HS8.2.2

Efficient groundwater management is the key to a sustainable use of freshwater aquifers. In the coastal areas worldwide, saltwater intrusions caused by sea-level rise, overuse of freshwater resources and changing groundwater recharge is a major threat to the availability of freshwater. A reduced groundwater recharge combined with an increased extraction can lead to vertical upconing or lateral movement of the freshwater-saltwater transition zones, therefore reducing the local freshwater resources. Long-term and continuous observation of the freshwater-saltwater transition zones is crucial to implement early warning procedures, yields more detailed insight into the groundwater system and therefore enables early adjustment and adaptation of extraction rates if needed.

The SAltwater MOnitoring System (SAMOS) consists of two main parts: a vertical electrode chain of steel ring electrodes permanently installed in a backfilled borehole and a measuring system at the surface. The number of electrodes (commonly about 80) and distance between adjacent electrodes (commonly about 25 cm) is generally flexible. The chain of electrodes is connected to a lightweight and small resistivity meter (LGM, 4-Point light 10W). Thanks to the maximum output current of 100 mA and a voltage of 380 V a low power consumption is achieved and long-term and autonomous monitoring is enabled by solar panel based power supply. Furthermore, the system is designed to run predefined measurement protocols and transfers the data to a remote server immediately after a measurement is performed. SAMOS is commonly installed in the transition zone between fresh- and saltwater allowing the detection of very slight resistivity changes (less than 1 Ohmmeter). While first systems were completely manufactured by LIAG, the latest subsurface systems were built by Solexperts which allowed us to include temperature sensors.

We present data from four SAMOS systems currently running at different locations. Two of them are installed in the central part of the freshwater lense of the North Sea island Borkum (in cooperation with Stadtwerke Borkum) in depths between 44 m and 65 m below the surface, close to freshwater wells of the local water supplier, thus monitoring the overall groundwater system and delivering data since 2009. Even though measurements immediately after the installation are disturbed by the drilling process and an adjustment to undisturbed natural conditions is observed, adapted inversion schemes allow to use all data. While in most cases only slight resistivity changes are observed up to now, at some depths larger seasonal resistivity changes occur at one Borkum site that can mostly be explained by changes of the groundwater recharge rate and changing pumping activities in a water catchment area. Two further systems have been installed in 2018 and 2020. One is located behind the dune line at the edge of the freshwater lense on the North Sea island Spiekeroog. In cooperation with the local water supply company OOWV (Oldenburg-Ostfriesischer Wasserverband) another system for their groundwater extraction fields is installed near Jever several kilometers from the coast-line used for early warning.

How to cite: Grinat, M., Ronczka, M., Günther, T., Epping, D., Kipke, V., and Mueller-Petke, M.: Long-term monitoring of coastal saltwater intrusion using the geoelectrical monitoring system SAMOS, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9379, https://doi.org/10.5194/egusphere-egu21-9379, 2021.

The coastal zone of the Netherlands is the densely populated economic heartland of the Netherlands. This low-lying area is predominantly located below current mean sea level. Groundwater in large parts of the Dutch coastal zone is saline, having infiltrated during Holocene transgressions. This saline groundwater is now slowly moving upward, driven by artificially lowered drainage levels and resulting land subsidence. Coastal groundwater in the Netherlands is vulnerable to climate change and rising sea levels, as groundwater levels rise, fresh groundwater reserves decrease, and surface water is salinized by exfiltrating saline groundwater.

We developed a high-resolution nationwide 3D fresh-salt groundwater flow and transport model to assess effects of climate change and sea level rise on groundwater salinization in the Netherlands. The fully scripted modelling workflow includes a 3D multiple indicator kriging interpolation of all available salinity measurements, that accounted for uncertainty in both measurements and interpolation. The developed model used a parallellized version of the SEAWAT model code to allow otherwise time-consuming calculations. It links to the existing national hydrological modelling framework to allow calculation of climate change effects on surface water supply and demand and agricultural damage. We used the resulting modelling framework to calculate groundwater effects of different climate change and sea level rise scenarios up to 2100.

Results show significant effects of climate change and especially sea level rise on coastal groundwater. Significant head increase (> 5% of SLR) is experienced in shallow aquifers between 2 to 10 km inland, dependent on the varying hydrogeological settings along the Dutch coast. In deeper aquifers, head increase generally propagates further, to up to 15 km inland. Through the combined effects of head increase and the inward movement of saline groundwater, salt loads to surface water increase over a significantly larger zone, extending to 25 km inward. Results signify the importance of including the long-term displacement of brackish and saline groundwater when assessing coastal groundwater effects of climate change and sea level rise.

How to cite: Delsman, J., Oude Essink, G., Mulder, T., and Huizer, S.: Modelling nationwide climate change effects on coastal groundwater in the Netherlands, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12103, https://doi.org/10.5194/egusphere-egu21-12103, 2021.

The Adriatic region is highly vulnerable to the adverse impacts of climate change. Although attention has been paid to understand the climate change impact and risks over the last decades, the Adriatic community still faces a lack of a common risk assessment. For this reason, ASTERIS project has been financed at the Call for proposal 2017 Priority Axis Safety and resilience of Interregional V Italy-Croatia 2014-2020 Program. To this overall objective, the project will provide two main outputs: i) a map of vulnerability to coastal salinization at the macro-regional scale (Adriatic) based on future scenarios for sea-level rise and the hydrological cycle and ii) best practice and guidelines for the management of vulnerable sites defined though the analysis of representative case studies in Italy and Croatia. Within these general purposes, hydrogeological and geochemical surveys in two specific shallow aquifer systems that develop in the coastal areas of Fano and Ravenna (central-eastern Italy), were carried out. Several periodical campaigns, aimed at measuring water level and physical-chemical parameters by vertical logs in wells or piezometers, were also conducted. Additionally, ground and surface water samples were also collected for chemical and isotopic analyses to define the compositional features and the main geochemical processes affecting the two shallow aquifers. Preliminary investigations suggested that the Ravenna shallow aquifer is already strongly spoiled by a significant seawater intrusion (up to 80 %), whereas at Fano the presence of the saline wedge can be regarded as negligible. This indicates that the aquifer system of Fano can be considered as a good proxy for evaluating and simulating potential processes of saline-fresh water interactions by either the increasing demand of water exploitation and sea level rise due to anthropogenic pressure and climate change, respectively. In order to simulate possible future ingressions of seawater in the aquifer system of Fano, groundwater flow and transport models are currently in progress. These models will be implemented and calibrated according to the hydrogeological and geochemical data collected within the framework of the ASTERIS project. The expected modelled scenarios, obtained through predictive simulations, are of pivotal importance for assessing the possible groundwater response to climate change and for a correct management and protection of water resources, which can be exported to other aquifers system along the Adriatic Sea.

How to cite: Nisi, B., Menichini, M., Doveri, M., Cabassi, J., Vaselli, O., Botteghi, S., Masetti, G., Raco, B., Franceschi, L., Calvi, E., and Trifirò, S.: Adaptation to Saltwater inTrusion in sEa level RIse Scenarios (ASTERIS): hydrogeochemical surveys and aquifer modelling for groundwater behaviour assessing in the coastal areas of Fano and Ravenna (central-eastern Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9069, https://doi.org/10.5194/egusphere-egu21-9069, 2021.

Like in other relatively flat coastal areas, flooding by aquifer overflow is a recurring problem on the western coast of Normandy (France). Threats are expected to be enhanced by the rise of the sea level and to have critical consequences on the future development and management of the territory. The delineation of the increased saturation areas is a required step to assess the impact of climate change locally. Preliminary models showed that vulnerability does not result only from the sea side but also from the continental side through the modifications of the hydrological regime.

We investigate the processes controlling these coastal flooding phenomena by using hydrogeological models calibrated at large scale with an innovative method reproducing the hydrographic network. Reference study sites selected for their proven sensitivity to flooding have been used to validate the methodology and determine the influence of the different geomorphological configurations frequently encountered along the coastal line.

Hydrogeological models show that the rise of the sea level induces an irregular increase in coastal aquifer saturations extending up to several kilometers inland. Back-littoral channels traditionally used as a large-scale drainage system against high tides limits the propagation of aquifer saturation upstream, provided that channels are not dominantly under maritime influence. High seepage fed by increased recharge occurring in climatic extremes may extend the vulnerable areas and further limit the effectiveness of the drainage system. Local configurations are investigated to categorize the influence of the local geological and geomorphological structures and upscale it at the regional scale.

How to cite: Gauvain, A., Abhervé, R., de Dreuzy, J.-R., Aquilina, L., and Gresselin, F.: Vulnerability of coastal areas to increased aquifer saturation due to climate change, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14870, https://doi.org/10.5194/egusphere-egu21-14870, 2021.

Groundwater represents 98% of the world's freshwater resource. This resource is strongly impacted by the increase in temperature and variation in precipitation. Therefore, the relationship between climate change and the dynamics of aquifer recharge is still poorly understood. It was not until the 1980s when investigations in this field were improved. This research aims to evaluate the studies carried out on the impact of climate change-related to the recharge of aquifers. The applied methodology is strictly based on the bibliographic review. Bibliographic references were selected from citation database Scopus. This database was studied from a quantitative analysis using the Bibliometric package in RStudio. This investigation evaluates growth performance research on aquifer recharge on climate change from the 1980s to 2020.

The results show an average growth of 14.38% and a significant increase in research from 2009. This study identifies 52 countries, just over 26% of total countries; the highest contribution has been made by Australia, the United States and Spain. The journals with the most increased contributions are Water Journal, Journal of Hydrology, Water Resources Research, Science of the Total Environment, and Hydrology and Earth System Sciences. According to the impact of climate change, the worst projections related to the decrease in recharge were identified in arid and desert areas. While the highest recharges were placed in the northern regions and at high altitudes where the recharge capacity is maintained or increases due to rapid thaw and increasing rain. More studies should be extended to analyse groundwater assessment in other latitudes to achieve a complete and comprehensive understanding. This understanding should be one of the priorities of water and governments' scientific society to safeguard this precious resource.

Key words: Climate change, aquifer recharge, climate models, precipitation, and temperature.

How to cite: Cárdenas-Castillero, G. and Kuráž, M.: Assessment interaction of climate change and aquifer recharge in different periods: an article review, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15171, https://doi.org/10.5194/egusphere-egu21-15171, 2021.

According to the results of processing long-term data series of hydrological and hydrogeological monitoring in the upper part of the Southern Bug river basin, it has been found that meteorological or climatic changes affect both terrestrial hydrosphere and shallow groundwater aquifer (level = 0.5…7.0 m). There are two stages of different effects of temperature changes on the groundwater regime: the first stage (1974-1998) had a positive impact, with an increased infiltration recharge and large-scale flooding, while the second stage (1999-2020) is characterized by increasing drought. The average annual infiltration recharge of groundwater on the first terrace above the flood-plain at the first stage has reached 191.6 mm that is quite high for this climatic zone, while at the second stage – 115.0 mm. The highest groundwater runoff to the river was recorded in 1987-1989 (the first terrace above the flood-plain), 1996-1998, 2005, and 2014 (from the left-bank catchment). By seasonal distribution, the spring runoff mostly prevailed in 1981-1986; starting from 1996-1999 (in different areas) – summer runoff, especially in years with maximum underground runoff; the winter runoff to the river slightly prevailed in certain years (1994, 1998, 2000, 2008, 2015).

With the transition from a low-water cycle of years to a water-rich cycle (and vice versa), the dominant cyclicity in the regime of groundwater and surface water changes from 5-6 years to 7-8 years.

1974-1975 and 1987-1989 had certain temperature limits that caused significant changes in the groundwater level regime: firstly, at long-term annual average depths of 1.5-1.8 m under the surface, and later at depths of 3.0-4.4 m having led to the transition and consolidation of levels at higher grades. At the second stage, the trends of precipitation, groundwater and surface runoff change significantly (surface runoff decreases most rapidly, while the intensity of groundwater runoff has slowed down), but the temperature rises with almost the same intensity. The dependence of the total river runoff on the underground increases.

In the long-term plan (40 years), groundwater and river runoffs change in opposite directions, as the regime-forming factors (temperature and precipitation) have different effects on them: rising temperatures at the first stage have led to increased groundwater runoff; at the same time, the intensity of the decrease in river runoff under the influence of temperature as well as the decrease in precipitation at the second stage increase. The difference in the rate of reactions of groundwater and surface water levels to precipitation still provides an increase in groundwater runoff by increasing the flow gradient to the river. With decreasing rainfall, this scenario will certainly lead to the depletion of groundwater reserves.

How to cite: Osadchyi, V., Shevchenko, O., and Krasovs’ka, A.: Formation features of river underground runoff under global warming conditions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15311, https://doi.org/10.5194/egusphere-egu21-15311, 2021.

*Correspondence: alaba@squ.edu.om

Abstract: The primary objective of this study was to quantify the impacts of climate change on groundwater recharge using the 3D numerical-based HydroGeoSphere (HGS) model in the Ubar/ Shisr Agricultural region in South of Oman. This region has multi-million US dollar irrigated agriculture project purposely developed for the food security of the country. Excessive abstraction of groundwater for irrigation use (using the center pivot irrigation system) has contributed to the “drying-up” of several groundwater wells located in this area. Therefore, there is an urgent need to characterize the long-term sustainability of this agricultural project under a changing climate. HGS model was calibrated on both steady and transient states using selected monitoring wells located within the study area (approximately 980-km²). The coefficient of determination (R²) for the steady-state performance was 0.93 while the transient state performances correctly reproduced the seasonality for each monitoring well. A transient-based calibrated version of the HGS model, using 30-year historical observations (1980-2018) was termed “Reference” while model configurations were developed for the immediate climatic projection (period: 2020 – 2039) based on two Representative Concentration Pathways (RCP): - RPC4.5 and RCP8.5 extracted from the World Bank Knowledge portal. These two configured models (scenarios) were evaluated for monthly transient simulations (2020-2039). From the total hydraulic head (THH) fluctuations standpoint, there were reductions when compared with “Reference” for all the scenarios with up to 20% THH reductions for groundwater well levels under persistent seasonal agricultural activities. This study is very important in quantifying the trade-offs and synergies involved between sustainable water management and food security initiatives, especially for an arid climate.

Keywords: groundwater recharge; climate change, hydrogeologic modeling; Sultanate of Oman

How to cite: Boluwade, A., Al-Mamani, A., Alruheili, A., and Al-Maktoumi, A.: Impacts of Climate Change on Groundwater Recharge & Discharge in Water Scarce Region: A Case Study of the Ubar/ Shisr Agricultural Region of Oman., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6577, https://doi.org/10.5194/egusphere-egu21-6577, 2021.

Groundwater is the main source of freshwater and maintains streamflow during drought. Potential future groundwater and baseflow drought hazards depend on the systems' sensitivity to altered recharge conditions. We performed groundwater model experiments using three different generic stress tests to estimate the groundwater- and baseflow drought sensitivity to changes in recharge. The stress tests stem from a stakeholder co-design process that specifically followed the idea of altering known drought events from the past, i.e. asking whether altered recharge could have made a particular event worse. Here we show that groundwater responses to the stress tests are highly heterogeneous across Germany with groundwater heads in the North more sensitive to long-term recharge and in the Central German Uplands to short-term recharge variations. Baseflow droughts are generally more sensitive to intra-annual dynamics and baseflow responses to the stress tests are smaller compared to the groundwater heads. The groundwater drought recovery time is mainly driven by the hydrogeological conditions with slow (fast) recovery in the porous (fractured rock) aquifers. In general, a seasonal shift of recharge (i.e., less summer recharge and more winter recharge) will therefore have low effects on groundwater and baseflow drought severity. A lengthening of dry spells might cause much stronger responses, especially in regions with slow groundwater response to precipitation. Water management may need to consider the spatially different sensitivities of the groundwater system and the potential for more severe groundwater droughts in the large porous aquifers following prolonged meteorological droughts, particularly in the context of climate change projections indicating stronger seasonality and more severe drought events.

How to cite: Hellwig, J., Stoelzle, M., and Stahl, K.: Stress-testing groundwater and baseflow drought sensitivity to recharge, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10511, https://doi.org/10.5194/egusphere-egu21-10511, 2021.

Clear signs of climate stress on groundwater resources have been observed in recent years even in generally water-rich regions such as Germany. Severe droughts, resulting in decreased groundwater recharge, led to declining groundwater levels in many regions and even local drinking water shortages have occurred in past summers. We investigate how climate change will directly influence the groundwater resources in Germany until the year 2100. For this purpose, we use a machine learning groundwater level forecasting framework, based on Convolutional Neural Networks, which has already proven its suitability in modelling groundwater levels. We predict groundwater levels on more than 120 wells distributed over the entire area of Germany that showed strong reactions to meteorological signals in the past. The inputs are derived from the RCP8.5 scenario of six climate models, pre-selected and pre-processed by the German Meteorological Service, thus representing large parts of the range of the expected change in the next 80 years. Our models are based on precipitation and temperature and are carefully evaluated in the past and only wells with models reaching high forecasting skill scores are included in our study. We only consider natural climate change effects based on meteorological changes, while highly uncertain human factors, such as increased groundwater abstraction or irrigation effects, remain unconsidered due to a lack of reliable input data. We can show significant (p<0.05) declining groundwater levels for a large majority of the considered wells, however, at the same time we interestingly observe the opposite behaviour for a small portion of the considered locations. Further, we show mostly strong increasing variability, thus an increasing number of extreme groundwater events. The spatial patterns of all observed changes reveal stronger decreasing groundwater levels especially in the northern and eastern part of Germany, emphasizing the already existing decreasing trends in these regions

How to cite: Wunsch, A., Liesch, T., and Broda, S.: Deep Learning based assessment of groundwater level development in Germany until 2100, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9590, https://doi.org/10.5194/egusphere-egu21-9590, 2021.

Groundwater level time series are the basis for various groundwater-related studies. The most valuable are long term, gapless and evenly spatially distributed datasets. However, most historical datasets have been acquired during a long-term period by various operators and database maintainers, using different data collection methods (manual measurements or automatic data loggers) and usually contain gaps and errors, that can originate both from measurement process and data processing. The easiest way is to eliminate the time series with obvious errors from further analysis, but then most of the valuable dataset may be lost, decreasing spatial and time coverage. Some gaps can be easily replaced by traditional methods (e.g. by mean values), but filling longer observation gaps (missing months, years) is complicated and often leads to false results. Thus, an effort should be made to retain as much as possible actual observation data.

In this study we present (1) most typical data errors found in long-term groundwater level monitoring datasets, (2) provide techniques to visually identify such errors and finally, (3) propose best ways of how to treat such errors. The approach also includes confidence levels for identification and decision-making process. The aim of the study was to pre-treat groundwater level time series obtained from the national monitoring network in Latvia for further use in groundwater drought modelling studies.

This research is funded by the Latvian Council of Science, project “Spatial and temporal prediction of groundwater drought with mixed models for multilayer sedimentary basin under climate change”, project No. lzp-2019/1-0165.

How to cite: Bikše, J., Retike, I., Kalvāns, A., Dēliņa, A., Babre, A., Popovs, K., Jemeļjanova, M., Zelenkevičs, A., Baikovs, A., and Avotniece, Z.: Rescue of groundwater level time series: how to identify and treat errors, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9877, https://doi.org/10.5194/egusphere-egu21-9877, 2021.

Recent groundwater data analyses show an increase of groundwater temperature related to climate warming. This trend is suspected to occur at springs as well, in particular springs draining shallow aquifer systems being affected by air temperature. Contrary, deeper circulating systems such as large karst aquifers and the related springs may not show this water temperature increase. In this study, we investigate long term spring data from all over Austria. This is done through trend analyses of long-term time series of discharge, water temperature, and electrical conductivity from 97 springs in Austria The data are provided by the Hydrographic Service of Austria  and the observation period ranges from several years up to more than 30 years. The springs drain a wide range of aquifer types, from karst areas to periglacial sediments. Importantly, the springs mainly drain mountainous regions that are less anthropogenically influenced than most of the groundwater wells in the intermontane valleys and basins.

Preliminary results show significant trends of increasing water temperatures in some springs, potentially related to climate warming and through changes in precipitation (e.g., occurring as snowfall or rainfall). However, such a trend cannot be observed for all springs and it is suggested that certain aquifer types are more prone to climate warming, others are better protected / shielded due to their extend and flow characteristics. Trend analysis is performed not only for water temperature, but also for electrical conductivity and spring discharge. There, trends are less obvious or not as consistent. Therefore, a direct impact from climate change needs to be treated cautiously, reflecting aquifer characteristics. However, a better understanding is essential to further predict future development and help in water management planning. Future work will focus on identifying changes in system characteristics over the observation period, by computing autocorrelations and master recession curves over different time periods.

How to cite: Hausleber, M., Obwegs, M., Collenteur, R., Vremec, M., Wagner, T., Eybl, J., and Winkler, G.: Analysis of long-term spring data in Austria – trends and changes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14493, https://doi.org/10.5194/egusphere-egu21-14493, 2021.