Groundwater is by far the largest unfrozen freshwater resource on the planet. It plays a critical role as the bottom of the hydrologic cycle, redistributing water in the subsurface and supporting plants and surface water bodies. However, groundwater has historically been excluded or greatly simplified in global models. In recent years, there has been an international push to develop global scale groundwater modeling and analysis. This progress has provided some critical first steps. Still, much additional work will be needed to achieve a consistent global groundwater framework that interacts seamlessly with observational datasets and other earth system and global circulation models. Here we outline a vision for a global groundwater platform for groundwater monitoring and prediction and identify the key technological and data challenges that are currently limiting progress. Any global platform of this type must be interdisciplinary and cannot be achieved by the groundwater modeling community in isolation. Therefore, we also provide a high‐level overview of the groundwater system, approaches to groundwater modeling and the current state of global groundwater representations, such that readers of all backgrounds can engage in this challenge.

The long-term sustainability of shallow geothermal systems in dense urbanized areas can be potentially compromised by the existence of thermal interfaces. Thermal interferences between systems have to be avoided to prevent the loss of system performance. Nevertheless, in this work we provide evidence of a positive feedback from thermal interferences in certain controlled situations. Two real groundwater heat pump systems were investigated using real exploitation data sets to estimate the thermal energy demand bias and, by extrapolation, to assess the nature of thermal interferences between the systems. To do that, thermal interferences were modelled by means of a calibrated and validated 3D city-scale numerical model reproducing groundwater flow and heat transport. Results obtained showed a 39% (522 MWh·yr⁻¹) energy imbalance towards cooling for one of the systems, which generated a hot thermal plume towards the downgradient and second system investigated. The nested system in the hot thermal plume only used groundwater for heating, thus establishing a positive symbiotic relationship between them. Considering the energy balance of both systems together, a reduced 9% imbalance was found, hence ensuring the long-term sustainability and renewability of the shallow geothermal resource exploited. The nested geothermal systems described illustrate the possibilities of a new management strategy in shallow geothermal energy governance.

Global demands for energy‐efficient heating and cooling systems coupled with rising commitments toward net zero emissions is resulting in wide deployment of shallow geothermal systems, typically installed to a depth of 100 to 200 m, and in the continued growth of the global ground source heat pump (GSHP) market. Ground coupled heat pump (GCHP) systems take up to 85% of the global GSHP market. With increasing deployment of GCHP systems in urban areas coping with limited regulations, there is growing potential and risk for these systems to impact the subsurface thermal regime and to interact with each other or with nearby heat‐sensitive subsurface infrastructure. In this paper, we present three numerical modeling case studies, from the UK and Canada, which examine GCHP systems' response to perturbation of the wider hydrogeological and thermal regimes. The studies demonstrate how GCHP systems can be impacted by external influences and perturbations arising from subsurface activities that change the thermal and hydraulic regimes in the area surrounding these systems. Additional subsurface heat loads near existing schemes are found to have varied impacts on system efficiency with reduction ranging from <1% to 8%, while changes in groundwater flow rates (due to a nearby groundwater abstraction) reduced the effective thermal conductivity at the study site by 13%. The findings support the argument in favor of regulation of GCHP systems or, to a minimum, their registration with records of locations and approximate heat pump capacity—even though these systems do not abstract/inject groundwater.

The development and validation of aquifer productivity and depth-to-source maps for England and Wales are described. Aquifer productivity maps can provide valuable support for the assessment, planning and management of groundwater and renewable heat energy resources. Aquifer productivity is often mapped using geostatistical interpolation techniques such as kriging, but these techniques tend to be unsuitable for mapping at the national scale due to the high data (and time) demands. A methodology is outlined for mapping aquifer productivity at the national scale using existing national-scale data sets. Pumping test data are used to characterise the potential borehole yields that different geological formations of varying lithologies and ages can provide. Based on this analysis and using expert knowledge, the corresponding map codes on the geological map are assigned to potential productivity classes. The subsurface (concealed) extent of aquifer units is mapped from geophysical data, and together with the attributed geological map, provide the bedrock-aquifer productivity map. Drilling and pumping costs can be an important consideration when evaluating the feasibility of developing a groundwater source. Thus, a map of the approximate depth to source is developed alongside the aquifer productivity map. The maps are validated using independent data sets, and map performance is compared against performance from maps derived by random and uniform attribution. The results show that the maps successfully predict potential productivity and approximate depth to the water source, although utility of the depth-to-source map could be improved by increasing the vertical discretisation at which depth intervals are mapped. Dieser Artikel beschreibt die Entwicklung und Validierung von Grundwasserproduktivitäts- und -tiefenkarten für England und Wales. Die Karten stellen wertvolle Informationen bereit zur Unterstützung bei der Evaluierung, Planung und Bewirtschaftung von Grundwasser- und erneuerbaren Wärmeressourcen. Grundwasserproduktivität wird oft mittels geostatistischer Interpolationsmethoden, wie z.B. Kriging, kartiert. Diese Techniken sind aufgrund ihrer hohen Daten- (und Zeit) -anforderungen generell ungeeignet für die Zuordnung auf nationaler Ebene. In dieser Studie wird eine Methode vorgestellt, die zur Kartierung der Grundwasserproduktivität auf nationaler Ebene geeignet ist und auf der Nutzung von bereits vorhandenen, nationalen Datensätzen basiert. Dafür wird zunächst die potenzielle Grundwasserproduktivität verschiedener geologischer Formationen anhand von Pumpversuchsdaten abgeschätzt. Basierend auf dieser Analyse und unter Verwendung von Expertenwissen wird jeder Formation in der geologischen Karte eine entsprechende (potenzielle) Produktivitätsklasse zugeordnet. Die räumliche Ausbreitung verdeckter Grundwasserleiter im Untergrund wird anhand geophysikalischer Daten ermittelt. Die resultierende Karte wird mit der attributierten geologischen Karte kombiniert und zusammen bilden diese die Grundwasserproduktivitätskarte. Bohr- und Pumpkosten sind ein wichtiger Aspekt bei der Bewertung der Wirtschaftlichkeit einer Grundwasserquelle. Um dies zu berücksichtigen, wurde zusätzlich zur Grundwasserproduktivitätskarte auch eine Karte zur ungefähren Grundwasser- und erforderlichen Bohrtiefe (=ungefähre Quellentiefe) erstellt. Beide Karten wurden durch den Vergleich mit unabhängigen Datensätzen validiert. Zusätzlich wurde ihre Fähigkeit, Grundwasserproduktivität und ungefähre Quellentiefe zu bestimmen mit der Vorhersagefähigkeit von Karten mit willkürlicher (random) und mit einheitlicher (uniform) Zuordnung verglichen. Die Ergebnisse zeigen, dass die Karten erfolgreich potenzielle Produktivität und ungefähre Quellentiefe vorhersagen können, obwohl letztere durch die Erhöhung der vertikalen Tiefendiskretisierung verbessert werden könnte. Le développement et la validation des cartes de productivité des aquifères et de profondeur d’accès à la nappe pour l’Angleterre et le Pays-de-Galles sont décrits. Les cartes de productivité des aquifères peuvent constituer une aide précieuse pour évaluer, planifier et gérer les eaux souterraines et les ressources en énergie renouvelable géothermique. La productivité d’un aquifère est souvent cartographiée en utilisant des techniques d’interpolation géostatistique, telles que le krigeage, mais ces techniques deviennent inadaptées pour la cartographie à une échelle nationale en raison du grand nombre de données (et du temps) nécessaire. Une méthodologie est présentée pour cartographier la productivité des aquifères à l’échelle nationale, en utilisant les données disponibles à cette échelle. Les données d’essai de pompage sont utilisées pour caractériser les débits potentiels d’exploitation de forages que les différentes formations géologiques, d’âges et de lithologies variées, peuvent fournir. A partir de cette analyse et en utilisant les connaissances à dire d’expert, des codes de correspondance cartographique sont établis entre la carte géologique et des classes de productivité d’aquifère. L’extension (sous couverture) de sub-surface des unités aquifères est cartographiée à partir des données géophysiques, et associé à la carte géologique, fournit la carte de productivité des aquifères du substratum rocheux. Les coûts de forage et de pompage peuvent être un facteur important pour évaluer la faisabilité de l’exploitation d’une ressource aquifère. Ainsi, une carte de la profondeur approximative d’accès à la nappe est développée en même temps que la carte de productivité des aquifères. Les cartes sont validées en utilisant des jeux de données indépendants, et la qualité de la carte est comparée à la qualité des cartes dérivées d’une attribution aléatoire ou uniforme. Les résultats indiquent que les cartes prédisent avec succès...

Fibre optic distributed temperature sensing (DTS) is used increasingly for environmental monitoring and subsurface characterization. Combined with heating of metal elements embedded within the fibre optic cable, the temperature response of the soil provides valuable information from which soil parameters such as thermal conductivity and soil moisture can be derived at high spatial and temporal resolution, and over long distances. We present a novel active distributed temperature sensing (A-DTS) system and its application to characterize spatial and temporal dynamics in soil thermal conductivity along a recently forested hillslope in Central England, UK. Compared with conventional techniques (needle probe surveys), A-DTS provided values with a similar spread although lower on average. The larger number of measurement points that A-DTS provides at higher spatial and temporal resolutions and the ability to repeat surveys under different meteorological or hydrological conditions allow for a more detailed examination of the spatial and temporal variability of thermal conductivities at the study site. Although system deployment time and costs are higher than with needle probes, A-DTS can be extremely appealing for applications requiring long-term monitoring, at high temporal repeatability, over long (kilometres) distances and with minimum soil disturbance, compared with one-off spatial surveys. Thematic collection: This article is part of the Measurement and monitoring collection available at: https://www.lyellcollection.org/cc/measurement-and-monitoring

Coastal dunes are delicate systems that are under threat from a variety of human and natural influences. Groundwater modelling can provide a better understanding of how these systems operate and can be a useful tool towards the effective management of a coastal dune system, e.g. by identifying strategically important locations for flora and fauna and guiding the planning of management operations through predicting impacts from climatic change, sea level rise and land use management. Most dune systems are small, typically of the size 10–100 km², compared with inland groundwater systems. Applying conventional groundwater modelling approaches to these small systems presents a number of challenges due to the local scale of the system and the fact that the system boundaries (sea, drains, ponds etc.) are close to the main body of the aquifer. In this paper, two case studies will be presented using different modelling approaches to understand the groundwater balance in two dune systems in the UK. The studies demonstrate that, although conventional hydraulic models can describe the general system behaviour, a fuller understanding of the recharge mechanisms and system boundaries is needed to represent adequately system dynamics of small groundwater systems.