural lands, natural reserves, and forests. While their hydrologic benefits are evident, the effects of flooding frequency and duration on soils and vegetation are more difficult to predict and may be either beneficial or detrimental, depending on climate, soil properties, and land use. Our case study site is in Horshim Forest, a small Mediterranean forest intersected by Wadi Qana, a tributary of the Yarkon River, which flows through the densely populated Tel Aviv metropolitan area, Israel. The site is part of a planned network of upstream runoff attenuation facilities designed to mitigate downstream flood risk. To examine the impacts of waterlogging on soils and vegetation during active attenuation, we conducted a controlled flooding experiment in a forest plot dominated by 35-year-old Aleppo pine trees (Pinus halepensis). Mature pine trees were selected due to their abundance and the limited data on their flood tolerance. Flooded and control plots were continuously monitored using soil sensors measuring water content, oxygen concentration, and redox potential, along with tree sensors measuring stem diameter changes (dendrometers) and sap flow. Flooding events lasting 48–72 hours were applied during winter in the flooded plot, while the control plot remained under natural conditions. Plant performance indicators, including stem girth, needle length, and greenness index, were measured monthly. Waterlogging led to declines in soil oxygen and redox potential, in some depths reaching anoxic conditions, with responses dependent on flood duration and antecedent soil moisture. In contrast, the control plot remained under oxic to suboxic conditions. Tree responses were variable and appeared to depend on pre-flood soil water availability and the timing of flooding during the winter season. Our study demonstrates how short-term flooding alters soil aeration conditions and tree responses, with implications for the ecohydrologic design of runoff attenuation facilities.
How to cite: Ganot, Y., Valdman, E., and Dahdal Turk, D.: Waterlogging Effects on Soil and Vegetation in Mediterranean Forests Used for Runoff Attenuation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14609, https://doi.org/10.5194/egusphere-egu26-14609, 2026.
Stand-replacing wildfire in Eucalyptus forested catchments alters streamflow, however these changes can be highly variable, ranging from moderate increases through to large reductions (greater than to 50%) over decades with serious consequences for the water supplies of dependent communities. Predicting change has proven difficult, with the most widespread models relying on time- based proxies for hydrologic changes caused by post-fire tree mortality and regrowth dynamics (e.g. Kuczera 1987). The aim of this research is to replace these time-based proxies, which have been found to be sometimes inconsitent with more recent catchment data, with a forest-stand self-thinning model of post-fire forest dynamics, such that streamflow is an explicit function of forest density, tree size, and growth rates, which are in turn functions of the initial condition of the stand (early regeneration), and the site conditions the stand is exposed to (i.e. climate and soil conditions). This presentation will; i) use a 42 year streamflow timeseries across 18 fire-affected catchments to illustrate the limitations of time-based proxies (Benyon et al 2023), ii) outline our initial analytic work to couple the forest self-thinning model with a hydrologic model (Inbar et al 2022), iii) present the results of forest inventories with age ranges from 1 to 80 years to quantify suitable self-thinning line parameter values (Harrison 2024), and lastly, iv) present the results from studies to identify abiotic and biotic (inter-species competition with Acacia) controls on self-thinning dynamics that could plausibly explain the large variation in post-fire streamflow responses. It is hoped that this research will enable the earliest possible identification of expected decadal-scale post-fire streamflow reductions so that water supply policy makers can respond appropriately and minimize water supply disruptions to dependent communities.
References
Kuczera, G. (1987). Prediction of water yield reductions following a bushfire in ash-mixed species eucalypt forest. Journal of Hydrology, 94(3-4), 215-236.
Inbar, A., Trouvé, R., Benyon, R. G., Lane, P. N., & Sheridan, G. J. (2022). Long-term hydrological response emerges from forest self-thinning behaviour and tree
sapwood allometry. Science of the Total Environment, 852, 158410.
Benyon, R. G., Inbar, A., Sheridan, G. J., Lyell, C. S., & Lane, P. N. (2023). Variable self-thinning explains hydrological responses to stand replacement in even-aged forests. Journal of Hydrology, 618, 129157.
Harrison, M., 2024. Could Eucalyptus regnans stocking density explain post-fire streamflow responses in Melbourne’s water catchments? (Master of Environmental Science). The University of Melbourne, Melbourne, Australia.
How to cite: Sheridan, G., Fischer, S., Lane, P., Inbar, A., Benyon, R., Lyell, C., Harrison, M., and Trouve, R.: Predicting post-fire changes to streamflow using forest self-thinning parameters, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16150, https://doi.org/10.5194/egusphere-egu26-16150, 2026.
Rainfall partitioning is a critical process shaping local hydrological cycles by governing canopy interception and subsequent soil water recharge. While canopy structure and meteorology are fundamental regulators, the role of plant self-organization and its interaction with meteorological drivers (non-precipitation variables in particular) remains underexplored. Here, this study investigated rainfall partitioning components, including the amount, intensity, efficiency, and temporal dynamics of throughfall and stemflow, in clumped versus scattered Vitex negundo shrubs in the Yangjuangou catchment of the Chinese Loess Plateau during the 2021–2022 rainy seasons. Despite comparable net precipitation (clumped: 83.5% vs. scattered: 84.2% of incident rains), divergent rainfall partitioning strategies emerged. Clumped V. negundo produced significantly higher stemflow (8.6% vs. 5.2%) with greater intensity, efficiency and favorable temporal dynamics, whereas scattered shrubs favored throughfall generation (79.0% vs. 74.9%). While rainfall amount remains the primary control, an integrated machine learning and variance decomposition analysis revealed that antecedent canopy wetness and wind speed thresholds (e.g., low wind vs. gusts) critically regulate partitioning efficiency and temporal dynamics. These findings advance the mechanistic understanding of the interplay between plant self-organization and hydrological processes, demonstrating how morphological adaptations in V. negundo optimize water harvesting in semi-arid ecosystems. Our results underscore the necessity of incorporating the dynamic interplay between plant structure (specifically, self-organized patterns) and meteorological factors (particularly non-precipitation variables) into ecohydrological models to improve predictions in water-limited regions.
How to cite: Yuan, C., Gao, Y., Zhang, Y., Hu, Y., Guo, L., Jiang, Z., Wang, S., and Wang, C.: Rainfall partitioning dynamics in xerophytic shrubs: Interplays between self-organization and meteorological drivers, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8695, https://doi.org/10.5194/egusphere-egu26-8695, 2026.
Assessing rainfall interception (IR) is a critical yet uncertain aspect in hydrological cycle, particularly the quantification of relative contributions from leaves and woody components (e.g., branches, stems, and trunks) to IR. Nevertheless, the role of woody components in IR estimation remains largely unexplored and thereby has been constantly overlooked. This study addressed this challenge and refined the widely-used Gash model to distinguish woody interception (IW) from leaf interception (IL). We incorporated the spatial variability of vegetation traits alongside satellite data in 2019 into the refined model, and spanned China’s major forest types. The refined model showed a strong agreement with field observations in estimating IR (r=0.83, p<0.01) and the fraction of rainfall interception to precipitation (IR/P) (r=0.77, p<0.01). The average IR was 112.4 ± 32.1 mm (with IR/P of 14.7 ± 8.2%) in 2019, of which IL accounted for 77.9% and IW contributed the rest 22.1%. Among different forest types, IW/IR exhibited the highest values in deciduous needle-leaf forests (DNF, mean: 51.9%) but lowest values in evergreen broad-leaf (EBF, mean: 14.3%). In addition, IW/IR was larger in the non-growing season than that of growing season in some forest types, such as exceeding 60% in winter for DNF, indicating that more rainwater was intercepted by woody components than by leaves. Our study underscores the substantial role of woody components in IR,particularly in needle-leaf forests, that are prevalent globally, a finding that can provide novel methods and valuable parameters for global hydrological models to improve the accuracy of model predictions.
How to cite: Jiang, Z., He, W., and Chen, Z.: Substantial Contribution of Woody Components to Rainfall Interception in Chinese Forests: Insights from a Refined Analytical Model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4246, https://doi.org/10.5194/egusphere-egu26-4246, 2026.
Interception by forest canopies constitutes an important control on ecosystem water fluxes, with direct effects on soil moisture and water availability. In Mediterranean environments, high variability in precipitation across space and time complicates the estimation of interception and net precipitation. Field-based observations across contrasting forest canopies are therefore required to disentangle species-specific interception processes.
Precipitation partitioning within the forest canopy was analyzed using throughfall and stemflow observations in Quercus robur (oak) and Fagus sylvatica (European beech) stands over nearly three years in a 44 km² mountainous catchment in central Italy. Four plots were monitored during more than 200 precipitation events, capturing seasonal and species-specific variability.
Observed interception losses differed between species at closely located plots under comparable rainfall conditions, reflecting the combined effects of canopy structure and local meteorological conditions. Relative interception, defined as the fraction of gross precipitation evaporated before reaching the forest floor, averaged about 39% for oak and 31% for beech during moderate rainfall events. Although beech stands exhibited higher leaf area index (LAI) and canopy cover, oak consistently showed greater interception during both the growing (42% vs. 33%) and dormant (33% vs. 26%) seasons, highlighting that canopy architecture, rather than LAI alone, governs interception dynamics.
We tested a LAI-based Gash model against observed interception loss. The model underestimated the flux, indicating that simplified descriptors, such as LAI, do not adequately represent species-specific canopy architecture. This suggests that accurate representation of canopy traits, including branching patterns, leaf distribution, and canopy roughness, is essential for reliable predictions of intercepted precipitation, particularly in heterogeneous Mediterranean forests.
Overall, this study demonstrates that interception in broadleaf Mediterranean forests is influenced by a complex interaction between canopy structure and local environmental conditions. Incorporating these factors into interception models is essential to resolve precipitation partitioning and to evaluate ecohydrological responses to climate variability and forest management. The findings further highlight the relevance of species-specific field data to improve model parameterizations and hydrological predictions in ungauged forest ecosystems with contrasting canopy structures.
Keywords: canopy interception, precipitation partitioning, Mediterranean forest, throughfall, stemflow, forest canopy structure, interception modelling.
How to cite: Barbetta, S., Dionigi, M., Filippucci, P., De Santis, D., Penna, D., Verdone, M., Donnini, M., Miralles, D. G., Holmes, T., and Massari, C.: Contrasting Forest Structure Shapes Rainfall Interception in a Mediterranean Mountain Catchment, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5141, https://doi.org/10.5194/egusphere-egu26-5141, 2026.
This study explores the potential of integrating structural information from the European Space Agency (ESA) BIOMASS P-band Synthetic Aperture Radar (SAR) mission with spectral information from PRISMA hyperspectral imagery to assess forest diversity in the Amazon. The study area was defined based on the spatial and temporal overlap of available PRISMA and BIOMASS acquisitions.
Forest structural diversity was derived from BIOMASS data acquired on 6 June 2025 using polarisation variability, polarimetric SAR (PolSAR) metrics, polarimetric interferometric SAR (PolInSAR), and texture measures of above-ground biomass to characterise variations in vertical structure and stand complexity. In particular, the cross-polarised backscattering coefficient (HV/VH), which is sensitive to volume scattering, was used to capture differences in forest height and canopy structure.
Spectral diversity was estimated from PRISMA Level-2D surface reflectance data acquired on 29 July 2025 (234 bands spanning 406–2497 nm). Principal Component Analysis (PCA) was applied, and several vegetation indices were derived. In addition, spectral diversity indicators—including Rao’s Q, spectral variance, and clustering-based “spectral species”—were computed to describe variability in canopy composition and biochemical properties associated with species and functional diversity.
The analysis examines relationships between radar-derived structural diversity and hyperspectral spectral diversity to evaluate how forest structural heterogeneity corresponds to compositional variability across different forest environments. Available LiDAR canopy height data and, where feasible, field-based observations of species composition and functional traits are used as supporting reference information. Correlation and multivariate analyses are applied to assess the consistency, complementarity, and added value of the combined indicators.
This multi-sensor Earth observation approach contributes to advancing satellite-based monitoring of forest biodiversity in tropical ecosystems and demonstrates the potential of the ESA BIOMASS mission for biodiversity-oriented forest applications.
How to cite: Dabiri, Z., Avoiani, E., Dong, Y., and Muthee, M. W.: Forest Diversity Assessment through the Integration of PRISMA Spectral Metrics and BIOMASS P-band SAR Structural Information, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21565, https://doi.org/10.5194/egusphere-egu26-21565, 2026.
