The growing global network of Critical Zone Observatories provides exciting insights into how terrestrial and subsurface environments are interconnected, emphasising the value of understanding the Critical Zone as a vertically integrated system. Yet this network is situated overwhelmingly in the frequently young and post-glacial or glacially-influenced landscapes of the Northern Hemisphere. The Southern Hemisphere offers diverse landscapes with geologic parent materials spanning the Archaean to the Cenozoic, which have experienced little glaciation relative to the Northern Hemisphere. The Australian Critical Zone Observatory Network was established in 2020 to provide insights into the structure and functioning of such landscapes on the ancient, chemically depleted, dry and diverse Australian continent. Five sites have been established with a common suite of instrumentation and operating principles, and are working collaboratively to develop Critical Zone datasets in landscapes ranging from rainforest to eucalyptus woodlands, dryland mallee, tropical savannah and rain-dependent agricultural lands.
This talk will introduce the OzCZO – the Australian Critical Zone Observatory Network, the five sites, their instrumentation and opportunities for scientific research within and by making comparisons among the sites. It will then share some of the initial observations being collected at one of the observatories – the ancient lateritic landscape of the Avon Critical Zone Observatory. We will illustrate how CZ structure, illuminated by bore logs and geophysics, organises soil physical and chemical properties across the landscape, and reveal how these properties then feed into land management decisions, hydrological functioning, and large-scale ecological health. The Avon CZO is located within a biodiversity hotspot in the South-West of Australia, where the health of land and waters, and the ecosystems and agricultural production that depend on them, is threatened by both dryland salinity and a drying climate – with outcomes all mediated by the Critical Zone.
All data from OzCZO will be publicly available for use, and the sites are intended to act as an open platform where researchers can develop and test their ideas. Given the scope for valuable cooperation and comparisons across these sites, we invite researchers at EGU to engage with OzCZO and keep progressing towards a global Critical Zone science.
How to cite: Gelsinari, S., Miotliński, K., Leopold, M., Weller, J., and Thompson, S.: Down Under(ground) – Introducing the Australian Critical Zone Observatory Network, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15141, https://doi.org/10.5194/egusphere-egu25-15141, 2025.
Headwater catchments, defined as the uppermost segments of drainage networks with intermittent and/or perennial third-order streams, are vital sources of freshwater and nutrients for downstream river basins. Despite their critical role in sustaining natural ecosystems and supporting human services, these systems remain poorly understood and are often referred to as 'aqua incognita1.' A key challenge lies in unraveling the hidden groundwater processes that contribute to storage-discharge dynamics. Recent advances in both in-situ and remote monitoring, combined with innovative modeling techniques, now offer opportunities to capture the complex interactions between surface and subsurface processes across diverse climatic, topographic, and geological contexts.
In this presentation, we will present recent findings from field investigations conducted in headwater observatories, complemented by numerical modeling experiments designed to evaluate the controls of key geomorphic factors on groundwater-surface water interactions. The presentation will explore how landforms, lithologies, subsurface stress, and faults shape hydrological behaviors, including stream baseflow recession, groundwater seepage distribution, flow intermittency, and water residence times. Additionally, we will highlight advances in numerical modeling techniques, particularly through the HydroModPy community modelling platform2, which enhance the representation and calibration of groundwater processes in catchment-scale hydrological models. Through the application of these models on pilot sites, we will illustrate how subsurface heterogeneity influences the predictions of water availability under future climate change scenarios, emphasizing the importance of integrating hydrogeological insights for supporting resilient water resource management.
1 Bishop, K., Buffam, I., Erlandsson, M., Fölster, J., Laudon, H., Seibert, J., Temnerud, J., 2008. Aqua Incognita: the unknown headwaters. Hydrological Processes 22, 1239–1242. https://doi.org/10.1002/hyp.7049
2 Gauvain, A., Abhervé, R., Coche, A., Le Mesnil, M., Roques, C., Bouchez, C., Marçais, J., Leray, S., Marti, E., Figueroa, R., Bresciani, E., Vautier, C., Boivin, B., Sallou, J., Bourcier, J., Combemale, B., Brunner, P., Longuevergne, L., Aquilina, L., and de Dreuzy, J.-R.: HydroModPy: A Python toolbox for deploying catchment-scale shallow groundwater models , EGUsphere [preprint], https://doi.org/10.5194/egusphere-2024-3962, 2025.
How to cite: Roques, C., Abhervé, R., Marti, E., Figueroa, R., Cornette, N., Gauvain, A., de Dreuzy, J.-R., Leray, S., Bouchez, C., Boisson, A., Aquilina, L., and Brunner, P.: Groundwater controls on headwater stream dynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12772, https://doi.org/10.5194/egusphere-egu25-12772, 2025.
How deep does the rain regularly infiltrate into the ground? Do plant roots follow? How much infiltration is pumped back to the atmosphere (short-circuiting) and how much passes below plant roots reaching the water table, flushing the regolith, recharging aquifers and rivers, and eventually reaching the ocean (long-circuiting) thus regulating global biogeochemical cycles and long-term climate? What is the depth that supplies evapotranspiration, and what is the regolith flush rate? What are the implications to global material and energy cycles? The answers depend on local climate–terrain–vegetation combinations. We use observations and high resolution numerical modeling at the global scale to shed light on multiscale causes–feedbacks among climate, drainage, substrate, and plant biomass that interactively create a global structure in the depths and rates of hydrologic plumbing of the Earth's critical zone, informing global models on critical depths and processes to include in Earth-system predictions.
How to cite: Miguez-Macho, G. and Fan, Y.: Infiltration depth, rooting depth, and regolith flushing—A global perspective, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12719, https://doi.org/10.5194/egusphere-egu25-12719, 2025.
The hyporheic exchange between the surface water and the underground water is considered a significant process in the natural water cycle system. Some sediment particles in the riverbed can be carried to the exchange channel under the stream effect. Over time, these particles accumulate on the channel can decrease the exchange efficiency of water resources, and induce clogs. The clogging problem of the exchange channel may further induce various geological and environmental disasters such as the shrinkage of lakes and desertification.
To detail the clogging mechanism in the exchange channel, we simulated the exchange clogging process on the exchange channel based on a coupled lattice Boltzmann method (LBM) and discrete element method (DEM). The results indicated particles could form an arch structure clogging the channel orifice. The formation of the clogging arch prevented the discharge of soil particles and greatly decreased the fluid velocity. Notably, the fluid velocity distribution around the orifice is in a certain shape according to the velocity of the LBM cells—the size of the shape regularly changes with the distance to the channel orifice. The variation of the average fluid velocity in the orifice first increases to a peak (about 0.497 cm/s) in the initial time and then decreases to an approximate value after clogging (about 0.037 cm/s). The maximum velocity is almost thirteen times the minimum, indicating that the clogging effect can reduce the water velocity of hyporheic exchange by more than one order of magnitude. In addition, it was found that the soil skeleton was necessary for forming clogs in polydisperse particle systems by analyzing the clogging arch-forming process. The sediment particles in different scales have different effects on the clogging arch. The large particles in the sediments are closely related to the formation of the soil skeleton. The fine particles were involved in the filling and enhancing of the soil skeleton.
Based on our simulation analysis, an explanation for the clogging formation under microscopic conditions was proposed, leading to a detailed description of the exchange clogging in the hyporheic exchange channel. In addition, some mechanism statements to better understand the exchange phenomenon in the water cycling ecosystem are also provided.
How to cite: Zhang, X., Takai, A., Kato, T., and Katsumi, T.: Clogging model of hyporheic exchange based on coupled lattice Boltzmann discrete element simulations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1952, https://doi.org/10.5194/egusphere-egu25-1952, 2025.
Critical Zone processes encompass interactions among rock, soil, water, air, and living organisms, essential for quantifying water and nutrient fluxes and predicting downstream river water quality. High-fidelity reactive transport models (RTMs) are important for understanding Critical Zone processes but are typically computationally expensive, which limits their applicability across large catchments. To address these challenges, we developed a scale-adaptive reactive transport simulation framework that balances process fidelity with computational efficiency. We developed the RiverFlotran Module, which employs fully dynamic 1D shallow-water equations for river hydrodynamics, and integrated it into PFLOTRAN, a subsurface reactive transport model. This integration enables us to simulate bidirectional exchanges at the land-water interface. Subsequently, we developed a machine learning-based exchange function, trained on the simulated data, and tailored for the East River. This function allows us to predict river water quality along the river continuum. This framework was applied to the East River Mountainous Watershed in Colorado, a study site of Berkeley Lab's Watershed Function Scientific Focus Area, to demonstrate its effectiveness in capturing intricate Critical Zone interactions and predicting downstream river water quality. Our study of the East River Floodplain's alluvial aquifer revealed that prevailing anoxic conditions generate pronounced redox gradients, resulting in the downstream export of dissolved iron and nitrogen near meander bends. These bends consistently serve as nitrogen hotspots, irrespective of water levels, driven by variations in river stage, bathymetry, and meander geometry, such as sinuosity. This modeling framework provides a foundation for quantifying river water quality at the catchment scale.
How to cite: Dwivedi, D., Özgen Xian, I., Arora, B., Faybishenko, B., Newcomer, M., Fox, P., Steefel, C., Williams, K., Nico, P., Hubbard, S., and Brodie, E.: A Scale-Adaptive Framework for Modeling Critical Zone Processes and River Water Quality in the East River Watershed, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13922, https://doi.org/10.5194/egusphere-egu25-13922, 2025.
Extreme winter precipitation events, associated with frequent and intense atmospheric rivers, deposit significant quantities of water in mountain regions over short periods of time. Precipitation is forecast to become more variable as climate change intensifies; however, it is unclear how that will affect mountain aquifer recharge. Here we use high-precision Global Navigation Satellite Systems (GNSS) surface displacements and elastic deformation models to surface loading to estimate total water storage changes. Using independent estimates of water stored within shallow subsurface and surface reservoirs, we isolate changes in mountain groundwater storage in two important mountain regions of the western US at high spatial (~30km) and temporal (~ 1 week) resolution. We find that groundwater storage is the dominant component of long-term total water loss within the Sierra Nevada and Cascades, composing up to 95% of the total water lost over the past two decades. However, extremely wet winters, such as that of 2023, can recharge groundwater storage by more than twice the average annual amount, driving the state of groundwater storage from historical lows to above or near-normal conditions over relatively short periods. Further, we find gains in groundwater storage associated with these events are relatively durable, persisting over several proceeding years following the extreme recharge event. Mountain aquifers have been increasingly recognized as a dynamic and critical source of water storage and release to adjacent low-elevation communities; however, persistent declines in mountain aquifer storage have been observed across the western US over the past two decades. In a future with increasingly variable precipitation, the strong influence of extreme events may act to maintain mountain groundwater, sustaining ecosystem health and buffering adjacent areas against drought conditions in between events.
How to cite: Gardner, W. P., Swarr, M., Argus, D., Martens, H., Young, Z., and Hoylman, Z.: Extreme Winter Precipitation Drives Recharge of Deep Mountain Groundwater, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14670, https://doi.org/10.5194/egusphere-egu25-14670, 2025.
Tropical vegetation plays a vital role in global ecosystem services, with one critical aspect lying in its hydrological functions of water cycle regulation. Climate change and accelerated human interventions threaten the stability of tropical vegetation, associated with profoundly hydrological changes particularly in recent decades. Despite various studies on land-atmosphere feedback using earth system models, the regulation of terrestrial hydrological components remains unclear over tropical regions, due primarily to inherent limitations of models in accurately simulating terrestrial water storage (TWS) and runoff. Here, we combine multisource observations to reveal a disparity pattern in storage-runoff interactions over tropical regions for the past two decades. Using satellite-based Landsat optical archives, Global Ecosystem Dynamics Investigation, GRACE gravimetry, and gauge-based runoff database, we show that large-scale forest degradation and cropland expansion have weakened moisture recycling over the eastern tropical South America and eastern tropical Africa (Region I), indicated by a significant decrease in net precipitation input (precipitation minus evapotranspiration). This further causes declines in both TWS and streamflow, shown as a pattern of “less storage and less runoff” due to vegetation degradation. In contrast, over the western tropical South America, western tropical Africa, and tropical Asia (Region II), we did not find marked changes in land cover but a significant increasing trend in vegetation greenness and leaf area index. This is associated with a significant increase in net precipitation input and an enhanced moisture recycling. The increased water input over Region II causes an increase in TWS but a decline in streamflow, shown as a pattern of “more storage but less runoff” due to the decrease in rainfall-runoff generation induced by vegetation growth. The disparity patterns between Region I and Region II highlight different responses of tropical terrestrial water system to a changing environment. Unlike most past studies relying on land surface or earth system models, this study leverages strengths in advanced observation techniques to explore different mechanisms underlying changes in the tropical terrestrial water system. Findings from this study provide valuable supplements to the current model-based analysis, and inform adaptive strategies for changes over tropical regions.
How to cite: Li, X. and Peng, J.: Multisource observations reveal different roles of tropical vegetation in terrestrial water regulation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7653, https://doi.org/10.5194/egusphere-egu25-7653, 2025.
The pathway for rainfall into stream flow in mountain catchments can be fast via surface run-off or short-lived storage in the weathered zone, or slow via the deep fractured bedrock groundwater system. In mountainous topography, springs can be found at almost all elevations, suggesting that groundwater storage occurs at all elevations. There is however uncertainty as if this storage is short lived, confined to the weathered zone, or longer lived and is part of the groundwater system. Intermittent streams and springs might reflect the storage of water within the subsurface. To measure stream intermittency and the migration of the associated headwater springs we installed intermittency loggers based on repurposed HOBO luminosity loggers along five gulleys within the Kahule Khola catchment in central Nepal.
The intermittency loggers measure an electric current when the circuit is closed by surface moisture and flowing water. The loggers were installed in spring 2023 before the pre-monsoon and were removed in November 2024. At low elevation, three series of loggers were installed in gullies below the village of Listi. These below Listi loggers had perennial springs at their lowest elevation. Furthermore, one series of loggers ended at an ERT repeat survey that showed evidence of year-round shallow subsurface saturation. At high elevation, two series of loggers were installed near the village of Bagham, below an open meadow where ephemeral springs were mapped (we call these the meadow loggers). A coincident ERT repeat survey showed evidence of lateral flow of groundwater within this region.
The loggers recorded three distinct phases: (1) The pre-monsoon, where individual storm events can be registered along each gulley as separate wetting events. (2) Monsoon, where there is a continuous and high conductivity measurement for all loggers, representing continuous flow of surface water. (3) The dry season, which starts with a recession in the electric current observed, followed by sparce wet events. The below Listi systems dried completely within the dry season, while the meadow gulleys recorded low but non-zero electric currents even throughout the dry season. The loggers did not record any evidence of spring migration down the gulleys, rather a uniform drying after rainfall events at all locations, with prolonged wetness post monsoon only seen for loggers that were situated just above known perennial springs. The observations would therefore suggest that intermittent run-off comes from the temporary storage in the weathered zone that dries out at the same rate across the catchment, while persistent flow is from points where the topography intersects with the deeper groundwater reservoir. Run-off within the steep catchment therefore operates through two coexisting systems, (1) an intermittent system that is fed from temporary storage of water in the weathered zone, where there is no distinct headwater spring, and (2) perennial streams fed by groundwater springs.
How to cite: Armitage, J., Teagai, K., Hovius, N., Illien, L., and Andermann, C.: Spring and stream intermittency in an instrumented steep Himalayan Mountain catchment, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2490, https://doi.org/10.5194/egusphere-egu25-2490, 2025.
In Mexico City, where population growth has significantly increased water demand, a well was drilled to a vertical depth of 1992 meters.
To understand the groundwater dynamic in the critical zone- an area extending from the surface to the base of the groundwater system, where complex interactions occur between the atmosphere, lithosphere, hydrosphere, and biosphere- various tools were employed, including geophysical log analysis, pumping tests, and groundwater sampling for hydrochemical and isotopic (stable and radioactive) analyses.
The results revealed consistent ion concentrations during hydrogeochemical monitoring, classifying the water as sodium-chloride type with minor nitrate contamination attributed to the use of drilling mud.
Isotopic analysis indicated that the water likely originated from precipitation infiltrating at approximately 3000 meters above sea level, possibly from nearby mountain ranges. Radiocarbon dating estimated a residence time of 2840 years, although additional testing is necessary for confirmation.
Hydraulic tests determined a transmissivity of 768 m²/day and a specific storage of 3.11 × 10⁻⁶ m⁻¹, corresponding to an average hydraulic conductivity of 0.885 m/day. This is a complex hydrogeological system characterized by deep, highly fractured saturated zones. Groundwater in this well originates from the deep infiltration of rainfall in the surrounding sierras, circulating through fractures in volcanic rocks. Initially, the water quality showed temporary mixing with surface water due to the interaction between formation water and drilling mud; however, it later exhibited a distinct chemical composition.
The residence time of the water indicates a dynamic system with varying water ages. The results suggest hydraulic connectivity between different hydrogeological units and an endorheic behavior of groundwater flow in the area. In summary, this study enhances the understanding of groundwater flows in Mexico City, emphasizing the critical zone's role in shaping subsurface processes and highlighting the importance of considering the complexity of these systems for sustainable management.
How to cite: Martínez Casas, Z., Morales Casique, E., Olea Olea, S., and Lezama Campos, J. L.: Deep flow behavior and the critical zone in a deep well: A hydrogeological study in Mexico City, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12792, https://doi.org/10.5194/egusphere-egu25-12792, 2025.
The Aix Marseille Provence metropolitan area experiences rapid urbanization that reinforces the need for infrastructure and implies considerable sealing of the substratum This region is a typical arid and Mediterranean environment where rain precipitation can be exceptionally catastrophic. This two factors creates runoff, overflow and flooding in the urban area. One solution to manage the flooding and overflow is to allow more water to penetrate into the soil, by removing the impermeable and anthropic materials where the geological substratum is naturally able to infiltrate the water.
Usually, standard parameters such as: topography, drainage density and hydrological balances, are used to estimate runoff and indirectly find the infiltrability values and ultimately tackle infiltration problematics. These approaches are informatic and mathematics-based that work in a small, delimited and homogeneous area. To integrate this problematics to large scale and heterogenous systems, reservoir geology concepts such as geomorphology, uncertainties of scale change processes or structural geology can be addressed. Therefore, this project aims to understand the geological processes that controls the infiltration potential in the geological substratum and its spatial distribution for the purpose of creating an infiltrability map of the Aix Marseille metropolis.
The goal of this study is to develop a method for predicting the infiltration capacity on a large scale and heterogenous area including urban zone. This involves acquiring local observational data points which classify rock outcrops in 4 “hydraulic types” (HT) defined as follows: HT-1 represents impermeable rocks or soils, where no infiltration is possible; HT-2 represents thin soils with variable porosity and permeability; HT-3 describes rocks with low to very high matrix porosity influenced by clay matrix presence and variable permeability; HT-4 describes rocks with fractures and/or karst networks with low to very high permeability depending on fracture/cavity density, with variable porosity. With the geolocated data points, a map is created on QGIS (a Geographic Information System free software) in order to up-scale the hydraulic types over a larger scale grid by spatial interpolation.
For an even acquisition area, geological heterogeneity and accessibility of outcrops determines the data number needed to upscale hydraulic types. This approach is well-known in reservoir geology and this large-scale project is the opportunity to apply the methodology to hydrogeology field.
Additionally, to address the lack of visibility of outcrops, subsurface data (shallow well data from the BRGM, Bureau of Geological and Mining Research) will be combined with field observations. Furthermore, a calibration of this method will be required to quantify and to establish thresholds within the Hydraulic Types classification. This project will ultimately provide specific values for infiltration capacity and facilitate flood risk management without having to use complex and costly technologies.
Keywords : SIG mapping, infiltration, runoff, geological substratum, stratigraphy, structural geology, heterogeneity, precipitation, de-sealing, available water
How to cite: Ruttyn, L., Fournier, F., Leonide, P., Jean, B., Arfib, B., Viseur, S., Goulet, L., Vignoulle, O., and Zaabar, N.: Elaboration of a geological and hydraulic mapping project of infiltrability potential on the Aix-Marseille Provence Metropole (SE, France), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18699, https://doi.org/10.5194/egusphere-egu25-18699, 2025.
Soil moisture is a critical component of the Earth’s hydrological cycle, influencing weather, climate, agriculture, and ecosystems. In situ soil moisture measurements are indispensable for validating satellite observations, calibrating hydrological and land surface models, and advancing our understanding of regional and global water cycles. Unlike remote sensing, in situ measurements provide direct observations of soil moisture variability across temporal and spatial scales, offering a benchmark for numerous environmental applications.
The International Soil Moisture Network (ISMN) serves as a vital repository of harmonized in situ soil moisture data collected from diverse networks worldwide. Since its inception, the ISMN has integrated measurements from over 80 networks with more than 3000 stations at various depths, standardizing and curating them to ensure accessibility and comparability. Beyond offering comprehensive in situ soil moisture data, ISMN disseminates additional environmental variables, including soil temperature, snow depth, snow water equivalent, precipitation, air temperature, surface temperature and soil water potential if they are available from our data providers. ISMN’s quality control framework addresses inconsistencies and errors, enabling researchers and practitioners to confidently utilize its datasets for applications ranging from hydrological modeling to climate change studies. ISMN’s free data access (https://ismn.earth) has fostered global collaboration and supported hundreds of studies in Earth system science.
Ongoing efforts are concentrated on expanding the database by incorporating additional stations and networks from institutional or governmental sources. Further resources are directed towards fortifying the operational system and improve usability to better serve our users. ISMN further contributes to the data-to-value chain on international initiatives like WMO, FAO and GCOS. One example is the contribution to WMO’s yearly Global State of the Water Resources report. To enhance data quality, ISMN is researching AI-based methods for detecting anomalies such as spikes, dips, and plateaus, showing promising initial results.
How to cite: Zink, M., Olarinoye, T., Boehmer, F., Kramer, K., Dietrich, S., and Korres, W.: The International Soil Moisture Network (ISMN): A global hub for in situ observations serving earth system science, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18247, https://doi.org/10.5194/egusphere-egu25-18247, 2025.
The international Critical Zone Network of Networks (CZ-NoN) project, launched in January 2025 and funded by the US National Science Foundation, promotes the study of the Earth’s Critical Zone (CZ), the vital near-surface environment where essential life-supporting processes converge. Building on previous investments in CZ research, CZ-NoN fosters collaboration and communication between existing and emerging environmental observatories and monitoring networks worldwide. By establishing a unified framework for collaboration and discussion, CZ-NoN addresses long-standing challenges such as fragmented methodologies, redundancies, poor communication, and barriers to data discoverability and accessibility. Key project components include planning meetings, workshops, and an online webinar series aimed at building community, showcasing new efforts, and increasing awareness of ongoing CZ research. In parallel, a global polling effort will compile a crowdsourced list of grand research questions to guide future CZ studies. By bringing together researchers from different countries and disciplines, and prioritizing cooperation over competition, CZ-NoN will accelerate scientific research and position the international research community for future funding opportunities to support complex, integrated study of the global CZ across diverse socio-environmental conditions.
How to cite: Munroe, J., Arora, B., Bishop, K., Blume, T., Bogena, H., Boyer, E., Braud, I., Gaillardet, J., Kiese, R., and Zacharias, S.: Accelerating Critical Zone Science with an International Network of Networks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2917, https://doi.org/10.5194/egusphere-egu25-2917, 2025.
In times of climatic unpredictability driven by a quickly changing climate, it is critical to investigate hydrological processes and water availability in different climatic and geomorphological contexts. Mountains have long been acknowledged as fundamental sources of abundant high-quality water for the densely populated downstream areas. The large volumes of water stored in mountain lakes, reservoirs, and snow caps are extremely important to buffer precipitation variability and sustain ecological and anthropic water uses during droughts. So far, the flow and storage of water in the deeply fractured rock formations constituting the core of mountain massifs have mostly been neglected, even for the long-term water balance. However, recent experimental evidence has shown that poorly porous and conductive fractured bedrock can host aquifers whose contribution to streamflow can be substantial, particularly during droughts.
This study systematically assesses, under a wide range of geomorphoclimatic conditions, how deep subsurface storage and flows affect critical hydrological and hydrogeological variables such as the age of streamflow (as opposed to the age of baseflow), surface seepage, and permanent drainage density. These critical hydrological processes are investigated via a large set of steady-state numerical experiments by modulating surface topography, groundwater recharge, and hydrogeological properties of the subsurface (e.g., formation depth, hydraulic conductivity, and its heterogeneity).
The results quantitatively show, for example, how different morphological and hydrogeological conditions may respond to climate change and can be useful in identifying vulnerable areas where mitigation strategies should be prioritized to cope with water shortages. The study can also help understand where ecological alterations driven by the lack of water can have a more profound impact on riverine habitats and where to expect the shift of species in the future.
How to cite: Bellin, A. and Betterle, A.: Assessing the Impact of Deep Subsurface Storage and Flows on Hydrological Processes and Water Availability in Mountainous Regions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11743, https://doi.org/10.5194/egusphere-egu25-11743, 2025.
The ground substrate is a new concept in the field of natural resources proposed by Chinese scientists in 2020 (Ministry of Natural Resources, 2020). It is the basic material that supports and nurtures various natural resources such as soil, forests, grasslands, wetlands, and water. The layer of ground substrate is the most active geological space for the exchange of substances and energy such as water, heat, salt, gas, carbon, etc. It is also serving as a bridge link between the land cover layer and the underground resource layer. The proposal on concept of ground substrate has clarified new directions and goals for geological survey to support ecological civilization construction and natural resource management, has great significance.
In different climate zones such as humid, semi humid, semi-arid, and arid in China, there are significant differences in the material composition, genetic types, and characteristic physicochemical properties of ground substrates, which call ground substrate heterogeneity by us. In recent years, based on multiple ground substrate surveys and research projects, some important conclusions has been gained. The first is we revealed the constraint mechanisms of the physical structure, mineral element composition, and chemical properties of ground substrates on the types, NDVI, NPP of vegetation ecology in the key ecological functional areas in northern China and hilly mountainous areas in southern China. The second is the determination of the bottom boundary of the ground substrate layer requires comprehensive consideration of five factors: they are depth of the underground variable temperate zone, the roots depth of crop and vegetation, the depth of the surface karst development zone, the thickness of the weathering crust, and the burial depth of the groundwater level. It is generally believed that the depth of the ground substrate layer is less than 20 meters. The third is the key constraint layer of ground substrate (rock and soil layers that have important control and influence on vegetation and crop growth, water and salt storage and transport, etc.) is a special layer that should be given special attention in ground substrate filed survey.
More detailed about the scientific connotation and theoretical framework of ground substrate, please see the published paper(Hao Aibing, Yin Zhiqiang*, Li Hongyu, Lu Qinyuan, Peng Ling, Shao Hai, Jiang Qida, Zhao Xiaofeng, Liu Jiufeng, Pang Jumei, Yang Ke, Chen Peng, Kong Fanpeng, Hou Hongxin, Lu Min. 2024. The scientific connotation and theoretical framework of ground substrate. Acta Geologica Sinica. 98(11):3225-3237)
How to cite: yin, Z., peng, L., and hao, A.: The concept of ground substrate and its physical structure & mineral element composition constrain mechanisms on vegetation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1441, https://doi.org/10.5194/egusphere-egu25-1441, 2025.
Lateritic landscapes are structurally complex systems formed through intense chemical weathering under tropical paleoclimates. These profiles are found in stable, low-relief landscapes across tropical, subtropical, and Mediterranean climates, particularly between 35°N to 35°S. Their vertical structure reflects long-term shifts in climatic, hydrological, and tectonic conditions, offering a valuable "memory" of past environmental changes. Despite their environmental and economic significance, lateritic landscapes remain underrepresented in CZ research, a bias compounded by the concentration of Critical Zone Observatories in the Northern Hemisphere, where shallow, truncated profiles prevail due to glacial erosion. This underrepresentation limits our understanding of long-term CZ processes and how they have shaped subsurface architecture.
This study investigates the subsurface architecture of a lateritic hillslope at the Avon River Critical Zone Observatory (AR-CZO) in Western Australia. Prolonged subaerial weathering since the Cretaceous, followed by mid-Miocene aridification, has created a stratigraphically complex regolith hillslope shaped by weathering, erosion, and colluvial deposition. To resolve the structural complexity of this hillslope, we applied a multi-method geophysical approach, combining electrical resistivity tomography (ERT), horizontal-to-vertical spectral ratio (HVSR) passive seismic methods, and borehole observations. ERT captured fine-scale stratigraphy, delineating the pallid zone, saprolite, and duricrust, while HVSR resolved broader interfaces, such as the duricrust-bedrock boundary and the base of the colluvial deposit.
The results reveal how landscape position influences CZ structure. The hilltop is capped by a duricrust that transitions downslope into an erosional surface, where the pallid zone of the lateritic weathering profile is exposed at the surface. At the foot slope, approximately 11 m of colluvial sediment has accumulated from the erosion of the hillslope material. Bedrock depth estimates differed between methods, with ERT indicating depths of 23 m on the slope and 32 m at the foot slope, while HVSR revealed deeper depths of 31 m and 39 m, respectively. The discrepancy highlights the limitations of ERT in saline environments, where conductivity masks key interfaces, while HVSR’s broader resolution provides more reliable bedrock detection in such conditions. Together, these methods reveal a laterally variable weathering profile that responds to shifts in landscape position, erosion, and deposition.
The complementarity of ERT and HVSR underscores the value of a multi-method geophysical approach for resolving the structural complexity of lateritic CZs. Our conceptual model demonstrates how weathering, erosion, and colluvial processes shape the structure of a deeply weathered hillslope, while also providing a transferable framework for characterizing saline, regolith-dominated systems. Given their depth, age, and capacity to preserve past climatic and tectonic conditions, lateritic CZs offer a vital opportunity to enhance global understanding of long-term CZ evolution. This research addresses the Northern Hemisphere bias in CZ science, highlights the underexplored role of stable, deeply weathered landscapes, and underscores the need for future comparative studies to understand the drivers of heterogeneity in subsurface architecture across CZs worldwide.
How to cite: Weller, J., Jakica, S., Thompson, S., and Leopold, M.: Combining electrical resistivity tomography and passive seismic to characterise the subsurface architecture of a deeply weathered lateritic hill within the Avon River Critical Zone Observatory, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1401, https://doi.org/10.5194/egusphere-egu25-1401, 2025.
The Himalayan region is crucial for providing water resources to millions of people in downstream regions across Asia. However, the processes governing groundwater storage and flow in steep mountain catchments remain poorly understood, particularly regarding the interplay between monsoonal rainfall, infiltration, and groundwater recharge in these highly dynamic landscapes. This study investigates the Kahule Khola watershed in central Nepal, combining field-based approaches encompassing Electrical Resistivity Tomography (ERT), infiltration measurements, and hydrogeochemical analyses, to investigate the pathways and storage mechanisms of groundwater across pre-, during, and post-monsoon seasons. Our findings highlight the critical role of a laterally extensive weathering layer, 10–25 m thick, in regulating hydrological processes. The weathering layer exhibits high infiltration capacities (<24.1 cm/h) that exceed even intense monsoonal rainfall rates (<162.8 cm/h), allowing surface water to rapidly penetrate the subsurface and replenish groundwater stores. The 2D ERT profiles reveal seasonal variations in the saturation of this layer, with significant vertical and lateral flow dynamics linking it to deeper fractured bedrock aquifers. Hydrogeochemical analyses of spring water further demonstrate a bi-compartmentalized flow regimes, where fast and shallow pathways dominate during the monsoon, while slower and long-term storage within the fractured bedrock sustains perennial spring discharge and stream baseflow throughout the dry season. This study enhances our understanding of the hydrological functioning of steep mountain landscapes, emphasizing the dual role of the weathering layer as both a temporary water reservoir and a conduit for deeper aquifer recharge, demonstrating heightened efficiency during monsoon season. By proposing a conceptual model of water transfer and storage in Himalayan catchments, this research provides critical insights into groundwater processes that are fundamental for sustainable water resource management under increasing pressures from climate variability and tectonic activity.
How to cite: Teagai, K., Armitage, J.-J., Hovius, N., Agélas, L., Fuji, N., Illien, L., Adhikari, B. R., and Andermann, C.: Groundwater dynamics in a steep Himalayan catchment: the role of a widespread weathering layer in water storage and transfer, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14421, https://doi.org/10.5194/egusphere-egu25-14421, 2025.
Daily fluctuations in shallow groundwater levels provide valuable insights into hydro-ecological dynamics and aquifer hydraulic properties. These fluctuations usually depend on hydrological/hydrogeological processes, such as precipitation, evaporation, snow/ice melting/thawing, as well as soil characteristics that influence aquifer response times. The Salar del Huasco basin (20.2°S, 68.8°W; 4,164 m a.s.l.; 1,470 km2) is an endorheic system located in the arid Chilean Altiplano, hosting wetlands and a saline lagoon that sustain part of the region essential biodiversity such as chilean, andean, parina and chica’s flamingos, and it serves as a refuge for migratory birds (e.g., peregrine falcon, golden plover and baird's sandpiper). The area experiences extreme thermal oscillations (4–14°C daily averages; winter lows of -20°C), high potential evaporation (1,200 mm/year), and variable summer precipitation (11–400 mm/year). To explore shallow groundwater dynamics, we monitored for ~1 year two sites near the basin’s salt flat: the north and the south sites. Meteorological, soil, and groundwater levels data were collected at 30-min intervals. At the northern site, daily groundwater level fluctuations ranged from 6 to 45 mm, with a sharp and abrupt 300 mm rise in austral spring. In contrast, the southern site showed daily groundwater level fluctuations between 7 and 58 mm, with multiple rises during winter, ranging from 100 to 300 mm. Distinct patterns emerged at these sites: in the northern site, the maximum diurnal fluctuations correlated with solar radiation, while the southern site showed a more stable behavior, with no clear daily peaks. We applied a water balance to determine how the amplitude of possible input and output fluxes in the system altered the daily level fluctuations, and whether, despite the proximity of both sites (~9 km), soil texture, vegetation cover, and local meteorological-hydrogeological conditions explain the differences in groundwater level behavior.
How to cite: Peña-Echeverría, A., Contreras, C., Renaud, J., Leray, S., and Suárez, F.: Quantifying hydrogeological drivers influencing daily fluctuations in shallow groundwater levels within an altiplanic pristine catchment in Chile., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10061, https://doi.org/10.5194/egusphere-egu25-10061, 2025.
The Bassée Observatory, located in the heart of the Seine catchment and part of the Zone Atelier Seine network, is an essential research platform for understanding the hydrological processes associated with the strategic challenges of sustainable water resource management. It focuses on the behaviour of the alluvial plain as a complex and anthropised hydrosystem, considering its long-term geohistorical evolution. Through an extensive network of surface water and groundwater monitoring stations, the observatory highlights the central role of groundwater and its interactions with surface water in the current dynamics of this region. We introduce the new groundwater model of the Bassée, developed as a tool combining the CaWaQS hydrogeological platform with the groundwater utilities of the PEST parameter estimation approach. This integration improves the representation of the heterogeneity of the alluvial plain and provides a solid basis for quantitative decision making. The model is designed to assist stakeholders in addressing the challenges of operating and conserving the alluvial plain in the context of a changing environment.
How to cite: Jost, A., Saias, C., and Renaud, A.: Groundwater modelling in the Bassée alluvial plain: A tool for understanding the dynamics of a complex socio-hydrosystem, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9355, https://doi.org/10.5194/egusphere-egu25-9355, 2025.
With a changing climate, major flood events are an increasing risk in many parts of the world, including temperate zones in Western Europe. Recent examples of destructive flooding in central European upland catchments, such as the 2021 Eifel floods in western Germany, highlight the importance of improving our understanding of the mechanisms behind stream response and sediment transport to precipitation events in upland catchments in temperate Western-Europe. The HIdden water and LANDscape ERosion (HILANDER) project that started in spring 2024 has two major goals: 1. To put in place an observatory in the Ahr catchment to characterize how water travels through the critical zone. 2. To incorporate surface/groundwater interactions in models of landscape evolution and river erosion.
The Ahr valley, ranging from 50m to 737m of elevation, is characterized by gently sloped hilltops and a steep, incised river valley. Preliminary recession analyses of the Ahr catchment, performed on data from four existing hydrographs, show a faster flowing aquifer in the upper parts of the catchment and a slow flowing aquifer in the lower regions. This implies that the upper parts of the catchment may be dominated by sub-surface flow through a more permeable shallow layer whereas the streamflow in lower reaches of the catchment is dominated by the deeper underlying aquifer. Two sub-catchments of the upper Ahr river, the Michelsbach, mainly forested and the Huhnenbach, largely agricultural with engineered drainage systems were chosen as study sites. The catchments are instrumented with pressure sensors, turbidimeters and seismometers, to continuously measure streamflow, suspended sediment concentrations, bedload transport and groundwater saturation. Furthermore, springs have been mapped and sampled for stable isotopes, dating and major elements.
Springs are found at both high and low elevations within both sub-catchments, and the locations of these springs do not vary from summer to winter. Observations from the summer spring mapping campaign of June 2024 found that the age of spring-water at high elevation is a mix of young water (ages of 2 to 3 years) and old water (age of 16 years). The presence of both young and old components in the spring water implies multiple pathways for groundwater within the catchment. In January 2025 we found that the ridge tops were saturated with substantial ponding of surface water. Down slope there was either diffuse release of this water or point release at the same locations of springs that were mapped and sampled in the summer. This, along with higher winter oxygen saturation in the springs, points to the potential for interflow during high rainfall events, where water flows laterally through the shallow soil and rock moisture layers (weathering zone) mixing with the groundwater supply. The future continuous monitoring in this critical zone observatory will give insight to the interplay between lateral water pathways in the weathering zone, and deep groundwater reservoirs allowing for a better understanding of how water flow through the catchments can impact erosion and landscape evolution.
How to cite: Abadie, B., Fracica, L., Andermann, C., Hovius, N., Dietze, M., and Armitage, J.: Understanding surface - groundwater interactions in central European upland catchments: the Ahr valley, Germany, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17724, https://doi.org/10.5194/egusphere-egu25-17724, 2025.
Quantifying the water and heat fluxes at the interface between surface water (SW) and groundwater (GW) is a key issue for hydrogeologists to consider for safe yield and good water quality. However, such quantification with field measurements is not straightforward because the SW-GW changes depend on the boundary conditions and the spatial description of the hydrofacies, which aren't well known and are usually guessed by calibrating models using standard data like hydraulic heads and river discharge. We provide a methodology to build stronger constraints to the numerical simulation and the hydrodynamic and thermal parameter calibration, both in space and time, by using a multi-method approach. Our method, applied to the Orgeval Critical Zone Observatory (France), estimates both water flow and heat fluxes through the SW-GW interface using long-term hydrological data, time-lapse seismic data, and modeling tools. We show how a thorough interpretation of high-resolution geophysical images, combined with geotechnical data, provides a detailed distribution of hydrofacies, valuable prior information about the associated hydrodynamic property distribution. The temporal dynamic of the WT table can be captured with high-resolution time-lapse seismic acquisitions. Each seismic snapshot is then thoroughly inverted to image spatial WT variations. The long-term hydrogeological data (such as hydraulic head and temperature) and this prior geophysical information are then used to set the parameters for the hydrogeological modeling domain. The use of the WT geometry and temperature data improves the estimation of transient stream-aquifer exchanges. Future developments to achieve the fully coupling of the hydrogeophysical model will be presented.
How to cite: Rivière, A., Bodet, L., Gautier, M., Gesret, A., Martin, R., Pasquet, S., Radic, N., Cunha Teixeira, J., Dangeard, M., and Renard, D.: Integrating Data into the Hydrogeophysical Model: A Case Study of the Orgeval Critical Zone Observatory, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20210, https://doi.org/10.5194/egusphere-egu25-20210, 2025.
Posters virtual: Mon, 28 Apr, 14:00–15:45 | vPoster spot A
EGU25-5314 | ECS | Posters virtual | VPS8
Seismicity and Groundwater Dynamics: Impacts on the Critical Zone in spring of center MexicoMon, 28 Apr, 14:00–15:45 (CEST) | vPA.16
The relationship between groundwater and seismicity has been documented in various regions worldwide. Mexico is no exception to this phenomenon. On September 19, 2017, a magnitude 7.1 earthquake struck between the states of Puebla and Morelos, as reported by the National Seismological Service.
Approximately 50 km from the epicenter, the Agua Hedionda spring exhibited significant physical and chemical changes as a result of the earthquake. These changes highlight the dynamic interactions within the critical zone—the near-surface environment where rock, soil, water, air, and living organisms interact to shape the Earth's surface. The spring's discharge showed notable alterations, including a decrease in flow rate, reductions in major ion concentrations, and shifts in its isotopic composition, providing clear evidence of the connection between regional seismicity and the quality and availability of groundwater.
The analysis of changes in the spring's groundwater over time revealed its vulnerability to losing essential properties, either temporarily or permanently. Hydrochemical and volumetric flow rate data indicated that the spring underwent noticeable changes even before the earthquake. While the water chemistry showed gradual recovery by 2022, the flow rate only returned to approximately 25% of its pre-earthquake level.
In a country like Mexico, where groundwater is essential for numerous activities and where the interaction of five tectonic plates creates a dynamic seismic environment, studying the interplay between seismicity, groundwater, and processes within the critical zone is crucial for understanding and managing water resources sustainably.
How to cite: Sierra Garcia, B. A., Escolero, O., Olea Olea, S., and Medina Ortega, P.: Seismicity and Groundwater Dynamics: Impacts on the Critical Zone in spring of center Mexico, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5314, https://doi.org/10.5194/egusphere-egu25-5314, 2025.
