Global Groundwater Research Articles

Global Groundwater Solute Composition and Concentrations.

Informed analysis of policies related to food security, global climate change, wetland ecology, environmental nutrient flux, element cycling, groundwater weathering, continental denudation, human health, and others depends to a large extent on quantitative estimates of solute mass fluxes into and out of all global element pools including the enigmatic global aquifer systems. Herein for the first time, we proffer the mean global solute concentration of all major and selected minor and trace solutes in the active groundwater that represents 99% of liquid fresh water on Earth. Concentrations in this significant element pool have yielded to a geospatial machine learning kNN-nearest neighbors' algorithm with numerous geospatial predictors utilizing a large new lithology/climate/aquifer age/elevation based solute database. The predicted concentrations are consistent with traditional solute ratios, concentrations, and thermodynamic saturation indices.

Sprinkler flow rate affects physiological, behavioural and production responses of Holstein cows during heat stress

Holstein Friesian cows are known for their high milk yield. They are popular in the commercial dairy sector of Pakistan. Heat stress is a major challenge for these animals owing to the longer summer season with high ambient temperatures (35 - 40 °C) and relative humidity (30 - 50%) in the area (Butt et al., 2020). Mitigating the effects of heat stress requires substantial investments in energy and water. Spraying dairy cows with water in the holding pen or at the feed bunk is common practice as it lowers body temperature and respiration rate (Kendall et al., 2007; Chen et al., 2013; 2016), and improves feed intake and milk yield (Keister et al., 2002). Owing to the recent decrease in global groundwater, studies have focused on strategies to reduce the use of water to cool dairy cows (Chen et al., 2016). Sprinkler flow rates of 1.3 and 4.9 L/min had similar effects on physiological responses of cows to heat load but produced a 73% difference in water use (Chen et al., 2016). Similarly, Tresoldi et al. (2019) concluded that a sprinkler flow rate of 4.9 L/min had poor efficiency compared with 3.3 L/min, as the additional water did not result in increased biologically relevant cooling. These studies were conducted in Mediterranean climates with an average temperature humidity index in the range of 76 to 78. A recent study with Nili Ravi buffaloes revealed a sprinkler flow rate 1.25 L/min was more efficient than one of 2.0 L/min during subtropical summers (Bah et al., 2021). Because water is projected to be scarce in Pakistan by 2030 (Mustafa et al., 2013), holistic strategies for water conservation in the dairy sector are important nationally. The objective of this study was to evaluate the effects of various sprinkler flow rates on the performance of lactating Holstein Friesian cows in a typical corporate dairy farm setting during the subtropical summer. Performance of these cows was assumed to be similar, irrespective of the sprinkler flow rates.

Groundwater Potential Zone Assessment using GIS and Remote Sensing

Over-exploitation of groundwater and marked changes in climate over the years have imposed immense pressure on the global groundwater resources. As demand of water increases across the globe for human consumption, agriculture and industrial uses, the need to evaluate the groundwater potential and productivity of aquifers also increases. This paper aimed to delineate the groundwater potential zones using GIS and remote sensing. Overlay analysis technique is used to develop the groundwater potential prospect zones by integrating different groundwater contributing thematic layers. The thematic layers of land use and land cover, drainage density, lineament density, soil, geology, slope and rainfall were prepared and used for groundwater potential map development by assigning weights to each thematic layer and features. The weights of each thematic layer were assigned based on their importance and relationship with groundwater recharge. Finally, the thematic maps were integrated by Raster calculator tool to develop groundwater potential zones.

Review on status of groundwater database and application prospect in deep-time digital earth plan

Groundwater is an important water resource. The total amount of active groundwater in a hydrological cycle is about 3.5 times that of the total amount of surface water. The information in the deep groundwater records the material exchange and dynamics in the earth’s evolution, which is an important aspect of the Deep-Time Digital Earth (DDE) plan. In recent years, scientists have discussed the distribution of transboundary aquifers and the environmental significance of groundwater resources through groundwater databases established by international organizations, such as the Global Groundwater Information System and the chronicles consortium, and national institutes, such as national geological surveys. The application of the groundwater database in the DDE plan, however, has been limited by the management, interactivity, and monitoring method of the groundwater data. The ability to further integrate data that are private and scattered across research institutions and individuals, while establishing an open, unified, and shared groundwater data platform, is essential to enhance our understanding of groundwater, ranging from shallow to deep water, which is a goal of the DDE plan. In this study, we introduced the current situation of groundwater database operations in domestic and international research and provided frontier research with groundwater big data. Considering the related objectives of the DDE plan and the limitations of existing groundwater databases, we proposed an improvement plan and new prospects for applying groundwater databases in the research of the deep earth.

A global perspective on assessing groundwater quality

An assessment of global groundwater quality is needed in response to the threats posed by anthropogenic and geogenic contaminants. This essay summarises the challenges involved, including a large number of potentially relevant water quality parameters, the poor availability of data in many regions and the complex nature of groundwater systems. Direct monitoring data can sometimes be augmented by indirect methods such as earth observations, and by involving citizen science. A new web portal is being developed to complement existing databases.

Seasonal Variations of Global Groundwater Arsenic Response to World Crop Cultivation Areas

Seasonal Variations of Global Groundwater Arsenic Response to World Crop Cultivation Areas

Global Groundwater Modeling and Monitoring: Opportunities and Challenges

AbstractGroundwater is by far the largest unfrozen freshwater resource on the planet. It plays a critical role as the bottom of the hydrologic cycle, redistributing water in the subsurface and supporting plants and surface water bodies. However, groundwater has historically been excluded or greatly simplified in global models. In recent years, there has been an international push to develop global scale groundwater modeling and analysis. This progress has provided some critical first steps. Still, much additional work will be needed to achieve a consistent global groundwater framework that interacts seamlessly with observational datasets and other earth system and global circulation models. Here we outline a vision for a global groundwater platform for groundwater monitoring and prediction and identify the key technological and data challenges that are currently limiting progress. Any global platform of this type must be interdisciplinary and cannot be achieved by the groundwater modeling community in isolation. Therefore, we also provide a high‐level overview of the groundwater system, approaches to groundwater modeling and the current state of global groundwater representations, such that readers of all backgrounds can engage in this challenge.

Climate and Seasonal Temperature Controls on Biogeochemical Transformations in Unconfined Coastal Aquifers

AbstractCoastal aquifers are host to a range of biogeochemical reactions that alter groundwater‐derived nutrient, metal, and other chemical loads to coastal ecosystems. Temperature is a strong control on microbially mediated reactions; thus, chemical reactivity in coastal aquifers may vary spatially and temporally with changes to groundwater temperature. In this study, we investigated the influence of global groundwater and sea surface temperature controls and seasonal temperature variability on biogeochemical processing in coastal aquifers using variable‐density groundwater flow, heat transport, and reactive transport models. The coupled models showed that nitrate removal efficiency in coastal aquifers increased from 5% to 88% as fresh groundwater temperature increased from 5°C to 35°C, while ocean temperature had a negligible effect on removal efficiency. Transient simulations based on monthly groundwater and ocean temperature measurements showed that denitrification and ammonification hotspots migrated seaward seasonally within warm fresh groundwater masses. The reaction hotspots were separated by colder groundwater emplaced during winter months. The reaction hotspots and nitrate plumes oscillated vertically along horizontal flow paths due to buoyancy effects between warm and cold groundwater. Comparison between transient and temperature‐equivalent steady‐state models suggests that steady‐state models adequately capture mean annual NO3− removal, but neglect local reactive transience and changes to plume geometry. The sensitivity analysis provides a first‐order estimate of the reactive potential of coastal aquifers considering globally diverse thermal regimes. The findings have implications for regional‐scale estimates of groundwater nutrient fluxes and for predicting coastal aquifer reactivity in a warming climate.

Large-scale sensitivities of groundwater and surface water to groundwater withdrawal

Abstract. Increasing population, economic growth and changes in diet have dramatically increased the demand for food and water over the last decades. To meet increasing demands, irrigated agriculture has expanded into semi-arid areas with limited precipitation and surface water availability. This has greatly intensified the dependence of irrigated crops on groundwater withdrawal and caused a steady increase in groundwater withdrawal and groundwater depletion. One of the effects of groundwater pumping is the reduction in streamflow through capture of groundwater recharge, with detrimental effects on aquatic ecosystems. The degree to which groundwater withdrawal affects streamflow or groundwater storage depends on the nature of the groundwater–surface water interaction (GWSI). So far, analytical solutions that have been derived to calculate the impact of groundwater on streamflow depletion involve single wells and streams and do not allow the GWSI to shift from connected to disconnected, i.e. from a situation with two-way interaction to one with a one-way interaction between groundwater and surface water. Including this shift and also analysing the effects of many wells requires numerical groundwater models that are expensive to set up. Here, we introduce an analytical framework based on a simple lumped conceptual model that allows us to estimate to what extent groundwater withdrawal affects groundwater heads and streamflow at regional scales. It accounts for a shift in GWSI, calculates at which critical withdrawal rate such a shift is expected, and when it is likely to occur after withdrawal commences. It also provides estimates of streamflow depletion and which part of the groundwater withdrawal comes out of groundwater storage and which parts from a reduction in streamflow. After a local sensitivity analysis, the framework is combined with parameters and inputs from a global hydrological model and subsequently used to provide global maps of critical withdrawal rates and timing, the areas where current withdrawal exceeds critical limits and maps of groundwater and streamflow depletion rates that result from groundwater withdrawal. The resulting global depletion rates are compared with estimates from in situ observations and regional and global groundwater models and satellites. Pairing of the analytical framework with more complex global hydrological models presents a screening tool for fast first-order assessments of regional-scale groundwater sustainability and for supporting hydro-economic models that require simple relationships between groundwater withdrawal rates and the evolution of pumping costs and environmental externalities.

Natural and anthropogenic drivers of the lost groundwater from the Ganga River basin

Ganga river basin is the most populated and among the worst water-stressed river basins in the world. The basin contributes to 40% of India’s gross domestic product. Despite the Ganga basin’s cultural, heritage, and economic importance, the interplay among the crucial factors that make the basin one of the global groundwater depletion hotspots is not well understood. Using observations from wells and Gravity Recovery and Climate Experiment satellites and simulations from a hydrological model, here we show that the Ganga river basin has lost 226.57 ± 25.22 km3 groundwater during 2002–2016, which is about 20 times the storage capacity of the largest (Indira Sagar) reservoir in India. A significant (p-value < 0.05) decline (∼11%) in the summer monsoon (June–September) during 1951–2016, severe and frequent droughts (2009, 2014, 2015), and groundwater pumping for irrigation have contributed to groundwater depletion. However, the non-renewable groundwater abstraction is the most significant (relative contribution = 80%) contributor to the groundwater depletion in the basin. Renewable groundwater pumping contributed to only 20% of the total groundwater depleted during the 2002–2016 period. Severe and frequent droughts in the basin pose a double whammy of reducing groundwater recharge and increasing withdrawal. Changes in cropping patterns, groundwater metering, and improved water use efficiency are needed to reduce the non-renewable groundwater abstraction for irrigation, which is crucial for water sustainability in the basin.

Anthropogenic depletion of Iran’s aquifers

Global groundwater assessments rank Iran among countries with the highest groundwater depletion rate using coarse spatial scales that hinder detection of regional imbalances between renewable groundwater supply and human withdrawals. Herein, we use in situ data from 12,230 piezometers, 14,856 observation wells, and groundwater extraction points to provide ground-based evidence about Iran's widespread groundwater depletion and salinity problems. While the number of groundwater extraction points increased by 84.9% from 546,000 in 2002 to over a million in 2015, the annual groundwater withdrawal decreased by 18% (from 74.6 to 61.3 km3/y) primarily due to physical limits to fresh groundwater resources (i.e., depletion and/or salinization). On average, withdrawing 5.4 km3/y of nonrenewable water caused groundwater tables to decline 10 to 100 cm/y in different regions, averaging 49 cm/y across the country. This caused elevated annual average electrical conductivity (EC) of groundwater in vast arid/semiarid areas of central and eastern Iran (16 out of 30 subbasins), indicating "very high salinity hazard" for irrigation water. The annual average EC values were generally lower in the wetter northern and western regions, where groundwater EC improvements were detected in rare cases. Our results based on high-resolution groundwater measurements reveal alarming water security threats associated with declining fresh groundwater quantity and quality due to many years of unsustainable use. Our analysis offers insights into the environmental implications and limitations of water-intensive development plans that other water-scarce countries might adopt.

Global Groundwater: Source, Scarcity, Sustainability, Security, and Solutions

Global Groundwater: Source, Scarcity, Sustainability, Security, and Solutions

Comparison of multi-influence factor, weight of evidence and frequency ratio techniques to evaluate groundwater potential zones of basaltic aquifer systems

Groundwater is the largest available reservoir of freshwater. But the rapid increase in the population and urbanisation, has led to over exploitation of groundwater which imposed tremendous pressure on global groundwater resources. Because of the hidden and dynamic nature of groundwater, it requires appropriate quantification for the formulation of groundwater planning and management strategies. The present study evaluates the efficacy of geospatial technology based Multi Influence Factor (MIF), Weight of Evidence (WofE) and Frequency Ratio (FR) technique to evaluate groundwater potential using a case study of basaltic terrain. The thematic layers influencing the groundwater occurrence viz. rainfall, slope, geomorphology, soil type, land use, drainage density, lineament density, and elevation were prepared using satellite images, hydrologic, hydrogeologic and relevant field data. Based on the conceptual frameworks of MIF, WofE and FR techniques these thematic layers and their features were assigned with appropriate weight and then integrated in the ArcGIS platform for the generation of aggregated raster layer which portray the groundwater potential zones. The results of validation showed that the groundwater potential delineated using MIF technique has a prediction accuracy of 81.94%, followed by WofE technique (76.19%) and FR techniques (71.43%). It is concluded that for evaluation of groundwater potential, the MIF technique is most reliable, followed by the WofE technique. The evaluated groundwater potential zones are useful as a scientific guide to identify the suitable location of wells and recharge structure in a cost-efficient way and also for the development of structured and pragmatic groundwater management strategies.

The use of the pilot points method on groundwater modelling for a degraded aquifer with limited field data: the case of Lake Karla aquifer

Abstract Groundwater depletion poses a major threat to global groundwater resources with increasing trends due to natural and anthropogenic activities. This study presents a surface-groundwater framework for water resources modelling of ill-posed problems in hydrogeologically data-scarce areas. The proposed framework is based on the application of a conceptual water balance model and composed of surface hydrological (UTHBAL) and groundwater flow simulation with the integration of a Newton formulation of the MODFLOW-2005 code (MODFLOW-NWT) and PEST suite modules. The groundwater simulation includes a preprocessor tool for automated calibration and a post-processor tool for automated validation. The methodology was applied to a rural region of Central Greece, Lake Karla Basin, which is degraded due to groundwater resources overexploitation to cover irrigation water demands. The aquifer is modelled focusing on a precise simulation–validation procedure of the conceptual model. The groundwater model was calibrated with the calibration preprocessor tool for spatially distributed hydraulic conductivity with the pilot points method. The calibration process achieved satisfactory results as validated by the post-process analysis of observed and simulated water levels. The findings for the groundwater budget indicate that the groundwater system is still under intense pressure even though farming activity in recent years has turned to less water-intensive crops. HIGHLIGHT My research deals with the pilot points method on groundwater modelling in an area with scarce hydrogeologic data.

Global groundwater wells at risk of running dry.

Groundwater wells supply water to billions of people, but they can run dry when water tables decline. Here, we analyzed construction records for ~39 million globally distributed wells. We show that 6 to 20% of wells are no more than 5 meters deeper than the water table, implying that millions of wells are at risk of running dry if groundwater levels decline by only a few meters. Further, newer wells are not being constructed deeper than older wells in some of the places experiencing significant groundwater level declines, suggesting that newer wells are at least as likely to run dry as older wells if groundwater levels continue to decline. Poor water quality in deep aquifers and the high costs of well construction limit the effectiveness of tapping deep groundwater to stave off the loss of access to water as wells run dry.

Old groundwater buffers the effects of a major drought in groundwater-dependent ecosystems of the eastern Sierra Nevada (CA)

Global groundwater resources are stressed and the effects of climate change are projected to further disrupt recharge processes. Therefore, we must identify the buffers to climate change in hydrogeologic systems in order to understand which groundwater resources will be disproportionally affected by these changes. Here, we utilize a novel combination of remote sensing (e.g. Landsat) and groundwater residence time data (3H, 36Cl) to identify the factors controlling the hydrogeologic stability of aridland mountain-front springs in response to a major climate event, the 2011–2017 California drought. Desert springs within Owens Valley (CA) support unique ecosystems that are surrounded by lush, green vegetation sustained only by discharging groundwater and are not reliant on localized precipitation. Therefore, the health or ecological response of this vegetation is a direct reflection of the hydrogeologic stability of the mountain-block groundwater system since water is the limiting resource for riparian plant growth in arid regions. We compared spring water residence times to vegetation health metrics computed from Landsat imagery leading up to and during the drought interval. We observe that the vegetation surrounding springs discharging a high fraction of modern and bomb-pulse groundwater (<100 years) showed evidence of increased drying and desiccation as the drought progressed. In comparison, springs discharging a higher fraction of old groundwater (>100 years) showed little response thereby supporting the conceptual model where old groundwater, i.e. a distribution of deep and stable groundwater flowpaths, buffers short- to long-term climate perturbations and may provide hydrogeologic resistance to future effects from climate change.

The interactive natural drivers of global geogenic arsenic contamination of groundwater

The effects of interactions between natural factors on the genesis of high arsenic groundwater on a global scale remain poorly understood. This paper develops a neural network model of global groundwater arsenic contamination using 26 indicators including climate, soil physical and chemical properties, and more than 70,612 data points worldwide to identify and quantify typical interaction effect. Importance analysis shows that the pivotal main effects are produced by climate and soil texture indicators. Among these main effects, seven true and six second-order interactions, with five related to precipitation in the latter, were identified to be responsible for about 10.5% of the variation in the occurrence probability of high arsenic groundwater. For the second-order interactions, the interaction strength in the torrid zone is stronger than that in the temperate zone. On a global scale, high precipitation is more likely to generate a dramatic interaction, with such interactions less likely to occur at the low end of the interactive indicators. High probabilities of elevated arsenic concentration are usually accompanied by synergy and vice versa.

A Snapshot of the World's Groundwater Challenges

Depletion and pollution of groundwater, Earth's largest and most accessible freshwater stock, is a global sustainability concern. A changing climate, marked by more frequent and intense hydrologic extremes, poses threats to groundwater recharge and amplifies groundwater use. However, widespread human development and contamination of groundwater reservoirs pose an immediate threat of resource extinction with impacts in many regions with dense population or intensive agriculture. A rapid increase in global groundwater studies has emerged, but this has also highlighted the extreme paucity of data for substantive trend analyses and assessment of the state of the global resource. Noting the difficulty in seeing and measuring this typically invisible resource, we discuss factors that determine the current state of global groundwater, including the uncertainties accompanying data and modeling, with an eye to identifying emerging issues and the prospects for informing local to global resource management in critical regions. We comment on some prospective management strategies.

What is the hydrologically effective area of a catchment?

Topographically delineated catchments are the common spatial unit to connect human activities and climate change with their consequences for water availability as a prerequisite for sustainable water management. However, inter-catchment groundwater flow and limited connectivity within the catchment results in effective catchment areas different from those suggested by surface topography. Here, we introduce the notion of effective catchment area quantified through an effective catchment index (ECI), derived from observed streamflow, precipitation and actual evapotranspiration estimates, to understand the prevalence and significance of substantial differences between topographic and effective catchment areas in a global dataset. We evaluate our ECI analysis by comparing it to hydraulic head simulations of a global groundwater flow model and to the Budyko framework. We find that one in three studied catchments exhibit an effective catchment area either larger than double or smaller than half of their topographic area. These catchments will likely be affected by management activities such as groundwater pumping or land use change outside their topographic boundaries. Or alternatively, they affect water resources beyond their topographic boundaries. We find that the magnitude of the observed differences is strongly linked to aridity, mean slope, distance to coast, and topographic area. Our study provides a first-order identification of catchments where additional in-depth analysis of subsurface connectivity is needed to support sustainable water management.

Evaluation of groundwater geochemical characteristics and quality in the central and Northern Shaanxi Province, China

Groundwater is of vital importance to many aspects of ecosystem services, especially in the central and northern Shaanxi Provence, China,— an area covered by loess deposits and short of water resources. We studied the solute geochemistry and water quality of groundwater in this area to improve the understanding of hydrogeochemical processes in loess deposits area. The results showed that the average pH of groundwaters was 8.03 ± 0.36 (1 SD) with large ranges (324 − 83,379 mg/L) of the total dissolved solids (TDS). The cations and anions followed the order of Na+ > Ca2+ > Mg2+ > K+ > SiO2 and HCO3− > Cl− > SO42− > F− > NO3−. Most groundwater samples show the HCO3−–Na+–Ca2+ water type and a small number of samples the Na+–Cl− type. Irrigation water quality assessments showed that 40% of the groundwater has good water quality, 42% moderate water quality, and 18% (the upper reaches of Wuding River and Wei River) poor water quality with very high salinity. About 40% of groundwater samples were not suitable for drinking due to the high TDS, fluoride, sulfide, and chloride. Gibbs plot and stoichiometry analysis showed that carbonate weathering is the main source of groundwater chemistry in central Shaanxi Province while evaporite dissolution dominates in northern Shaanxi Provence. The loess weathering significantly influences the dissolved solutes of groundwater in the Loess Plateau. The ion-exchange between Mg2+ and Ca2+ in groundwater and Na+ in clay minerals and the deposition of carbonate minerals increased Na+ but decreased the Ca2+ in groundwater. Our research results improve our understanding of hydrogeochemical processes that affect the solutes chemistry of groundwater in the loess area and provide essential data to the global groundwater database.