Groundwater-dependent Ecosystems Research Articles

Global groundwater warming due to climate change

Aquifers contain the largest store of unfrozen freshwater, making groundwater critical for life on Earth. Surprisingly little is known about how groundwater responds to surface warming across spatial and temporal scales. Focusing on diffusive heat transport, we simulate current and projected groundwater temperatures at the global scale. We show that groundwater at the depth of the water table (excluding permafrost regions) is conservatively projected to warm on average by 2.1 °C between 2000 and 2100 under a medium emissions pathway. However, regional shallow groundwater warming patterns vary substantially due to spatial variability in climate change and water table depth. The lowest rates are projected in mountain regions such as the Andes or the Rocky Mountains. We illustrate that increasing groundwater temperatures influences stream thermal regimes, groundwater-dependent ecosystems, aquatic biogeochemical processes, groundwater quality and the geothermal potential. Results indicate that by 2100 following a medium emissions pathway, between 77 million and 188 million people are projected to live in areas where groundwater exceeds the highest threshold for drinking water temperatures set by any country.

GROUNDWATER AND ECOSYSTEMS: UNDERSTANDING THE CRITICAL INTERPLAY FOR SUSTAINABILITY AND CONSERVATION

Groundwater, a vital component of the Earth's hydrological cycle, plays a central role in supporting ecosystems worldwide. This research paper explores the multifaceted relationship between groundwater and ecosystems, emphasizing its critical importance for the health and resilience of both aquatic and terrestrial habitats. The paper delves into the ecosystem services provided by groundwater, including habitat provision, water purification, and nutrient cycling. The intricate connection between groundwater availability and biodiversity is examined, highlighting the significance of groundwater in sustaining diverse habitats such as wetlands, springs, and riparian zones. Additionally, the research investigates the role of groundwater in hydrological processes, particularly its contribution to base flow in rivers and the sustenance of stream ecosystems during dry periods. Anthropogenic factors leading to groundwater depletion, such as over-extraction for agriculture and urbanization, are analyzed, emphasizing the far-reaching consequences for ecosystems. The paper proposes strategies for sustainable groundwater management, including monitoring, water-efficient agricultural practices, and nature-based solutions. It underscores the importance of policy development, community engagement, and international collaboration in preserving groundwater-dependent ecosystems. Looking towards the future, the research identifies challenges and opportunities, including uncertainties related to climate change, population growth, and global water trade. It suggests areas for further research, such as integrated hydrological models and studies on social-ecological systems, and emphasizes the need for innovative policies that prioritize ecosystem health. In conclusion, the research emphasizes the critical need for sustainable groundwater management practices, recognizing groundwater as a finite resource essential for maintaining biodiversity, ecosystem functionality, and human well-being. KEYWORDS: Biodiversity, Ecosystems, Groundwater, Sustainability, Water Management.

Nature-Based Solutions for the Restoration of Groundwater Level and Groundwater-Dependent Ecosystems in a Typical Inland Region in China

The rapid drop in groundwater level and the degradation of groundwater-dependent ecosystems (GDEs) has led to serious imbalances in the development of the socio-ecological system (SES) in Minqin Oasis, northwest China. In this study, the interactions between the elements of the SES were analyzed, and the effects of the implementation of nature-based solutions (NbS) and the resilience of the SES were assessed using the methods of linear trend analysis, correlation, and fuzzy comprehensive evaluation. The results showed that: (i) the most important contributing factor to the increase in groundwater depth (GLD) and the degradation of GDEs was the continuous groundwater extraction for the irrigation of farmland; and (ii) the natural vegetation began to be degraded when the GLD surpassed 5 m; (iii) the initial goal of NbS was achieved, the increase in GLD has been curbed, and the vegetation and the wetland area of Qingtu lake have begun to be restored. The SES resilience index increased by a factor of 1.82 from 2009 to 2017; however, it was still below 0.6, and thus the NbS should be continued in the future. This study provides a reference for the sustainable development of the SES in other similar areas under various environmental challenges.

Groundwater for People and the Environment: A Globally Threatened Resource.

The intensity of global groundwater use rose from 124 m3 per capita in 1950 to 152 m3 in 2021, for a 22.6% rise in the annual per capita use. This rise in global per capita water use reflects rising consumption patterns. The global use of groundwater, which provides between 21% and 30% of the total freshwater annual consumption, will continue to expand due to the sustained population growth projected through most of the 21st century and the important role that groundwater plays in the water-food-energy nexus. The rise in groundwater use, on the other hand, has inflicted adverse impacts in many aquifers, such as land subsidence, sea water intrusion, stream depletion, and deterioration of groundwater-dependent ecosystems, groundwater-quality degradation, and aridification. This paper projects global groundwater use between 2025 and 2050. The projected global annual groundwater withdrawal in 2050 is 1535 km3 (1 km3 = 109 m3 = 810,713 acre-feet). The projected global groundwater depletion, that is, the excess of withdrawal over recharge, in 2050 equals 887 km3, which is about 61% larger than in 2021. This projection signals probable exacerbation of adverse groundwater-withdrawal impacts, which are worsened by climatic trends and the environmental requirement of groundwater flow unless concerted national and international efforts achieve groundwater sustainability.

Effects of Groundwater Table Decline on Vegetation in Groundwater-Dependent Ecosystems

The distribution map of groundwater-dependent ecosystems (GDEs) is generally used for the scientific management of vegetation and groundwater resources, and is instructive for forest resource conservation. The groundwater table in the Loess zone has declined over the past few years, but no study has yet been conducted to assess the impact of this decline on GDEs. This study used data from the GRACE gravity satellite to delineate groundwater fluctuation periods from 2002 to 2021, to develop a method to identify whether vegetation is potentially associated with groundwater using three criteria, and to verify the accuracy of this method. Study results show that the groundwater changes in the Loess zone can be divided into two periods, 2002–2014 and 2015–2021, with groundwater declines becoming more rapid after 2015. We did not observe the spatial variation pattern of GDEs in the Loess areas, but there was a significant change in the area of GDEs during the two periods studied, with a 13.56% decrease in the very likely GDEs’ group area and an 11.68% increase in the unlikely GDEs’ group area between 2015 and 2021 compared to 2002–2014, with little change in the neutral, likely, and very unlikely group areas. This study provides a reference for exploring the relationship between vegetation and groundwater, as well as for the scientific management of water resources.

An overview of groundwater response to a changing climate in the Murray-Darling Basin, Australia: potential implications for the basin system and opportunities for management

The Murray-Darling Basin (MDB) is a highly allocated and regulated, mostly semiarid basin in south-eastern Australia, where groundwater is a significant water resource. Future climate predictions for the MDB include an expansion of arid and semiarid climate zones to replace temperate areas. The impacts of climate change are already evident in declining groundwater levels and changes in the connection status between rivers and groundwater, and modelling has predicted a further reduction in future groundwater recharge and ongoing declines in groundwater levels. This is predicted to further reduce river baseflow and negatively impact groundwater-dependent ecosystems (GDEs), and these system responses to a changing climate and extreme events are complex and not always well understood. This report provides an overview of the current state of knowledge of groundwater response to a changing climate for the MDB, and outlines challenges and opportunities for future groundwater research and management. Opportunities for the region include improving data systems and acquisition through automation and novel data sources, and growing capability in integrated, risk-based modelling. Quantification of the groundwater/surface-water connection response to declining groundwater levels, and assessing GDE water requirements and thresholds, would enable identification of vulnerable systems and inform the development of metrics for adaptive management, improving the ability to respond to climate extremes. There is potential to adapt policy to support active management of groundwater where required, including conjunctive use and water banking. Improving knowledge sharing and water literacy, including understanding community values of groundwater and GDEs, would support future decision-making.

Wetland Management in Recharge Regions of Regional Groundwater Flow Systems with Water Shortage, Nyírség Region, Hungary

Climate change and increasing human impacts are more emphasised in recharge regions, where the main flow direction is downward, resulting in negative water balance. Two wetlands located in the recharge position of regional groundwater flow systems were investigated in the Nyírség region, Hungary, as pilot areas for representing wetlands in similar hydraulic positions. Hydraulic data processes, chemical data evaluations, and numerical simulations revealed that the wetlands are fed via local flow systems, superimposing regional-scale recharge conditions in the area. The wetlands are discharge and flow-through types in connection with local flow systems. Nevertheless, in the case of significant regional water table decline—due to the high vulnerability of recharge areas to climate change—local flows are degraded, so they are not able to sustain the wetlands. To preserve the groundwater-dependent ecosystems in the areas, water retention at the local recharge areas of the wetlands may help in the mitigation of water level decline under present-day conditions. If the regional water table continues to decline, comprehensive water retention solutions are needed in the whole region. The results highlight that understanding the natural wetland–groundwater interactions at different scales is crucial for the preservation of wetlands and for successful water retention planning.

Coastal Groundwater-Dependent Ecosystems are Falling Through Policy Gaps.

Coastal groundwater-dependent ecosystems (GDEs), such as wetlands, estuaries and nearshore marine habitats,are biodiversity hotspots that provide valuable ecosystem services to society. However, coastal groundwater and associated ecosystems are under threat from groundwater exploitation and depletion, as well as climate change impacts from sea-level rise and extreme flood and drought events. Despite many well-intentioned policies focused on sustainable groundwater use and species protection, coastal GDEs are falling through gaps generated by siloed policies and as a result, are declining in extent and ecological function. This study summarized then examined policies related to the management of coastal groundwater and connected ecosystems in two key case study areas: Queensland (Australia) and California (USA). Despite both areas being regarded as having progressive groundwater policy, our analysis revealed three universal policy gaps, including (1) a lack of recognition of the underlying groundwater system, (2) fragmented policies and complex governance structures that limit coordination, and (3) inadequate guidance for coastal GDE management. Overall, our analysis revealed that coastal GDE conservation relied heavily on inclusion within protected areas or was motivated by species recovery, meaning supporting groundwater systems remained underprotected and outside the remit of conservation efforts. To close these gaps, we consider the adoption of ecosystem-based management principles to foster integrated governance between disparate agencies and consider management tools that bridge traditional conservation realms. Our findings advocate for comprehensive policy frameworks that holistically address the complexities of coastal GDEs across the land-sea continuum to foster their long-term sustainability and conservation.

Distribution, threats and protection of selected karst groundwater-dependent ecosystems in the Mediterranean region

Karst groundwater-dependent ecosystems (KGDEs) in the Mediterranean region are important in terms of ecosystem services and biodiversity but are increasingly under anthropogenic pressures and climate-change constraints. For this study, the ecohydrological characteristics, threats, and protection status of 112 selected KGDEs around the Mediterranean Sea, including caves, springs, rivers and wetlands, were evaluated, based on local expert knowledge and scientific literature. Results demonstrate that KGDEs contribute considerably to regional biodiversity. The diversity of karst landscapes, combined with the groundwater emergence at springs, leads to exceptional habitat diversity, particularly in arid climates, where KGDEs serve as a refuge for species that could not thrive in the surrounding environment. The most common threats identified among the selected sites are direct human disturbances, such as mass tourism or overfishing, water-quality deterioration and water shortage from aquifer overdraft and/or climate change. Although most of the selected sites are under protection, conservation measures are frequently insufficient. Such shortcomings are often caused by poor data availability, little knowledge on conservation needs of invertebrate species, and conflicts of interest with the local population. For this purpose, it is necessary to raise environmental awareness and promote interdisciplinary research, in order to monitor water quality and quantity in addition to the status of the biocenoses.

Divergent responses of native and invasive macroalgae to submarine groundwater discharge

Marine macroalgae are important indicators of healthy nearshore groundwater dependent ecosystems (GDEs), which are emergent global conservation priorities. Submarine groundwater discharge (SGD) supports abundant native algal communities in GDEs via elevated but naturally derived nutrients. GDEs are threatened by anthropogenic nutrient inputs that pollute SGD above ambient levels, favoring invasive algae. Accordingly, this case study draws on the GDE conditions of Kona, Hawai‘i where we evaluated daily photosynthetic production and growth for two macroalgae; a culturally valued native (Ulva lactuca) and an invasive (Hypnea musciformis). Manipulative experiments—devised to address future land-use, climate change, and water-use scenarios for Kona—tested algal responses under a natural range of SGD nutrient and salinity levels. Our analyses demonstrate that photosynthesis and growth in U. lactuca are optimal in low-salinity, high-nutrient waters, whereas productivity for H. musciformis appears limited to higher salinities despite elevated nutrient subsidies. These findings suggest that reductions in SGD via climate change decreases in rainfall or increased water-use from the aquifer may relax physiological constraints on H. musciformis. Collectively, this study reveals divergent physiologies of a native and an invasive macroalga to SGD and highlights the importance of maintaining SGD quantity and quality to protect nearshore GDEs.

Groundwater-dependent ecosystems at risk – global hotspot analysis and implications

Many land-based ecosystems are dependent on groundwater and could be threatened by human groundwater abstraction. One key challenge for the description of associated impacts is the initial localisation of groundwater-dependent ecosystems (GDEs). This usually requires a mixture of extensive site-specific data collection and the use of geospatial datasets and remote sensing techniques. To date, no study has succeeded in identifying different types of GDEs in parallel worldwide. The main objective of this work is to perform a global screening analysis to identify GDE potentials rather than GDE locations. In addition, potential risks to GDEs from groundwater abstraction shall be identified. We defined nine key indicators that capture GDE potentials and associated risks on a global grid of 0.5° spatial resolution. Groundwater-dependent streams, wetlands and vegetation were covered, and a GDE index was formulated incorporating the following three aspects: the extent of groundwater use per GDE type, GDE diversity and GDE presence by land cover. The results show that GDE potentials are widely distributed across the globe, but with different distribution patterns depending on the type of ecosystem. The highest overall potential for GDEs is found in tropical regions, followed by arid and temperate climates. The GDE potentials were validated against regional studies, which showed a trend of increasing matching characteristics towards higher GDE potentials, but also inconsistencies upon closer analysis. Thus, the results can be used as first-order estimates only, which would need to be explored in the context of more site-specific analyses. Identified risks to GDEs from groundwater abstraction are more geographically limited and concentrated in the US and Mexico, the Iberian Peninsula and the Maghreb, as well as Central, South and East Asia. The derived findings on GDEs and associated risks can be useful for prioritising future research and can be integrated into sustainability-related tools such as the water footprint.

Editorial: Threatened aquatic gems: freshwater springs and groundwater-dependent ecosystems

Editorial: Threatened aquatic gems: freshwater springs and groundwater-dependent ecosystems

Socio-hydrogeological survey and assessment of organic pollutants to highlight and trace back pollution fluxes threatening a coastal groundwater-dependent ecosystem

Despite being a vector of pollution towards connected ecosystems, groundwater is often underestimated or not taken into account in management frameworks. To fill this gap, we propose to add socio-economic data to hydrogeological investigations to identify past and present pollution sources linked to human activities at watershed scale in order to forecast threats towards groundwater-dependent ecosystems (GDEs). The aim of this paper is to demonstrate, by a cross-disciplinary approach, the added value of socio-hydrogeological investigations to tackle anthropogenic pollution fluxes towards a GDE and to contribute to more sustainable management of groundwater resources. A survey combining chemical compounds analysis, data compilation, land use analysis and field investigations with a questionnaire was carried out on the Biguglia lagoon plain (France). Results show a pollution with a two-fold source, both agricultural and domestic, in all water bodies of the plain. The pesticide analysis reveals the presence of 10 molecules, including domestic compounds, with concentrations exceeding European groundwater quality standards for individual pesticides, as well as pesticides already banned for twenty years. On the basis of both the field survey and the questionnaire, agricultural pollution has been identified as very local highlighting the storage capacity of the aquifer, whereas domestic pollution is diffuse over the plain and attributed to sewage network effluents and septic tanks. Domestic compounds present shorter residence time within the aquifer highlighting continuous inputs, related to consumption habits of the population. Under the Water Framework Directive (WFD), member states are required to preserve the good ecological status, quality and quantity of water bodies. However, for GDEs it is difficult to achieve the ‘good status’ required without considering the groundwater's pollutant storage capacity and pollution legacy. To help resolve this issue, socio-hydrogeology has proved to be an efficient tool as well as for implementing effective protection measures for Mediterranean GDEs.

Effects of Multiple Drivers of Environmental Change on Native and Invasive Macroalgae in Nearshore Groundwater Dependent Ecosystems

AbstractGroundwater dependent ecosystems (GDE) are increasingly recognized as critical components of sustainable groundwater management, but are threatened by multiple drivers of environmental change. Despite this importance, data that link drivers of hydrologic change to GDEs are scarce. This study adapts a land‐sea modeling framework by calibrating marine models with macroalgal experiments to quantitatively assess impacts of climate and land use change on submarine groundwater discharge (SGD) and subsequent habitat suitability for a native (Ulva lactuca) and an invasive (Hypnea musciformis) macroalgae in nearshore GDEs in Kona, Hawai'i. Lab analyses demonstrate that while U. lactuca grows optimally in low‐salinity, high‐nutrient waters, H. musciformis appears constrained to a salinity threshold and exhibits low growth in low salinity despite high nutrient concentrations. Land‐sea model results predict that while a dry future climate (Representative Concentration Pathway 8.5 mid‐century) coupled with increased urban development will likely reduce SGD, protecting native forests may prevent further loss of SGD quantity. This prevention thus partially mitigates the decline in habitat suitability of U. lactuca due to the combined effects of climate and land use change. Findings also suggest that, in contrast to the native U. lactuca, reductions in SGD may favor H. musciformis growth if introduced to Kona. Collectively, this study demonstrates the importance of considering multiple drivers of environmental change on GDEs. This study bridges experiments with models to spatially map changes in species abundance beyond their current habitat conditions, and thus informs management actions that can explicitly incorporate future human and climate‐related impacts.

Ecosystem services produced by groundwater dependent ecosystems: a framework and case study in California

Groundwater is an important freshwater supply for agricultural, domestic, and environmental uses and critical buffer against a warming climate, particularly in semi-arid and arid regions of the world. Groundwater dependent ecosystems (GDEs), which rely on groundwater for some or all of their water requirements, include terrestrial vegetation, rivers, springs, wetlands, and riparian zones. These GDEs provide benefits to people ranging from habitat for pollinators to carbon sequestration. Accounting for these benefits, called ecosystem services, can inform management by expanding the potential group of groundwater users to include groundwater dependent ecosystems. Here we develop an approach to inventory the ecosystem services of GDEs by identifying the ecosystem functions of a range of GDEs and assessing how they are linked to a wide range of ecosystem services. We apply this approach as a case study in California, USA, where we found ecosystem services from GDEs is widespread across the state; over 30% of California's pollinator dependent crops may benefit from GDEs, and carbon storage of GDEs is equivalent to 790 million tons, twice as much as California emits annually.

Mapping and validation of groundwater dependent ecosystems (GDEs) in a drought-affected part of Bundelkhand region, India

The importance of groundwater in preserving the health of water resources such as rivers, lakes, streams, and associated vegetation is often ignored or underestimated, which shows a lack of groundwater management policies. Therefore, in order to manage and protect groundwater and groundwater-dependent ecosystems (GDEs), a complete framework is needed, which is necessary for accomplishing the sustainability aim. The present study utilized remote sensing-based input, in-situ data, and a GIS framework for mapping and validation of GDEs. The weights of the input layers were assigned using experts’ opinions. In the study area, GDEs are heterogeneous, and the impact of groundwater overdraft on its dependent ecosystems was also assessed using long-term in–situ groundwater level data. The results show a decreasing trend in groundwater storage; many wells have dried in recent years, whereas surface runoff through the natural streams is also reduced, which reduces the supply of water and the need to identify new well locations. The validation of GDEs shows an accuracy of 73.40% through the area under the curve method. Further, the GDEs map was categorized into five classes, and the moderate GDEs are the dominant in the area. The study shows an overall decrease in vegetation over the past two decades. Considering the risks of groundwater overdraft, the policy implications to support the conservation of GDEs within a sustainable withdrawal context have also been discussed in this work.

Purpose-Designed Hydrogeological Maps for Wide Interconnected Surface–Groundwater Systems: The Test Example of Parma Alluvial Aquifer and Taro River Basin (Northern Italy)

Hydrogeological maps must synthesize scientific knowledge about the hydraulic features and the hydrogeological behavior of a specific area, and, at the same time, they must meet the expectations of land planners and administrators. Thus, hydrogeological maps can be fully effective when they are purpose-designed, especially in complex interconnected systems. In this case study, purpose-designed graphical solutions emphasize all the hydraulic interconnections that play significant roles in recharging the multilayered alluvial aquifer, where the majority of wells have been drilled for human purposes, artificial channels are used for agricultural purposes, and the shallow groundwater feeds protected groundwater-dependent ecosystems. The hydrogeological map was then designed to be the synthesis of three different and hydraulically interconnected main contexts: (i) the alluvial aquifer, (ii) the hydrographic basin of the Taro losing river, and (iii) those hard-rock aquifers whose springs feed the same river. The main hydrogeological map was integrated with two smaller sketches and one hydrogeological profile. One small map was drawn from a modeling perspective because it facilitates visualization of the alluvial aquifer bottom and the “no-flow boundaries.” The other small sketch shows the artificial channel network that emphasizes the hydraulic connection between water courses and groundwater within the alluvial aquifer. The hydrogeological profile was reconstructed to be able to (i) show the main heterogeneities within the aquifer system (both layered and discontinuous), (ii) visualize the coexistence of shallower and deeper groundwater, (iii) emphasize the hydraulic interconnections between subsystems, and (iv) suggest the coexistence of groundwater pathways with different mean residence times.

Resilience, stress and sustainability of alluvial aquifers in the Murray-Darling Basin, Australia: Opportunities for groundwater management

Study regionMain alluvial aquifers of the Murray-Darling Basin (MDB), Australia Study focusAround 75% of total metered groundwater use within Australia’s Murray-Darling Basin (MDB), arguably the nation’s most important food and fibre production region, is extracted from eight main alluvial aquifer systems. To date, regional-scale analyses of groundwater resilience, stress and sustainability for the region have not been completed. This study provides a systemic overview of the main alluvial systems anchored in these concepts. To achieve this, we combined three lines of evidence encompassing: a) long-term trend analysis of groundwater levels; (b) calculation of groundwater footprint indices considering volume and quality; and (c) an explicit comparison of groundwater management areas in terms of groundwater usage, sustainable use, storage volumes, presence and diversity of groundwater-dependent ecosystems (GDEs), and buffering capacity to absorb changes in recharge rates. New hydrological insights for the regionThe novelty of our work rests upon an integrated assessment of these three lines of evidence incorporating twelve different metrics to prioritise future groundwater management efforts. Results indicate that eleven out of twenty-two groundwater management areas show resilience, stress and/or sustainability issues, and a further two with emergent issues. Efforts to improve our understanding and management of these key groundwater resources would be most effective if focussed on these areas.

Groundwater connections and sustainability in social-ecological systems.

Groundwater resources are connected with social, economic, ecological, and Earth systems. We introduce the framing of groundwater-connected systems to better represent the nature and complexity of these connections in data collection, scientific investigations, governance and management approaches, and groundwater education. Groundwater-connected systems are social, economic, ecological, and Earth systems that interact with groundwater, such as irrigated agriculture, groundwater-dependent ecosystems, and cultural relationships to groundwater expressions such as springs and rivers. Groundwater-connected systems form social-ecological systems with complex behaviours such as feedbacks, non-linear processes, multiple stable system states, and path dependency. These complex behaviours are only visible through this integrated system framing and are not endogenous properties of physical groundwater systems. The framing is syncretic as it aims to provide a common conceptual foundation for the growing disciplines of socio-hydrogeology, eco-hydrogeology, groundwater governance, and hydro-social groundwater analysis. The framing also facilitates greater alignment between the groundwater sustainability discourse and emerging sustainability concepts and principles. Aligning with these concepts and principles presents groundwater sustainability as more than a physical state to be reached; and argues that place-based and multi-faceted goals, values, justice, knowledge systems, governance and management must continually be integrated to maintain groundwater's social, ecological, and Earth system functions. The groundwater-connected system framing can underpin a broad, methodologically pluralistic, and community-driven new wave of data collection and analysis, research, governance, management, and education. These developments, together, can invigorate efforts to foster sustainable groundwater futures in the complex systems groundwater is embedded within. This article is protected by copyright. All rights reserved.

Overlooked risks and opportunities in groundwatersheds of the world’s protected areas

Protected areas are a key tool for conserving biodiversity, sustaining ecosystem services and improving human well-being. Global initiatives that aim to expand and connect protected areas generally focus on controlling ‘above ground’ impacts such as land use, overlooking the potential for human actions in adjacent areas to affect protected areas through groundwater flow. Here we assess the potential extent of these impacts by mapping the groundwatersheds of the world’s protected areas. We find that 85% of protected areas with groundwater-dependent ecosystems have groundwatersheds that are underprotected, meaning that some portion of the groundwatershed lies outside of the protected area. Half of all protected areas have a groundwatershed with a spatial extent that lies mostly (at least 50%) outside of the protected area’s boundary. These findings highlight a widespread potential risk to protected areas from activities affecting groundwater outside protected areas, underscoring the need for groundwatershed-based conservation and management measures. Delineating groundwatersheds can catalyse needed discussions about protected area connectivity and robustness, and groundwatershed conservation and management can help protect groundwater-dependent ecosystems from external threats. Global initiatives to expand protected areas focus on controlling ‘above ground’ impacts such as land use, overlooking the potential human impacts on protected areas through groundwater flow. This study analyses the potential extent of these impacts by mapping groundwatersheds.