- Email: [email protected]
Groundwater recharge: The intersection between humanity and hydrogeology
Accepted Manuscript Research papers Groundwater recharge: The intersection between humanity and hydrogeology Brian D. Smerdon, Jörg E. Drewes PII: DOI: Reference:
S0022-1694(17)30751-5 https://doi.org/10.1016/j.jhydrol.2017.10.075 HYDROL 22355
To appear in:
Journal of Hydrology
Received Date: Accepted Date:
26 October 2017 30 October 2017
Please cite this article as: Smerdon, B.D., Drewes, J.E., Groundwater recharge: The intersection between humanity and hydrogeology, Journal of Hydrology (2017), doi: https://doi.org/10.1016/j.jhydrol.2017.10.075
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Groundwater recharge: The intersection between humanity and hydrogeology
Brian D. Smerdona* and Jörg E. Drewesb
a
Alberta Geological Survey, Edmonton, Alberta, Canada
b
Chair of Urban Water Systems Engineering, Department of Civil, Geo and Environmental Engineering, Technical University of Munich, Garching, Germany
*Corresponding author: Email: [email protected] Phone: +1 780 641 9759 Postal address: Brian D. Smerdon, Alberta Geological Survey, 402 Twin Atria Building, 4999-98 Avenue, Edmonton, Alberta T6B 2X3, Canada
1.0
Introduction Groundwater recharge is an essential part of subsurface water circulation and the beginning of
groundwater flow systems that can vary in duration from days to millennia. Globally, there is a growing body of evidence suggesting that many of Earth’s aquifers contain ‘fossil’ groundwater that was recharged more than 12,000 years ago (Jasechko et al., 2017), and a very small portion of groundwater that was recharged within the last 50 years (Gleeson et al., 2015). Together, this information demonstrates the irregular distribution of groundwater circulation within the Earth and the wide variability of recharge conditions that replenish aquifer systems (Befus et al., 2017). Knowledge of groundwater recharge rates and distribution are needed for evaluating and regulating the quantity and quality of water resources, understanding consequences of landscapes use, identifying where managed aquifer recharge can augment supply, and predicting how groundwater systems will respond to a changing climate. In-turn, these topics are of central importance for the health of humans and ecosystems, and security of food and energy. Yet, despite the global importance, quantifying groundwater recharge remains challenging as it cannot be measured directly, and there is uncertainty associated with all currently known estimation methods (Scanlon et al., 2002). This Special Issue on ‘Aquifers Recharge: Modeling, Experiments and Climatic Change Effects’ explores the recharge process through different estimation methods and approaches to modeling. Some of the articles in the Special Issue describe techniques for estimating naturally occurring groundwater recharge to better understand a process or particular region, which help learn about the variability of Earth’s groundwater and make informed choices for better management of water resources. Other articles of the Special Issue examine artificially occurring groundwater recharge to augment water supply, or improve water quality. The aspect of climate change is incorporated in many of the studies, whereby uncertainty of recharge estimation methods is compounded with uncertainty of future climate conditions. The aspect of urbanization and groundwater recharge is gaining more attention recently, especially as societies accept the legacy of previous land use choices and plan for the future. This Special Issue brings together 18 articles that offer a perspective of the current thinking about groundwater recharge.
2.0
Overview of research
This overview categorizes the articles into four groups: (i) field and modeling techniques, (ii) isotopic techniques, (iii) effects of climate change, and (iv) land use change and urban recharge. 2.1
Field and modelling techniques Rathay et al. (2017) analyze the response of fractured bedrock to high intensity rainfall events in
the Gulf Islands of British Columbia, Canada. The investigation uses a combination of piezometry, thermal infrared imagery of a seepage face, and stable isotopic analysis of seepage water to examine ponding and infiltration. Rathay et al. (2017) find that higher intensity precipitation events lead to more ponding and less recharge. Guzman et al. (2017) investigate recharge, depth to the water table, and soil nutrients for a watershed in Ethiopia, where soil and water degradation can occur due to agricultural practices. Through field study they learn that land use and crop growth are governed by shallow groundwater conditions (i.e. groundwater perched above a low permeability layer), which in-turn governs the exchange of cations. Xie et al. (2017) investigate the uncertainty of recharge estimation using coupled water and energy balance models and a Monte Carlo analysis of data for the Campaspe River catchment in Victoria, Australia. In this study, recharge varies from about 2 to 36% of annual rainfall for a single set of pedotransfer functions, and up to 60% when different sets of pedotransfer functions are used when modelling. Xie et al. (2017) conclude that time series of soil moisture data did not help reduce uncertainty, whereas time series estimates of evapotranspiration help constrain recharge uncertainty. Doble et al. (2017) develop an approach to link a process-based soil-vegetation-atmosphere transfer (SVAT) model with a regional-scale groundwater flow model. Relationships between net recharge and water table depth are illustrated for parts of South Australia and Victoria, Australia that have a shallow water table and varied land use. Crosbie et al. (2017) demonstrate a regression kriging approach to estimate recharge across large regions having varying data density. For a portion of New South Wales, Australia, 1000 stochastic replicates of available chloride data (rainfall, runoff, and groundwater) supported this geostatistical methodology. Regression kriging allowed upscaling for data-sparse areas, while honouring points-scale
recharge estimates in data-dense areas. In assessing the uncertainty, Crosbie et al. (2017) find that the magnitude of uncertainty was related to the magnitude of estimated recharge rate. 2.2
Isotopic techniques Cartwright et al. (2017) review applications of isotopic tracers to estimate residence time and
rates of groundwater recharge. They highlight that isotopic tracers provide a record of long-term average recharge conditions and residence time, which can be helpful for system conceptualization but are not readily comparable to other techniques. Cartwright et al. (2017) discuss the challenge of acquiring samples from subsurface systems that inherently experience mixing and dispersion. Taylor et al. (2017) use a novel combination of direct push technology and environmental tracers to examine the recharge process for a semi-arid catchment in Queensland, Australia. They find the combination of techniques very useful in a remote region, and efficiently discover that although recharge to alluvial deposits is generally high and originates from overbank flooding, the storage capacity of these systems is limited. Pavlovskii et al. (2017) examine the seasonal dynamics of snowpack isotopic signature and its implications for estimating recharge using an isotopic approach. From snowpack data measured in Alberta, Canada, isotopic signature exhibits large variation over small distances, thus limiting the usefulness for estimating recharge. However, slightly different isotopic signatures appear to exist between diffuse recharge and depression-focused recharge, potentially offering an approach to characterize recharge for key features in a Prairie setting. 2.3
Effects of climate change Smerdon (2017) provides a synopsis of review articles on climate change and groundwater
recharge published between 2011 and 2016. A common finding of the review articles is that the uncertainty of modelling future precipitation drives widely varying predictions of recharge to the point of not being able to predict whether recharge will increase or decrease. The review articles also suggest steps to overcome uncertainty. Rossman et al. (2017) propose an approach to assess the uncertainty of future recharge conditions within regional groundwater flow models. From a series of future climate projections for the Nebraska, United States, cumulative potential recharge (i.e., precipitation minus evapotranspiration) for
a 90-year period was calculated. Subsequently, median, wet and dry scenarios (1 standard deviation from the median) were input to a groundwater flow model. By focusing on a limited number of groundwater flow simulation scenarios, the sensitivity of projected climate can be more rapidly assessed. Corona et al. (2017) investigate the effect of cyclical infiltration from periodic climate forcing and the effect on recharge periodicity. Through a modeling approach and extensive sensitivity analysis, it is shown that some periodic infiltration rates dampen with depth (indicating steady-state recharge), while other periodic infiltration rates do not (indicating transient recharge). The findings establish a framework that helps explain under what conditions the effect of a changing climate could be observed in the subsurface. Havril et al. (2017) evaluate the potential effect of variations in future recharge to the hydrological conditions of groundwater-dependent wetlands in Hungary. Using a cross-sectional numerical model of groundwater flow, they demonstrate the dissolution of nested groundwater flow systems to single flow cells, which can lead to disappearance of the wetlands. 2.4
Land use change and urban recharge Han et al. (2017) review the effect of land use change on groundwater recharge, and
categorized changes due to either agriculture (i.e. land clearing) or urbanization (i.e. expansion of infrastructure). There have been many studies about the effect of agriculture, but very few field-based studies on the effect of urbanization, a trend also noted by Minnig et al. (2017). Manna et al. (2017) describe an extension of the chloride-mass-balance approach to estimate recharge in fractured bedrock of southern California, United States. From porewater profiles and numerical modelling, dual porosity recharge was evaluated. Manna et al. (2017) find that changes in historic recharge rates correspond with changes in land use, and that the majority of the recharge signal occurs from diffuse flow through the rock matrix in a semi-arid region. Viaroli et al. (2017) use a water budget approach and time-series observations to evaluate recharge conditions for an exploited aquifer system in the Riardo Plain, Italy. Although the water budget suggests a deficit, regional observations suggest additional recharge from groundwater adjacent to the primary aquifer.
Minnig et al. (2017) investigate the effect of urbanization on variation in groundwater recharge rates through a water-budget approach and Monte Carlo analysis. For a small region centred in the city of Zurich in Switzerland, a strong positive correlation is found between recharge rate and extent of urbanization. While this finding could appear counter-intuitive, the effect of impervious areas in reducing evapotranspiration is considered to be a significant factor. This study demonstrates that change to recharge conditions in urban settings is not well understood and requires the hydrogeological community to focus on urban regions. Gottschalk et al. (2017) describe two geophysical frameworks construct rock-physics transforms between lithological and electrical resistivity tomography data without the need for co-located lithological and electrical resistivity measurements. Integrating the geophysical data is shown to improve simulation of groundwater conditions at an artificial recharge site in Colorado, United States. Hellauer et al. (2017) describe a pilot field study in Berlin, Germany to evaluate the idea of sequential managed aquifer recharge technology (SMART). This innovative method appears to better remove moderately degradable organic pollutants, demonstrating that ‘engineered recharge’ has the potential to improve water quality under the right conditions.
3.0
Summary and outlook The articles presented in this Special Issue provide a glimpse of the current research and
thinking about the groundwater recharge process. Studies continue to use small scale field sites to learn and refine understanding of mechanisms, and modeling approaches have included more process complexity and been applied to large regions with spatial variability. Fifteen years ago, deVries and Simmers (2002) noted that “the combination of reliable local data, remote sensing, and GIS technology offers promise for a better understanding and quantification of recharge over large areas.” In many regards the articles presented in this Special Issue demonstrate such an evolution has occurred. The nature of field-based studies to learn about recharge mechanisms and develop new techniques will likely continue to be appropriate for smaller spatial scales. Control of the geological setting and ability of understand local climate allows investigation of multiple observation methods with constraint. The structure of numerical models has evolved to include balances of water, energy and
carbon and present day computing certainly allows spatially distributed modeling to be completed as part of regional (or even continental) assessments. However, with increased complexity of model structure and coupling with climate change forecasting, the uncertainty of numerical model results has increased. Because the complexity has grown, the research community suggests that calibration of recharge models can only be achieved for individual components such as soil moisture distribution or evapotranspiration. The assumption being that if the individual pieces are represented accurately, then the net result will have some certainty as well. The need for calibration data reinforces the need for multiple methods of observation at smaller scale research sites that can be used to constrain simulation models. Large datasets and a global perspective (e.g., Döll and Fiedler, 2008; Gleeson et al., 2012) have highlighted the importance of groundwater recharge in relation to sources of water and food for humans, and in maintaining healthy ecosystems and biodiversity. Global-scale studies have also shown that some regions are threatened because of poor water management, irreversible consequences of land use choices, and a changing climate. Susceptibility of aquifer systems is related to near-term future climate (i.e. the next 10 years), where localized, young groundwater flow systems will respond rapidly to change. Susceptibility is also closely related to population density, whereby urban regions are under increasing pressure from development and resource use, and the groundwater recharge processes can be complex to predict. In conclusion, we reiterate the recent editorial by Post and Werner (2017), where research of fundamental hydrogeological processes (such as recharge) is essential, but must also help determine appropriate management responses.
References Befus, K.M., Jasechko, S., Luijendijk, E., Gleeson, T., Cardenas, M.B., 2017. The rapid yet uneven turnover of Earth’s groundwater. Geophys. Res. Lett. 44, 5511–5520. doi:10.1002/2017GL073322 Cartwright, I., Cendon, D., Currell, M., Meredith, K., 2017. A review of radioactive isotopes and other residence time tracers in understanding groundwater recharge: possibilities, challenges, and limitations. J. Hydrol. 5XX, XXX–XXX. Corona, C.R., Gurdak, J.J., Dickinson, J.E., Ferré, T.P.A., Maurer, E.P., 2017. Climate variability and vadose zone controls on damping of transient recharge. J. Hydrol. 5XX, XXX–XXX.
Crosbie, R.S., Peeters, L.K., Herron, N., McVicar, T.R., Herr, A., 2017. Estimating groundwater recharge and its associated uncertainty: Use of regression kriging and the chloride mass balance method. J. Hydrol. 5XX, XXX–XXX. de Vries, J.J., Simmers, I., 2002. Groundwater recharge: an overview of processes and challenges. Hydrogeol. J. 10, 5–17. doi:10.1007/s10040-001-0171-7 Doble, R.C., Pickett, T., Crosbie, R.S., Morgan, L., Turnadge, C., Davies, P., 2017. Emulation of recharge and evapotranspiration processes in shallow groundwater systems. J. Hydrol. 5XX, XXX–XXX. Döll, P., Fiedler, K., 2008. Global-scale modeling of groundwater recharge. Hydrol. Earth Syst. Sci. 12, 863–885. doi:10.5194/hess-12-863-2008 Gleeson, T., Wada, Y., Bierkens, M.F.P., van Beek, L.P.H., 2012. Water balance of global aquifers revealed by groundwater footprint. Nature 488, 197–200. doi:10.1038/nature11295 Gleeson, T., Befus, K.M., Jasechko, S., Luijendijk, E., Cardenas, M.B., 2015. The global volume and distribution of modern groundwater. Nature Geoscience 9, 161–167. doi:10.1038/ngeo2590 Gottschalk, I.P., Hermans, T., Knight, R., Caers, J., Cameron, D.A., Regnery, J., McCray, J.E. 2017. Integrating non-colocated well and geophysical data to capture subsurface heterogeneity at an aquifer recharge and recovery site. J. Hydrol. 5XX, XXX–XXX. Guzman, C.D., Tilahun, S.A., Dagnew, D.C., Zimale, F.A., Zegeye, A.D., Boll, J., Parlange, J-Y, Steenhuis, T.S., 2017. Spatio-temporal patterns of groundwater depths and soil nutrients in a small watershed in the Ethiopian highlands: Topographic and land use controls. J. Hydrol. 5XX, XXX–XXX. Han, D., Currell, M., Cao, G., Hall, B., 2017. Alterations to groundwater recharge due to anthropogenic landscape change. J. Hydrol. 5XX, XXX–XXX. Havril, T., Tóth, A., Molson, J.W., Galsa, A., Mádl-Szőnyi, J., 2017. Impacts of predicted climate change on groundwater flow systems: Can wetlands disappear due to recharge reduction? J. Hydrol. 5XX, XXX–XXX. Hellauer, K., Karakurt, S., Sperlich, A., Burke, V., Massman, G., Hübner, U., Drewes, J.E., 2017. Establishing sequential managed aquifer recharge technology (SMART) for enhanced removal of trace organic chemicals: Experiences from field studies in Berlin, Germany. J. Hydrol. 5XX, XXX–XXX. Jasechko, S., Perrone, D., Befus, K.M., Cardenas, M.B., Ferguson, G., Gleeson, T., Luijendijk, E., McDonnell, J.J., Taylor, R.G., Wada, Y., Kirchner, J.W., 2017. Global aquifers dominated by fossil groundwaters but wells vulnerable to modern contamination. Nature Geoscience 10, 425–429. doi:10.1038/ngeo2943 Manna, F., Walton, K., Cherry, J.A., Parker, B.L., 2017. Mechanisms of recharge in a fractured porous rock aquifer in a semi-arid region. J. Hydrol. 5XX, XXX–XXX.
Minnig, M., Moeck, C., Radny, D., Schirmer, M., 2017. Impact of urbanization on groundwater recharge rates in Dübendorf, Switzerland. J. Hydrol. 5XX, XXX–XXX. Pavlovskii, I., Hayashi, M., Lennon, M.R., 2017. Transformation of snow isotopic signature along groundwater recharge pathways in the Canadian Prairies. J. Hydrol. 5XX, XXX–XXX. Post, V.E.A., Werner, A.D., 2017. Coastal aquifers: Scientific advances in the face of global environmental challenges. J. Hydrol. 551, 1–3. doi:10.1016/j.jhydrol.2017.04.046 Rathay, S.Y., Allen, D.M., Kirste, D., 2017. Response of a fractured bedrock aquifer to recharge from heavy rainfall events. J. Hydrol. 5XX, XXX–XXX. Rossman, N.R., Zlotnik, V.A., Rowe, C.M., 2017. Using cumulative potential recharge for selection of GCM projections to force regional groundwater models: a Nebraska Sand Hills example. J. Hydrol. 5XX, XXX–XXX. Scanlon, B.R., Healy, R.W., Cook, P.G., 2002. Choosing appropriate techniques for quantifying groundwater recharge. Hydrogeol. J. 10, 18–39. doi:10.1007/s10040-001-0176-2 Smerdon, B.D., 2017. A synopsis of climate change effects on groundwater recharge. J. Hydrol. 5XX, XXX–XXX. Taylor, A.R., Smith, S.D., Lamontagne, S., Suckow, A., 2017. Characterising alluvial aquifers in a remote ephemeral catchment (Flinders River, Queensland) using a direct push tracer approach. J. Hydrol. 5XX, XXX–XXX. Viaroli, S., Mastrorillo, L., Lotti, F., Paolucci, V., Mazza, R., 2017. The groundwater budget: a tool for preliminary estimation of the hydraulic connection between neighboring aquifers. J. Hydrol. 5XX, XXX– XXX. Xie, Y., Cook, P.G., Simmons, C.T., Partington, D., Crosbie, R.S., Batelaan, O., 2017. Uncertainty of groundwater recharge estimated from a water and energy balance model. J. Hydrol. 5XX, XXX–XXX.
S0022-1694(17)30751-5 https://doi.org/10.1016/j.jhydrol.2017.10.075 HYDROL 22355
To appear in:
Journal of Hydrology
Received Date: Accepted Date:
26 October 2017 30 October 2017
Please cite this article as: Smerdon, B.D., Drewes, J.E., Groundwater recharge: The intersection between humanity and hydrogeology, Journal of Hydrology (2017), doi: https://doi.org/10.1016/j.jhydrol.2017.10.075
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Groundwater recharge: The intersection between humanity and hydrogeology
Brian D. Smerdona* and Jörg E. Drewesb
a
Alberta Geological Survey, Edmonton, Alberta, Canada
b
Chair of Urban Water Systems Engineering, Department of Civil, Geo and Environmental Engineering, Technical University of Munich, Garching, Germany
*Corresponding author: Email: [email protected] Phone: +1 780 641 9759 Postal address: Brian D. Smerdon, Alberta Geological Survey, 402 Twin Atria Building, 4999-98 Avenue, Edmonton, Alberta T6B 2X3, Canada
1.0
Introduction Groundwater recharge is an essential part of subsurface water circulation and the beginning of
groundwater flow systems that can vary in duration from days to millennia. Globally, there is a growing body of evidence suggesting that many of Earth’s aquifers contain ‘fossil’ groundwater that was recharged more than 12,000 years ago (Jasechko et al., 2017), and a very small portion of groundwater that was recharged within the last 50 years (Gleeson et al., 2015). Together, this information demonstrates the irregular distribution of groundwater circulation within the Earth and the wide variability of recharge conditions that replenish aquifer systems (Befus et al., 2017). Knowledge of groundwater recharge rates and distribution are needed for evaluating and regulating the quantity and quality of water resources, understanding consequences of landscapes use, identifying where managed aquifer recharge can augment supply, and predicting how groundwater systems will respond to a changing climate. In-turn, these topics are of central importance for the health of humans and ecosystems, and security of food and energy. Yet, despite the global importance, quantifying groundwater recharge remains challenging as it cannot be measured directly, and there is uncertainty associated with all currently known estimation methods (Scanlon et al., 2002). This Special Issue on ‘Aquifers Recharge: Modeling, Experiments and Climatic Change Effects’ explores the recharge process through different estimation methods and approaches to modeling. Some of the articles in the Special Issue describe techniques for estimating naturally occurring groundwater recharge to better understand a process or particular region, which help learn about the variability of Earth’s groundwater and make informed choices for better management of water resources. Other articles of the Special Issue examine artificially occurring groundwater recharge to augment water supply, or improve water quality. The aspect of climate change is incorporated in many of the studies, whereby uncertainty of recharge estimation methods is compounded with uncertainty of future climate conditions. The aspect of urbanization and groundwater recharge is gaining more attention recently, especially as societies accept the legacy of previous land use choices and plan for the future. This Special Issue brings together 18 articles that offer a perspective of the current thinking about groundwater recharge.
2.0
Overview of research
This overview categorizes the articles into four groups: (i) field and modeling techniques, (ii) isotopic techniques, (iii) effects of climate change, and (iv) land use change and urban recharge. 2.1
Field and modelling techniques Rathay et al. (2017) analyze the response of fractured bedrock to high intensity rainfall events in
the Gulf Islands of British Columbia, Canada. The investigation uses a combination of piezometry, thermal infrared imagery of a seepage face, and stable isotopic analysis of seepage water to examine ponding and infiltration. Rathay et al. (2017) find that higher intensity precipitation events lead to more ponding and less recharge. Guzman et al. (2017) investigate recharge, depth to the water table, and soil nutrients for a watershed in Ethiopia, where soil and water degradation can occur due to agricultural practices. Through field study they learn that land use and crop growth are governed by shallow groundwater conditions (i.e. groundwater perched above a low permeability layer), which in-turn governs the exchange of cations. Xie et al. (2017) investigate the uncertainty of recharge estimation using coupled water and energy balance models and a Monte Carlo analysis of data for the Campaspe River catchment in Victoria, Australia. In this study, recharge varies from about 2 to 36% of annual rainfall for a single set of pedotransfer functions, and up to 60% when different sets of pedotransfer functions are used when modelling. Xie et al. (2017) conclude that time series of soil moisture data did not help reduce uncertainty, whereas time series estimates of evapotranspiration help constrain recharge uncertainty. Doble et al. (2017) develop an approach to link a process-based soil-vegetation-atmosphere transfer (SVAT) model with a regional-scale groundwater flow model. Relationships between net recharge and water table depth are illustrated for parts of South Australia and Victoria, Australia that have a shallow water table and varied land use. Crosbie et al. (2017) demonstrate a regression kriging approach to estimate recharge across large regions having varying data density. For a portion of New South Wales, Australia, 1000 stochastic replicates of available chloride data (rainfall, runoff, and groundwater) supported this geostatistical methodology. Regression kriging allowed upscaling for data-sparse areas, while honouring points-scale
recharge estimates in data-dense areas. In assessing the uncertainty, Crosbie et al. (2017) find that the magnitude of uncertainty was related to the magnitude of estimated recharge rate. 2.2
Isotopic techniques Cartwright et al. (2017) review applications of isotopic tracers to estimate residence time and
rates of groundwater recharge. They highlight that isotopic tracers provide a record of long-term average recharge conditions and residence time, which can be helpful for system conceptualization but are not readily comparable to other techniques. Cartwright et al. (2017) discuss the challenge of acquiring samples from subsurface systems that inherently experience mixing and dispersion. Taylor et al. (2017) use a novel combination of direct push technology and environmental tracers to examine the recharge process for a semi-arid catchment in Queensland, Australia. They find the combination of techniques very useful in a remote region, and efficiently discover that although recharge to alluvial deposits is generally high and originates from overbank flooding, the storage capacity of these systems is limited. Pavlovskii et al. (2017) examine the seasonal dynamics of snowpack isotopic signature and its implications for estimating recharge using an isotopic approach. From snowpack data measured in Alberta, Canada, isotopic signature exhibits large variation over small distances, thus limiting the usefulness for estimating recharge. However, slightly different isotopic signatures appear to exist between diffuse recharge and depression-focused recharge, potentially offering an approach to characterize recharge for key features in a Prairie setting. 2.3
Effects of climate change Smerdon (2017) provides a synopsis of review articles on climate change and groundwater
recharge published between 2011 and 2016. A common finding of the review articles is that the uncertainty of modelling future precipitation drives widely varying predictions of recharge to the point of not being able to predict whether recharge will increase or decrease. The review articles also suggest steps to overcome uncertainty. Rossman et al. (2017) propose an approach to assess the uncertainty of future recharge conditions within regional groundwater flow models. From a series of future climate projections for the Nebraska, United States, cumulative potential recharge (i.e., precipitation minus evapotranspiration) for
a 90-year period was calculated. Subsequently, median, wet and dry scenarios (1 standard deviation from the median) were input to a groundwater flow model. By focusing on a limited number of groundwater flow simulation scenarios, the sensitivity of projected climate can be more rapidly assessed. Corona et al. (2017) investigate the effect of cyclical infiltration from periodic climate forcing and the effect on recharge periodicity. Through a modeling approach and extensive sensitivity analysis, it is shown that some periodic infiltration rates dampen with depth (indicating steady-state recharge), while other periodic infiltration rates do not (indicating transient recharge). The findings establish a framework that helps explain under what conditions the effect of a changing climate could be observed in the subsurface. Havril et al. (2017) evaluate the potential effect of variations in future recharge to the hydrological conditions of groundwater-dependent wetlands in Hungary. Using a cross-sectional numerical model of groundwater flow, they demonstrate the dissolution of nested groundwater flow systems to single flow cells, which can lead to disappearance of the wetlands. 2.4
Land use change and urban recharge Han et al. (2017) review the effect of land use change on groundwater recharge, and
categorized changes due to either agriculture (i.e. land clearing) or urbanization (i.e. expansion of infrastructure). There have been many studies about the effect of agriculture, but very few field-based studies on the effect of urbanization, a trend also noted by Minnig et al. (2017). Manna et al. (2017) describe an extension of the chloride-mass-balance approach to estimate recharge in fractured bedrock of southern California, United States. From porewater profiles and numerical modelling, dual porosity recharge was evaluated. Manna et al. (2017) find that changes in historic recharge rates correspond with changes in land use, and that the majority of the recharge signal occurs from diffuse flow through the rock matrix in a semi-arid region. Viaroli et al. (2017) use a water budget approach and time-series observations to evaluate recharge conditions for an exploited aquifer system in the Riardo Plain, Italy. Although the water budget suggests a deficit, regional observations suggest additional recharge from groundwater adjacent to the primary aquifer.
Minnig et al. (2017) investigate the effect of urbanization on variation in groundwater recharge rates through a water-budget approach and Monte Carlo analysis. For a small region centred in the city of Zurich in Switzerland, a strong positive correlation is found between recharge rate and extent of urbanization. While this finding could appear counter-intuitive, the effect of impervious areas in reducing evapotranspiration is considered to be a significant factor. This study demonstrates that change to recharge conditions in urban settings is not well understood and requires the hydrogeological community to focus on urban regions. Gottschalk et al. (2017) describe two geophysical frameworks construct rock-physics transforms between lithological and electrical resistivity tomography data without the need for co-located lithological and electrical resistivity measurements. Integrating the geophysical data is shown to improve simulation of groundwater conditions at an artificial recharge site in Colorado, United States. Hellauer et al. (2017) describe a pilot field study in Berlin, Germany to evaluate the idea of sequential managed aquifer recharge technology (SMART). This innovative method appears to better remove moderately degradable organic pollutants, demonstrating that ‘engineered recharge’ has the potential to improve water quality under the right conditions.
3.0
Summary and outlook The articles presented in this Special Issue provide a glimpse of the current research and
thinking about the groundwater recharge process. Studies continue to use small scale field sites to learn and refine understanding of mechanisms, and modeling approaches have included more process complexity and been applied to large regions with spatial variability. Fifteen years ago, deVries and Simmers (2002) noted that “the combination of reliable local data, remote sensing, and GIS technology offers promise for a better understanding and quantification of recharge over large areas.” In many regards the articles presented in this Special Issue demonstrate such an evolution has occurred. The nature of field-based studies to learn about recharge mechanisms and develop new techniques will likely continue to be appropriate for smaller spatial scales. Control of the geological setting and ability of understand local climate allows investigation of multiple observation methods with constraint. The structure of numerical models has evolved to include balances of water, energy and
carbon and present day computing certainly allows spatially distributed modeling to be completed as part of regional (or even continental) assessments. However, with increased complexity of model structure and coupling with climate change forecasting, the uncertainty of numerical model results has increased. Because the complexity has grown, the research community suggests that calibration of recharge models can only be achieved for individual components such as soil moisture distribution or evapotranspiration. The assumption being that if the individual pieces are represented accurately, then the net result will have some certainty as well. The need for calibration data reinforces the need for multiple methods of observation at smaller scale research sites that can be used to constrain simulation models. Large datasets and a global perspective (e.g., Döll and Fiedler, 2008; Gleeson et al., 2012) have highlighted the importance of groundwater recharge in relation to sources of water and food for humans, and in maintaining healthy ecosystems and biodiversity. Global-scale studies have also shown that some regions are threatened because of poor water management, irreversible consequences of land use choices, and a changing climate. Susceptibility of aquifer systems is related to near-term future climate (i.e. the next 10 years), where localized, young groundwater flow systems will respond rapidly to change. Susceptibility is also closely related to population density, whereby urban regions are under increasing pressure from development and resource use, and the groundwater recharge processes can be complex to predict. In conclusion, we reiterate the recent editorial by Post and Werner (2017), where research of fundamental hydrogeological processes (such as recharge) is essential, but must also help determine appropriate management responses.
References Befus, K.M., Jasechko, S., Luijendijk, E., Gleeson, T., Cardenas, M.B., 2017. The rapid yet uneven turnover of Earth’s groundwater. Geophys. Res. Lett. 44, 5511–5520. doi:10.1002/2017GL073322 Cartwright, I., Cendon, D., Currell, M., Meredith, K., 2017. A review of radioactive isotopes and other residence time tracers in understanding groundwater recharge: possibilities, challenges, and limitations. J. Hydrol. 5XX, XXX–XXX. Corona, C.R., Gurdak, J.J., Dickinson, J.E., Ferré, T.P.A., Maurer, E.P., 2017. Climate variability and vadose zone controls on damping of transient recharge. J. Hydrol. 5XX, XXX–XXX.
Crosbie, R.S., Peeters, L.K., Herron, N., McVicar, T.R., Herr, A., 2017. Estimating groundwater recharge and its associated uncertainty: Use of regression kriging and the chloride mass balance method. J. Hydrol. 5XX, XXX–XXX. de Vries, J.J., Simmers, I., 2002. Groundwater recharge: an overview of processes and challenges. Hydrogeol. J. 10, 5–17. doi:10.1007/s10040-001-0171-7 Doble, R.C., Pickett, T., Crosbie, R.S., Morgan, L., Turnadge, C., Davies, P., 2017. Emulation of recharge and evapotranspiration processes in shallow groundwater systems. J. Hydrol. 5XX, XXX–XXX. Döll, P., Fiedler, K., 2008. Global-scale modeling of groundwater recharge. Hydrol. Earth Syst. Sci. 12, 863–885. doi:10.5194/hess-12-863-2008 Gleeson, T., Wada, Y., Bierkens, M.F.P., van Beek, L.P.H., 2012. Water balance of global aquifers revealed by groundwater footprint. Nature 488, 197–200. doi:10.1038/nature11295 Gleeson, T., Befus, K.M., Jasechko, S., Luijendijk, E., Cardenas, M.B., 2015. The global volume and distribution of modern groundwater. Nature Geoscience 9, 161–167. doi:10.1038/ngeo2590 Gottschalk, I.P., Hermans, T., Knight, R., Caers, J., Cameron, D.A., Regnery, J., McCray, J.E. 2017. Integrating non-colocated well and geophysical data to capture subsurface heterogeneity at an aquifer recharge and recovery site. J. Hydrol. 5XX, XXX–XXX. Guzman, C.D., Tilahun, S.A., Dagnew, D.C., Zimale, F.A., Zegeye, A.D., Boll, J., Parlange, J-Y, Steenhuis, T.S., 2017. Spatio-temporal patterns of groundwater depths and soil nutrients in a small watershed in the Ethiopian highlands: Topographic and land use controls. J. Hydrol. 5XX, XXX–XXX. Han, D., Currell, M., Cao, G., Hall, B., 2017. Alterations to groundwater recharge due to anthropogenic landscape change. J. Hydrol. 5XX, XXX–XXX. Havril, T., Tóth, A., Molson, J.W., Galsa, A., Mádl-Szőnyi, J., 2017. Impacts of predicted climate change on groundwater flow systems: Can wetlands disappear due to recharge reduction? J. Hydrol. 5XX, XXX–XXX. Hellauer, K., Karakurt, S., Sperlich, A., Burke, V., Massman, G., Hübner, U., Drewes, J.E., 2017. Establishing sequential managed aquifer recharge technology (SMART) for enhanced removal of trace organic chemicals: Experiences from field studies in Berlin, Germany. J. Hydrol. 5XX, XXX–XXX. Jasechko, S., Perrone, D., Befus, K.M., Cardenas, M.B., Ferguson, G., Gleeson, T., Luijendijk, E., McDonnell, J.J., Taylor, R.G., Wada, Y., Kirchner, J.W., 2017. Global aquifers dominated by fossil groundwaters but wells vulnerable to modern contamination. Nature Geoscience 10, 425–429. doi:10.1038/ngeo2943 Manna, F., Walton, K., Cherry, J.A., Parker, B.L., 2017. Mechanisms of recharge in a fractured porous rock aquifer in a semi-arid region. J. Hydrol. 5XX, XXX–XXX.
Minnig, M., Moeck, C., Radny, D., Schirmer, M., 2017. Impact of urbanization on groundwater recharge rates in Dübendorf, Switzerland. J. Hydrol. 5XX, XXX–XXX. Pavlovskii, I., Hayashi, M., Lennon, M.R., 2017. Transformation of snow isotopic signature along groundwater recharge pathways in the Canadian Prairies. J. Hydrol. 5XX, XXX–XXX. Post, V.E.A., Werner, A.D., 2017. Coastal aquifers: Scientific advances in the face of global environmental challenges. J. Hydrol. 551, 1–3. doi:10.1016/j.jhydrol.2017.04.046 Rathay, S.Y., Allen, D.M., Kirste, D., 2017. Response of a fractured bedrock aquifer to recharge from heavy rainfall events. J. Hydrol. 5XX, XXX–XXX. Rossman, N.R., Zlotnik, V.A., Rowe, C.M., 2017. Using cumulative potential recharge for selection of GCM projections to force regional groundwater models: a Nebraska Sand Hills example. J. Hydrol. 5XX, XXX–XXX. Scanlon, B.R., Healy, R.W., Cook, P.G., 2002. Choosing appropriate techniques for quantifying groundwater recharge. Hydrogeol. J. 10, 18–39. doi:10.1007/s10040-001-0176-2 Smerdon, B.D., 2017. A synopsis of climate change effects on groundwater recharge. J. Hydrol. 5XX, XXX–XXX. Taylor, A.R., Smith, S.D., Lamontagne, S., Suckow, A., 2017. Characterising alluvial aquifers in a remote ephemeral catchment (Flinders River, Queensland) using a direct push tracer approach. J. Hydrol. 5XX, XXX–XXX. Viaroli, S., Mastrorillo, L., Lotti, F., Paolucci, V., Mazza, R., 2017. The groundwater budget: a tool for preliminary estimation of the hydraulic connection between neighboring aquifers. J. Hydrol. 5XX, XXX– XXX. Xie, Y., Cook, P.G., Simmons, C.T., Partington, D., Crosbie, R.S., Batelaan, O., 2017. Uncertainty of groundwater recharge estimated from a water and energy balance model. J. Hydrol. 5XX, XXX–XXX.