Natural hazard susceptibilities and inequities reduced by short-term groundwater use

The negative impacts of natural hazards are compounded by social, political and economic challenges^1,2,3, including political polarization, racism, misinformation and economic challenges. Yet responses to different natural hazard events from around the world, including earthquakes in Japan, wildfires in California, droughts in South Africa and floods in the Czech Republic, hint at an emerging strategy (Supplementary Information). Although groundwater depletion and contamination are widespread around the world^4,5, in each of these events short-term groundwater use reduced the impact of the natural hazard event (see Box 1 for terminology).

The 2002–2013 UNESCO project ‘Groundwater for Emergency Situations’ identified methodologies, examples and challenges of groundwater use during natural hazards, considering diverse geoscience methods^6,7, international case studies and governance⁸. This work has few citations academically or in natural hazard mitigation plans, and is not incorporated into the recent flagship UN groundwater report⁹ or the Sendai Framework for Disaster Risk Reduction¹⁰, suggesting that this important work has not significantly impacted regional, national or international natural hazard mitigation. We elevate and extend this previous work through a more interdisciplinary and social-science-oriented approach (beyond primarily geoscience), consistently and explicitly considering equity, describing recent case studies from around the world and including wildfires, which have emerged as a more common natural hazard. Specifically, we develop a visualization to examine susceptibility (Fig. 1) and suggest different tools and approaches to reduce it (Fig. 2). Moreover, we offer a way of thinking about groundwater use for natural hazards inspired by a recent, popular approach¹¹ to groundwater governance (Table 1). For groundwater governance during emergencies, Vrba⁸ proposed a framework of institutional and technical capacities, and identified serious gaps, including low compatibility between governmental and community level organizations, and the lack of legal frameworks for water rights in emergency situations. Figure 2 is a concrete way of visualizing how technical and institutional capacities can reduce susceptibility.

Groundwater use for natural hazards can be considered across the whole ‘disaster cycle’: mitigation, preparedness, response and recovery^8,12. The impact of natural hazards on water supply can be direct, such as water pipes breaking in earthquakes, or indirect, such as electrical system damage. Herein we focus on the direct impacts but allude to the more complex indirect impacts below by considering how natural hazards relate to the food–energy–water nexus. We focus herein on earthquakes, wildfires, droughts and floods, which represent different causes, potential warning times and water impacts. There is limited current literature that is focused on groundwater use with the other types of natural hazard or on combining groundwater and surface water use after natural hazards, both areas for future research.

We consider the nine different natural hazards tracked by the Centre for Research on the Epidemiology of Disasters¹³, which represent a range of causes and consequences for water supply (Fig. 1). Various factors could be used to examine if or how groundwater could be useful during or after natural hazards. We suggest two factors that relate to the timing and severity of possible impacts: the potential warning before the natural hazard event and its potential to impact water resources (Fig. 1). The potential warning ranges from seconds (for rapid-onset natural hazards such as earthquakes) to years (for slow-onset natural hazards such as droughts) and determines the time available for prediction and deliberation about how to react. The potential impact on water supply also ranges from low impact (negligible change in water supply) to high impact (water supply temporarily lost in a ‘water outage’). Combining these two factors conceptually results in a susceptibility of water supply to natural hazards.

Groundwater is less likely to be impacted by natural hazards than is surface water^6,7. Natural hazards such as earthquakes, volcanic activities, floods, storms or wildfires often impact centralized water infrastructure that is more often dependent on surface water. These infrastructure impacts such as breaking pipes are more likely to be single point failures. Groundwater is generally more decentralized¹¹ so less likely to be impacted by single point failures. Second, surface water can be contaminated or salinized rapidly and extensively by natural hazards such as floods, wildfires, tsunamis or storm surges. Groundwater is less likely to be contaminated rapidly and extensively, although this depends on the aquifer type as well as other factors such as land use, natural hazard type and connectivity to surface water. Generally, contamination of unconfined aquifers (those directly connected to surface water and atmosphere) will be slow. For example, salinization after a tsunami or storm surge can take months to move downwards¹⁴. Confined aquifers are separated from surface water and atmosphere by a low-permeability confining layer that makes contamination or salinization from the surface much less likely. For these reasons, we argue that groundwater can and should be used strategically during or after natural hazard events, sometimes in conjunction with surface water.

Policies and practices for earthquakes, wildfires, droughts and floods in a variety of countries provide clues for how groundwater could be strategically used to reduce susceptibility to natural hazards.

Earthquakes in Japan, where privately owned wells become public assets in emergency situations, are the most closely studied example^15,16,17. The 1995 Hanshin-Awaji earthquake struck highly urbanized Kobe and adjacent cities, highlighting both the susceptibility of modern water infrastructure and the resilience of local groundwater as an emergency water supply, prompting the establishment of ‘disaster emergency well’ programmes. Private well owners pre-register and are expected to provide groundwater voluntarily after an earthquake. Currently 1,316 of the 1,741 municipalities in Japan have plans to use groundwater during emergencies, including major cities such as Kyoto, Sapporo and Sendai¹⁶. Key policies include enhancing social capital, pre-registering local wells for emergency use and facilitating information sharing and collaboration between well owners and public relief organizations. Marginalized communities can be disproportionately impacted by earthquakes in Japan¹⁸ and elsewhere¹⁹, and although the disaster emergency wells could ensure that water is accessible for marginalized communities, to date municipal plans do not explicitly consider equity or marginalized communities.

Groundwater is a useful water source before (prevention and protection), during (suppression) and after (recovery) wildfires, while also helping to maintain soil moisture. Wildfires can have disproportionate impacts on marginalized communities^20,21,22; climate change is increasing the frequency and intensity of weather conducive to fire ignition and spread²³ and the importance of groundwater for wildfires is magnified by drought, water scarcity or seasonal water availability. Policies in various jurisdictions such as British Columbia²⁴ clarify the importance of groundwater use for wildfires but do not explicitly consider equity and could consider the use of non-potable groundwater before or during wildfires. The literature^25,26,27 on water supply and wildfires is dominated by examples and warnings of erosion, mudslides and contamination of water supply. It is crucial to rapidly test and repair water supply after fires, while also elevating the crucial role of groundwater use before, during and after fires as a source of potable water, less likely to be contaminated or affected by erosion or landslides. For example, two large wildfires in California damaged thousands of structures and caused extensive damage to the water distribution systems, but the potable water sources including wells were not impacted²⁸.

Droughts are slower-onset events, usually with more warning than other natural hazards (Fig. 1). Short-term strategic groundwater use can be important when surface water resources are limited or unavailable. Droughts can exacerbate groundwater use and depletion^4,29,30, so it is important that groundwater use during droughts considers equity and does not exacerbate long-term groundwater depletion (sometimes called strategic aquifer depletion)³⁰. A case in point is the 2015–2018 drought in South Africa, which culminated with the Day Zero water crisis in the city of Cape Town, where drought impacts were unevenly distributed because of stark social inequalities characterized by unsustainably high levels of water consumption by the city elites^31,32. During drought restrictions, wealthier households drilled wells and integrated municipal water supply with groundwater.

Flood events often contaminate surface water and thus can severely affect water supply. Groundwater resources can be used as a substituting supply during flood emergencies³³. The 2002 flooding in the Czech Republic is a case in point. Isotope groundwater dating was applied in the flooded region to identify aquifers with the longest groundwater residence, recommended as alternative supply in the case of major flooding³⁴. Similarly to the other hazards, flood risk is unevenly distributed across societies^1,35. The unequal impacts of the 2005 flooding in New Orleans, for example, are emblematic of how marginalized communities often have less resources to prevent, cope with and recover from floods^36,37. Finally, it is important to integrate the response to floods and droughts in relation to groundwater—for example, by alleviating droughts by strategically recharging aquifers during floods, as argued in a recent California water policy white paper³⁸.

Importantly, in each of these types of natural hazard, we are not discussing or proposing entirely different technology or groundwater resources—generally the same wells, pumps and aquifers would be used (although in some cases strategic well drilling may be useful). We propose to shift thinking, policy and planning when addressing natural hazards.

Here we differentiate short-term groundwater use during or after natural hazard events from normal long-term use. Long-term thinking is broadly advocated for groundwater—the largest available freshwater resource, which is essential for drinking water, irrigation and ecosystems around the world³⁹. Long-term thinking over years to decades is crucial to support the sustainability of this slowly renewed resource, but here we propose short-term use over days and months during various natural and human-made disasters. For natural hazards, the timescales are probably hours to months; the primary uses are probably domestic water and fire suppression and key challenges include rapid and equitable access and contamination (Table 1). Groundwater resources in normal times have three distinctive characteristics (invisible, slow and distributed), which challenge resource management of this common-pool resource¹¹. Invisibility leads to underprioritization, slowness makes it challenging to observe management changes and the distributed nature means there are many well owners spread over great distances.

However, short-term thinking is more important during or after natural hazards, which suggests considering alternative characteristics (inexpensive, speedy and distributed). Groundwater sharing at community level after a natural hazard can be inexpensive because it does not need new equipment or facilities. Wells can quickly supply water to a community, potentially faster than water trucks or other means, depending on the organizational response or damage to infrastructure. Finally, the distributed characteristic has a positive meaning during or after natural hazards since a broader population can access water supply. Importantly, inexpensive, speedy and distributed may also lead to more equitable outcomes in that more people have water access regardless of socio-economic status, race and geographic location. Adopting such ‘short-term thinking’ has various barriers, including deciding quickly, having systems and plans in place before the natural hazard event, legal barriers to water use (for example changing private wells into public usage) and concerns about water quality (wildfires, tsunamis, storm surges). While we argue that short-term thinking is useful, groundwater use in these circumstances still needs to be sustainable in the longer term so as not to compromise access to sufficient, good quality groundwater for future generations. Next, we draw on insights and practices from other disciplines to enable this short-term thinking.

We highlight interdisciplinary literature and transdisciplinary practices including disaster and environmental justice, disaster sociology, sustainability science and sociohydrology to frame or better understand the potential of groundwater use for natural hazards or possibly accelerate the adoption of this new approach. Geoscientific methods and groundwater governance are also important but have been previously summarized^6,7,8. Figure 2 highlights how scientific analysis and communication could possibly increase the warning time before earthquakes, floods, storms and wildfires, while a host of interdisciplinary and transdisciplinary practices and approaches introduced below could reduce the impact of natural hazards on water supply.

Marginalized communities are often disproportionately impacted by all four types of natural hazard described above, highlighting the importance of equity, specifically disaster and environmental justice. Disaster and environmental justice emphasize the importance of equitable treatment and involvement of all communities, particularly those that are historically marginalized in interwoven processes related to disasters and the environment^37,40,41. Marginalized communities are better included after disasters by removing challenges, recognizing diversity, participating in decision-making and tailoring approaches⁴². Additionally, established environmental justice tools could be applied, such as geospatial, statistical or demographic analysis^43,44,45, as well as community-based research and knowledge co-production^46,47. For example, to equitably include groundwater use more explicitly in California earthquake or wildfire planning, it could be important to consistently include all stakeholders who have been largely excluded from groundwater sustainability planning to date⁴⁸. For groundwater’s inexpensive, speedy and distributed characteristics to reduce the differential impacts on marginalized communities, hazard planning needs to better incorporate disaster and environmental justice.

Important social dynamics examined by disaster sociology during or after natural hazard events include emergent groups and temporary altruism. Organizations are classified^49,50 as established, extending, expanding and emergent on the basis of whether the tasks conducted by an organization during and after disasters are regular or not, and whether the organizational structure is existing or new. Figure 3 highlights how groundwater use after earthquakes could be enabled by these different types of organization, and herein we focus on emergent groups (an ad hoc association of volunteers who appear spontaneously after a disaster), since we envision these organizations catalysing and enabling groundwater use in different natural hazards. The disaster emergency wells in Japan are an example of such an emergent organization, and we need to develop strategies to seed and support such organizations for other types of natural hazard, as well as coordinating emergent organizations with the other organizational types (Supplementary Information). Additionally, temporary altruism is common to people affected by natural hazards and is important to consider and amplify, since this can extend and strengthen the impact of the different types of organization^51,52,53.

Using or adopting approaches from sustainability science could enable groundwater use during natural hazard events. Groundwater sustainability^39,54 and the groundwater connected systems framing⁵⁵ argue for the importance of equity (intra- and intergenerational), adaptive management and groundwater as a social–ecological system. Groundwater is a common-pool resource, so principles for how commons can be governed sustainably and equitably by communities⁵⁶ could complement insights from disaster sociology, further enabling emergent groups. Instead of considering groundwater only as a physical resource, the groundwater connected systems framing suggests identifying the ecological (for example groundwater-dependent ecosystems), Earth system (for example groundwater–climate interactions) and social (for example food security) functions to prioritize. These key functions could maintain resilience through natural hazards and/or be important to recovery after natural hazards. Two additional concepts from the broad sustainability science domain could be important: nature-based solutions⁵⁷ and the food–energy–water nexus^58,59. Nature-based solutions include a broad set of green infrastructures that can complement or replace traditional grey infrastructure⁵ to reduce hazard impact (for example, to increase slope stability after wildfires). The food–energy–water nexus reminds us that the direct impacts of natural hazards on water discussed above can be magnified when natural hazards damage and disrupt energy systems and reduce food production⁶⁰.

Sociohydrology focuses on the complex web of interactions and feedbacks between hydrological and social processes⁶¹ to advance the understanding of complex human–water systems, and inform sustainable water resource management. Qualitative and quantitative methods including historical analyses and system dynamics models draw on diverse fields⁶², including water resource systems⁶³, integrated water resource management⁶⁴ and social–ecological systems⁶⁵. Sociohydrological approaches are important since they analyse how community resilience and social networks can help mitigate the negative impacts of natural hazards. Sociohydrological methods also emphasize the potential for unexpected cascading effects or unintended consequences, such as how groundwater use in the short term can backfire on long-term goals such as reduced groundwater depletion³⁰. Sociohydrology has helped recognize that the effect of hazard-preventing interventions deteriorates over time; this community and institutional memory loss⁶⁶ may also affect procedures for emergency groundwater use. Social capital, the networks and resources available to people through their connection to others⁵³, is important but yet to be included in the sociohydrology literature related to natural hazards. It is crucial to consider equity along with social capital, since social capital can ameliorate or exacerbate the impacts of natural hazards, depending on social dynamics⁵³. Finally, in relation to groundwater, sociohydrogeology specifically includes social sciences in hydrogeological assessments and elevates the importance of reciprocity and responsibilities, as well as the ethical, social and cultural implications of groundwater-related research⁶⁷.

Short-term groundwater use is one possible strategy to reduce the impacts of natural hazards but certainly not a panacea. Unfortunately, current social and economic conditions could challenge some of the suggestions above: political polarization and misinformation could undermine efforts to improve scientific prediction, economic challenges could reduce funding of such efforts and systemic racism could challenge reduction of these impacts on marginalized communities. However, we hope to galvanize research, policy and practice with this vision of a deeply interdisciplinary and equity-driven approach incorporating disaster and environmental justice, disaster sociology, sustainability science and sociohydrology (see Supplementary Information for important research questions).