Displays

Groundwater is of fundamental importance to strategies for poverty reduction in tropical Africa and understanding the sustainability of more widespread groundwater abstraction for improving water and food provision is a key challenge. However, the hydraulic processes governing groundwater recharge that sustain this resource, and their sensitivity to climatic variability and change, are poorly constrained. Here we present results from The Chronicles Consortium initiative, which has collated multi-decadal groundwater hydrographs and co-located rainfall records across tropical Africa to better understand climate controls, among others, on groundwater recharge.

We find that recharge in more arid environments is generally highly dependent on infrequent large rainfall events causing focused recharge through losses during ephemeral overland flows. This process is not included in any large scale hydrological or land surface models, and these events are often driven by synoptic climate controls, which are themselves poorly constrained in existing climate models. In more humid locations, we find surprisingly linear relationships between rainfall and recharge indicating an apparent lack of threshold behaviour that is embodied in most hydrological models and hypothesise this is due to prevalence of preferential flow processes in the soil zone. While aridity exerts a strong control on the predominant recharge process, geological variations can dominate the observed sensitivity of recharge to climate variability.

Our results reveal the critical importance of long-term observational records for understanding the sensitivity of recharge to climate processes with implications well beyond Africa. This especially true in dryland environments where interpretations of short records would miss fundamental, episodic climate-controls on recharge expressed in longer records. We conclude that without a sound long-term observational basis for groundwater-climate sensitivity, climate change forecasts cannot be confidently constrained.

How to cite: Cuthbert, M. and Taylor, R.: The critical importance of multi-decadal groundwater level observations for informing robust climate change impact assessments: lessons from sub-Saharan Africa, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1490, https://doi.org/10.5194/egusphere-egu2020-1490, 2020.

Billions of people rely on groundwater that is an accessible source for drinking water and irrigation especially in times of drought. This importance will likely increase with a changing climate. It is still unclear, however, to what extent climate change will globally impact groundwater systems and thus the availability of this important resource. Groundwater recharge is a central indicator for groundwater availability but projections vary. In this talk we will present global-scale results of a multi-model ensemble approach incorporating eight global hydrological models and four global circulation models to show the impact of global warming (GW) on global groundwater recharge. Preindustrial and current (at 1 °C GW) groundwater recharge is compared with recharge for different GW levels as a result of different representative concentration pathways (RCPs). Results suggest that the uncertainty range is large and predictions with confidence can be only made for specific regions worldwide. Furthermore, because most hydrological models do not include CO₂ driven vegetation processes we investigate how including the effect of changing CO₂ into the calculation of future groundwater recharge impacts the results. In some regions, inclusion of these processes leads to differences in groundwater recharge changes of up to 100 mm/yr in case of 3 °C GW.

How to cite: Reinecke, R., Müller Schmied, H., and Döll, P.: Changes of groundwater recharge at different global warming levels: A global-scale multi-model ensemble approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2189, https://doi.org/10.5194/egusphere-egu2020-2189, 2020.

The vulnerability of the Alsatian aquifer to climate change and water abstraction has hardly been investigated whilst climate change impacts such as decreasing snowfall, droughts and heat waves are becoming stronger and water abstraction for irrigation is seasonally intensifying as a result. Despite being influenced by a European temperate climate, seasonal drying up of groundwater-fed streams has been recently observed in the region of the Grand Ried of the Middle Alsatian Plain and drought decrees in Alsace have intensified. The Alsatian aquifer, an alluvial aquifer located on the French side of the Upper Rhine, belongs to one of the largest aquifers in Europe. It not only provides drinking water to approximately 1.5 million inhabitants but is also a highly important water supply for industry and agriculture. This study aims to improve our understanding of the interactions between groundwater levels of the Alsatian aquifer and river discharge during drought periods. Lying within the Upper Rhine Graben, this complex basin is flanked by the Vosges and Black Forest mountains to the West and East respectively. As such, the aquifer is influenced by both the River Rhine, its main tributaries and the Vosges mountains. At present, it is difficult to differentiate climate and anthropogenic signals in groundwater level lowering during the summer. In this study, spatial and temporal correlations of river discharge and groundwater levels were analysed based on meteorological and hydrological data available since 1955 from national and regional agencies and will form the base for hydrogeological modelling in the next phase. High resolution field data enables to capture complex interactions and for this purpose an intensive interdisciplinary field study was carried out in the summer. Water levels of 7 groundwater-fed streams, including 3 springs, were recorded automatically at hourly time steps and accompanied by manual measurements of temperature, dissolved oxygen and turbidity as well as biological observations. Streams show subdaily water level variations mainly due to evapotranspiration and water withdrawals for irrigation. Even though irrigation represents on average only 18.5% of annual groundwater abstraction in the Alsace region over a territory that is 50% agricultural, water withdrawals are concentrated over a few months in summer and their impacts are visible. Climate change has decreased snow storage and snow water equivalent as well as increased periods without precipitation and thereby increased evapotranspiration over the last decades. The challenge is to determine whether irrigation effects are stronger than evapotranspiration which would imply that water abstraction impact could outweigh that of climate change during summer droughts. Because they can affect the sustainability of drinking water supply, biodiversity and economic activities, awareness on droughts impacts and water abstraction should be increased.

How to cite: Labarchède, A., de Jong, C., Giuglaris, É., and Dumont, S.: Resilience of the Alsatian aquifer, France to climate and anthropogenic change: A case study of the Grand Ried, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1178, https://doi.org/10.5194/egusphere-egu2020-1178, 2020.

Nossana represents an important pre-Alpine karst spring located in Lombardy Region (Northern Italy). It is used for drinking supply and it sustains a water distribution system serving 300,000 people, including the city of Bergamo. The objective of this study was to project Nossana discharges, to evaluate potential supply limits for four future periods (2021-2040, 2041-2060, 2061-2080, 2081-2100). The study was carried out following a four-step approach. First, the EURO-CORDEX bias-corrected Regional Climate Models (RCMs) available for all the emission scenarios (RCP2.6, RCP4.5, RCP8.5) were evaluated in terms of precipitation and temperature monthly climatology. Second, they were statistically downscaled by means of change factors and a stochastic weather generator. Third, a rainfall-runoff model ensemble accounting also for snow dynamics (GR4J with CemaNeige module) was calibrated and validated on historical time series (1998-2017). Finally, the future downscaled time series were used as input in the calibrated model and the projected discharges evaluated in terms of low flow. In detail, two warning discharge thresholds - one for high water demand periods and one for ordinary water demand periods - were recognized with the service company managing the spring (Uniacque S.p.A.). Then, the number of (consecutive) days below them were calculated for each future period and compared to the historical time series. For each emission scenario, the calibrated model ensemble counted three RCMs and ten rainfall-runoff parameterizations. Projected ensemble mean discharges are lower than observations for all future periods and RCPs (from -3% for 2021-2040 and RCP4.5 to -23% for 2081-2100 and RCP8.5), although they do not show a clear trend between the four time periods. Days characterized by discharges lower than the warning thresholds are projected to decrease except for the RCP8.5 emission scenarios and the period 2081-2100 (14% increase for the ordinary-demand threshold, 10% increase for the high-demand threshold). Conversely, consecutive days are expected to increase between 2061 and 2100 for all emission scenarios and the two thresholds (by 0% and 26% for RCP 2.6, by 8% and 15% for RCP 4.5, by 28% and 48% for RCP 8.5). These results reflect the projected precipitation trend, characterized by longer, drier summer periods and wetter autumns in comparison to today’s climate. Also, they indicate the need to develop a plan for the research and use of alternative drinking water resources for the long-term period. Therefore, the proposed methodology demonstrated to deliver useful information for water management planning. Future studies are intended to focus on chemistry and isotopic composition of water.

How to cite: Camera, C., Citrini, A., and Beretta, G. P.: Effects of climate change on the Nossana karst spring (northern Italy): future discharge projections and water distribution system sustainability, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3448, https://doi.org/10.5194/egusphere-egu2020-3448, 2020.

The analyses of ecosystem response to climatic variability have been primarily concentrated on the last decades, due mainly to the lack of long-term meteorological records. Here, we assessed long-term precipitation-aquifer recharge dynamics in the Jerusalem region by exploring a unique 4500 years reconstructed annual precipitation time series (Morin et al 2019) and proxy information on air temperature, solar radiation, and atmospheric CO₂ concentration [CO₂]. We combined these data to reconstruct continuous hourly time series of climatic variables from 2500 B.C. to present using a weather generator model. The reconstructed climatic variables were then used to force the T&C mechanistic ecohydrological model (Fatichi and Pappas, 2017). Simulation results quantified the change in groundwater recharge, a key variable for water resource management in the region, which is simulated as deep drainage from the soil profile. For the recent years, modeled vegetation dynamics were evaluated with remote sensing observations of Leaf Area Index (LAI) while modeled recharge was validated with observed discharge from a number of local springs. The 4500 years of simulations revealed that groundwater recharge was strongly affected by precipitation not only at the annual scale, as expected, but also by a multi-decadal average, suggesting an important memory effect of soil moisture conditions on recharge. Almost the entire variability in groundwater recharge over 4500 years was explained by precipitation alone, with minor effects of temperature and [CO₂], which both displayed significant changes in the last 50 years. The compensating biophysical and ecophysiological effects of [CO₂] increase on plants could explain this pattern: while an increase in [CO₂] stimulates productivity and LAI, increasing also evapotranspiration (ET) and decreasing recharge, it also improves water use efficiency, thus largely cancelling the aforementioned effect on ET. A sensitivity analysis to expected future levels of [CO₂] and temperature clearly showed that elevated CO₂ contributes to maintain current groundwater recharge values also in the future by closing stomata. However, a +2-3°C air temperature increase could reduce groundwater recharge of 30-40% due to enhanced ground evaporation and evaporation from interception, but also because of larger transpiration due to higher vapor pressure deficit, despite an enhanced plant water stress. The link between groundwater recharge and precipitation in the Jerusalem region has been very stable in the last 4500 years, but this stability is jeopardized in a warmer future, with potentially strong implications for water resources management.

Morin, E., Ryb, T., Gavrieli, I., & Enzel, Y. (2019). Mean, variance, and trends of Levant precipitation over the past 4500 years from reconstructed Dead Sea levels and stochastic modeling. Quaternary Research, 91(2), 751-767. doi:10.1017/qua.2018.98

Fatichi S., and C. Pappas (2017). Constrained variability of modeled T:ET ratio across biomes. Geophysical Research Letters. 44(13), 6795-6803, doi:10.1002/2017GL074041

How to cite: Fatichi, S., Peleg, N., Mastrotheodoros, T., Pappas, C., and Morin, E.: An ecohydrological journey of 4500+ years reveals a surprisingly stable precipitation-aquifer recharge relation in the Jerusalem region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8647, https://doi.org/10.5194/egusphere-egu2020-8647, 2020.

Under conditions of a changing climate winters are predicated to be warmer and wetter in the northern hemisphere. As a result, midwinter melts and rain on snow (ROS) events have the potential to contribute to groundwater recharge. An understanding of the impacts of repeated freeze-thaw and ROS on groundwater recharge is critical for predicting and managing future groundwater resources in seasonally frozen environments. In particular, fractured rock aquifers have received little attention regarding these processes. To explore the impacts of midwinter melts and ROS on bedrock recharge, a granitic outcrop has been heavily instrumented in Eastern Ontario, Canada over the 2019-2020 winter season. The low-lying outcrop is approximately 10 m X 8 m and the water table resides in the bedrock approximately 3 m below ground surface. Two wells have been drilled to 15 m and 30 m depths. The first well is open and the second has two isolated intervals with pressure transducers and temperature sensors installed in both wells. Three temperature probes have been drilled into the rock outcrop with two installed just beneath the soil to explore if heat transferred from exposed warming rock could melt adjacent frozen soil. Two soil moisture and temperature profiles (5 measurements each) have been installed in the adjacent soil and extend from the surface to the soil-bedrock contact. Finally, a weather station has been installed that measures precipitation, snow depth, air temperature, relative humidity, solar radiation and wind speed. The instrumented area allows for detailed measurements of atmosphere-subsurface interaction that can be used for coupled snowpack and subsurface flow modelling. Preliminary field observations indicate that rapid recharge in the bedrock can take place despite frozen conditions. This is evidenced by sharp drops in groundwater temperature accompanied by rises in water level in response to snowmelt or ROS events. The soil moisture and temperature profiles indicate that shallow (20 cm) soil remains frozen, limiting infiltration from above. However, runoff from the outcrop can flow along the soil-rock contact allowing for infiltration and recharge to occur beneath the frozen layer. These results suggest that areas of exposed rock can be localized hotspots for groundwater recharge when midwinter warming or ROS occurs. This may result in increased recharge to bedrock aquifers during winter months under future climate change scenarios.

How to cite: Wright, S. and Novakowski, K.: Field observations of rapid midwinter recharge in a seasonally frozen bedrock aquifer, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10763, https://doi.org/10.5194/egusphere-egu2020-10763, 2020.

ABSTRACT

Due to polar amplification of climate change, high latitudes are warming up twice as fast as the rest of the world. This warming leads to permafrost thawing, which induces greenhouse gases release, ground subsidence, and modifies surface and subsurface hydrologic regimes. Ground subsidence in turn affects local infrastructure stability. In this context and to better manage future infrastructures and water resources of northern regions, it is crucial to be able to evaluate the thawing rate of permafrost.

In many Arctic zones, the frequency of environmental disturbances caused by permafrost thawing increases so rapidly that maintaining an accurate inventory of the state of permafrost at a regional scale represents a great challenge. Moreover, depending on the study area and the permafrost ice content, the thawing rate can vary from millimetres to decimeters per year. Another current challenge is the limited availability of temporal and spatial data on permafrost thawing rates.

To address the above challenges, two indirect methods are used: (1) Arctic river streamflow analysis method and (2) Ground settlement analysis method via satellite image observation. Both methods use free-access data that have an exceptionally large temporal and spatial coverage capacity for such a poorly instrumented region. The first method analyses the recession events’ behavior of Arctic streams and relates those behaviors to changes in catchment-scale depth to permafrost that influences storage-discharge dynamics. This work differs from previous hydrological system analysis in northern systems in that it looks at long-term trends (>10 years) in recession intercept to assess permafrost dynamics, while other studies looked at recession characteristics within a season to assess active-layer dynamics. The second method analyses satellite images of the Arctic ground and associates surface elevation change to long-term permafrost degradation due to climate change.

Both methods have already been tested through multiple local investigations and gave promising results. The recession flow analysis method has been applied to Yukon river basin, northern Sweden basins and Lena basin in Siberia, while the remote sensing analysis method has been tested on Baffin Island, Herschel Island in Canada, North Slope of Alaska and the Tibetan Plateau. However, no comparative study and no large-scale application have been conducted so far. Extending the analysis to hundreds of Arctic basins and comparing the resulting permafrost-thawing rate values from both methods constitute the innovative aspect of this project.

KEY WORDS: climate change, permafrost thawing, storage-discharge dynamics, ground subsidence, satellite images

How to cite: sergeant, F., therrien, R., oudin, L., jost, A., and anctil, F.: Comparing streamflow analysis and remote sensing observations to assess climate change impact on permafrost degradation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21789, https://doi.org/10.5194/egusphere-egu2020-21789, 2020.

This paper synthesizes recent data-driven advances in our understanding of hydro-climatic variability and change, and explores their implications for groundwater-related shifts and critical thresholds. As a starting point in this exploration, large-scale warm-season co-variability patterns between temperature and hydrology over Europe, from 850 CE to present, show negative association, i.e., drier conditions in terms of precipitation and soil moisture under warming for hydro-climatically vulnerable southern parts of Europe. While warming thereby decreases regional water inputs and water availability for vegetation and groundwater recharge, other recent studies show that common irrigation and flow regulation developments for enhanced food and energy supply over the last century have increased evapotranspiration and associated water outputs from the landscape back to the atmosphere in many parts of the world. Particularly under decreasing precipitation, such human-driven enhancement of water availability for plants and crops, as reflected in the observed evapotranspiration increases, has been achieved at the cost of even greater than the precipitation-driven decreases in groundwater recharge and runoff, and thus in water availability for other uses; data for multiple hydrological catchments around the world reveal such decreases over the last half century to present time. Groundwater mining with associated groundwater table lowering (i.e., decreased subsurface storage of water) may also feed the evapotranspiration increases associated with agricultural expansion, intensification and irrigation. For example, long-term hydro-climatic data time series (including also groundwater data) for multiple catchments across Iran show systematic groundwater depletion feeding such evapotranspiration increases to levels well beyond those sustainable by the annually renewable water inputs through precipitation.Moreover, long-term time series of calculated soil moisture and groundwater table variation and change indicate high drought risk enhancement also in humid parts of the world, such as the Swedish Stockholm County region, after major agricultural expansion and intensification with related increases in evapotranspiration as well as in short-term soil moisture and runoff variability, while average soil moisture and runoff have decreased over the last century. For coastal regions, the groundwater recharge, table, and flow lowering associated with such human-driven (and possible additional climate-driven) decreases in soil moisture and runoff may combine with expected sea level rise in driving increasingly larger (nonlinear) responses of seawater intrusion towards different critical limits for fresh coastal groundwater. These limits include that of intruded seawater reaching key locations of pumping for water supply, and the tipping point of complete seawater intrusion up to the prevailing groundwater divide of a coastal aquifer. Recent investigation of prominent aquifers in the eastern Mediterranean region shows human-driven modifications of hydrologic regimes and associated salinization histories towards various current levels of proximity to these critical limits for essential groundwater resources.

How to cite: Destouni, G.: Groundwater shifts and critical thresholds in the changing hydro-climate, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13435, https://doi.org/10.5194/egusphere-egu2020-13435, 2020.

Coastal areas, including deltas, are hotspots for population growth and economic development. The rising demand for fresh water that results from these developments has resulted in increased rates of groundwater pumping and an associated enhanced risk of groundwater salinization. Future sea-level rise, climate change and surface sealing due to urbanisation are likely to further increase salinization risk in the near future. In order to correctly project the future fate of fresh groundwater resources in coastal areas under climate and socio-economic change, a correct estimate of the current fresh-brackish-salt groundwater occurrence is imperative. The reason for this is that future salinity projections are very sensitive to initial conditions, due to the large inertia of variable-density groundwater systems. Here, we make a case that estimating the current fresh-brackish-salt groundwater distribution by itself is a major challenge. The presence of conductivity contrasts in coastal areas, the past occurrence of sea-level transgressions and the aforementioned system inertia makes that traditional estimation methods such as interpolations between in-situ salinity observations or equilibrium (steady-state) modelling approaches are incapable of producing sufficiently realistic fresh-brackish-salt groundwater distributions. Using examples from the Rhine-Meuse delta, the Nile delta and the global coast, we show that advancements in airborne geophysics and high-resolution paleo-groundwater modelling may be key to providing distributions that are both realistic and accurate.

How to cite: Bierkens, M. F. P., King, J. A., van Engelen, J., Verkaik, J., Zamrsky, D., and Oude Essink, G.: Estimating regional to global fresh-brackish-salt groundwater occurrence to support future projections, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1835, https://doi.org/10.5194/egusphere-egu2020-1835, 2020.

 Seawater intrusion in coastal aquifers is a worldwide problem caused by natural processes but significantly worsened by aquifer overexploitation for drinking water supply and irrigation, land subsidence, sea levels rise, and climate changes, which contribute to the reduction of groundwater natural recharge.

Within the framework of an Interreg Italy-Croatia collaboration project (Italy – Croatia 2014 – 2020 CBC Programme), MoST (MOnitoring Sea-water intrusion in coastal aquifers and Testing pilot projects for its mitigation), a study area located at Ca’ Pasqua, in the southern part of the Venice lagoon, Italy, is used as a pilot site to develop and test possible solutions to issues of coastal seawater intrusion. The project consists of two main phases. The first phase is devoted to the collection of hydro-geophysical information and data in the study area and to mimic the dynamics of the relevant processes in laboratory experiments. In the second phase, appropriate countermeasures (e.g., underground barriers, recharge wells, recharge drains, cut-off walls) will be considered to limit or mitigate the seawater intrusion/contamination and their efficiency will be tested. These activities will be carried out with the involvement of local populations and authorities, which will benefit the most by these actions, thanks to their final implications in terms of enhanced crop productivity and touristic activities.

Within the context of this project, we present the results of a numerical modeling study, whereby a finite difference model, SEAWAT, is used to test the potential effects of one of the aforementioned countermeasures, a recharge drain located in a sandy paleochannel which seems to represent a preferential pathway for saline intrusion but can also be used to convey freshwater to reduce soil salinization. The model is set up by integrating information derived from in-situ monitoring and observations of precipitation, rivers hydrometric heads, evapotranspiration and tide levels for a period of about 10 years. A number of different scenarios are modelled and compared, allowing us to predict the resulting seawater intrusion mitigation and its uncertainty.

How to cite: Botto, A., Camporese, M., and Salandin, P.: Mitigation strategies to reduce saltwater intrusion in coastal aquifers: the testing site of Ca’ Pasqua, Italy., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13299, https://doi.org/10.5194/egusphere-egu2020-13299, 2020.

A method to conceptualise the assessment of the impact of sea-water intrusion in island and coastal aquifer systems is being proposed.  The method will enable the undertaking of a first assessment of the sea-water intrusion problem, hence providing an early-stage and simple to apply “warning system” enabling the informed and timely application of mitigation measures intended to protect the quantitative and qualitative status of the aquifer system. The method proposes the discretization of the aquifer to enable the correlation of the current aquifer “freshwater domain” with reference conditions representing the aquifer system under undisturbed conditions.  The “freshwater domain” is defined by the volume of water between the piezometric surface and the seawater interface, and can be obtained from numerical models, where available, or the application of simple analytical approaches such as the Ghyben-Herzberg solution. . The dynamic of the seawater intrusion is defined as the change in natural “freshwater domain” and chloride concentrations within it. Therefore, the method is applicable to island and coastal aquifers with low-data availability, and in particular to cases where a numerical-model is not-yet developed. The application of the method will enable the quantification of sea-water intrusion impacts at an aquifer scale, enabling the visual-conceptual representation of the sea-water intrusion affected area, as well as identify the level of intrusion.  The method also enables the temporal assessment of sea-water intrusion, identifying the evolution of intrusion throughout the exploitation period of the aquifer system.  The method has been implemented in a GIS tool, and applied to the Mean Sea Level Aquifer system in Malta.

Aknowledgement: This research has been partially supported by the GeoE.171.008-TACTIC project from GeoERA organization funded by European Union’s Horizon 2020 research and innovation program and by the SIGLO-AN project (RTI2018-101397-B-I00) from the Spanish Ministry of Science, Innovation and Universities (Programa Estatal de I+D+I orientada a los Retos de la Sociedad)

How to cite: Sapiano, M., Baena-Ruiz, L., Debattista, H., and Pulido-Velazquez, D.: Conceptualisation of Sea-Water Intrusion in an Island Aquifer System, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21336, https://doi.org/10.5194/egusphere-egu2020-21336, 2020.

Groundwater is the primary source of freshwater supply on remote small islands, where it exists as a freshwater lens. It is extremely vulnerable to over-extraction, pollution and seawater intrusion. Ensuring long-term sustainable management of the groundwater resource is of the utmost importance when there are growing water demands, sea-level rise and/or recharge decline. This study used a three-dimensional, variable-density numerical groundwater flow and solute transport model to investigate vulnerability of a freshwater lens in a multi-layered aquifer system on Milingimbi Island, a small tropical island in northern Australia. The model was used to explore the impacts and possibility of increased groundwater demand on the freshwater lens, its volume, geometry as well as the thickness of the transition zone. The risks of saltwater intrusion, both laterally from the ocean and by localised up-coning from the deeper, more saline aquifers beneath the freshwater lens, were also assessed. Model calibration used observed hydraulic heads and salinity observations from pumping and observation wells. Subsurface bulk conductivity values, which were calculated from inverted airborne electromagnetic (AEM) and near-surface geophysical data, were also used in the calibration process. The results showed that the hydraulic heads and observed salinity achieved the ‘best fit’ in the calibration process, whereas the addition of the geophysical data assisted in constraining the lens geometry in the steady state model and integrated the data poor areas based on traditional hydrogeological datasets. The models’ calibration sensitivity to the range of measured salinities could be enhanced by improving the conversion factor between the AEM-derived conductivity values and the observed salinity data. This would best be accomplished by targeted monitoring wells at discrete depths and locations across the lens and improvements in the sampling/restoration of existing ones. The numerical model provided a framework to evaluate the key underlying hydrogeological processes on the island, as well as an important decision-making tool to ensure a sustainable and reliable water supply for the island community.

How to cite: Banks, E. W., Noorduijn, S., Batelaan, O., Post, V., Werner, A., Munday, T., Soerensen, C., Cahill, K., Jolly, P., and Ellis, J.: Evaluating Freshwater Lens Vulnerability in a Multi-layered, Island Aquifer System in the Tropics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19553, https://doi.org/10.5194/egusphere-egu2020-19553, 2020.

Excessive groundwater pumping due to immense agricultural, industrial and municipal demand poses a major threat of aquifer depletion in many areas around the world. The impact of climate change on the global hydrological cycle has further exacerbated the situation. Accurate and reliable prediction of long-term aquifer balance terms is a key prerequisite to manage groundwater sustainably. To deal with uncertainties of such predictions, lumped (conceptual) hydrological models could help with their computational speed that allows for Monte-Carlo simulation. Compared to more complex models, lumped models are fast, lean on data requirement and capable to quantify uncertainty. However, lumped models are mainly designed to simulate river discharge only, not aquifer storage. Even the standard practice for calibrating lumped hydrological models only includes river discharge, as data on groundwater storage is not directly accessible. In this study, we hypothesize that we can extend the HBV model by additional water budget and groundwater storage terms, and calibrated it on both groundwater storage data and discharge data. Then, we test whether its predictions of groundwater storage levels withstand validation tests. To avoid problems with unavailability of data for calibration and validation in a first proof of concept, we build a virtual reality with a MODFLOW-based model, driven with synthetic weather data over a period of more than 50 years. For rigorous testing, we cast calibration into the framework of Bayesian parameter inference, and validate with metrics that assess the appropriateness of the Bayesian prediction distribution of groundwater storage. We test our idea in the Wairau Plain aquifer, New Zealand. Poor understanding of recharge mechanisms and hence declining groundwater levels are the major hindrance for sustainable groundwater management in our study area. We pay specific attention to river-groundwater exchange processes, to the forecast of aquifer storage dynamics, and to groundwater depletion in a hypothetical, persistent draught. The purpose is to provide a proof of concept whether lumped models can be adapted and made suitable to predict declining groundwater resources up to full depletion, as an uncertainty-aware decision support system for sustainable management.

How to cite: Ejaz, F., Wöhling, T., and Wolfgang, N.: Lumped hydrological model for reasonable, long- term predictions of groundwater storage and depletion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1310, https://doi.org/10.5194/egusphere-egu2020-1310, 2020.

Urban aquifers represent an undeveloped resource and utilization is also arising as a method to improve storm water management. In dry climate, these aquifers are an alternative water supply source and in tropical climate can mitigate waterlogging and floods. However, sources and pathways of urban groundwater are more numerous and complex than those in rural environments. Furthermore, climate change and more frequent and intense climate extremes increase the variability in precipitation, soil moisture, and surface water. Therefore, a long-term effective urban water management is imperative.

This study investigates the groundwater in Shenzhen, a major financial and high-tech center in southern China, along the left side of the Zhujiang Estuary (Pearl River Delta). Shenzhen has a population of about 14 million permanent residents and currently has a total water consumption of 2 billion m³ per annum. Previous research has investigated the hydrogeological setting and groundwater budgets via numerical flow simulations under steady-state conditions. In the present research, a MODFLOW transient model has been constructed to estimate the groundwater budgets in Shenzhen in response to projected climate change.

Model conditions are varied, considering the typical Representative Concentration Pathway (RCP) scenarios (RCP 2.6, RCP4.5, RCP 6.0 and RCP 8.5) from 2019 to 2049. Simulations are grouped into two numerical analyses. For the first analysis, the rainfall rate decreases by 37.4% (RCP2.6, RCP4.5) together with a sea-level increment of 0.36 m (RCP 4.5); for the second analysis rainfall increases by 11.82% (RCP 6.0, RCP 8.5) and a sea-level increment of 0.5 m (RCP 8.5).

In the first analysis (RCP 2.6, RCP 4.5) the groundwater budget decreases by approximately 26% within the study domain, and the water table declines from 1 to 26 m. The second analysis shows a 15.48% increase in the groundwater budget, as the water level rises on average from 0.5 to 8 m. Given the sensitivity of the model results to the choice of future climate scenario, this study indicates the importance of accurate climate change predictions to help local authorities better manage water resources in tropical urban aquifers.

How to cite: Su, H., Lancia, M., Zheng, C., and Hiscock, K.: Analysis of tropical urban aquifers in response to climate change, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17872, https://doi.org/10.5194/egusphere-egu2020-17872, 2020.

Arguably, the groundwater community has responded more slowly to the challenges posed by climate change than other fields of (hydrological) science. However, in recent years a strong increase in studies addressing climate change impacts on groundwater is observed, and recommendations on the methodology of such studies have been developed and discussed (e.g. Holman et al., Hydrogeology Journal, 2012). Following the common practice in other fields of climate change research, it was suggested that assessments of climate change impacts on groundwater should be based on multiple emission scenarios and a range of global and regional climate models. This scenario-based, top-down approach involves the propagation of multi-model ensembles through a model chain starting from emission scenarios to global and regional climate models to impact models such as hydrological and groundwater models. However, as the uncertainty increases at each step of the model chain, the uncertainty in the assessment of local climate change impacts and the resulting recommendations for adaptation options likely are very high and thus of little use in practice. A vulnerability-based, bottom-up approach starting from the identification and analysis of the factors that are relevant for coping with climate change in a given system, therefore, was proposed as a complementary approach (e.g. Wilby and Dessai, Weather, 2010). “Storylines” (Shephard et al., Climatic Change, 2018) that aim at representing uncertainty in physical aspects of climate change in an event-based rather than probabilistic way appear to be consistent with the latter concept. In this poster we relate these concepts of climate change research to methodological frameworks established in hydrogeological research (e.g. multi-model approaches). We present an overview of potential tools, such as trading-space-for-time, historical data analysis, sensitivity analysis, climate projections and controlled experiments, that can be used to study climate change impacts, and we discuss their role and applicability within more general methodological frameworks.

How to cite: Birk, S. and Collenteur, R.: Reviewing our options: How can we address climate change impacts in hydrogeological studies?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16143, https://doi.org/10.5194/egusphere-egu2020-16143, 2020.

In recent decades, the frequent occurrence of extreme weather events, coupled with the continuous increase in the intensity of artificial mining led to a general decline in the groundwater level in the karst areas of northern China. Some large springs even dried up.

Under the background of climate change, the analysis of spring water dynamic characteristics and its response to the atmospheric precipitation are of great significance to reveal the internal relation of groundwater system in karst spring area and the prediction and protection of spring water flow.

This paper selected a typical karst spring Longzici in southern Shanxi province as the object where the karst aquifer developed well. Based on the long time series precipitation monitoring and spring water flow data from 1987-2018, this paper analyzed the characteristics of spring and rainfall and found that they both have some periodicity. The precipitation has 2-3-year peak cycle and the annual average spring flow rate is 3.82 m³/s which had a dynamic fluctuation period of spring about 10 years. The result of regression model analysis of spring flow response to precipitation shows that the spring flow response has a time lag of four years to precipitation. It is most affected by its own spring flow in the previous year and different degrees affection of precipitation in the previous year and three years ago. It is also found that the sensitivity of spring flow to precipitation is influenced by precipitation amount. The effect of annual precipitation with abundant water and dry water on the flow rate of springs is with different delay length. The spring flow response to precipitation in the dry year is more pronounced. The trend analysis shows the groundwater in spring area is greatly influenced by spring own storage capacity and human exploitation.

How to cite: Qiao, X. and Wang, D.: Analysis of the Response of Karst Spring to Precipitation in Longzici karst Area, Southern Shanxi province, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12468, https://doi.org/10.5194/egusphere-egu2020-12468, 2020.

Global air-temperature changes over the last 150 years and in particular during the last 30 – 40 years are well documented world-wide. In alpine areas in Europe the increase in air-temperature is even higher in the range of 2° C. Very few studies exist about groundwater temperature changes due to global warming. The increase or decrease in temperature at the point of discharge depends besides the air temperature at the time of infiltration on the amount of precipitation, the local meteorological conditions, the mean residence time, the land use, and the natural and anthropogenic heat flow during the passage underground.

Nearly no papers exist about the water quality changes due to global change impacts and Mean Residence Times (MRT). This is very difficult to evaluate due to missing long-term quality measurements and strong impacts by anthropogenic activities and land use changes. To avoid the complication by anthropogenic land use changes and activities the authors investigated the on-line discharge, temperature, and electric conductivity measurements as well as quarterly hydro-chemical and isotope analyses of 40 Alpine springs from a monitoring network all over the Austrian Alps (approx. 60,000 km²). All the selected springs have a recharge area with no or minimal anthropogenic impacts during the last 30 – 40 years. About 235,000 on-line measurements and 11,000 chemical analyses were evaluated for trends and compared to daily measurements at meteorological and surface water stations close to the recharge areas of the springs. To show the connection to the paleoclimatology changes of existing δ¹⁸O measurements on precipitation and spring water was evaluated as well indicating altitudes of recharge areas in range of 500 – 2400m.

Forty springs with a minimum record of 16 years have been selected for trend analysis over a period of 20 years (1993 – 2013). 28 (74%) of the selected spring show a significant mean increase in water temperature of 0.34 °C in the range of 0.06 to 1.03 °C. This increase is half of the air- and water temperature increase in meteorological stations and surface waters close to the recharge areas of the investigated springs. The electric conductivity linearly increased in 21 (55%) of the investigated springs at about 4%. The discharge stayed the same in most springs. In 23 (72%) springs the content of dissolved oxygen decreased over these 20 years at about 9% percent.

The reasons of the changes in water-temperature, dissolved load and the oxygen content as well as the impact of different Mean Residence Times (MRT) will be discussed and interpreted.

How to cite: Kralik, M. and Papp, E.: Isotope-age-dating of alpine spring water and global change : Evidence from temperature, chemistry and tritium data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19430, https://doi.org/10.5194/egusphere-egu2020-19430, 2020.

The recognized evidence of global warming demands assessment of the present and future water cycle in Europe and worldwide. Recently, evidence of modified hydrological regime in the Alps under climate change has been documented. In particular, several studies (e.g. Bocchiola, 2014; Soncini et al. 2016) indicated an increase in hydrological flows in autumn and winter in response to snowfall trading with intense rainfall, shorter snow cover during winter, as well as decreased flows during dry spring and summer and large shrinking of glaciers at high altitude. However, according to the IPCC Fifth Assessment Report, it is still necessary to deepen our understanding of the impact of climate change and land use on groundwater recharge and levels in the alpine catchment areas (Cochand et al. 2019).

For this purpose, a water balance of the last three hydrogeological years (March 2017 - March 2020) was carried out on the Valtellina catchment (northern Italy, Central Italian Alps). This basin is a perfect case study for its wide unconfined aquifer in the floodplain, which makes it highly sensitive to this type of change. Moreover, the management of the water resource is of considerable importance, being crucial in a wide range of sectors (tourism, irrigation, domestic use, energy and industry).

Due to the extensive and diversified study area (26,000 km²) and the low ground data density (7 meteorological stations, 4 surface-water monitoring points, and 9 groundwater monitoring points), the water balance terms were estimated by exploiting and combining Earth Observation data products with ground data, also taking into account the geological and geomorphological characteristics of the basin. In particular, the evapotranspiration and the snow cover were provided, by MOD16A2 (MODIS/Terra Evapotranspiration 8-Day Level-4 Global 500m SIN Grid) and MOD10A2 (MODIS/Terra Snow Cover 8-Day L3 Global 500m SIN Grid, Version 6) satellite data, respectively.

As a result, the groundwater storage of a wet hydrogeological year compared with the groundwater storage of a dry hydrogeological year allowed analysing the sensitivity of groundwater resources to climate change.

Bocchiola, D.: Long term (1921–2011) Hydrological regime of Alpine catchments in Northern Italy. Advances in Water Resources, 70, 51-64, 2014.

Cochand, M., Christe, P., Ornstein, P., & Hunkeler, D.: Groundwater storage in high alpine catchments and its contribution to streamflow. Water Resources Research, 55(4), 2613-2630, 2019.

Soncini, A., Bocchiola, D., Confortola, G., Minora, U., Vuillermoz, E., Salerno, F., Viviano, G., Shrestha, D., Senese, A., Smiraglia, C. and Diolaiuti, G.A.: Future hydrological regimes and glacier cover in the Everest region: The case study of the upper Dudh Koshi basin. Science of the Total Environment, 565, 1084-1101, 2016.

How to cite: Perico, R., Frattini, P., Celesti, M., Colombo, R., and Crosta, G. B.: Water balance of an extensive alpine catchment area under the effect of climate change, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10364, https://doi.org/10.5194/egusphere-egu2020-10364, 2020.

A numerical analysis of the groundwater flow and contaminant transport equations, based on the variable density flow approach, is used for the construction of non-dimensional diagrams to predict seawater intrusion to confined coastal aquifers. The classical Henry’s seawater intrusion problem is analysed by using a finite element model. The model’s equations are written in non-dimensional form and the numerical solutions depend solely on three non-dimensional parameters:

α=q΄/Κ⁰, β=(bΚ⁰)/(nD_m), α΄=bS⁰/n                                                                                           (eq. 1 a,b,c)

where q’ is the freshwater recharge rate (m/d), K⁰ the freshwater hydraulic conductivity (m/d), b the aquifer thickness, n the porosity (-), D_m the molecular diffusion coefficient (m²/d) and S⁰ the freshwater specific storage (1/m). Please note that hydraulic conductivity appears in two of the non-dimensional parameters, α and β.

The non-dimensional formulation has led to the construction of non-dimensional diagrams of salt distribution for a homogeneous and isotropic confined aquifer with horizontal base and constant thickness that is uniformly recharged with freshwater. These diagrams illustrate the influence of the key hydrological and hydraulic parameters, and furthermore, can be used to predict the evolution of seawater intrusion in real case studies.

The numerical simulations were carried out up to the equilibrium state for different values of the non-dimensional parameters of equation 1. By decreasing the value of parameter α=q΄/Κ⁰, seawater intrusion is advancing inland and the width of dispersion zone is increasing. By increasing the parameter β=(bΚ⁰)/(nD_m), the seawater-freshwater transition zone is narrowing and shifted to the seaside at the upper part of the aquifer, while the intrusion of saltwater is advancing inland at the lower part of the aquifer. The distribution of the salts in the aquifer was found essentially identical for different values of the parameter α΄=bS⁰/n; hence this parameter exhibits very low sensitivity, which makes it of low importance, especially for real case studies.

Overall, the non-dimensional diagrams – constructed by following the variable density flow approach and under specific assumptions – can be used for a quick and direct prediction of seawater intrusion in real aquifers. These diagrams would be useful for an initial prediction at the case studies of the PRIMA MEDSAL project (www.medsal.net), namely the coastal aquifers in Rhodope (Greece), Samos island (Greece), Bouficha (Tunisia), Bouteldja (Algeria), Tarsus (Turkey) and under specific assumptions to the karstic aquifer in Salento (Italy).

How to cite: Doulgeris, C., Tziritis, E., Pisinaras, V., Panagopoulos, A., and Külls, C.: Prediction of seawater intrusion to coastal aquifers based on non-dimensional diagrams, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4073, https://doi.org/10.5194/egusphere-egu2020-4073, 2020.

Coastal aquifers provide fresh drinking water to over 20% of the world’s population. In recent times, they have come under immense pressure due to salinization. This study aims to investigate the origin of groundwater salinity and elucidate the major processes controlling shallow groundwater (depth of 0~50m) evolution in the Luanhe River Delta since the Holocene. Rapid increase in Electric Conductivity (EC) profile was observed in the area, as such, based on the vertical distribution of EC and sedimentary history, shallow groundwater was generalized into two zones for analysis: the groundwater in Holocene stratum (HSG) and groundwater in Late Pleistocene stratum (PSG). The isotopic (δ¹⁸O, δ²H and ¹⁴C) analyses showed that the HSG is recharged by modern surface water, while the PSG having enriched isotopic values could have been recharged during a warmer Holocene transgression period. The hydrochemistry analyses demonstrated that seawater is the major source of salinity in groundwater and overtime a series of geochemical processes (mineral weathering and/or cation exchange) modified the chemistry of the groundwater. The combined use of Cl^- and δ¹⁸O yielded four classes of groundwater (fresh water, brackish water, saline water and brine), while the mixing phenomena between fresh water and seawater was identified to be the main evolutionary process of the shallow groundwater. To improve understanding of evolution of multiple groundwater types in a spatial context, a conceptual model was developed integrating the results derived from the presented study in a vertical cross-section. The conceptual model shows that the residual seawater mixes with freshwater from surface recharge at the shallow aquifer of the delta plain where the lagoon environment provides salinity concentration conditions for the formation of hyper-saline water. Due to the precipitation and accumulation of the salinity from hyper-saline water, some brine might form formed in late Pleistocene continental stratum.

How to cite: Dang, X., Gao, M., Wen, Z., and Hou, G.: Evolutionary process of saline groundwater influenced by palaeo-seawater trapped in coastal deltas: A case study in Luanhe River Delta, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6363, https://doi.org/10.5194/egusphere-egu2020-6363, 2020.

This comprehensive study shows the behavior of major and trace alkali and alkali-earth elements in a coastal sedimentary aquifer of Mexico moderately impacted by saltwater intrusion and anthropogenic activities. For this purpose, the concentrations of major cations (Na⁺, K⁺, Ca²⁺ and Mg²⁺), major anions (Cl^-, SO₄^2-, HCO₃^-, NO₃^-) and several alkali and alkali-earth trace elements (Li, Rb, Ba and Sr) were analyzed in all the active groundwater wells of the Todos Santos aquifer, Baja California Sur, northwestern Mexico. The results indicates that the percentage of seawater intruded into the aquifer ranges from 0.2% to 2.7%, with an average of 0.9%. In the recharge areas, groundwater is Ca²⁺–HCO₃^- type. However, groundwater evolves from Ca²⁺–HCO₃^- type to Na⁺–Cl^- type when salinity is increased in the direction of the flow path, suggesting that the intrusion of saltwater is affecting the groundwater chemistry in wells close to the coastline. The excess of Ca²⁺ and Mg²⁺ over the corresponding anions SO₄^2- and HCO₃^- shows that both alkali-earth elements are being replaced by Na⁺ in the aquifer matrix. Overall, the excess of all alkali-earth elements over the freshwater-seawater mixing line suggests that this process is extensive to all alkali-earth elements. Overall, the alkali-earth elements Ca²⁺, Mg²⁺, Ba²⁺ and Sr²⁺ are mobilized from the aquifer matrix during seawater intrusion, whereas the alkali elements Na⁺, K⁺ and Rb⁺ are removed from solution. This phenomenon can be driven by a cationic exchange process, where alkali-earth element are exchanged by alkali elements in the aquifer matrix. Unlike the other alkali elements, Li is mobilized during saline intrusion, probably also by cationic exchange. The high diffuse NO₃^- concentrations in wells close to the Todos Santos downtown indicates that nitrates could be provided by anthropogenic activities, specifically by sewage infiltration. This work can be useful as reference for knowing the effect of salinization in the concentration of alkali and alkali-earth trace elements in groundwater of coastal aquifers under sea level rise scenarios driven by climate change.

How to cite: Mora, A., Mahlknecht, J., and Sanford, W.: Behavior of dissolved alkali and alkali-earth elements in a coastal aquifer of Mexico affected by saltwater intrusion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6115, https://doi.org/10.5194/egusphere-egu2020-6115, 2020.

More severe and frequent drought events are one of the main challenges faced worldwide in the context of climate change. Now droughts can be observed in the areas that are typically not classified as drought prone regions and more often groundwater vulnerability to prolonged drought events is reported. Groundwater drought is relatively new drought type defined as lower than normal groundwater level.

Most recent drought event in Europe in 2018 significantly affected shallow groundwater aquifers in the Baltic states. That year, groundwater droughts in Latvia caused large financial losses to many farmers, and rural households frequently reported dry dug wells. Even though main groundwater drought consequences are depleted aquifers and/or reduced base flows to rivers, drought may have an influence on groundwater quality as well (e.g. reduced denitrification rates due to lower groundwater levels and shorter travel times in anoxic zone).

This study presents groundwater chemical composition changes with respect to groundwater level variations between six sampling campaigns carried out during the groundwater drought event in 2017-2018 in central part of Latvia. Groundwater samples were taken from specifically established monitoring network with seven stations, each having two to four shallow groundwater wells with the maximum depth of four meters. In total more than 100 groundwater, surface water and spring water samples were collected every two months for a one-year period. Major ions, water stable isotopes, biogenic and trace elements were analyzed in laboratory. Patterns were analyzed by multivariate statistical analysis (Principal Component Analysis, Cluster Analysis and Discriminant Analysis).  

The study is supported by fundamental and applied science research programme, project Nr.lzp-2019/1-0165 “Spatial and temporal prediction of groundwater drought with mixed models for multilayer sedimentary basin under climate change”.

How to cite: Retike, I., Bikše, J., Dēliņa, A., Kalvāns, A., Babre, A., and Popovs, K.: Groundwater chemical composition response to the recent 2018 drought event in Europe (central part of Latvia), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18596, https://doi.org/10.5194/egusphere-egu2020-18596, 2020.

The effect of climate change on groundwater system is still not extensively understood. Studies often focuses on changes in recharge to the groundwater system but rarely investigate the resulting impacts on hydraulic head levels especially the spatial distribution of the change across larger domains.

Only few countries in the world have access to a detailed national hydrological model, and fewer still have done nationwide climate change assessments. This study applies a combination of the newest updated national hydrological model for the entire Denmark (the DK-model 2019, http://dk.vandmodel.dk/in-english/) and 20 climate model projections from the Euro-Cordex project (Jacob et al., 2014) for the RCP4.5 and the RCP8.5 emission scenario (4 and 16 runs respectively). The climate dataset are bias-corrected for the Danish area using double Gamma distribution-based scaling for temperature and precipitation (Pasten-Zapata et al., 2019).

This large dataset is used to evaluate the distribution of the magnitude and direction of changes with special focus on the phreatic surface and the main water-bearing groundwater layers for drinking water consumption in Denmark. The spatial variations in the near-surface impact signal across the entire country is also analyzed, as different Quaternary geology is represented from sandy layers in the west to moraine clay tills in the east and marine sand and clay to the north. The climate dataset is a successive time series from 1970ties to the end of the century and thus also enables an analysis of long-term changes in the state of the groundwater system and aquifers. 

Jacob, D., Petersen, J., Eggert, B., Alias, A., Christensen, O. B., Bouwer, L. M., Braun, A., Colette, A., Déqué, M., Georgievski, G., Georgopoulou, E., Gobiet, A., Menut, L., Nikulin, G., Haensler, A., Hempelmann, N., Jones, C., Keuler, K., Kovats, S., Kröner, N., Kotlarski, S., Kriegsmann, A., Martin, E., van Meijgaard, E., Moseley, C., Pfeifer, S., Preuschmann, S., Radermacher, C., Radtke, K., Rechid, D., Rounsevell, M., Samuelsson, P., Somot, S., Soussana, J.-F., Teichmann, C., Valentini, R., Vautard, R., Weber, B., and Yiou, P.: EURO-CORDEX: new high-resolution climate change projections for European impact research, Regional Environmental Change, 14, 563-578, 10.1007/s10113-013-0499-2, 2014.

Pasten-Zapata, E., Sonnenborg, T. O., and Refsgaard, J. C.: Climate change: Sources of uncertainty in precipitation and temperature projections for Denmark, Geological Survey of Denmark and Greenland Bulletin 43, e2019430102-2019430101-e2019430102-2019430106, https://doi.org/10.34194/GEUSB-201943-01-02 2019.

How to cite: Karlsson, I. B., Eisenbruchner, L. T., Kidmose, J., and Højberg, A. L.: National scale climate change impact assessment – investigating long-term variations in the climate change signal for groundwater levels across geologies and aquifers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4741, https://doi.org/10.5194/egusphere-egu2020-4741, 2020.

How to cite: Zaadnoordijk, W.: separating groundwater response to climate and anthropogenic changes using long-term groundwater head time series in the Netherlands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7659, https://doi.org/10.5194/egusphere-egu2020-7659, 2020.

Climate change is mostly associated with the term of “global warming” and thus conjures images of a hotter and dryer future. Indeed, the Alpine region already has seen much higher warming compared to the average of the northern hemisphere [1]. However, because of the impact of other climate variables (e.g. precipitation) and vegetation responses, warming does not necessarily have to mean higher evapotranspiration and dryer conditions [2]. This matter is further complicated as groundwater is closely interlinked with surface water. While surface water is of course related to precipitation, it is also one of the major pathways for humans to have a large and direct impact on the water cycle, e.g. by the construction of run-of-river powerplants. A further direct human impact is the abstraction of groundwater. For this factor, it is generally understood that water use increased with economic activity until the rise of environmentalism in the 1980s and more efficient water use stopped this trend and turned it into a decrease in many industrialized countries.

Assessing impacts of climate change on groundwater resources therefore is a challenging task. In order to assess these, as well as direct human impacts on groundwater, we analyzed a large dataset (1017 groundwater level-, 426 stream stage- and 646 precipitation time series) covering Austria from earlier than 1930 until 2015, with the majority of the data from the 1970s on.

It is shown that groundwater shows a strong falling trend, followed by a rise, fitting the human water use, whereas precipitation shows a more moderate trend. River stages show a completely deviating behavior before the 1980s but also follow the rising trend afterwards [3]. While this does not yet prove a causal link, it does highlight the possibility that human use could affect groundwater levels more than the climate, especially since Austria almost exclusively uses groundwater for human use and the wells in the dataset are all located in the populated lowlands.

Going beyond [3], we take a closer look at the history and future of the human factor, namely water abstraction for public water supply and the effects of humans on rivers. We show that Austria has a very particular form of water supply, mainly due to the special role of the capital, Vienna, whose history could see a repeat in the near future. Under a changing climate, there is also a possibility for further changes in Austria’s rivers. In addition to effects of such changes on groundwater levels, we try to address potential impacts on the chemical quality and ecological status of groundwater.

References:

[1] Gobiet et al., 2014, 21^st century climate change in the European alps-a review. Sci. Total. Environ. 493, 1138 – 1151.

[2] Pangle et al., 2014, Rainfall seasonality and an ecohydrological feedback offset the potential impact of climate warming on evapotranspiration and groundwater recharge, Water Resour. Res., 50, 1308–1321

[3] Haas & Birk, 2019, Trends in Austrian groundwater – climate or human impact? J. Hydrol.: Reg. Stud. 22, 100597

How to cite: Haas, J. C. and Birk, S.: Climate change vs. human impact. A look into Austrian groundwater, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8148, https://doi.org/10.5194/egusphere-egu2020-8148, 2020.

India, the country which is highly dependent on groundwater for its drinking and irrigation requirements (88% and 85% respectively), is already facing an acute water crisis. The groundwater storage in major cities is predicted to reach absolute zero by the end of 2020 (CWMI report 2018). While the demand is projected to increase double fold than the supply by 2030, the need for better understanding the behaviour of groundwater storage is very important to come up with better management policies. Analysing the presence of non-parametric linear trend in groundwater studies has been well recognised as it clearly reveals the detail of declining groundwater storage.  For this endeavour, methods like Theil-Sen Slope estimator (SS), to detect linear trend, has often been applied with the assumption of stationary. However, highly complex, dynamic and non-linear behaviour of groundwater systems require alternate methods besides SS to improve our understanding in the cases where groundwater system exhibits non-stationarity in the trend. Recently wavelet based method has been explored for the trend analysis of several hydro-climatic variables including the groundwater storage.  Wavelet being empirical in nature still requires further investigation as the selection of particular wavelet function carries subjectivity. In this study, we made an attempt to comprehensively analyse the use of different wavelet function in the groundwater storage trend analysis and to further reduce the uncertainty to select the best suitable wavelet function. To demonstrate our approach, the groundwater data collected from two contrasting river basin (i.e., Beas in the Himalayas and Godavari in the Deccan plateau) which has high distress for declining storage, were used. In the overall context, the focus of the study was to overcome the mis-conclusions due to the survivor biases caused by data gaps while predicting the actual long term groundwater storage trend.

How to cite: Kasiapillai Sudalaimuthu, K., Mohanavelu, A., Bankaru-Swamy, S., and Teutschbein, C.: A comprehensive evaluation of wavelet functions to analyse the groundwater storage trends, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21270, https://doi.org/10.5194/egusphere-egu2020-21270, 2020.

Streamflow recession usually exists between rainfall events, and the recession can be expressed as the power relationship between the streamflow and the recession rate. Under the assumption that groundwater drainage from the aquifer to the river channel, this method can inversely evaluate the basin-scale groundwater storage using observed streamflow. It has often been used to explore regional groundwater storage conditions and storage-discharge relationships, and even to estimate hydrogeological parameters. However, the groundwater storage generating the streamflow is only a component of the dynamic storage that includes streamflow and evapotranspiration dynamic, or other forms of mobile groundwater. In order to understand the mechanism of the aquifer dynamic storage responses under environmental changes (included climate change, human activities, etc.), this study used the analytic streamflow distribution model to optimize the estimation of recession parameters during the dry and wet seasons, and explored the parameters change over time and the relationship with seasonal evapotranspiration and basin wetness conditions. Combining the water balance methods, we also quantified the dynamic storage relevant to groundwater drainage and vegetation available water (i.e. storage insensitive to streamflow), respectively, to explore the hydrological response mechanism of aquifer dynamic storage in two seasons. The results showed that the difference in recession parameters in the dry and wet seasons is related to the basin wetness condition, and the evapotranspiration effect is relatively limited. In addition, the parameters change over time also indicated that the environmental change has gradually changed the streamflow recession mechanism. By comparing the response of dynamic storage components to rainfall events and evapotranspiration, this study also demonstrated that the variability in different forms of dynamic storages during each season, which is helpful for understanding the store and loss process of groundwater storage at the basin scale and improving the possibility for predicting the different environmental impacts on groundwater storage.

How to cite: Huang, C.-C. and Yeh, H.-F.: Hydrological Response Mechanism of Aquifer Dynamic Storage during the Dry and Wet Seasons, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12336, https://doi.org/10.5194/egusphere-egu2020-12336, 2020.

More severe and frequent drought events are one of the challenges faced worldwide in the context of climate change. There are multiple anecdotal evidence of dug wells and small streams running dry during  drought events in years 2015 and 2018 in Latvia. However, no comprehensive research has been made to assess groundwater drought and its ecological and socioeconomic impacts in Latvia and wider Baltic region. More intensive irrigation can further exaggerate the groundwater drought problem in the future. 

We aim to analyse past drought events from meteorological and groundwater drought perspective. Groundwater drought development and propagation is complex, however, we try to find the best simple predictors that can be used for evaluating purposes. We examine groundwater level data set from “Dricani” monitoring station with 14 groundwater wells uncovering unconfined heterogenous quaternary aquifer with well depths ranging from 2.5 to 15 m and monthly data records starting from 1970.-ies. Such a high number of wells in a single monitoring station permit detailed groundwater level analysis with a focus on local scale disturbances and groundwater drought propagation that could be caused by heterogeneous sediments in the aquifer, terrain and other drivers. 

We us “Dricani” groundwater level data series to calculate Standardized groundwater level index (SGI) (Bloomfield, Marchant 2013) revealing several major groundwater drought events during the last 50 years. Although largest groundwater drought events shows similar pattern within all the wells, minor changes in SGI can be identified that can be attributed to different depths of groundwater wells. 

The study is supported by fundamental and applied science research programme, project No. lzp-2019/1-0165 “Spatial and temporal prediction of groundwater drought with mixed models for multilayer sedimentary basin under climate change”.

References

Bloomfield JP, Marchant BP. 2013. Analysis of groundwater drought building on the standardised precipitation index approach. Hydrology and Earth System Sciences 17 (12): 4769–4787 DOI: 10.5194/hess-17-4769-2013

How to cite: Bikše, J., Kalvāns, A., Retike, I., Babre, A., Popovs, K., and Dēliņa, A.: Preliminary identification of groundwater drought events in unconfined aquifer with standardized drought indices in single multilevel groundwater station, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18299, https://doi.org/10.5194/egusphere-egu2020-18299, 2020.

The study investigates how topographic and hydrogeological properties influence groundwater dynamics. Using the concept of the fundamental hydrologic landscape (FHL; Winter, 2001), the impact of slope angle, wavelength and amplitude, as well as boundary conditions and hydraulic conductivity on groundwater dynamics is systematically assessed. This type of global sensitivity study has been done for stream flow (e.g. Carlier et al., 2019) or within groundwater focusing solely on groundwater flow and fractions of regional versus local recharge at steady state (e.g. Gleeson and Manning, 2008). In contrast, we study the influence of controls on groundwater level dynamics by using transient models. The coupled, physically based Groundwater and Surface-Water Flow simulator GSFLOW (Markstrom et al., 2008) is employed, to run a set of simulations for a FHL, where topographic and hydrogeological properties are varied across a range of possible value. The model is run at a daily time-step with climate data obtained from a measuring station in Southern Germany. Subsequently, groundwater level time series are read from the model domain across the set of simulations. These time series are decomposed into amplitude, magnitude, timing, flashiness and inter-annual variability by using dynamics indices (Heudorfer et al., 2019). Sensitivity of groundwater dynamics to the different topographic and hydrogeological controls is discussed and contrasted with the results from a prior empirical study (Haaf et al., under review). This type of global sensitivity study may aid understanding hypothesis testing of climate change impacts on groundwater level dynamics.

Carlier C, Wirth SB, Cochand F, Hunkeler D, Brunner P. 2019. Exploring Geological and Topographical Controls on Low Flows with Hydrogeological Models. Groundwater, 57: 48-62. DOI: 10.1111/gwat.12845.
Gleeson T, Manning AH. 2008. Regional groundwater flow in mountainous terrain: Three-dimensional simulations of topographic and hydrogeologic controls. Water Resources Research, 44. DOI:10.1029/2008wr006848.
Haaf E, Giese M, Heudorfer B, Stahl K, Barthel R. Physiographic and climatic controls on groundwater dynamics on the regional scale. (under review).
Heudorfer B, Haaf E, Stahl K, Barthel R. 2019. Index-Based Characterization and Quantification of Groundwater Dynamics. Water Resources Research, 55: 5575-5592. DOI: 10.1029/2018wr024418.
Markstrom SL, Niswonger RG, Regan RS, Prudic DE, Barlow, PM. 2008. GSFLOW-Coupled Ground-water and Surface-water FLOW model based on the integration of the Precipitation-Runoff Modeling System (PRMS) and the Modular Ground-Water Flow Model (MODFLOW-2005): U.S. Geological Survey Techniques and Methods 6-D1, 240 p.
Winter TC. 2001. The concept of hydrologic landscapes. Journal of the American Water Resources Association, 37: 335-349. DOI: DOI 10.1111/j.1752-1688.2001.tb00973.x.

How to cite: Haaf, E., Kavousi, A., Reimann, T., Giese, M., and Barthel, R.: Topographic and hydrogeologic controls of groundwater dynamics in generalized hydrologic landscapes with a humid climate, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10769, https://doi.org/10.5194/egusphere-egu2020-10769, 2020.

This study deals with modelling the distribution of the subsurface pore pressure in space and the respective evolution in time in response to variations in hydromechanical surface loading during a full glacial-interglacial cycle. The aim here is to better understand (i) the feedback mechanisms between the atmosphere and solid earth components, and (ii) to which degree this coupling might be relevant for subsurface hydromechanical modelling studies. The study area is the Central European Basin System (CEBS) in northern and Central Europe and state-of-the-art ice reconstructions for the last glacial-interglacial period have been used to model the surface hydromechanical loading conditions. Thereby, investigations on how transient ice coverage influences the pore pressure distribution with depth and over time within a heterogeneous sedimentary cover were carried out. The subsurface beneath the CEBS consists of more than 10 km thick sediments, which have been heavily restructured by salt movements during the whole Mesozoic evolution. Our 3D geological model resolves all major sedimentary and crustal domains, and we relied on the GLAC1-D (1.0 degree longitude by 0.5 degree latitude spatial resolution) ice sheet chronology. Starting from ice-free initial conditions, transient simulation runs are performed (hydraulic vs hydromechanical) which cover the entire last glacial cycle, i.e. encompassing 122ka BP till present day conditions. Results are discussed in terms of pore pressure evolution over time and space. The focus will lie on quantifying subsurface conditions favourable to the establishment and maintenance of overpressure evolution and the related equilibration time within the sedimentary pile. We also investigate how these transient conditions influence the subsurface hydrodynamics, showcasing representative time steps during the evolution of the system. We will finally attempt to quantify the memory effect of such loading conditions on the basin-wide hydromechanics, a feedback mechanism that has been neglected so far in 3D subsurface studies.

How to cite: Frick, M., Cacace, M., Klemann, V., Tarasov, L., and Scheck-Wenderoth, M.: The effects of glacial-interglacial loading on the 3D pore pressure evolution in sedimentary basins: case study from the Central European Basin System , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9595, https://doi.org/10.5194/egusphere-egu2020-9595, 2020.

The influences of lunar semidiurnal tides on coastal groundwater aquifers have been conceptualized for decades. However, in estuarine aquifers, comprehensive work is needed to quantify the impact of the tides on groundwater dynamics due to the widely distributed waterways and heterogeneous sediments. Taking the Pearl River estuary in southeast China as a study site, the tidal impacts on the groundwater dynamics have been investigated through wavelet and time series analysis. The groundwater level and electrical conductivity (EC) in four monitoring wells, along with waterway water level (tidal level) at three tidal stations, were monitored every 30 minutes over a 2-month period to determine how nearshore groundwater responds to tidal forcing. The results show that the estuarine groundwater fluctuations have two significant short periodicities (0.51 and 1 day), which correspond to the major tidal constituents in the tides: M₂ (semidiurnal), K₁ and O₁ (diurnal) signals. The significant impacts decrease with increasing distance inland of the locations of the wells. Additionally, the coherence analysis displays a higher correlation between tides and groundwater levels for the spring tide than for the neap tide. The tidal influences on groundwater EC are weaker. In addition, when the tide level increases, the EC decreases in the wells located in the estuarine entrance. This phenomenon is related to the high salinity of retained paleo-seawater in the strata lens. A conceptual model is proposed to illustrate the complex groundwater flow dynamics, which provides useful insights into understanding groundwater systems in other geographically similar coastal estuarine regions.

How to cite: Zhang, X., Dai, Z., Hu, B., Dai, H., Ma, Z., Qi, L., Dong, F., Cao, Y., and Ma, F.: Quantification of the impact of lunar semidiurnal tides on groundwater dynamics in estuarine aquifers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21029, https://doi.org/10.5194/egusphere-egu2020-21029, 2020.

Rapid groundwater depletion is one of the most vital issues related to food and water security in India. However, the crucial role of groundwater pumping and associated policy measures on Flood Potential (FP) in Indian subcontinental river basins remains unexplored. In this study, we examine the impact of groundwater pumping on FP in the Indian subcontinental river basins, having different climatic characteristics. We used Terrestrial Water Storage (TWS) from Gravity recovery climate experiment (GRACE) satellites and precipitation data from the India Meteorological Department (IMD) and Tropical Rainfall Measuring Mission (TRMM) to estimate FP. We estimated the trends of TWS and FP using the nonparametric Mann–Kendall (M-K) method and Sen’s slope method was used to calculate trend magnitudes. We evaluated the results of FP with observed monthly discharge. Moreover, we find a decline in FP in river basins having rapid groundwater depletion. However, no significant change in FP was found for basins where strong policy measures have taken against groundwater pumping.

How to cite: Shah, D. and Mishra, V.: Impact of Groundwater Pumping on Flood Potential (FP) in Indian Sub-continental River Basins, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1125, https://doi.org/10.5194/egusphere-egu2020-1125, 2020.

Excess salinity in drinking water is a serious issue along the southwest coastal of Bangladesh, mainly in reclaimed lands where around 14 million people live and sustain in low-lying deltas. The low-lying deltas are particularly vulnerable to episodic tropical cyclones. The tropical cyclones induced storm surges cause severe floods and extensive damage and result in the salinity in surface water and subsurface water, which have serious impacts on human health such as hypertension and food security due to loss in agricultural yield. In 2011, two years after Cyclone Aila hit the southwest regions of Bangladesh (in 2009), many parts of these regions were still underwater which caused disruption of water supply and contamination of drinking water. The lands were unproductive due to excessive salt in soil and water. A fully coupled surface-subsurface model of a coastal low-lying land is used to investigate the role of tropical cyclonic storm on long-term salinity of water resources in Bangladesh. The hydrogeological parameters of the model were calibrated using data from fieldwork at the site of a pond in Dacope, Khulna. We used the observed water level data from a station at Mongla during Cyclone Aila hit southwest regions of Bangladesh (26 May 2009).The results show how groundwater salinity changes in response to storm surges and monsoon in the coastal low-lying areas. Near-surface groundwater salinity (below 1m-2.3m) takes 4-6 years to return the salinities to pre-surge levels by monsoonal rainfall.

How to cite: Tsai, C. S., Butler, A. P., and Hoque, M. A.: Impact of tropical cyclone storm surges on groundwater salinity in southwest regions of Bangladesh, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19403, https://doi.org/10.5194/egusphere-egu2020-19403, 2020.

Global climate change models predict an increase in both the frequency and severity of extreme weather events, including prolonged drought conditions, thus posing a unique set of challenges for regions traditionally unaccustomed to severe climate phenomena. This is particularly significant for the occurrence of severe drought events in areas characterised by temperate maritime climates, such as the Republic of Ireland (ROI). While numerous studies have explored the impacts of drought on groundwater levels and chemical contamination, few studies have sought to investigate the impacts of sporadic drought events on the microbial quality of groundwater for human consumption. Accordingly, the 2018 (June-August) European drought event represented a unique opportunity to investigate the effects of prolonged low rainfall and elevated temperature (relative to seasonal means) on the incidence of faecal indicator organisms (FIOs) among unregulated domestic groundwater supplies in the ROI.

A dual-sampling fieldwork regime (during and post-event) of private wells (n=74) and subsequent risk factor (logistic regression) and bivariate analyses were used to evaluate the potential role of meteorological and site specific (hydrogeology, contaminant sources etc.) conditions on the incidence of microbial contamination. During absolute drought conditions (≥15 days characterised by no measureable precipitation, June 2018), the sampled cohort exhibited a significantly decreased risk of microbial contamination (OR: 0.356, p = 0.024) with 12.2% (n = 9/74) of supplies contaminated with Escherichia coli (E. coli), increasing to 28.4% (n = 21/74) upon abatement of drought conditions (October 2018). No analysed risk factors were associated with E. coli presence at the 95% confidence level, although, the presence of onsite domestic wastewater treatment systems (U = 1.03 p = 0.057) approached statistical significance during the drought. Findings suggest that the 2018 European drought served to decrease background levels of FIO within private wells in the ROI, likely due to reduced hydraulic loading from the surface, soil moisture deficits and consequently, significantly decreased bacterial survival. Results would seem to reiterate the significance of onsite domestic wastewater treatment systems as a source of subsurface contaminants in Ireland. The presented opportunistic field study provides a critical characterization of the impacts of unprecedented drought events on microbiological water quality in domestic groundwater supplies in temperate regions, and may be used by sanitary/environmental engineers, hydrologists, hydrogeologists, policy-makers, planners and healthcare practitioners to safeguard against the future human health effects of climate change and extreme weather events.   

How to cite: O'Dwyer, J., Weatherill, J., Chique, C., and Hynds, P.: Microbial impact assessment of the 2018 European drought on groundwater quality in the Republic of Ireland: An opportunistic field study , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6071, https://doi.org/10.5194/egusphere-egu2020-6071, 2020.