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This study investigates the influence of topography on the desaturation rates of groundwater-dependent wetlands in response to changes in recharge. We examined sixty catchments across northern Chile, which feature a wide variety of landforms. We categorized the landforms using geomorphon descriptors, identifying three distinct clusters: lowland, transition, and mountain settings. Using steady-state 3D groundwater models, we derived flow partitioning and seepage area extent for each catchment. Each cluster revealed consistent seepage areas evolution under varying wet-to-dry conditions. Our findings indicate that mountains exhibit reduced seepage area compared to lowlands at equivalent hydraulic conductivity to recharge (K/R) ratios but are less sensitive to recharge fluctuations with slower rates of seepage area variation. Statistical evidence demonstrates that geomorphons-defined landforms correlate with desaturation indicators, enabling the prediction of catchment sensitivity to climate change based solely on a topographic analysis. [ABSTRACT FROM AUTHOR]

Streamflow generation and biochemical hotspots are significantly influenced by groundwater contributions distributed along the drainage network. However, identifying the geomorphic landscape features that drive groundwater‐surface water interactions remains challenging. In this study, we investigate the role of knickpoints in controlling these interactions in a mountainous stream in Switzerland. We employ a combination of synoptic sampling of environmental tracers, endmember mixing calculations, and groundwater flow simulations. Our findings reveal substantial groundwater seepage concentrated near the knickpoint of the main river stem. Using parsimonious groundwater flow modeling, we validate the hypothesis that the topographical shape of the knickpoint enhances local groundwater discharge rates. We quantify that approximately 20% of the total catchment streamflow originates from around the knickpoint. These results indicate that knickpoints are significant hotspots for groundwater seepage and physicochemical mixing, providing a clear method for identifying major localized sources of streamflow generation. Plain Language Summary: In ice‐free catchments, groundwater is the main water source maintaining streamflow during extended dry periods. In addition to its importance for water resources, locations where groundwater contributes to surface stream water are important hotspots where interactions between biological and chemical processes occur, that have major implications for aquatic ecosystems. However, those hotspots remain difficult to identify. Specifically, our understanding on the relationships between landscape and groundwater discharge in streams remains limited. In our study of a Swiss Alpine catchment, we sampled a stream for water chemical analysis and used statistical and numerical models to find where groundwater emerges into the stream. We discovered that most groundwater enters the stream around a "knickpoint", a location where the stream profile becomes steeper. According to our calculations, this knickpoint, although of minimal extent, contributed one fifth of the total streamflow in the catchment. Although our results are site‐specific, knickpoints are ubiquitous in mountain areas, thus they might be important when predicting water availability and biogeochemical fluxes at regional scale. Key Points: We highlight the sporadic nature of groundwater seepage hotspots along a river profileKnickpoints influence groundwater flow patterns, creating preferential mixing zones between groundwater and surface watersBiogeochemical hotspots are influenced by knickpoints in mountainous hydrographic network [ABSTRACT FROM AUTHOR]

Non‐perennial streams play a crucial role in ecological communities and the hydrological cycle. However, the key parameters and processes involved in stream intermittency remain poorly understood. While climatic conditions, geology and land use are well identified, the assessment and modelling of groundwater controls on streamflow intermittence remain a challenge. In this study, we explore new opportunities to calibrate process‐based 3D groundwater flow models designed to simulate hydrographic network dynamics in groundwater‐fed headwaters. Streamflow measurements and stream network maps are considered together to constrain the effective hydraulic properties of the aquifer in hydrogeological models. The simulations were then validated using visual observations of water presence/absence, provided by a national monitoring network in France (ONDE). We tested the methodology on two pilot unconfined shallow crystalline aquifer catchments, the Canut and Nançon catchments (Brittany, France). We found that both streamflow and stream network expansion/contraction dynamics are required to calibrate models that simultaneously estimate hydraulic conductivity K$$ K $$ and porosity Φ$$ \varPhi $$ with low uncertainties. The calibration allowed good prediction of stream intermittency, both in terms of flow and spatial extent. For the two catchments studied, Canut and Nançon, the hydraulic conductivity is close reaching 1.5 × 10−5 m/s and 4.5 × 10−5 m/s, respectively. However, they differ more in their storage capacity, with porosity estimated at 0.1% and 2.2%, respectively. Lower storage capacity leads to higher groundwater level fluctuations, shorter aquifer response times, an increase in the proportion of intermittent streams and a reduction in perennial flow. This new modelling framework for predicting headwater streamflow intermittence can be deployed to improve our understanding of groundwater controls in different geomorphological, geological and climatic contexts. It will benefit from advances in remote sensing and crowdsourcing approaches that generate new observational data products with high spatial and temporal resolution. [ABSTRACT FROM AUTHOR]

The sealing characteristics of the geological formation located above a CO2 storage reservoir, the so-called caprock, are essential to ensure efficient geological carbon storage. If CO2 were to leak through the caprock, temporal changes in fluid geochemistry can reveal fundamental information on migration mechanisms and induced fluid–rock interactions. Here, we present the results from a unique in-situ injection experiment, where CO2-enriched fluid was continuously injected in a faulted caprock analogue. Our results show that the CO2 migration follows complex pathways within the fault structure. The joint analysis of noble gases, ion concentrations and carbon isotopes allow us to quantify mixing between injected CO2-enriched fluid and resident formation water and to describe the temporal evolution of water–rock interaction processes. The results presented here are a crucial complement to the geophysical monitoring at the fracture scale highlighting a unique migration of CO2 in fault zones. [ABSTRACT FROM AUTHOR]

The assessment of effective hydraulic properties at the catchment scale, i.e., hydraulic conductivity (K) and transmissivity (T), is particularly challenging due to the sparse availability of hydrological monitoring systems through stream gauges and boreholes. To overcome this challenge, we propose a calibration methodology which only considers information from a digital elevation model (DEM) and the spatial distribution of the stream network. The methodology is built on the assumption that the groundwater system is the main driver controlling the stream density and extension, where the perennial stream network reflects the intersection of the groundwater table with the topography. Indeed, the groundwater seepage at the surface is primarily controlled by the topography, the aquifer thickness and the dimensionless parameter K/R , where R is the average recharge rate. Here, we use a process-based and parsimonious 3D groundwater flow model to calibrate K/R by minimizing the relative distances between the observed and the simulated stream network generated from groundwater seepage zones. By deploying the methodology in 24 selected headwater catchments located in northwestern France, we demonstrate that the method successfully predicts the stream network extent for 80 % of the cases. Results show a high sensitivity of K/R to the extension of the low-order streams and limited impacts of the DEM resolution as long the DEM remains consistent with the stream network observations. By assuming an average recharge rate, we found that effective K values vary between 1.0×10-5 and 1.1×10-4 m s -1 , in agreement with local estimates derived from hydraulic tests and independent calibrated groundwater model. With the emergence of global remote-sensing databases compiling information on high-resolution DEM and stream networks, this approach provides new opportunities to assess hydraulic properties of unconfined aquifers in ungauged basins. [ABSTRACT FROM AUTHOR]

We used numerical modelling to explore the role of the vertical compartmentalization of hillslopes on groundwater flow and recession discharge. We found that, when hydraulic properties are vertically compartmentalized, streamflow recession behaviour may strongly deviate from what is predicted by groundwater theory that considers the drainage of shallow reservoirs with homogeneous properties. We further identified the hillslope configurations for which the homogeneous theory derived from the Boussinesq solution approximately holds and, conversely, for those for which it does not. By comparing the modelled recession discharge Q and the groundwater table dynamics, we identified the critical hydrogeological conditions controlling the emergence of strong deviations. The three main controls are (i) the contribution of a deep aquifer connected to the stream, (ii) the heterogeneity in hydraulic properties, and (iii) the slope of the interface between a shallow permeable compartment and deep bedrock one with lower hydraulic properties. Our results confirm that a correct physical interpretation of the recession discharge exponent b from the classical equation -dQ/dt=aQb , and its temporal progression, requires knowledge of the structural configuration and heterogeneity of the aquifer. [ABSTRACT FROM AUTHOR]

To supplement the use of hydraulic tests and assess catchment-scale hydraulic conductivity (K), we propose a methodology for shallow aquifers only based on the Digital Elevation Model (DEM) and on the observation of the stream network. The methodology requires the groundwater system to be a main determinant of the stream density and extension. It assumes that the perennial stream network is set by the intersection of the groundwater table with the topography. The topographical structures and the subsurface hydraulic conductivity divided by the recharge rate K/R determine the groundwater table depth and the development of the stream network. Using a parsimonious 3D groundwater flow model, we calibrate K/R by minimizing newly defined distances between the simulated groundwater seepage zones and the observed stream network. Deployed on 24 selected headwater catchments from 12 to 141 km² located in north-western France, the method successfully matches the stream network in 80% of the cases and provides catchment-scale hydraulic conductivities between 9 x 10-6 and 9 x 10-5 m s-1 for shallow aquifers sedimentary and crystalline rocks. Results show a high sensitivity of K to the density and extension of the low-order streams and limited impacts of the DEM resolution as long the DEM remains consistent with the stream network observations. With the emergence of global remote-sensing databases combining information of highresolution DEM and stream network, this approach will contribute to assess hydraulic properties of in shallow headwater aquifers. [ABSTRACT FROM AUTHOR]

Rock slope failures often result from progressive rock mass damage which accumulates over long timescales. In deglaciating environments, rock slopes are affected by stress perturbations driven by mechanical unloading due to ice downwasting and concurrent changes in thermal and hydraulic boundary conditions. Since in‐situ data are rare, the different processes and their relative contribution to slope damage remain poorly understood. Here, we analyze borehole monitoring data from a rock slope adjacent to the retreating Great Aletsch Glacier (Switzerland) and compare it to englacial water levels, climate data, and decreasing ice levels. Rock slope pore pressures show a seasonal signal controlled by infiltration events as well as effects from the connectivity to the englacial hydrological system. We find that reversible and irreversible strains are driven by: (a) hydromechanical effects caused by englacial pressure fluctuations and infiltration events, (b) stress transfer related to changing mechanical glacial loads from short‐term englacial water level fluctuations and longer term ice downwasting, and (c) thermomechanical effects from annual temperature cycles penetrating the shallow subsurface, which primarily result in reversible deformation. We relate most observed irreversible strain (damage) to mechanical unloading from ice downwasting. Damage is strongest directly at the ice margin and moves through the slope at the pace of glacial retreat and advance. Locations with many retreat/advance cycles are very sensitive to landslide formation. The current climate warming impacts very sensitive valley sectors, which is confirmed by landslide distributions and activity in the study area. Plain Language Summary: The formation of rock slope instabilities is a long‐term process related to continuous rock mass weakening. For rock slopes in glaciated valleys, increased rates of rock mass damage are assumed to occur during ice retreat due to a reduction of the glacier weight and concurrent changes in rock temperatures and slope groundwater pressures. However, because direct field measurements are missing, governing processes and their relative importance are still poorly understood. Here, we analyze borehole monitoring data and compare it to englacial water levels, climate data, and decreasing ice levels. We find that the glacial hydrology influences the dynamics of the groundwater pressures in the adjacent rock slope at various timescales. We record micrometer‐scale reversible (elastic) deformation and irreversible rock mass damage and identify the involved drivers. Several processes contribute to progressive rock mass weakening at different timescales and magnitudes, but most damage is related to mechanical unloading from ice downwasting and is strongest directly at the ice margin. Locations with many retreat/advance cycles are sensitive to increased damage accumulation and landslide formation. The current climate warming impacts very sensitive valley sectors, which is confirmed by landslide distributions and activity in the study area. Key Points: We monitored subsurface pore pressures and micrometer scale strain in a rock slope during strong glacial retreat caused by climate warmingWe identified thermo‐hydro‐mechanical drivers for reversible deformation and irreversible rock mass damage acting at various timescalesSlope damage intensity can be related to landslide spatial and temporal distribution [ABSTRACT FROM AUTHOR]

We used numerical modelling to explore the role of vertical compartmentalization of hillslopes on groundwater flow and recession discharge. We found that when hydraulic properties are vertically compartmentalized, streamflow recession behaviour may strongly deviate from what is predicted by groundwater theory that considers the drainage of shallow reservoirs with homogeneous properties. We further identified the hillslope configurations for which the homogeneous theory derived from the Boussinesq solution approximately hold and conversely for which it fails. By comparing the modelled recession discharge and the groundwater table dynamics, we identified the critical hydrogeological conditions responsible for the emergence of strong deviations. The three main controls are i) the contribution of a deep aquifer connected to the stream, ii) the heterogeneity in hydraulic properties, and iii) the slope of the interface between shallow permeable compartment and deep bedrock one with lower hydraulic properties. Our results confirm that a physical interpretation of the recession discharge exponent b from the classical equation -dQ/dt = aQb, and its temporal progression, are information that can only be interpreted with knowledge on structural configuration and heterogeneity of the aquifer. [ABSTRACT FROM AUTHOR]

We investigated how geomorphological structures shape Transit Time Distributions (TTDs) in shallow aquifers. Extensive three‐dimensional simulations were performed to determine the TTDs for synthetic convergent, straight, and divergent hillslopes with a constant slope. The uniform recharge applied on top of the aquifer is transferred to the receiving stream through steady‐state groundwater flows, return flows and saturation excess overland flows. Without seepage, TTDs evolve from uniform‐ to power law‐like‐ distributions depending on the average distance of the groundwater volume to the river (barycenter). Remarkably, the coefficient of variation (ratio of the standard deviation to the mean) of the TTDs scales linearly with the barycenter in agreement with a theoretical prediction based on three analytical approximations derived for specific cases. With seepage, the TTD has three separate modes corresponding to rapid saturation excess overland flows, to the intermediate flow paths ending in seepage area and to the slower flow paths going all the way to a discharge in the river. The coefficient of variation additionally depends on the extent of the seepage area. For a natural hillslope in the crystalline basement of Normandy (France), the same synthetic analysis demonstrates that the coefficient of variation is not only determined by the extent of the seepage zone but also by its structure in relation to the local and global geomorphological organization. The results suggest the possibility to assess the variability of transit times by combining geomorphological analysis, surface soil saturation observations and environmental tracers. Key Points: Transit times are determined by integrated features of groundwater and seepage distribution in constant slope convergent/divergent hillslopeThe coefficient of variation of the transit time distribution scales linearly with the mean distance of the groundwater volume to the riverThe extent and structure of seepage modify the groundwater outlet and impact the distribution of transit time and increase its variability [ABSTRACT FROM AUTHOR]

The success of geological carbon storage depends on the assurance of permanent containment for injected carbon dioxide (CO 2) in the storage formation at depth. One of the critical elements of the safekeeping of CO 2 is the sealing capacity of the caprock overlying the storage formation despite faults and/or fractures, which may occur in it. In this work, we present an ongoing injection experiment performed in a fault hosted in clay at the Mont Terri underground rock laboratory (NW Switzerland). The experiment aims to improve our understanding of the main physical and chemical mechanisms controlling (i) the migration of CO 2 through a fault damage zone, (ii) the interaction of the CO 2 with the neighboring intact rock, and (iii) the impact of the injection on the transmissivity in the fault. To this end, we inject CO 2 -saturated saline water in the top of a 3 m thick fault in the Opalinus Clay, a clay formation that is a good analog of common caprock for CO 2 storage at depth. The mobility of the CO 2 within the fault is studied at the decameter scale by using a comprehensive monitoring system. Our experiment aims to close the knowledge gap between laboratory and reservoir scales. Therefore, an important aspect of the experiment is the decameter scale and the prolonged duration of observations over many months. We collect observations and data from a wide range of monitoring systems, such as a seismic network, pressure temperature and electrical conductivity sensors, fiber optics, extensometers, and an in situ mass spectrometer for dissolved gas monitoring. The observations are complemented by laboratory data on collected fluids and rock samples. Here we show the details of the experimental concept and installed instrumentation, as well as the first results of the preliminary characterization. An analysis of borehole logging allows for identifying potential hydraulic transmissive structures within the fault zone. A preliminary analysis of the injection tests helped estimate the transmissivity of such structures within the fault zone and the pressure required to mechanically open such features. The preliminary tests did not record any induced microseismic events. Active seismic tomography enabled sharp imaging the fault zone. [ABSTRACT FROM AUTHOR]

We propose a non-local, meso-scale approach for coupling multiphysics processes across scale. The physics is based on discrete phenomena, triggered by local Thermo-Hydro-Mechano-Chemical (THMC) instabilities, that cause cross-diffusion (quasi-soliton) acceleration waves. These waves nucleate when the overall stress field is incompatible with accelerations from local feedbacks of generalized THMC thermodynamic forces that trigger generalized thermodynamic fluxes of another kind. Cross-diffusion terms in the 4 x 4 THMC diffusion matrix are shown to lead to multiple diffusional P- and S-wave equations as coupled THMC solutions. Uncertainties in the location of meso-scale material instabilities are captured by a wave-scale correlation of probability amplitudes. Cross-diffusional waves have unusual dispersion patterns and, although they assume a solitary state, do not behave like solitons but show complex interactions when they collide. Their characteristic wavenumber and constant speed define mesoscopic internal material time-space relations entirely defined by the coefficients of the coupled THMC reaction-cross-diffusion equations. For extreme conditions, cross-diffusion waves can lead to an energy cascade connecting large and small-scales and cause solid-state turbulence. [ABSTRACT FROM AUTHOR]

Temporal changes in groundwater chemistry can reveal information about the evolution of flow path connectivity during crustal deformation. Here, we report transient helium and argon concentration anomalies monitored during a series of hydraulic reservoir stimulation experiments measured with an in situ gas equilibrium membrane inlet mass spectrometer. Geodetic and seismic analyses revealed that the applied stimulation treatments led to the formation of new fractures (hydraulic fracturing) and the reactivation of natural fractures (hydraulic shearing), both of which remobilized (He, Ar)-enriched fluids trapped in the rock mass. Our results demonstrate that integrating geochemical information with geodetic and seismic data provides critical insights to understanding dynamic changes in fracture network connectivity during reservoir stimulation. The results of this study also shed light on the linkages between fluid migration, rock deformation and seismicity at the decameter scale. [ABSTRACT FROM AUTHOR]

Unexpected interface complexities were found resulting from the miscible displacement of saltwater by a miscible shear-thinning solution (xanthan gum) in a radial Hele-Shaw cell, for both convergent and divergent flow. Such complex patterns have not been described before for either Newtonian or non-Newtonian solutions. A more viscous solution was injected into the cell to displace a less viscous solution (divergent flow) and then withdrawn at the injection site (convergent flow). A variegated mixing fringe between the solutions developed during the injection phase, against the stabilizing viscous effects, which would tend to promote a stable piston-like displacement. This interface geometry is markedly different from what is seen in displacement experiments performed with glycerol under otherwise similar viscosity contrast and flow conditions. The concentration field heterogeneity resulting from the presence of the fringe, quantified using a spatial autocorrelation measure, is mostly controlled by the applied shear rate, or equivalently, by the ratio of the volumetric flow rate to the flow cell's aperture. It is significantly correlated with the radial width of the mixing zone. In addition to producing a large volume of blended solution during the injection phase, the mixing fringe impacted the development of viscous fingers (VFs) during the withdrawal phase. Such VFs are expected due to the viscosity ratio, but the initial roughness of the interface from which they develop and, hence, their later dynamics are controlled by the geometry of the mixing fringe at the end of the injection. We characterize the dynamics as a function of the imposed flow rate and cell thickness. The observed complexities of miscible displacement involving shear-thinning solutions have implications for subsurface engineering applications such as oil recovery and groundwater remediation. We explore the geometry of injection of shear-thinning fluid into a water-filled cavity. Concentration maps for two xanthan gum injection/withdrawal experiments with apertures of 2.54 mm (A and B) and 0.762 mm (C and D) show that in narrow fissures, the displacement of water has a ragged interface, which was not expected. This irregular interface gave rise to radically different withdrawal geometries (right frames). These results suggest that the use of such fluids for chasing hydrocarbons, or for testing aquifer properties, will not follow standard theories which take displacement of less viscous fluids by more viscous fluids to have stable interfaces. [ABSTRACT FROM AUTHOR]

Recession analysis is a classical method in hydrology to assess watersheds' hydrological properties by means of the receding limb of a hydrograph, frequently expressed as the rate of change in discharge (-dQ/dt) against discharge (Q). This relationship is often assumed to take the form of a power law -dQ/dt=aQb , where a and b are recession parameters. Recent studies have highlighted major differences in the estimation of the recession parameters depending on the method, casting doubt on our ability to properly evaluate and compare hydrological properties across watersheds based on recession analysis of -dQ/dt vs. Q. This study shows that estimation based on collective recessions as an average watershed response is strongly affected by the distributions of event inter-arrival time, magnitudes, and antecedent conditions, implying that the resulting recession parameters do not represent watershed properties as much as they represent the climate. The main outcome from this work highlights that proper evaluation of watershed properties is only ensured by considering independent individual recession events. While average properties can be assessed by considering the average (or median) values of a and b , their variabilities provide critical insight into the sensitivity of a watershed to the initial conditions involved prior to each recharge event. [ABSTRACT FROM AUTHOR]

Recession analysis is a classical method employed in hydrology to assess watersheds’ hydrological properties by means of the receding limb of a hydrograph, frequently expressed as the rate of change in discharge (dQ/dt) against discharge (Q). This relationship is often assumed to take the form of a power law −dQ/dt = aQb where a and b are recession parameters. Recent studies have highlighted major differences in the estimation of the recession parameters depending on the method, casting doubt on our ability to properly evaluate and compare hydrological properties across watersheds based on recession analysis. This study shows that estimation based on collective recessions as an average watershed response is strongly affected by the distributions event inter-arrival time, magnitudes, and antecedent conditions, implying that the resulting recession parameters do not represent watershed properties as much as they represent the climate. The clear conclusion is that proper evaluation of watershed properties using recession analysis requires considering individual recession events. [ABSTRACT FROM AUTHOR]

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Liang et al. (2017) presented an analysis of the impacts of unsaturated zone processes on streamflow recession using methodology from Brutsaert and Nieber (1977) with a constant time step in computation of the time derivative of flow. Over the past 10 years, many authors have demonstrated that this method may produce artifacts that lead to incorrect interpretations. To demonstrate the impact of the choice of analysis methods, this comment presents an estimation of recession parameters using the Liang et al. (2017) discharge data that eliminates artifacts introduced through the constant time step. Here we use the exponential time step method, which revealed recession coefficient b greater than 1 which is inconsistent with the fitting framework used in Liang et al. (2017). [ABSTRACT FROM AUTHOR]

This study deals with the effects of hydrodynamic functioning of hard-rock aquifers on microbial communities. In hard-rock aquifers, the heterogeneous hydrologic circulation strongly constrains groundwater residence time, hydrochemistry, and nutrient supply. Here, residence time and a wide range of environmental factors were used to test the influence of groundwater circulation on active microbial community composition, assessed by high throughput sequencing of 16S rRNA. Groundwater of different ages was sampled along hydrogeologic paths or loops, in three contrasting hardrock aquifers in Brittany (France). Microbial community composition was driven by groundwater residence time and hydrogeologic loop position. In recent groundwater, in the upper section of the aquifers or in their recharge zone, surface water inputs caused high nitrate concentration and the predominance of putative denitrifiers. Although denitrification does not seem to fully decrease nitrate concentrations due to low dissolved organic carbon concentrations, nitrate input has a major effect on microbial communities. The occurrence of taxa possibly associated with the application of organic fertilizers was also noticed. In ancient isolated groundwater, an ecosystem based on Fe(II)/Fe(III) and S/SO4 redox cycling was observed down to several 100 of meters below the surface. In this depth section, microbial communities were dominated by iron oxidizing bacteria belonging to Gallionellaceae. The latter were associated to old groundwater with high Fe concentrations mixed to a small but not null percentage of recent groundwater inducing oxygen concentrations below 2.5 mg/L. These two types of microbial community were observed in the three sites, independently of site geology and aquifer geometry, indicating hydrogeologic circulation exercises a major control on microbial communities. [ABSTRACT FROM AUTHOR]

Climate change is thought to have major effects on groundwater resources. There is however a limited knowledge of the impacts of past climate changes such as warm or glacial periods on groundwater although marine or glacial fluids may have circulated in basements during these periods. Geochemical investigations of groundwater at shallow depth (80-400 m) in the Armorican basement (western France) revealed three major phases of evolution: (1) Mio-Pliocene transgressions led to marine water introduction in the whole rock porosity through density and then diffusion processes, (2) intensive and rapid recharge after the glacial maximum down to several hundred meters depths, (3) a present-day regime of groundwater circulation limited to shallow depth. This work identifies important constraints regarding the mechanisms responsible for both marine and glacial fluid migrations and their preservation within a basement. It defines the first clear time scales of these processes and thus provides a unique case for understanding the effects of climate changes on hydrogeology in basements. It reveals that glacial water is supplied in significant amounts to deep aquifers even in permafrosted zones. It also emphasizes the vulnerability of modern groundwater hydrosystems to climate change as groundwater active aquifers is restricted to shallow depths. [ABSTRACT FROM AUTHOR]