Given the increasing challenges posed by climate change, especially more frequent and severe droughts experienced globally, effective exploration and management of groundwater resources is essential to ensure a sustainable and resilient society. As part of this effort, it is necessary to acquire comprehensive knowledge of the distribution of significant and readily accessible freshwater reservoirs on continents. This outlines the critical need for an efficient and cost-effective imaging method to assess this vital resource. In response, we propose a novel imaging method that utilizes observations of air-pressure-induced seismic velocity changes. We utilize findings of our study (Kramer et al., 2023) which shows atmospheric tides and their interaction with the groundwater body are the primary cause of sub-daily seismic velocity changes. Analyzing these velocity changes can reveal valuable information on the hydro-geophysical properties of the underlying groundwater body. Building on this knowledge, we introduce this imaging method and apply it to the seismic data collected across South and Central Europe. For this purpose, we use coda-wave-interferometry to investigate four years of continuous data from AlpArray and other locations throughout Europe.

Kramer, R., Lu, Y., & Bokelmann, G. (2023). Interaction of air pressure and groundwater as main cause of sub-daily relative seismic velocity changes. Geophysical Research Letters, 50, e2022GL101298. https://doi.org/10.1029/2022GL101298

The Mekong Delta, including Ca Mau province in the south, faces severe land subsidence, attributed in part to the excessive groundwater extraction. Addressing this issue requires finding alternative water sources while considering technical, environmental and social challenges. This study aims to understand the significance of groundwater to the people of Ca Mau, their water usage habits and awareness with environmental issues. Supported by local Provincial People's Committees, a comprehensive survey and group interviews were conducted across 9 districts of Ca Mau province. The research aimed to identify the spatial distribution of the required water management solutions and acceptance levels of alternative water resources. Water samples were collected and analyzed to establish the connection between water quality and people's water usage habits. Groundwater plays a vital role in people’s life, serving various purposes such as washing, cooking, drinking, and other activities. Groundwater usage depends on people's perceptions of its quality. For activities requiring higher levels of hygiene, additional water treatment or alternative water sources are preferred. The analytical approach from general viewpoints to details in this study investigates deeper into the story behind their water usage habits. It emphasizes the need to inform people about environmental challenges and raise awareness of cause-effect relationships. Evaluating alternative water resources and designing new water utilization concepts is based on local demands and willingness to change water-related habits. This research sheds light on people's awareness and concern while providing valuable insights for sustainable water management strategies in the Mekong Delta, specifically in Ca Mau province.

With escalating global freshwater scarcity, the Mekong Delta basin has emerged as one of the most socially and ecologically vulnerable regions, experiencing severe freshwater stress and storage loss. This vulnerability is primarily driven by the progressive "loss of land and freshwater" phenomenon, which encompasses a range of interconnected environmental issues, including land subsidence and seawater intrusion. The exponential growth in population, urbanization, climate change and rapid industrial and agricultural development has significantly increased the demand for freshwater, placing already limited supplies under immense pressure. In the coastal zones of the Mekong Delta, groundwater has become the primary and increasingly overexploited source of freshwater. Consequently, a decline in hydraulic heads and the threat of saline intrusion have become pressing concerns. To gain a comprehensive understanding of the hydrogeochemical processes at play, a meticulous investigation was conducted in the coastal province of Ca Mau, Vietnam. Through extensive sampling campaigns and rigorous hydrogeochemical analysis, this study sheds light on the intricate dynamics of groundwater chemistry in the region. The results reveal that ion-exchange processes and the decomposition of organic matter play dominant roles in shaping the groundwater chemistry. These findings hold significant implications for the sustainable management of water resources in the Mekong Delta. By unraveling the past and current hydrogeochemical groundwater dynamics, stakeholders can develop effective strategies to mitigate freshwater scarcity. The knowledge gained from this research contributes to the scientific understanding of hydrological systems and aids in the formulation of integrated water management policies for the region's long-term sustainability.

The transboundary Cuvelai-Etosha Basin (CEB), located in Southern Angola and Northern Namibia, is part of the Kalahari Basin, one of the world´s largest intracontinental basins. It contains mostly unconsolidated sandy sediments, often deposited by so-called megafans. The most prominent one in the CEB is the Cubango Megafan (CM). Megafans can contain large aquifers and thus have huge potential for water supply, especially in semi-arid regions. The CM hosts three aquifers: a locally present, perched aquifer, a regional mostly unconfined and a deep confined aquifer.

The regional climate is semi-arid, with very high evapotranspiration (> 2000 mm/yr) that far exceeds the highly seasonal and variable precipitation (400-800 mm/yr). The widespread salinity in the contemporary groundwater of the CM can be attributed to both sub-recent and co-sedimentary evaporative processes.

In the lower parts of the CEB, specifically at the southwestern rim of the megafan towards the Etosha Pan, saline groundwater predominates. Hydrochemical data indicate large-scale and long-term ion exchange processes. Together with environmental tracers, this shows that younger groundwater infiltrating to the north of the basin is slowly displacing the originally brackish-saline pore water. ⁸¹Kr ages range between 40 to 170 ka indicating the fossil nature of this resource. Analysis of stable isotopes and noble gases reveals that climatic conditions during recharge of the confined aquifer were approximately 3 – 5°C colder than today.

Considering the population growth and predicted impact of climate change on water availability, careful management of this vulnerable and only partially replenishable resource is advisable.