Groundwater Flooding Research Articles

Storm surge, seawater flooding, and sea-level rise paradoxically drive fresh surface water expansion

Abstract Coastal storms and sea-level rise are expected to increase seawater flooding in low-elevation coastal zones. High sea levels and seawater flooding can drive groundwater table rise via ocean-aquifer connections. These dynamics are often overlooked but can cause groundwater flooding and salinization hazards, increasing freshwater security challenges for coastal communities and driving ecosystem transgressions. Field data and numerical modeling were used to evaluate how heavy rainfall, storm surge, and seawater flooding and infiltration during Hurricane Fiona (September 2022) and projected sea-level rise impact groundwater levels, inland surface waters, and saltwater intrusion on Sable Island National Park Reserve, Canada. During the passage of Hurricane Fiona, precipitation increased groundwater and pond levels before seawater flooded the beach. Seawater flooding and infiltration caused a sharp rise in beach groundwater levels, which in turn caused inland pond levels to rise without coincident direct inputs from precipitation or seawater. Model simulations reveal that seawater infiltration on beaches flooded the subsurface and drove the observed inland groundwater rise and freshwater pond expansion. Simulations of projected sea-level rise show that seawater flooding will only inundate a small area of land along the coast; however, inland groundwater rise and flooding, which is less well-studied, may inundate up to 30 times more land area. Further, groundwater flooding driven by rising sea levels decreases hydraulic gradients and increases saltwater intrusion via freshwater lens contraction. Findings demonstrate that seawater flooding from coastal storms and sea-level rise paradoxically cause concurrent fresh surface water expansion but freshwater lens contraction. This study provides new insights into the spatiotemporal dynamics of island freshwater resources and highlights that unseen and often overlooked groundwater-surface water exchanges are critical to consider when evaluating coastal flooding and groundwater salinization hazards and management strategies for low-elevation coastlines.

Remote Sensing and Assessment of Compound Groundwater Flooding Using an End-to-End Wireless Environmental Sensor Network and Data Model at a Coastal Cultural Heritage Site in Portsmouth, NH.

The effects of climate change in the forms of rising sea levels and increased frequency of storms and storm surges are being noticed across many coastal communities around the United States. These increases are impacting the timing and frequency of tidal and rainfall influenced compound groundwater flooding events. These types of events can be exemplified by the recent and ongoing occurrence of groundwater flooding within building basements at the historic Strawbery Banke Museum (SBM) living history campus in Portsmouth, New Hampshire. Fresh water and saline groundwater intrusion within basements of historic structures can be destructive to foundations, mortar, joists, fasteners, and the overlaying wood structure. Although this is the case, there appears to be a dearth of research that examines the use of wireless streaming sensor networks to monitor and assess groundwater inundation within historic buildings in near-real time. Within the current study, we designed and deployed a three-sensor latitudinal network at the SBM. This network includes the deployment and remote monitoring of water level sensors in the basements of two historic structures 120 and 240 m from the river, as well as one sensor within the river itself. Groundwater salinity levels were also monitored within the basements of the two historic buildings. Assessments and model results from the recorded sensor data provided evidence of both terrestrial rainfall and tidal influences on the flooding at SBM. Understanding the sources of compound flooding within historic buildings can allow site managers to mitigate better and adapt to the effects of current and future flooding events. Data and results of this work are available via the project's interactive webpage and through a public touchscreen kiosk interface developed for and deployed within the SBM Rowland Gallery's "Water Has a Memory" exhibit.

Impacts of Sea‐Level Rise on Coastal Groundwater Table Simulated by an Earth System Model With a Land‐Ocean Coupling Scheme

AbstractSea‐level rise (SLR) poses a severe threat to the coastal environment through seawater intrusion into freshwater aquifers. The rising groundwater table also exacerbates the risk of pluvial, fluvial, and groundwater flooding in coastal regions. However, current Earth system models (ESMs) commonly ignore the exchanges of water at the land‐ocean interface. To address this gap, we developed a novel land‐ocean hydrologic coupling scheme in a state‐of‐the‐science ESM, the Energy Exascale Earth System Model version 2 (E3SMv2). The new scheme includes the lateral exchange between seawater and groundwater and the vertical infiltration of seawater driven by the SLR‐induced inundation. Simulations were performed with the updated E3SMv2 for the global land‐ocean interface to assess the impacts of SLR on coastal groundwater under a high CO2 emission scenario. By the middle of this century, seawater infiltration on the inundated areas will be the dominant component in the land‐ocean coupling process, while the lateral subsurface flow exchange will be much smaller. The SLR‐induced seawater infiltration will raise the groundwater levels, enhance evapotranspiration, and increase runoff with distinct spatial patterns globally in the future. Although the coupling process is induced by SLR, we found topography and warming temperature have more control on the coupling impacts, probably due to the relatively modest magnitude of SLR during the selected future period. Overall, our study suggests significant groundwater and seawater exchange at the land‐ocean interface, which needs to be considered in ESMs.

Shoreline barriers may amplify coastal groundwater hazards with sea-level rise

Subsurface barriers have been proposed to protect coastal aquifers from sea-level rise induced seawater intrusion, but the potential for groundwater emergence near subsurface barriers remains unknown. Here, we investigated how emergence changes groundwater flow conditions and influences the protective performance of subsurface barriers with sea-level rise. We tested the subterranean consequences of sea-level rise for cutoff walls and subsurface dams with cross-shore groundwater flow and salt transport models, investigating how barrier design, aquifer properties, and hydrological conditions control the potential for emergence, groundwater partitioning at the barrier, and seawater intrusion with sea-level rise. We find that most subsurface infrastructure cannot prevent seawater intrusion and emergence simultaneously. Subsurface dams spanning more than half of the aquifer thickness created emergence hazards and subsequent groundwater partitioning for all scenarios tested. Cutoff walls were less effective at reducing seawater intrusion for all opening sizes but could reduce the emergence potential compared to similarly sized subsurface dams. Our results demonstrate the challenging trade-offs in mitigating the coastal groundwater hazards of seawater intrusion and emergence with sea-level rise, where groundwater flooding inland of protective infrastructure would require combinations of subsurface impoundments and other mitigation techniques, such as pumping or drains.

A conceptual framework for understanding community resilience to flooding

Abstract Flooding, an already prevalent global hazard, is predicted to worsen in frequency and intensity. Flood Risk Governance has evolved from exclusively combating flooding to now also coexisting with it, aiming to enhance resilience comprehensively and over the long term. A narrative literature review presents diverse conceptualisations of resilience to flooding, highlighting ongoing debates about whether resilience is an outcome or process. This paper contends that resilience can and should encompass both the process and outcome-based components. Critically reviewing existing conceptualisations, this paper proposes a holistic framework for understanding community resilience. The framework comprises three components: the capacity to resist, the capacity to respond and recover, and the capacity to adapt. Six specific and potentially overlapping, capacities are identified as Social, Physical, Human, Economic, Institutional, and Natural. The paper also discusses the importance of qualitative research in providing more nuance when assessing resilience. The paper clarifies the complexity of resilience in the face of evolving flood risks, proposing an integrated framework that spans capacities, ongoing processes, and ultimate outcomes. This framework will provide the foundation for understanding and analysing community resilience to groundwater flooding in Buckinghamshire, UK.

Groundwater flooding – a hidden hazard

Groundwater flood forecasting and management has not yet been fully integrated with other types of flooding. Better recognition is needed of the role of groundwater and its interactions with infrastructure as part of holistic hydrological and engineering multi-source flood management.

USING GRACE AND GLDAS DRIVEN DATA TO ASSESS GROUNDWATER FLUCTUATIONS OF NIGER-SOUTH HYDROLOGICAL AREA OF NIGERIA

Gravitational Recovery and Climate Experiments Terrestrial Water Storage and Global Land Data Assimilation Systems Surface Water and Soil Moisture including Nigerian Hydrological Service Agencys Groundwater Level were used to assess the temporal groundwater fluctuations of Niger-south Hydrological Area of Nigeria. The study adopted a cross-sectional research design; descriptive and inferential statistics was used for data analysis; Table was used for presentation. The study finds that there is no statistical significant difference between average monthly net recharge and average month storage changes at 95% probability level, it further concluded that the use of these satellites to acquire data and make decision will mark a new era and bring about fewer causalities on natural event(s), and therefore recommended us to take advantage of this free available resource to ameliorate challenges trying to extinct the existence of man from earth surface; therefore, increasing groundwater levels in Niger-south Hydrological Area needed to be properly managed because of rising groundwater flooding. KEY WORDS: GRACE, GLDAS, QGIS, Groundwater, Fluctuation

Simulation of the impact of sea level rise groundwater flooding along the south-eastern coast of India

Sea-level rise affects low-lying coastal regions that jeopardize superficial infrastructure through groundwater flooding, which also impacts near-surface artificial structures, inhumed networks, and near-shore ecosystems. In the present study, groundwater flow modeling has been utilized to simulate different scenarios of sea level rise to evaluate the groundwater level changes and predict possible vulnerable zones to groundwater inundation along the coast of the Nagapattinam district. The model has been simulated for ten years (2010–2019) under the transient condition with MODFLOW-2000 engine in Visual MODFLOW. Calibration and validation of the simulated model have been performed by trial-and-error method considering groundwater heads of selected observations well data, which results in a root mean square value of 1.765 m, 0.941 as correlation coefficient, and a value of 0.687 m as the standard error. Groundwater flooding due to a 0.6 m sea level rise is forecasted to cause significant flooding, covering 23.83% of the study area. A 1.0 m rise in sea level impacts 26.2% of the study region. The sea level rise scenarios evaluate that the coastal groundwater heads will reduce as they are restricted by topography from rising landward. The present study suggests groundwater in the coastal regions is influenced by sea level rise due to climate change impacting the coastal ecosystems.

Groundwater Flooding on Atolls Caused by Storm Surges: Effects of the Dual‐Aquifer Configuration

AbstractStorm surges associated with tropical cyclones endanger atolls through groundwater flooding, where groundwater is discharged from the land surface as the sea level rises. Atolls are characterized by a “dual‐aquifer” configuration, where recent Holocene sediments unconformably overlie highly permeable Pleistocene limestone, creating an interface called a “Thurber discontinuity.” This study aimed to quantitatively analyze how the dual‐aquifer configuration of atolls controls the temporal dynamics of groundwater flooding caused by storm surge. To this end, we ran surface‐subsurface coupled synthetic numerical simulations using HydroGeoSphere and compared 12 scenarios with different Thurber discontinuity elevations and hydraulic conductivities of the Pleistocene aquifer (KP). The results showed that the shallower the Thurber discontinuity and the higher the KP value, the higher the maximum water depth in the freshwater swamp on the atoll during the storm surge and the longer the flooding duration. Despite the effects of the different dual‐aquifer configurations, the initial water table elevation and salinity distribution were almost identical in all the simulation cases. These findings suggest that accurate information on the dual‐aquifer configuration is necessary to evaluate the potential risk of groundwater flooding on atolls accompanying storm surges. Furthermore, the results indicate that groundwater flooding caused by storm surges substantially contributes to cyclone‐driven flooding on atolls, and hence, it should not be neglected in flood predictions to avoid underestimation.

Short-Term Ocean Rise Effects on Shallow Groundwater in Coastal Areas: A Case Study in Juelsminde, Denmark

Coastal areas situated at lower elevations are becoming more vulnerable to flooding as a result of the accelerating rise in the global sea level. As the sea level rises, so does the groundwater. Barriers designed to shield against marine flooding do not provide protection against flooding caused by rising groundwater. Despite the increasing threat of groundwater flooding, there is limited knowledge about the relationship between sea level rise and groundwater fluctuations. This hinders the ability to adequately consider sea level rise-induced groundwater flooding in adaptation initiatives. This study aims to investigate how local groundwater in Juelsminde, Denmark, responds to changes in sea level and to evaluate the predictability of these changes using a machine learning model. The influence of the sea on the shallow groundwater level was investigated using six groundwater loggers located between 45 and 210 m from the coast. An initial manual analysis of the data revealed a systematic delay in the rise of water levels from the coast to inland areas, with a delay of approximately 15–17 h per 50 m of distance. Subsequently, a support vector regression model was used to predict the groundwater level 24 h into the future. This study shows how the groundwater level in Juelsminde is affected by sea level fluctuations. The results suggest a need for increased emphasis on this topic.

An introduction to the chalk aquifers of northern Europe

AbstractWe briefly outline the progressive development of approaches to both the characterization and simulation of the hydrogeology of northern European chalk aquifers, which were some of the first in the world to be studied. The volume's scope includes work on water resources and quality, chalk streams and wetland ecosystems, chalks as heat reservoirs for building temperature regulation, sources of groundwater flood risk and impacts of engineering on the subsurface, and diffuse and point-source pollution affecting these aquifers. It excludes hydrocarbon-related studies and those focused on offshore chalk sequences. We briefly outline the current state of knowledge of hydrogeological processes, characterization, assessment and modelling, and the increasingly recognized importance of karst features. The latter were little discussed 20 years ago and are still often neglected. There follows a brief quantitative analysis of publication topics relating to chalk hydrogeology in the scientific literature over the past three decades, which highlights key trends including both the purposes of studies and the methods employed. We present a summary of the topics and contributions within this volume, and conclude by identifying the key issues that need to be addressed in order to ensure the sustainability of our chalk aquifers for the future.

Arsenic release dynamics of paddy field soil during groundwater irrigation and natural flooding

Irrigation water in rice cultivation significantly affects the arsenic (As) mobilization in the paddy field soil. This research assessed the effect of rainwater (RW) and groundwater (GW) on the dissolution dynamics of arsenic (As) in paddy field soil. Up-flow column flooding experiments were conducted continuously for 80 d with simulated RW and GW to evaluate As dissolution phenomena in actual field conditions. Arsenic dissolution from the soil was lower in GW (309 μg/kg) irrigation than in RW flooding conditions (1086 μg/kg). The redox potential (Eh) of the soil pore water decreased, and pH increased over-irrigation time in both flooding conditions. The dissolution of arsenic (As) and iron (Fe) in the soil pore increased, while the dissolution of manganese (Mn) decreased over flooding time. The release of As in the soil pore water was attributed to the dissolution of Fe–As and Mn–As minerals and microbial reduction of As. Fe–As dissolution ratios in the soil pore water were relatively low and estimated as 0.68 mol/mol and 4.9 mol/mol for RW and GW, respectively. The dissolution of As and Mn dominated in the initial phase (0–40 d) of flooding, while the dissolution of As and Fe dominated in the second phase (40–80 d). The release of As was much lower in GW flooding than in RW flooding conditions. The Presence of Ca, Mg, and Mn in the GW facilitated the reduction of As dissolution by precipitating Ca–As and Mg–As and the oxidizing dissolved Mn in the soil pore water. The findings of this study provide valuable insights into the mechanisms of As release during monsoon flooding and groundwater flooding to assess the potential risks of As contamination in rice grown in paddy field soils.

Groundwater flooding hazard assessment in a semi-urban aquifer through probability modelling of surrogate data

Many areas of the world are experiencing groundwater flooding (GF) events with serious impacts on the environment and human health. In Europe, GF has received specific attention with the Directive 2007/60/EC, which requires Member States to map GF hazard and risk and propose mitigation measures. In Italy, despite the commitment assigned by the Legislative Decree 49/2010 to River Basin District Authorities, no models have been developed for groundwater flooding hazard (GFH) evaluation also for the lack of standard methods based on commonly available data. In this paper, a new method has been developed through a specific procedure that accounts for i) probability of GF events estimation based on available time series of groundwater levels and ii) probability mapping through a newly developed MATLAB™ code, high-resolution topographic data and groundwater table model. The methodology has been tested and validated in the Metropolitan City of Naples (Italy), affected by GF since 2010, for which i) sixty-two-year long time series of groundwater levels, ii) high-resolution Digital Elevation and Digital Terrain Models and iii) basement/building geometry, are available. The results show that about 59% of the buildings present in the study area have potentially floodable underground structures. In the 2010–2021 period, only 2% of these buildings were flooded and most of them were built in the period 1980–2000, when the piezometric levels were deeper due to over-pumping of the groundwater. The obtained GFH map shows that only 2% of the built area is involved by 1- to 2- year events, while 6% is affected by 1- to 10- year events. A good spatial correspondence between the return period and locations of GF events occurred during 2010–2021 period was observed, thus indicating the significant performance of the model. The obtained GFH map output can support decisions of authorities and policy-makers to reduce the GF risk.

Integrating hydrogeological and economic analyses of groundwater flooding in an urban aquifer: the plain of Naples (Italy) as a case study

ABSTRACT The study applies the defensive expenditure approach via hydrogeological data for a sector of the plain of Naples to value the economic damages produced by groundwater flooding on private properties. It follows from the integrated analysis that the value of the economic damages is increasing over time at a compound pace. The over-pumping of groundwater during the industrialisation period, and its stop in the subsequent de-industrialisation one, impaired the long-run natural equilibrium of the groundwater resources. Thus, the myopic decisions taken with respect to land and groundwater use, and a short-sight urban design planning have caused increasing economic costs in the medium and long terms.

Coastal urban reliance on groundwater during drought cycles: Opportunities, threats and state of knowledge

Abstract Urbanisation and population growth are concentrated on the coast with approximately 40% of the human population living within 100 km of the ocean. The freshwater systems on which coastal urban areas rely are vulnerable to bidirectional pressures including coastal processes such as sea-level rise and coastal erosion coupled with land use changes and pollution occurring in inland catchment areas. These threats are likely to be amplified in the future under climate change conditions and more frequent and severe drought periods are expected to jeopardise already constrained water supply systems. Groundwater is used as a freshwater resource globally and is especially important as a conjunctive supply during drought periods due to perceived buffer capabilities. However, several threats impact coastal aquifers due to over-abstraction, such as salinisation, land subsidence and groundwater flooding and often these subterranean resources are “out of sight and out of mind” when it comes to management strategies. Here, we present an assessment of current issues and management options relevant to coastal aquifers using recent literature. These insights provide knowledge on global issues relevant to groundwater resources, especially regarding water use during droughts. This is exemplified using a South African case study of two metropolitan municipalities that have experienced or are experiencing severe multi-year droughts. Both municipalities have grappled with the depletion of surface water resources, which constitutes the bulk of the local water supply systems. Consequently, groundwater resources have been explored as an augmentation strategy. Although groundwater resources may be useful in alleviating drought effects, it is crucial that a local understanding of the aquifers is developed through baseline hydrological studies and long-term monitoring. Furthermore, unregistered groundwater use needs to be quantified. Finally, a holistic groundwater management view, and the communication thereof, is required to ensure the sustainable management of coastal aquifers.

Evaluating Preventive Measures for Flooding from Groundwater: A Case Study

Groundwater (GW) flooding mechanisms differ from river flooding, both spatially and temporally, and preventative methods against groundwater flooding must take this into account. Although groundwater flooding caused by a rise of river water seldom occurs, it can occasionally become severe and last for a long time if the river is significantly flooded. In the southwest portion of the research domain, Friedrichshafen, Germany, with a few urban communities, the level of the groundwater table was discovered to be roughly 1 m below the surface. In the study region, it is typical for the bottom level of the foundation of a single-story building to extend up to a depth of about 1.5 m. Therefore, flood mitigation methods are taken into account for the southwest portion of the study region. In this study, FEFLOW is used to explore the preventative methods for groundwater flooding caused by river water increase in urban settings, the spread of contamination, and the strategizing of effective mitigation solutions for flooding. The installation of a pumping well, drainage, and a barrier in the affected area are three different flood control strategies that are taken into consideration for the study area. Pumping well installation, reducing up to 1.5 m of hydraulic head, was found to be the most effective flood control measure locally in a small region. By contrast, removing groundwater by building drainage and barriers was shown to be ineffective for lowering the groundwater table over an extended region, and was significantly more expensive than the installation of wells. Additionally, when river flooding is taken into account, compared to the default scenario where no intake of water from the river is included along the western border of the study area, it was discovered that the spread of pollution (nitrate concentration) is significantly greater.

Investigating compound flooding in a low elevation coastal karst environment using multivariate statistical and 2D hydrodynamic modeling

Miami-Dade County is vulnerable to flash, pluvial, fluvial, coastal and groundwater flooding due to its low-elevation karst morphology. Despite considerable advances in understanding the impact of compound flooding events by considering major flood drivers (precipitation, river discharge, and coastal surge), little is known regarding the severity of groundwater hazards in this region. This study links a multivariate statistical analysis with a coupled physically-based 2D hydraulic model to estimate the flood hazard in the Arch Creek Basin located in North Miami. A bivariate copula analysis was used to capture the joint probability of key flood drivers with predefined water table thresholds to set-up the flood modeling conditions. Results demonstrate the high vulnerability to extreme precipitation events compared to coastal surge in the study area. Similarly, groundwater flooding is relevant in shallow water table environments, as it influences the severity of flood hazards in terms of flood inundation depth, extent, and damage to the built environment. This research demonstrates that groundwater flooding is a latent risk that should be incorporated in flood hazard mapping in regions susceptible to high water tables and sea level rise.

Groundwater Rise and Associated Flooding in Coastal Settlements Due To Sea‐Level Rise: A Review of Processes and Methods

AbstractCoastal settlements are experiencing the effects of climate change‐induced sea‐level rise, including a significant but often poorly‐characterized impact on groundwater. The shallow water tables present in the built coastal environment contribute to an increased risk from natural hazards such as groundwater flooding and saltwater intrusion. Historical urban development was accompanied by impacts on shallow groundwater, and in the future subsurface environments, including underground infrastructure, will face additional pressure. This article reviews processes of the coastal groundwater zone and simulation tools used to evaluate possible impacts of sea‐level rise. The benefits and limitations of the two main methods to assess coastal groundwater rise and contribution to flooding are discussed using studies and investigations up to 2021. The review addresses challenges associated with the simulation tools to evaluate changes in urban hydrogeology due to sea‐level rise. The models reviewed do not specifically estimate groundwater contribution to land‐surface flooding. We highlight a critical need for methodology comparisons between spatial interpolation and numerical tools that will guide future work. An adequate validation of assessment methods is required and will be supported by improved coastal groundwater monitoring networks focused on water quality, saltwater intrusion, and continuous groundwater levels records. From current monitoring practices, evidence for groundwater rise with rising sea level is not widely observed at present. New monitoring sites are recommended near the coastline and tidally influenced surface water bodies, to better evaluate the rise of the water table and impacts on infrastructure.

Influence of low-frequency variability on high and low groundwater levels: example of aquifers in the Paris Basin

Abstract. Groundwater levels (GWLs) very often fluctuate over a wide range of timescales (intra-annual, annual, multi-annual, and decadal). In many instances, aquifers act as low-pass filters, dampening the high-frequency variability and amplifying low-frequency variations (from multi-annual to decadal timescales) which basically originate from large-scale climate variability. Within the aim of better understanding and ultimately anticipating groundwater droughts and floods, it appears crucial to evaluate whether (and how much) the very high or very low GWLs are resulting from such low-frequency variability (LFV), which was the main objective of the study presented here. As an example, we focused on exceedance and non-exceedance of the 80 % and 20 % GWL percentiles respectively, in the Paris Basin aquifers over the 1976–2019 period. GWL time series were extracted from a database consisting of relatively undisturbed GWL time series regarding anthropogenic influence (water abstraction by either continuous or periodic pumping) over metropolitan France. Based on this dataset, our approach consisted in exploring the effect of GWL low-frequency components on threshold exceedance and non-exceedance by successively filtering out low-frequency components of GWL signals using maximum overlap discrete wavelet transform (MODWT). Multi-annual (∼7-year) and decadal (∼17-year) variabilities were found to be the predominant LFVs in GWL signals, in accordance with previous studies in the northern France area. By filtering out these components (either independently or jointly), it is possible to (i) examine the proportion of high-level (HL) and low-level (LL) occurrences generated by these variabilities and (ii) estimate the contribution of each of these variabilities in explaining the occurrence of major historical events associated with well-recognized societal impacts. A typology of GWL variations in Paris Basin aquifers was first determined by quantifying the variance distribution across timescales. Four GWL variation types could be found according to the predominance of annual, multi-annual, or/and decadal variabilities in these signals: decadal-dominant (type iD), multi-annual- and decadal-dominant (type iMD), annual-dominant (type cA), and annual- and multi-annual-dominant (type cAM). We observed a clear dependence of high and low GWL on LFV for aquifers exhibiting these four GWL variation types. In addition, the respective contribution of multi-annual and decadal variabilities in the threshold exceedance varied according to the event. In numerous aquifers, it also appeared that the sensitivity to LFV was higher for LLs than HLs. A similar analysis was conducted on the only available long-term GWL time series which covered a hundred years. This allowed us to highlight the potential influence of multidecadal variability on HLs and LLs too. This study underlined the key role of LFV in the occurrence of HLs and LLs. Since LFV originates from large-scale stochastic climate variability as demonstrated in many previous studies in the Paris Basin or nearby regions, our results point out that (i) poor representation of LFV in general circulation model (GCM) outputs used afterwards for developing hydrological projections can result in strong uncertainty in the assessment of future groundwater extremes (GWEs), and (ii) potential changes in the amplitude of LFV, be they natural or induced by global climate change, may lead to substantial changes in the occurrence and severity of GWEs for the next decades. Finally, this study also stresses the fact that due to the stochastic nature of LFV, no deterministic prediction of future GWEs for the mid- or long-term horizons can be achieved, even though LFV may look periodic.

Data-driven decision management of urban underground infrastructure through groundwater-level time-series cluster analysis: the case of Milan (Italy)

The significant increase in urbanization has resulted in greater use of the subsurface in urban planning and, therefore, increased interaction between groundwater and underground infrastructure. Numerical models are the primary tool adopted to manage the resulting problems; however, their construction is time- and cost-consuming. Groundwater-level time-series analysis can be a complementary method, as this data-driven approach does not require an extensive understanding of the geological and boundary conditions, even if providing insights into the hydrogeologic behaviour. Thus, a data-driven approach was adopted to analyse groundwater time-series of the shallow aquifer, occupied by several underground structures, beneath Milan city (Northern Italy). Statistical (Mann-Kendall and Sen’s slope estimator, autocorrelation and cross-correlation, hierarchical cluster analysis) and geospatial techniques were used to detect the potential variables influencing the groundwater levels of 95 monitoring wells, covering the period 2005–2019. A general rising trend of the water table was identified, with local hydrogeologic differences in the western and southernmost areas. Based on time-series analysis results, four management areas have been identified. These areas could act as future geographic units with specific groundwater management strategies. In particular, subsurface public car parks can be classified with respect to groundwater flooding as (1) not submerged, (2) possibly critical, or (3) submerged at different groundwater conditions. According to these outcomes, targeted guidelines for constructing new car parks have been elaborated for each management area. The methodology proved to be efficient in improving the urban conceptual model and helping stakeholders design the planned underground development, considering groundwater aspects.