Groundwater is het largest available freshwater resource on earth and is critical to humans and the environment. Groundwater is especially important for irrigated agriculture, and thus for global crop production and food security; approximately 40% of the today’s irrigated agriculture depends on groundwater. In many regions around the world, unsustainable groundwater pumping exceeds recharge from precipitation and rivers. This leads to substantial drops in groundwater levels and losses of groundwater from its storage, especially in intensively irrigated regions, as well as reduction of river flows with possible devastating impacts on freshwater ecosystems.

In my research I simulate groundwater flows and groundwater surface water interactions globally, using a high resolution coupled groundwater and surface water model, and study the impacts of groundwater pumping from the recent past until the far future. In this talk I will present recent findings on current and projected impacts of groundwater pumping on river flows, including an estimate where and when environmentally critical thresholds for groundwater discharge are reached. Second, I will present novel developments and future research steps me and my team will take towards estimating global groundwater availability that can be sustainably exploited and the trade-off between sustainable groundwater use and crop production.

How to cite: de Graaf, I.: Groundwater availability and sustainability, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11454, https://doi.org/10.5194/egusphere-egu23-11454, 2023.

Insufficient and fragmented management of TBAs might affect sustainable development both within and beyond a country's borders. There are several examples worldwide of disagreements over whether a certain infrastructure scheme planned by one riparian country would have negative impacts on a riparian state. Transborder cooperation and knowledge of transboundary aquifers (TBAs) has evolved through an inventory under the convention on the protection and use of transboundary watercourses and international lakes (Water Convention) from 1992. Within EU countries, the Water Framework Directive (WFD), 2000/60/EC, intends to contribute to achieve the objectives of the Water Convention. The national groundwater management systems in Norway and Sweden and their implementation of the WFD has been studied as a case area. Emphasis has been placed on international river basin districts (IRBD) and transborder cooperation. The findings offer recommendations for authorities and policymakers on how they could improve the long-term management and ensuring transparent decision-making of transboundary groundwater management.

In Norway and Sweden, TBAs play a minor role in supplying freshwater resources and sustaining socio-economic development in transborder areas. The analysis shows that surface water overrules ‘the invisible’ groundwater. The study highlights several factors that need to be addressed. First, the Norwegian national water management systems are fragmented and over-complex, which complicates national and transnational cooperation. Second, Swedish legislation must be revised to meet the requirements of the WFD regarding IRBD delineation. Finally, transborder dialogue and joint projects on groundwater mapping are necessary for mobilising resources and the necessary political support to obtain knowledge on TBAs.

More information on the study preformed through funding from the EEA and Norway Grants Fund for Regional Cooperation can be achieved from Flem at al., (2022).

Acknowledgements:

This study has been done within project No.2018-1-0137 “EU-WATERRES: EU-integrated management system of cross-border groundwater resources and anthropogenic hazards” which benefits from a € 2.447.761 grant from Iceland, Liechtenstein and Norway through the EEA and Norway Grants Fund for Regional Cooperation. The aim of the project is to promote coordinated management and integrated protection of transboundary groundwater by creating a geoinformation platform.

References:

Flem, B., Stalsberg, L., Seither, A., 2022. Groundwater governance in international river basins - An analysis of the Norwegian-Swedish transborder area. J. Hydrol. Reg. Stud, 44, 2022, 101216. https://doi.org/10.1016/j.ejrh.2022.101216

How to cite: Flem, B. and Stalsberg, L.: International River Basin Planning Under the Water Framework Directive and the SDG indicator 6.5.2 – Case area: Norway - Sweden, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2342, https://doi.org/10.5194/egusphere-egu23-2342, 2023.

While several studies deal with description and causes leading to aquifer overexploitation, relatively few face the challenge of reverting unbalanced situations. Since 60 years, intensive exploitation of groundwater of the lower Cornia valley aquifer system (Tuscany, Italy) resulted in consistent head lowering and water balance deficit, subsidence, reduction of groundwater dependent terrestrial ecosystems, and salinization of freshwater resources. There, groundwater is the only source of water for drinking, irrigation, industrial purposes and it also contributes to the water needs of the nearby Elba island. We present here the main results achieved within the EU funded LIFE REWAT project (sustainable WATer management in the lower Cornia valley through demand REduction, aquifer Recharge and river REstoration; http://www.liferewat.eu) aiming at rebalancing the water budget of the Cornia river hydrologic system by means of innovation and participatory processes.

Since 2018, five demonstration measures (river restoration works; Managed Aquifer Recharge; reuse of treated wastewater for irrigation; high irrigation efficiency scheme; leakage management in water distribution systems) were built and set in operation for promoting sustainable groundwater resource management, along with capacity building and participatory actions.

Results show an increase in recharge/storage of about 2.5 Mm³ per year, with noticeable effects related to the increase in natural recharge from the Cornia riverbed to the aquifer (for about 1.5 Mm³/year) due to morphological restoration works. The Managed Aquifer Recharge two-stage infiltration basin of Suvereto guaranteed an increase in recharge of about 0.5 Mm³/year. Additional storage increase is related to the reduction in leakage losses from drinking water network and thanks to a more careful use of irrigation water in farming. In about two years, thanks also to favorable hydrologic conditions, the groundwater head generally arose of about 2 to 3 m in the Cornia plain. All the technical works have been complemented by a two years long participatory process leading to the signature of The Cornia River Contract. This is a voluntary agreement among the main stakeholders to promote a shared vision on next 50 years needed actions to achieve environmental sustainability along with proper water resources management. The results achieved so far provide a clear trend towards the Cornia aquifer restoration by means of low-impact and nature-based solutions along with a large involvement of the main stakeholders in creating a shared knowledge on the value of the groundwater resource.

Acknowledgement

This contribution is presented within the framework of the LIFE REWAT project. The LIFE REWAT project received funding from the European Union's Life Programme LIFE 14 ENV/IT/001290.

How to cite: Rossetto, R., Caligaris, E. R., Ercoli, L., Barbagli, A., Francini, A., Lazzaroni, F., Pei, A., Menonna, V., Masi, M., Brilli, M., Benucci, C., Palumbo, F., Maggiorelli, R., Rotelli, L., and Fabbrizzi, A.: Restoring an overexploited aquifer: insights from the Val di Cornia coastal aquifer (Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13896, https://doi.org/10.5194/egusphere-egu23-13896, 2023.

The mountains often “subsidize” water resources to lowlands in arid and semi-arid regions. In the case of Central Asia (CA), the mountain cryosphere is the “water tower” for the population residing in the intermountain valleys and lowland plains. Much of the water research in CA is focused on surface water provision by mountain glaciers and snow such as rivers, lakes, and reservoirs, whilst groundwater recharge is much less investigated. The preliminary hydrogeologic models of deep (up to 3km) groundwater recharge for sedimentary basins (southern Kazakhstan) in the upper Ily and lower Syr Darya river valleys are derived from interpretations of stable isotopes of oxygen, hydrogen, and tritium. The results show that in these basins groundwater at different depths (both shallow and deep) bears depleted abundance of heavy stable-isotope species indicative of winter precipitation (snow). In Ily basin (Zharkent depression) the proportion of snow(melt) contribution increases with depth with water from very deep geothermal wells (~3000 m, the upper cretaceous aquifer) being more isotopically depleted compared to shallower geothermal wells (i.e. depths up to 650m) and shallow groundwaters. Additionally, formation water in the deep geothermal wells (Zharkent area) had no detectible tritium (< 0.71 TU) pointing to an absence of modern recharge (within the past ~ 70 years). Geothermal water from wells (shallow ground water and depth of ~ 1200 m) and a spring in the lower Syr Darya river and the North Aral area, also shows deleted stable water isotope imprints suggesting strong winter recharge contributions. This is surprising as the Aral Sea depression has very low precipitation (less than 200 mm/year) and very little snowfall. These isotope data suggest regional aquifers are recharged primarily by lateral groundwater flows via deep flow paths from mountain regions. This is further corroborated by low salinity (< 1 g/l) of most deep geothermal water samples pointing to dilution by snowmelt. We suggest the aquifers in these CA regions may be replenished mostly by Mountain Block and/or Front recharge mechanisms, but this hypothesis requires further investigation.

How to cite: Yapiyev, V., Kozhagulova, A., Karabayanova, L., Kalitova, A., Zavaley, V., Dillinger, A., Karakozhayeva, A., Holbrook, J., Kurbaniyazov, S., Ongdas, N., Stefan, C., and Fustic, M.: Mountain Block and Front Recharge to the aquifers in sedimentary basins in Kazakhstan: evidence from geothermal studies and water isotopes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8380, https://doi.org/10.5194/egusphere-egu23-8380, 2023.

The assessment of groundwater quality and its geochemical mechanism is crucial for the sustainable use and management of groundwater resources in arid and semi-arid regions of developing nations. 120 groundwater samples were collected from the Komadugu-Yobe basin to determine its overall quality and the factors that controls the geochemical mechanisms of the groundwater of the study region. The pH, electrical conductivity (EC), and total dissolved solids (TDS) of the groundwater samples were analysed in situ using a handheld (Model 99720 pH/Conductivity meter). The concentrations of Na⁺, Ca²⁺, Mg²⁺, and K⁺ were analyzed using ICP-OES, iCAP 6200, Thermo Fisher Scientific while Cl^-, F^-, SO₄^2-, and NO₃^- were analysed using Ion Chromatography (Metrohm 850 Professional IC). Moreover, the total Alkalinity and bicarbonate were determined using KONE Aquakem v. 7.2.AQ2 equipment by titrimetric method. The hydrochemical analysis results reveals that less than 10% of the groundwater samples exceeded the maximum permissible limits for Electrical conductivity, total dissolved solids, total hardness, sodium, potassium, calcium, magnesium, chloride, sulfate, and fluoride for drinking purposes as recommended by the world Health Organization (WHO, 2018) standards except for bicarbonate and nitrate. The Gibbs diagrams reveals that rock-weathering/rock water interaction is the dominant mechanism controlling groundwater of the study region. However, the chemical relationships in Piper trilinear plots identified Ca²⁺-Mg²⁺- HCO^-₃ water type predominated the study area constituting about 59% of the groundwater samples collected. The findings of the study are paramount for implementing a sustainable management strategy of groundwater resources in the Komadugu-Yobe basin towards the realization of Goal 6 of sustainable development goals.

Keywords: Groundwater, Komadugu-Yobe basin, Geospatial analysis, Water quality, Rock-water interaction

How to cite: Shuaibu, A., M. Kalin, R., and Phoenix, V.: Groundwater Quality Assessment and Geochemical Mechanism of Groundwater of Komadugu-Yobe Basin, West Africa, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-491, https://doi.org/10.5194/egusphere-egu23-491, 2023.

Key Words: Groundwater Infrastructure, Functionality, Accountability, Right to water

The Malawi 2018 Sector Performance Report produced by the Ministry of Water and Sanitation found that the proportion of people with access to safe water in the country was 86%, with 57% of improved water points in rural areas being boreholes with hand-pumps. However, a persistent sustainability challenge plagues the water sector: for over 20 years, the functionality of improved water points has remained between 69% and 77%. A study on borehole forensics conducted by the CJF programme found that 30% of hand-pumps fail within five years of installation.

Over the past decade hand pump non-functionality has been attributed to poor community ownership and lack of responsibility to manage the operation and maintenance of the wells. However, in some cases this has been merely hypothetical as the non-functionality of some boreholes has been due to factors that are beyond what communities can manage in terms of operation and maintenance.

BASEflow with support from the Scottish Government conducted Borehole Forensics, which is a detailed investigation of a borehole and hand pump performance.  Twenty one (21) boreholes were technically assessed and out of these, 13 were found to have unacceptable low yield as per the required Government constant pumping rate test standard of 0.25 liters per second for not less than 4 hours. The failure of the 13 boreholes indicate that the boreholes were developed and constructed to completion and handed over to users when they did not have enough water to meet the required standards.

These findings were shared with the relevant stakeholders at Community, District and National level. One major policy recommendation at National level is for the need for adherence to water infrastructure construction standards and the need to empower citizens of rights to water and to hold service providers accountable for failed groundwater supply infrastructure.

How to cite: Kumwenda, S., Nhlema, M., Ngwira, G., Banda, P., and Nyasulu, T.: Triggering social accountability for failed groundwater supply infrastructure in rural Malawi: Chiradzulu case study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-891, https://doi.org/10.5194/egusphere-egu23-891, 2023.

The spatial and temporal resolution of global-scale hydrological modeling has enormously increased in recent years. Outputs are becoming available at spatial resolutions of 1x1 km, showing regional structures and changes, often in beautiful figures and large datasets covering the entire globe. The complexity of the underlying models has increased in parallel, as did the amount of input data. Model outputs start more and more to look like the actual planet.

If humanoids start to look more and more like actual humans, an adverse emotional reaction can be seen in humans. In robotics and other disciplines, the term “uncanny valley” was coined for this phenomenon of the creepy impression that humanoids that are too human-like leave on humans.

The increasing resolution of global hydro (geo)logical modeling outputs is partly mirrored by the increasing resolution of input data, e.g., satellite-derived climate data or vegetation information. However, input data based on in-situ observations can remain limited in resolution and remain highly uncertain. In addition, higher resolution models do not necessarily entail that our process understanding has improved. Here, we review and analyze the primary input data of global hydro(geo)logical models, identify critical datasets and discuss the implications of the reliance on these datasets for modern hydro(geo)logical model results. Moreover, we discuss if results that look more and more like the real planet should lead to skepticism in their interpretation similar to the emotional reaction to the uncanny valley in robotics.  

How to cite: Moosdorf, N., Reinecke, R., and Befus, K.: Global hydro(geo)logical modeling: are we missing an uncanny valley?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9452, https://doi.org/10.5194/egusphere-egu23-9452, 2023.

In the course of climate change serious effects on groundwater resources are expected. Future groundwater recharge is usually assessed via hydrological models. Various studies have shown that most models fail in depicting pronounced trends observed in groundwater monitoring data at regional scales. Likewise, global hydrological models seem to systematically underestimate the low-frequency dynamics of regional water storages in the GRACE mission data (Scanlon et al. 2018) or long-lasting memory effects in terms of discharge (Fowler et al. 2022). Thus groundwater recharge modelling appears to have some fundamental problems that go far beyond the usual model uncertainties in each individual case.

This was systematically investigated. The empirical basis was given by the analysis of groundwater data of the authorities’ monitoring networks in Northeast Germany, covering an area of more than 50,000 km². About 240 long-term time series of groundwater head and lake water level were studied. It could be shown that at weekly or monthly time scales lake water level dynamics very closely mimicked that of the adjacent groundwater body.

A very close correlation between the direction and strength of the trends and the degree of damping of the signal of groundwater recharge was found. The probability of long-term trends systematically increased with the thickness of the vadose zone. This indicates the crucial role of long-term accumulation of soil moisture deficits in the deeper unsaturated zone.

In contrast, models of groundwater recharge generally consider only the uppermost soil layers. In addition, modellers usually assume initial steady-state equilibrium conditions and thus ignore long-term memory effects in the subsurface. Simulations with different models clearly showed that this resulted in a systematic underestimation of long-term trends. Finally, it was found that model parameterizations which had been optimized with respect to discharge or topsoil moisture dynamics were not necessarily optimal for the simulation of groundwater recharge. Based on these findings clear recommendations for monitoring and model-based assessment of groundwater recharge will be given.

References:

Scanlon et al. (2018), PNAS, http://ww.pnas.org/cgi/doi/10.1073/pnas.1704665115

Fowler et al. (2022), WRR, https://doi.org/10.1029/2021WR031210

Lischeid et al. (2021), JHyd, https://doi.org/10.1016/j.jhydrol.2021.126096

How to cite: Lischeid, G. and Steidl, J.: Why do our models underestimate regional groundwater trends?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2565, https://doi.org/10.5194/egusphere-egu23-2565, 2023.

If not addressed and remedied, the unsustainable use of non-renewable groundwater will negatively impact many future generations. To effectively manage global groundwater reserves, we first need accurate estimates of its current availability and how much of this we can feasibly extract. Landscape characteristics have a high impact on local groundwater recharge, groundwater-surface water interactions, and abstractions. It is therefore key to model groundwater at an appropriate spatial resolution so that landscape heterogeneities are captured. Our objective is to enable groundwater modelling at fine spatial (~ 1 km) resolution, with the final aim to assess the physical limits of groundwater withdrawal by providing the first global estimates of fresh groundwater availability (attainable volumes and supply) subject to past human water use. The first step to attaining this objective is the ability to simulate groundwater recharge and surface water levels at 1 km spatial resolution using a global hydrological model. In this study, we aim to tackle this challenge and present the first global case of the PCR-GLOBWB at the 1 km spatial resolution. To do this, we implemented a statistical downscaling routine for meteorological forcing, created a new global 1km land surface parameterization and improved the parallelization of the PCR-GLOBWB model. The meteorological downscaling approach followed here provides outputs that are at a finer resolution than the original meteorological forcing products. This approach relies on Worldclim data to provide realistic sub-grid distributions of precipitation and temperature. In addition, sub-grid distributions of potential reference evaporation were retrieved from the Global Aridity Index and Potential Evapotranspiration Climate Database, which uses Worldclim data to calculate potential reference evaporation following the Penman-Monteith formulation.

We investigate whether these high-resolution meteorological fields, in combination with an improved 1km land surface parameterization, provided improved outcomes by validating against remote sensing observations (soil moisture, total water storage) and local observations of discharge and compare these to simulation at coarser 10 & 50km resolutions. Furthermore, we discuss the computational challenges encountered along the way and outline future directions and opportunities in high-resolution groundwater modelling.

How to cite: van Jaarsveld, B., Dunn, F., Sutanudjaja, E. H., van Beek, R., Bierkens, M. F. P., and Wanders, N.: Hyper resolution hydrological modeling: the need and benefit of improving spatial resolutions of global models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4052, https://doi.org/10.5194/egusphere-egu23-4052, 2023.

The Global Gravity-based Groundwater Product (G3P) developed a satellite-based groundwater storage anomaly (GWSA) data set as a prototype for a future product within the EU Copernicus Climate Change Service. As the world’s largest distributed freshwater storage, GW is a key resource for mankind, industrial, and agricultural demands. In Copernicus, there is no service available yet to deliver data on this fundamental resource, nor is there any other data source worldwide that operationally provides information on changing groundwater resources in a consistent way, observation-based, and with global coverage. Therefore, G3P developed the global data set of groundwater storage variations as a cross-cutting extension of the existing Copernicus portfolio. G3P capitalizes from the unique capability of GRACE and GRACE-FO satellite gravimetry as the only remote sensing technology to monitor subsurface mass variations, and from other satellite-based water storage products to provide a data set of groundwater storage change for large areas with global coverage. G3P is obtained by using a mass balance approach, i.e., by subtracting satellite-based water storage compartments (WSCs) such as snow water equivalent, root-zone soil moisture, glacier mass, and surface water storage from GRACE/GRACE-FO monthly terrestrial water storage anomalies (TWSA). For a consistent subtraction of all individual WSCs from GRACE-TWSA, the individual WSCs are filtered in a similar way as GRACE-TWSA, where optimal filter types were derived by analyses of spatial correlation patterns. G3P groundwater variations are provided for almost two decades (from 2002 to 2020), with a monthly resolution, and at a 0.5-degree spatial resolution globally.

In this contribution, we also illustrate selected results of the G3P-based GWSA data set, including the global trends of groundwater storage and the uncertainties of the GWSA data as well as of the contributing storage compartments. The GWSA is also evaluated against in-situ groundwater observations, using 13 large aquifers worldwide with available in-situ groundwater observations. Results show a high correlation between the variations of in-situ groundwater data and G3P-based GWSA for most of the aquifers, such as the Ogallala aquifer, Floridan aquifer, Paris Basin, South of Outer Himalayas aquifer.

This study has received funding from the European Union’s Horizon 2020 research and innovation programme for G3P (Global Gravity-based Groundwater Product) under grant agreement nº 870353.

How to cite: Sharifi, E., Güntner, A., Haas, J., Dorigo, W., Jäggi, A., and Ruz Vargas, C. and the G3P team: G3P: A global data set of groundwater storage variations based on satellite gravimetry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10289, https://doi.org/10.5194/egusphere-egu23-10289, 2023.

Groundwater resources are generally evaluated by quantifying groundwater recharge and its storage into the aquifer using for example conceptual or numerical models. Recharge modelling provides a preliminary estimation of the renewable part of the groundwater resource. Moreover, results of regional groundwater recharge models may be used as input data for models on a smaller scale, i.e. at the catchment scale dedicated to water management for present and future conditions. It is thus necessary to constrain the recharge models for example by comparing their outputs to historical long-term observations of groundwater flows that can be derived from time series of groundwater levels or spring discharge.

Karst systems with their high infiltration rate and preferential flow in enlarged conduit networks, react quickly to climatic events and changes. Thus, they can be used as proxies to evaluate the impact of global change on groundwater resources. Karst systems are present in different climatic regions of Europe, which allows comparing long-term trends of groundwater recharge with spring discharge (similar or opposing trends). In our study, two different regional recharge models covering entire Europe – one calculating potential groundwater recharge using simple soil water balance methods and one calculating groundwater recharge over karst areas only using 1-D physical equations for infiltration – are compared to the measured spring discharge from a large European database of more than 100 monitored karst systems. To identify and highlight changes in dominant recharge processes related to changing climatic or physiographic (land cover / land use) conditions, different variables used in the regional recharge models will be correlated to indices describing dynamics of karst spring discharge. The results of our study will help to understand the impact of climatic and groundwater recharge related influences on various geographic locations and give insights on uncertainties in the model structure of the applied regional groundwater recharge models.

How to cite: Giese, M., Charlier, J.-B., Hartmann, A., and Caballero, Y.: Groundwater evolution in Europe - comparing recharge model outputs with spring discharge from hydroclimatic sensitive karst areas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15124, https://doi.org/10.5194/egusphere-egu23-15124, 2023.

This work presents two web-based, freely-available dynamical tools for the assessment and the mapping of the groundwater vulnerability to both pesticides and nitrate, within the geospatial Decision Support system (s-DSS) LandSupport (www.landsupport.eu).

The pesticide fate tool simulates the transport of reactive solutes, i.e., pesticides, and maps the percentage of pollutant mass that reaches the groundwater depth within a user defined time-interval. The tool is based on the extended transfer function model (TFM-ext) and its main inputs are: the soil and, eventually, the vadose zone physical and hydrological properties, the climate, the groundwater table depth, the investigated crop and its management (sowing and harvesting dates, pesticides doses and time of application).

The nitrate fate tool simulates the crop growth dynamics and assess the transport of nitrate through the unsaturated zone till the groundwater table depth. The output maps represent the number of years for the arrival to the groundwater of the 50% of the mass of nitrate leachate from the root zone. The tool is based on the coupling of the dynamical crop-growth ARMOSA model and of the TFM-ext model and its main inputs are: the type of crop and/or crop-rotation and related managements (tillage, irrigation, fertilization and residues), the soil physical and hydrological properties, the climate and the groundwater table depth.

Eventually, both tools were extended using the COMPSs programming framework that allows to parallelize the execution of multiple model runs.

The work presents the implementations of both tools for different case studies across three European regions (Campania Region-IT, Marchfeld Region-AT, Zala County-HU), characterized by different spatial scales, pedo-climatic conditions and land-use, showing some examples of applications in support of local farmers, public authorities and environmental planners for the Water, Pesticides and Nitrate Directive applications.

How to cite: Bancheri, M., Acutis, M., Botta, M., Fusco, F., Langella, G., Lezzi, D., Perego, A., and Basile, A.: A DSS for the dynamical assessment and mapping of the groundwater vulnerability: the pesticide and the nitrate fate tools  , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2090, https://doi.org/10.5194/egusphere-egu23-2090, 2023.