Forests play a critical role in land-atmosphere dynamics, significantly influencing soil-water-climate interactions. A realistic and accurate representation of forest carbon pools in land surface models is essential to understand, monitor, and predict droughts, wildfires, and weather and climate dynamics. Satellites offer detailed and global observations of forest characteristics, such as 10-250m resolution biweekly leaf area index (LAI) from Sentinel and MODIS and 30m resolution canopy height from GEDI-Landsat data products. By integrating these satellite observations with vegetation allometric relationships, we can reconstruct forest carbon biomass pools across roots, trunks, and leaves since the 2000s. These approaches have been pivotal in mapping and reconstructing global above-ground carbon stock at fine spatial scales (10-250m resolution). However, integrating these detailed satellite observations into predictive Earth System Models (ESMs) remains challenging due to the complexity of dynamic vegetation models and the spatiotemporal mismatch between satellite data and the grid size of ESMs.
To bridge this gap and enable a detailed and realistic representation of forest dynamics in ESMs, we introduce an approach to integrate MODIS LAI and GEDI-Landsat canopy height data through the assimilation of carbon biomass pools (roots, trunk, and leaves) into the vegetation dynamics component of the NOAA-GFDL Land Model version 4 (LM4). Leveraging the HydroBlocks sub-grid tiling scheme and LM4 allometric relationships for LAI and canopy height, we assimilate monthly biomass pools at an effective 250m resolution across the continental United States. We assess how improving forest representation through the assimilation of biomass pools impacts transpiration, canopy and soil evaporation, soil moisture, and runoff. By improving the spatiotemporal accuracy of forests-soil-water dynamics at local scales, we can now better map and quantify the role of forests driving ecohydrological hotspots. Such advancements can contribute to improved capabilities to model and predict droughts, wildfires, and deforestation impacts at the spatial scales closer to the scales where conservation and mitigation strategies are implemented (~100s meters).
How to cite: Vergopolan, N., Malyshev, S., Chaney, N., and Shevliakova, E.: Improving Forest Realism in Earth System Models through Satellite Observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3775, https://doi.org/10.5194/egusphere-egu25-3775, 2025.
Green-water fluxes are a major component of the hydrological cycle globally. According to recent models and experimental observations, during droughts, wetter regions respond by increasing evapotranspiration (ET), while drier regions exhibit decreasing trends due to vegetation water stress. To comprehensively dissect the ET signature of natural forests in a Mediterranean region, typically regarded as a dry environment, in this work, we reconstruct the green-water fluxes of 15 natural unmanaged forests in Central Italy from 2000 to 2022 and explore their dependencies on local temperature and precipitation. Historical ET data are estimated through a time-domain parameterization of the traditional “triangle method”, which leverages satellite imagery to compute actual latent heat flux as a residual term of the land surface energy balance. Based on our results, all forests show a statistically significant increase in Summer ET, and, in warm years, such an increase has occurred in spite of negative precipitation anomaly. These satellite-based observations support the instance of a “drought paradox”, which is not related to temperature nor precipitation anomalies, and probably builds on multi-year temperature and precipitation trends.
How to cite: Tauro, F., Tadesse, A. M., De Gregorio, T., and Huerta, E. S.: Reconstructing forest green water fluxes in a Mediterranean region over the past 20 years: Evidence for the drought paradox, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4328, https://doi.org/10.5194/egusphere-egu25-4328, 2025.
Transpiration contributes up to 70% of regional rainfall during the dry season in the Amazon through precipitation recycling. But the source, spatial distribution of transpiration and the key plant hydraulic drivers of transpiration source water remains unclear. Here, we quantify transpiration sources across a topographic gradient in the eastern Amazon, at the Tapajós National Forest. We leverage embolism resistance data collected on the same sites during this same campaign. We asked: i) What is the source of transpiration? And ii) how do transpiration depth and origin vary across topographic gradients and species with different embolism resistance growing under the same climate? Our data show that on hills, dry-season transpiration sources are mostly shallow soil water mainly recharged by current dry-season rainfall. In contrast, transpiration source water in the valley includes both shallow and deep soil layers, with both dry and wet season contributions. The observed pattern in transpiration source water is largely explained by species embolism resistance, but with contrasting trade-offs between hill- and valley-species. The significant relationship between embolism resistance and depth of water uptake in both topographic positions influencing transpiration age could be used to parameterize vegetation water use in land surface models.
How to cite: Nehemy, M., R. C. Mattos, C., S. Oliveira, R., Hirota, M., Fan, Y., Bohora Schlickmann, M., Penha, D., Giacomin, L., S. G. M. Silva, J., Rocha, M., Rodrigues, G., and McDonnell, J.: Transpiration Source Water and Embolism Resistance Across a Topographic Gradient in the Eastern Amazon Rainforest, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10389, https://doi.org/10.5194/egusphere-egu25-10389, 2025.
Climate warming and the associated rise in atmospheric vapor pressure deficit (VPD) have increased transpirational demand and coupled with droughts have increased susceptibility of plants. Plant water use strategies along the isohydry gradient during hot-drought determines maintenance of plant water status. While a number of studies have investigated drought response of different tree physiological processes and found species-specific behavior, studies with a holistic approach to understand growth, water use and stem water status under different neighborhood constellations in mature trees are still lacking.
We measured stem growth and water consumption in pure and mixed European beech and Douglas fir stands during two moist (2021, 2023) and one dry year (2022) on deep sandy soil in northern Germany, using a dataset from 16 trees equipped with high-resolution band dendrometers and 32 trees with sap-flow sensors (dual-method approach). In addition, radial sap flow profiles were measured in each tree with heat-field-deformation sensors, canopy structure analysed with mobile laser scanning, soil moisture content and soil matric potential recorded at multiple depths to interpret the growth and water use patterns.
During a period of persisting drought, pure Douglas fir reached 50% soil desiccation nearly twice as fast as the pure beech and mixed beech-Douglas fir stand. However, compared to the previous, wet year (2021), pure Douglas fir had the lowest reduction in growth (12%) and mixed Douglas fir the highest (36%). Beech ranged in between, with lower growth reduction in the mixed stand. Daily sap flow rates increased with higher VPD, but decreased at <20% of relative extractable water (REW) with greatest reduction in isohydric Douglas fir compared to beech. Stem water content remained relatively high (>50%) until 20% REW, but showed a sharp decrease afterwards, along with increasing tree water deficit.
We show how different tree physiological processes and their relation change in interaction with soil moisture and VPD. The partially contrasting patterns in water use can be explained by the relatively more isohydric and anisohydric behaviour of Douglas fir and beech, respectively. Furthermore, canopy structural traits may play a key role in shaping tree species-mixture effects, favoring beech in mixture with Douglas fir under drought. Our results demonstrate how tree functional traits are influencing the forest water cycle in the face of climate change.
How to cite: Hackmann, C., Paligi, S., Audisio, M., Penanhoat, A., Schick, J., Coners, H., Mund, M., Seidel, D., Leuschner, C., and Ammer, C.: Understanding tree-water relations under drought stress – a case study, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19214, https://doi.org/10.5194/egusphere-egu25-19214, 2025.
We examined stream water temperature variations in response to air temperature and precipitation in 22 steep forested catchments. We conducted an elasticity approach, based on hysteresis loop analysis, stream water temperature, air temperature, and precipitation. Here, hysteresis loops were classified by rising and falling limbs on air temperature. Temporal variations of stream water temperature depended on air temperature rising and falling periods. Based on stream water temperature and both temperature and precipitation elasticities, temperature elasticity increased with increases in stream water temperature during the rising period. However, precipitation elasticity increased with decreases in stream water temperature. The stream water temperature of the steep forested catchments was sensitive to air temperature from an elasticity perspective. Therefore, from an elasticity standpoint, our findings showed that temperature elasticity increased with increasing stream water temperature, whereas precipitation elasticity increased as stream water temperature decreased. Additionally, the variations in stream water temperature were attributed to elasticity responses due to the effect of forested ecosystems and hydrological conditions, even if our study design allowed for the creation of inferences regarding the resilience of forested headwater streams. Further long-term sustainable stream water management plans should be made carefully to include site monitoring for the sensitivity of stream water temperature to environmental factors depending largely on spatial characteristics that had temporal variations.
How to cite: Nam, S., Lim, H., Li, Q., and Choi, B.: Stream water temperature responses to air temperature and precipitation changes using an elasticity approach in steep forested catchments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5385, https://doi.org/10.5194/egusphere-egu25-5385, 2025.
Montane watersheds of California’s Sierra Nevada are critical to sustaining local water security and economic wellbeing. However, decades of fire suppression have led to overgrown forests that are highly vulnerable to drought and wildfire risks. Moreover, climate change is further compounding the negative impacts of increased forest density. Land managers are implementing active forest management to restore source watersheds and build climate resilience. In this study, we investigated the individual and compounding impact of forest thinning and warming on watershed hydrologic response using a process-based model (i.e., SWAT+) in a large (3,998 km2) Sierra Nevada watershed. The model was parameterized using a multi-objective calibration of streamflow, snow water equivalent, and evapotranspiration. We conducted multiple numerical experiments with forest treatments (25% and 40% reduction in leaf area index implemented in a wet and a dry year) and warming (ambient temperature, +1.5 oC, and +3.0 oC) to evaluate the variability of the hydrological response across a water-energy gradient and the extent to which forest treatments can offset the response to warming. Results indicate that warming increased evapotranspiration in energy-limited forests, while a reduction in evapotranspiration was observed in water-limited forests due to an increase in water stress. The water made available through forest thinning was directed towards increasing streamflow or sustaining the remaining trees, depending on water and energy availability and forest regrowth. We found that large-scale forest restoration in the upper Kings River Basin has the potential to partially mitigate warming impacts on streamflow by a maximum of 48% and 36% for +1.5 ◦C and +3.0 ◦C temperature increase, respectively, thus reducing the severity of warming impacts on streamflow and forest water stress.
How to cite: Safeeq, M. and Casirati, S.: Forest Management in a Warming World: Enhencing Insights into Compounding Hydrologic Impacts, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7981, https://doi.org/10.5194/egusphere-egu25-7981, 2025.
Mountain forest catchments supply most of the water in the Western United States (US). These catchments are experiencing forest changes that can result in alteration of vegetation cover and soil characteristics, causing changes in streamflow. This paper describes research to understand streamflow response to forest changes in the Western US using the HBV (Hydrologiska Byråns Vattenbalansavdelning) hydrological model. The study was conducted using data from 100+ CAMELS (Catchment Attributes and Meteorology for Large Sample Studies) watersheds from 1990 to 2019. The HBV model was applied to analyze streamflow changes during two distinct periods: the control period (October 1990 to September 2009) and the assessment period (October 2009 to September 2019). This analysis thus focuses on large scale decadal changes. Changes in streamflow were analyzed using (1) Reconstruction of assessment period streamflow based on control period calibration, (2) Comparison of behavioral model parameter sets between control and assessment periods and (3) Comparison of simulations using control period and assessment period parameter sets. Differences in model simulations were related to forest change data, as reported by the US National Forest Inventory dataset, for 2010-2019. Results indicated that several watersheds experienced an increase in streamflow during the assessment period compared to the control period. Conversely, some watersheds showed a decrease in streamflow during the same period. Associations between changes in streamflow with determinative factors such as aridity, disturbance severity, and process indicators inferred from model parameters, were investigated.
How to cite: Abualqumboz, M., Tarboton, D., and Goeking, S.: Investigating streamflow response to forest changes in the Western United States using a modelling approach, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14020, https://doi.org/10.5194/egusphere-egu25-14020, 2025.
High-yield silvicultural practices (e.g short-rotation woody crops (SRWCs)) increase the pressure on the hydrological and biogeochemical cycles of forest watersheds. These forest systems experience more intensive mechanical and chemical practices compared to traditional forestry. Despite a plethora of studies on the effects of forest management on catchment function, some of the long-term effects of SRWC cultivation on water quality and quantity remain poorly understood.
Following harvest of existing mature loblolly pine stands, we implemented intensive silvicultural management, using high fertilization rates, high tree planting density, and competition control with herbicides on pine plantations covering approximately 50% of two first-order watersheds (B and C) in the southeastern U.S. Coastal Plain. Over a nine year period, we monitored streamflow, stream chemistry, and groundwater chemistry in these watersheds and an adjacent reference watershed (R) prior to and after harvest and planting. The objective of this watershed manipulation experiment was to evaluate the changes on catchment hydrology and biogeochemistry and relate that to the efficiency of the applied traditional forestry best management practices (BMPs).
Our results suggest a significant initial shift in hydrological processes and the catchment water balance, with increased streamflow following clear-cutting. Over time, we observed a return to baseline conditions. The water quality response was variable between chemical compounds and different across watershed compartments. For example, nitrate levels in groundwater increased post-fertilization with no drop in the 6-year post-harvest observation period. Contrary, we detected no significant water quality changes in the riparian groundwater nor stream water, likely due to effective denitrification and nutrient uptake in the riparian zones of these groundwater-dominated watersheds.
The experiment suggest that watershed-scale conversion to SRWC loblolly pine systems may cause short-term alterations in catchment processes of Coastal Plain watersheds. Our findings highlight the critical role of riparian zones in mitigating impacts on stream water quality. However, elevated nitrate concentrations after the last application of fertilizer stresses the critical need for observations to fully characterize long-term water quality impacts of SRWCs across entire watersheds.
How to cite: Klaus, J., Goetzie, J., Raulerson, S., Griffiths, N., and Jackson, R.: Long-Term Impacts of Woody Crop Conversion on Hydrology and Biogeochemistry in Forest Watersheds, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13182, https://doi.org/10.5194/egusphere-egu25-13182, 2025.
For centuries, forests located in drinking water protection areas have been regarded as a natural safeguard for maintaining high drinking water quality. However, the growing occurrence and severity of droughts increasingly threaten the forests’ protective function. An important event is the severe drought from 2018 to 2020 in Germany, which induced an unprecedented pulse of forest dieback. Using this event as a showcase, we provide evidence that forest dieback might jeopardize the forests’ essential role in protecting drinking water quality. Initially, we have compiled the first comprehensive overview of forest cover, forest type, dominant tree species, and canopy cover loss in all drinking water protection areas in Germany. Our results show that forests cover a substantial area of around 43% of all drinking water protection areas. During the multi-year drought of 2018-2020, an excessive fraction of approximately 5% of the canopy cover was lost. We further analyzed a sample of groundwater nitrate concentration records in drinking water protection areas with and without severe forest dieback. We show that 7 out of 13 sites with severe forest dieback showed a significant increase in groundwater nitrate concentrations. On average, nitrate concentrations in the forest dieback sites have more than doubled. In contrast, we did not observe significant changes in sites without forest dieback. Nevertheless, the variable responses in sites affected by forest dieback underscore the necessity for further research to understand the underlying mechanisms controlling resistance to nitrate leaching. Our assessment serves as an initial effort to underscore the hidden threat forest dieback might pose to our drinking water resources. This assessment highlights the need for intensified and collaborative research into how forest dieback affects water quality.
How to cite: Winter, C., Kattenborn, T., Stahl, K., Szillat, K., Weiler, M., and Schnabel, F.: Forest Dieback Poses a Hidden Threat to Drinking Water Quality, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3475, https://doi.org/10.5194/egusphere-egu25-3475, 2025.
Droughts affect the vitality of trees and their central role in regulating ecosystems and the climate. Moreover, climate change is expected to increase the frequency and intensity of dry periods endangering the stability and functionality of forests. It is therefore essential to adequately represent drought impacts on forests in catchment scale eco-hydrologic models.
In this study, we aim at assessing the effects of water stress on tree vitality and evapotranspiration with the eco-hydrologic model SWAT+. To this end, the catchment of the Ellerbach (182 km² area) at gauge Schleifmühle and its tributary the Gräfenbach at gauge Argenschwang (32 km²) in the low mountain ranges of the Soonwald in southwest Germany were modelled. A spatially distributed parameterisation was applied to represent the spatial heterogeneity of the catchment. Model calibration was based on Latin Hypercube Sampling to derive 1000 parameter sets for eleven model parameters. From these model runs the best model run in terms of the smallest absolute percentage bias at both gauges was chosen. The model showed a good performance at the daily time scale at the catchment outlet and a lower but still acceptable performance in the upstream indicated by Kling-Gupta efficiencies of 0.81 (Ellerbach) and 0.66 (Gräfenbach) in the calibration period (2011 to 2016) and 0.83 (Ellerbach) and 0.64 (Gräfenbach) in the validation period (2017 to 2021).
Plant water stress was identified on a daily basis when the actual plant transpiration deviated from the potential plant transpiration. The highest water stress was found for forests in the low mountain range areas in the years 2011 and 2022, with durations ranging from 62 to 119 days in 2011 and from 43 to 130 days in 2022 for different tree species. These values are up to 2.1 times (2011) and 1.5 times (2022) higher than the long-term average. Generally, coniferous trees are more affected by water stress (long-term average: 91 days) than deciduous trees (long-term average: 31 days). However, in the two analyzed years deciduous trees experienced 2.1 (+34 days, 2011) and 1.5 (+15 days, 2022) times more water stress as compared to their long-term average, whereas coniferous trees experienced 1.3 (+25 days, 2011) and 1.4 (+34 days, 2022) times more water stress.
Water stress affected tree vitality in the respective years indicated by the development of the leaf area index. Moreover, drought conditions led to a reduction in evapotranspiration by 14% (2011) and 12% (2022) when compared to mean annual evapotranspiration. Spatio-temporal differences in evapotranspiration patterns can be explained by an interplay between tree species, soil properties and precipitation patterns. As tree species perform different strategies for coping with water stress, future research shall focus on evaluating drought-induced transpiration decreases for the main tree species based on independent species-specific transpiration data.
How to cite: Wagner, P., Wendell, A.-K., Müller, E. V., and Fohrer, N.: Modelling the impact of drought-induced water stress on tree vitality and evapotranspiration , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7057, https://doi.org/10.5194/egusphere-egu25-7057, 2025.
Increasing demand for water resources makes quantification of agricultural and industrial demand essential for sustainable water management. This study was undertaken in the Lower Limestone Coast of South Australia where plantation forests are known to access groundwater. As the resource is shared between plantation growers, other agricultural users and natural ecosystems, extraction from groundwater resource is licensed by local authorities and water has an associated cost. This study forms part of a broader investigation to accurately quantify plantation water use.
This study investigated the feasibility of instrumenting field sites with fewer sap flow sensors to increase total site monitoring capacity. Research has not yet established the optimal number and arrangement of sap flow sensors required for accurate estimation of sap velocity to estimate evapotranspiration of a forest stand. Field sites of approximately 20 m x 20 m have been used with at least six sap flow sensors in the region to estimate plantation water use characteristics. This study sought to establish whether field sites utilizing three sap flow sensors was feasible to estimate sap flow velocity of a Eucalyptus globulus plantation forest over a 10-month period. It also sought to determine whether a wholly random selection of trees was appropriate, or whether the average water use was influenced by tree size.
A monitoring plot of 20 m x 20 m was established. A census of tree diameters at breast height (DBH, measured at 1.3 m above ground level, over bark) was conducted as an indicator of tree size, and the plot was subsequently categorized into three DBH size classes, namely, low (L); Medium (M); and High (H). Within each size class, two sample trees were selected at random and a total of six sap flow sensors were instrumented. A total of 20 tree combinations, involving the sub-selection of 3 sensors out of a possible 6, were analyzed for a selected month during the autumn, winter, and spring seasons.
The average sap velocity was characterised across three seasons with all sap flow combinations. Sap velocity was greatest during spring and lowest during winter, as expected. The average sap velocity increased progressively from LLM (combinations with the smallest DBH trees) to (those with the largest). Larger tree combinations (MMH, HHL, HMM) generally exhibited higher average monthly sap velocities. When examined to determine total water use, this results in an over-estimation of stand evapotranspiration. In contrast, smaller tree combinations (LLM, LLH, LMM) tended to produce lower sap velocities, potentially leading to underestimation.
Selecting an ‘average’ combination (LMH) was the most representative approach to measure the average monthly sap velocity using three sensors. This combination produced the same average monthly sap velocity as that based on using six sensors. This suggested that the use of three sap flow sensors can reliably estimate sap velocity on a spatial and temporal basis within a study plot, and also emphasised the need to consider variables like DBH when selecting trees in any monitoring study. Further research will be undertaken to verify the findings at other locations.
How to cite: Karunatilaka, P., Myers, B., Umali, B., Hewa, G., and O'Hehir, J.: Optimizing the approach required to accurately predict seasonal water use variation in a Eucalyptus Globulus plantation: A Case Study from the Lower Limestone Coast of South Australia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7541, https://doi.org/10.5194/egusphere-egu25-7541, 2025.
Northern forests exhibit strong sensitivity to recent climate change, which brings risks of carbon reemission from mature forests and threatening biodiversity. Understanding the role of these forests in regional carbon and hydrological cycle is fundamental for implementing effective forest management strategies and projecting future terrestrial dynamics. Currently, most studies investigating vegetation growth or responses to climate change rely on the fraction of photosynthetically active radiation (fPAR) as an indicator of plant productivity. However, while fPAR primarily reflects carbon assimilation within the current growing season, it provides limited insights into long-term carbon storage, such as above-ground biomass (AGB). This discrepancy arises from the complex vertical structure of forests, leading to an incomplete understanding of how forest AGB responds to local climate conditions. In this study we utilize a wall-to-wall AGB dataset derived from microwave remote sensing observations to investigate the asymmetric responses of AGB and fPAR to climatic factors and explore the underlying mechanisms driving these differences. The key contributions of this study are twofold: (1) demonstrating that AGB and fPAR exhibit distinct and asymmetric responses to local climate conditions, and (2) elucidating the factors contributing to the mismatch between AGB and fPAR. Using annual mean precipitation, temperature, and radiation data from 2015 to 2020, we analyzed the climatic responses of AGB and fPAR. Results reveal an asymmetric relationship with precipitation: AGB is negatively correlated with local precipitation, while fPAR exhibits a positive correlation. Temperature and radiation, however, show no significant constraints on either AGB or fPAR. To further investigate this asymmetry, we introduced the difference between normalized AGB and fPAR (AGB-fPAR) as an indicator and divided the study area into 12 sub-regions of 1° × 1° where precipitation and downwelling radiation energy were treated as invariant. Our findings demonstrate that topographic factors account for approximately 60% of the variation in AGB-fPAR, driven by the redistribution of energy caused by local terrain. Additionally, surface runoff reallocates water availability beyond local precipitation, with proximity to open surface water showing a significant positive relationship with higher AGB-fPAR. Forest structural complexity, such as mixed species composition and older tree age, further amplifies the AGB-fPAR gap due to their influence on vertical structure. This study highlights the importance of considering the divergence between fPAR and AGB in assessing forest responses to climate change. Local topographic effects, hydrological dynamics, and forest structural traits jointly drive the disparity between these indicators, which evidences the need for integrated approaches to understand and predict forest-climate interactions.
How to cite: Tan, S., Liu, Q., Huang, H., and Gao, G.: Asymmetric Responses of AGB and fPAR in Northern Forest to Climate Condition, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9598, https://doi.org/10.5194/egusphere-egu25-9598, 2025.
Precipitation is partitioned and redistributed by vegetation when it passes through a forest canopy resulting in interception, stemflow and throughfall. Throughfall is known to be spatially highly heterogeneous beeing lower than precipitation in certain areas and higher in others. As these emerging spatial throughfall patterns infiltrate, they may propagate into soil moisture patterns and influence root water uptake, percolation, runoff generation and ultimately the entire forest water balance. Despite the relevancy of throughfall in water resources research, there is a scarcity on experimentally-derived high-quality datasets on its spatio-temporal dynamics. Sampling procedures changed little over the past decades and are often not optimal for systems under study. Large sampling efforts especially for complex vegetation structures limit most studies to investigate on either high temporal or spatial resolution of throughfall.
We present an innovative throughfall sampling approach for continuous measurement of throughfall at high spatial resolution. The sampling scheme allows to quantify the spatio-temporal throughfall variability at both intra-event and intra-stand levels and assess spatial throughfall patterns and their temporal persistence across precipitation events of varying size during leafed and non-leafed periods. 60 self-built throughfall sampler boxes featuring a cost-efficient design with four troughfall collectors and tipping bucket units each, were distributed in a stratified sampling design in forest plots of pure and mixed Beech, Douglas and Silver fir (total area 0,4 ha). The tipping buckets are controlled with newly developed micro boards connected to data loggers so that the network measures continuously, automatically and requires minimal maintenance during precipitation events. The sampler boxes operate with an inlay of litter material on top of a grid and mesh, which allows to include forest floor interception as part of the overall throughfall process and reduces throughfall splash. The placement of the boxes at the forest floor boxes is minimally invasive as quantified throughfall can percolate into the soil below allowing to monitor soil moisture patterns in the same plot. The network of sampler boxes is supplemented with classical throughfall samplers, stemflow- and lysimeter measurements at every plot. Throughfall data were analysed from the network at a Beech, Douglas fir, Silver fir and mixed plot for the first three months of measurement. Using spatial correlation and temporal stability analysis of the observed data, we show spatio-temporal throughfall dynamics of different tree species, during and among precipitation events of varying size and for a stand that develops from dormancy to vegetation period.
How to cite: Dedden, L. and Weiler, M.: An innovative monitoring approach to measure spatio-temporal throughfall patterns in forests, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10636, https://doi.org/10.5194/egusphere-egu25-10636, 2025.
Water fluxes in forests inherit complex dynamics remains poorly understood. Precipitation in forests is intercepted by the canopy and spatially redistributed, resulting in distinct patterns of throughfall and stemflow. Canopy throughfall creates spatially heterogeneous water flux patterns beneath the forest canopy, which leads to 'hot spots' of water and nutrient input to the ground and affects soil infiltration, groundwater recharge and runoff. Despite its importance, the influence of forest structure on vegetation driven water partitioning and on the emerging spatio-temporal patterns remains poorly understood. The quantification of forest morphology in high spatial and temporal resolution is a challenge. as direct approaches are labour-intensive and often require destructive sampling (e.g. count total leaf number). Light Detection and Ranging (LiDAR) sensing from Uncrewed Aerial Vehicles (UAVs) has emerged as an effective technique to measure the three-dimensional forest structures.
Previous studies considering LiDAR derived structural metrics investigated throughfall on forest stand level with airborne laser scanning (ALS)(Schumacher & Christiansen (2015)), developed models on throughfall kinetic energy (Senn et al. (2020)) and identified water drip points in branch architecture with TLS (Wischmeyer et al. (2024)). However, these studies are limited in their spatio-temporal resolution. Recent advances of UAV based LiDAR sensor technologies (ULS) enabled the representation of forest structures both with adequate temporal and spatial detail. Such data may be the key to track and understand precipitation dynamics in forests.
Here, we present an innovative approach that combines ULS-derived forest structure metrics and in-situ-derived throughfall measurements to explore the relationship between changes in forest structure and spatio-temporal throughfall dynamics. The ULS datasets was collected starting from April 2024 with 1-2 flights per month over a forest plot in the black forest, Germany. The dataset captures forest morphology variation within the year including tree growth and changes in structure and foliage density. Continuous throughfall measurements were collected in the center (0,4 ha area) of the forest plot. 100 tipping bucket units of an automated throughfall sampling network were mounted along transects on the ground of a mixed and pure Beech and Douglas fir stand monitoring throughfall from precipitation events of different sizes, starting November 2024. Classic trough throughfall measurements starting summer 2024 complement the dataset, which covers throughfall during dormant- and vegetation period. From the LiDAR data, we derive different metrics describing forest morphology, from voxel based point densities to experimental occlusion-related permeability metrics.
In a combined correlation analysis of density- and permeability metrics with corresponding daily spatial throughfall, the influence of phenological changes on throughfall patterns at a high spatial and temporal resolution is investigated. With this study, we aim to identify the potential of LiDAR-derived metrics of forest structure from multi-temporal datasets for forest hydrology research and to develop approaches on how to integrate metrics that are suitable descriptors for complex forest canopy structures into investigation of water fluxes in forest.
How to cite: Gassilloud, M., Dedden, L., Koch, B., Kattenborn, T., Weiler, M., and Göritz, A.: Elucidating spatio-temporal throughfall dynamics with ULS derived forest structure density metrics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19485, https://doi.org/10.5194/egusphere-egu25-19485, 2025.
Climatic change, including an increasing frequency of large-scale disturbances, is progressively threatening the resilience and productivity of forests. Against this backdrop, the LabForest project, funded by the German Federal Ministry of Education and Research (BMBF), investigates the effectiveness and efficiency of silvicultural measures following such calamities. LabForest includes a living lab in a forest of the Ludwig-Maximilians-University (450 ha), facilitating the comparison of forestry and timber management effects (e.g., advance regeneration, clearance, and planting versus natural regeneration) on disturbed areas. The silvicultural measures are examined and evaluated for their impacts on important ecosystem services (e.g., hydrology, carbon sequestration, and timber production) and biodiversity. Ultimately, the project aims to establish a multidimensional assessment matrix to support decision-making in forestry, balancing climate change mitigation, economic interests, biodiversity, and hydrology.
The Hydrometeorology work package develops high-resolution hydrometeorological models of varying complexity to accurately represent and compare water and matter fluxes relative to the differently managed forest plots. For this purpose, a newly setup measurement network captures components of the water balance (evaporation, soil moisture, soil temperature, fraction of photosynthetically active radiation), water quality, and micrometeorological variables. The measured quantities serve as the basis for the parameterization and validation of the models.
The modeling results and analysis of the hydrological conditions of the different forest management strategies will be incorporated into the assessment matrix for silvicultural practices. This will enable regional recommendations and an improved understanding for establishing economically and ecologically resilient forests to cope with anticipated climatic changes.
How to cite: Svanidze, D., Ludwig, R., Obermeier, W., and Lehnert, L.: Hydrometeorological Aspects of Sustainable Forest Regeneration Management in Climate Change, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12627, https://doi.org/10.5194/egusphere-egu25-12627, 2025.
This study summarized the results of long-term monitoring of various functions obtained from forest restoration, including increased plant diversity and water resource recovery. The study area is a long-term monitoring area for degraded forests, and the characteristics of valley runoff and vascular flora have been continuously observed since 1970, and the annual changes in valley runoff and plant species diversity were compared. As a result of the study, the average runoff was confirmed to be approximately 90 days in the 1980s, approximately 310 days in the 1990s, and 365 days in the 2000s. Compared to the number of days of runoff in the initial degraded area, it increased 3.7 times in 1990 and 4.4 times after 2000. In particular, it was confirmed that the valley flow was maintained throughout the year regardless of rainfall characteristics after 2000. In the case of vascular plants, there were 30 species including Miscanthus sinensis, Lespedeza bicolor, and Arundinella hirta in the 1980s, 62 species including Quercus serrata, Callicarpa japonica, and Rhus chinensis in the 1990s, and 80 species including Quercus mongolica, Viburnum dilatatum, and Fraxinus sieboldiana in the 2000s. In a recent survey, there were 116 taxa including Maackia amurensis, Alnus japonica, and Sorbus alnifolia, and the number has continuously increased. In terms of vegetation structure, in the 1980s, simple communities of shrubs and herbs with a height of about 5 m were the main focus, but in the 1990s, they developed into 10 m tall sub-tree vegetation, and after the 2000s, broad-leaved forests and coniferous-broadleaf mixed forests with a height of about 15 m were formed. It is expected that this study can be used as basic data for estimating ecosystem services and evaluating public interest functions according to the restoration of desolate and damaged forests.
How to cite: Choi, B., Li, Q., Lim, H., and Nam, S.: Monitoring study on plant diversity and water resource recovery characteristics due to restoration of desolate mountain areas, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13549, https://doi.org/10.5194/egusphere-egu25-13549, 2025.
Studies on climate change effects reveal that the natural water cycle will continue to shift, often intensifying pressure on water resources. Understanding the interaction between forest ecosystems, soil water dynamics, and groundwater recharge under these changes is essential. This study investigates the forested areas of the Hessian Ried in Hesse, Germany—a low-lying, fertile region crucial for agriculture, forestry, nature conservation, and groundwater supply to the Frankfurt/Rhine-Main metropolitan region. Ensuring sustainable water management for this vital resource zone is necessary to meet future demands.
The LWFBrook90 model, a 1D Soil-Vegetation-Atmosphere-Transfer (SVAT) tool, was utilized to examine future soil water variability and its impact on groundwater resources in the study area. The model simulates the soil water balance using Richards’ equations and, with its latest version (LWFBrook90R 0.6.0), incorporates capillary rise. Historical daily climate data (1960 to present) and climate projections based on the RCP8.5 scenario (extending to 2100) were used. The forested area was discretized into 500 m x 500 m cells, each with representative vegetation, soil, and climate data. Vegetation data was obtained from forest inventories and used in combination with forest yield tables to derive leaf and stem area index using allometric functions. Calibrated model parameters for the main tree species—oak, beech, and pine—were obtained from Weis et al. (2013). A detailed discretization of soil profiles was performed and the corresponding soil physical properties were assigned layer-wise using pedotransfer functions (Wessolek et al., 2009).
The cell-based framework effectively captured spatial variability in tree species and soil properties, ensuring computational efficiency despite excluding lateral flow. Future projections (especially in 2081–2100) indicate a significant decline in soil water availability during summer months (July–September), increasing water stress and potentially impairing plant growth. In winter, soil moisture recovery may still occur but is less pronounced. Monthly transpiration ratios, averaged across periods 2021–2050, 2051–2080, and 2081–2100, revealed severe stress across all projections. Even scenarios with wetter conditions suggest that increased rainfall and infiltration may not sufficiently mitigate tree stress in vulnerable areas.
The model successfully simulated vertical water movement in the profile and groundwater recharge dynamics. Groundwater recharge during winter is projected to maintain current rates under moderate scenarios or slightly increase under wetter ones. However, under the driest scenario, the average rate was less than 50 mm per year for the period 2081–2100. These findings highlight significant stress on forest ecosystems under changing climate conditions, emphasizing the need for adaptive water management strategies. Ongoing research seeks to refine this prototype by examining vertical fluxes at sites with shallow groundwater depths and further investigate recharge rates under various forest conversion scenarios. These advancements will contribute to a more comprehensive understanding of forest ecosystem responses and guide water management efforts in the Hessian Ried and similar regions.
How to cite: Morales, A. G., Köhler, M., Sutmöller, J., Ahrends, B., and Meesenburg, H.: Modelling Climate Change Effects on Soil Water Dynamics and Groundwater Recharge in Temperate Forests in Germany, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14995, https://doi.org/10.5194/egusphere-egu25-14995, 2025.
Vegetation interacts with both soil moisture and atmospheric conditions, contributing to water flow partitioning at the land surface. Therefore, both climate and land cover changes impact water resource availability. This study aimed to determine the differential effects of climate change on the soil water regime of two common Central European forest types: Norway spruce (Picea abies L.) and European beech (Fagus sylvatica L.) stands.
A unique dataset, including 22 years (2000–2021) of measured soil water potentials, was used with a bucket-type soil water balance model to investigate differences in evapotranspiration and groundwater recharge both between the forest types and across years. While long-term column-averaged pressure head indicated drier soil at the spruce site overall, this was driven by the wettest years in the dataset. Seasonal and interannual variability of meteorological conditions drove complex but robust differences in flow partitioning between the forest types. Higher snow interception by spruce (27 mm season-1) resulted in drier soil below the spruce canopy in the cold season. Higher transpiration by beech (70 mm season-1) led to increasingly drier soils over the warm seasons. Low summer precipitation inputs exacerbated soil drying under beech as compared to spruce. Estimated summer recharge was lower under beech (25 mm season-1) due to its lower transpiration. The difference was more pronounced (over 40 mm season-1) during wetter summers.
These suggest that expected trends in regional climate and forest species composition may interact to produce a disproportionate shift of recharge from the summer to the winter season.
How to cite: Sipek, V., Zelikova, N., Touskova, J., Kocum, J., Vlcek, L., Tesar, M., Pátek, K., and Bouda, M.: Future changes in water availability: Insights from a long-term monitoring of soil moisture under two tree species, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18908, https://doi.org/10.5194/egusphere-egu25-18908, 2025.
