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Making the transition from open-access groundwater rights to sustainable groundwater management is a formidable task for newly formed groundwater sustainability agencies in California. As agencies begin to decide how to make equitable water allocations, how to monitor groundwater use and what mix of supply- and demand-side mechanisms to adopt to sa...
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... Among of these basins, nearly all of the groundwater basins located within Central Valley are classified as high-and medium priority, and nearly half are further designated critically overdrafted 22 . In response to SGMA, or to any groundwater management plan, it is essential to accurately monitor and characterize groundwater storage variations 25 . ...
... However, it can be challenging to construct an accurate picture of groundwater levels from well data scattered across a regional domain due to the lack of a high density and fairly uniform distribution of monitoring wells. In addition, in the Central Valley, many farmers oppose expanding well monitoring under SGMA 25 . Therefore, it remains difficult to compile and standardize long term groundwater information at the regional scale through monitoring wells alone 23 . ...
Groundwater provides nearly half of irrigation water supply, and it enables resilience during drought, but in many regions of the world, it remains poorly, if at all managed. In heavily agricultural regions like California’s Central Valley, where groundwater management is being slowly implemented over a 27-year period that began in 2015, groundwater provides two–thirds or more of irrigation water during drought, which has led to falling water tables, drying wells, subsiding land, and its long-term disappearance. Here we use nearly two decades of observations from NASA’s GRACE satellite missions and show that the rate of groundwater depletion in the Central Valley has been accelerating since 2003 (1.86 km ³ /yr, 1961–2021; 2.41 km ³ /yr, 2003–2021; 8.58 km ³ /yr, 2019–2021), a period of megadrought in southwestern North America. Results suggest the need for expedited implementation of groundwater management in the Central Valley to ensure its availability during the increasingly intense droughts of the future.
... Metering of groundwater extraction has become a selfevident best practice of integrated water resource management (Molle and Closas 2021) as it can provide high-quality volumetric extraction data with a measurement performance of ±5%, provided the meter is fitted and maintained in accordance with manufacturing standards (Molle and Closas 2021;DAWE 2021). However, groundwater metering is rare-metering is typically only required by government agencies where extraction must comply with licence or permit volume limits, for example for high volume use for irrigation in heavily stressed aquifers (Charalambous 2011;Molle and Closas 2021;Newman et al. 2018;Sinclair Knight Merz 2012;Torak and Painter 2011;Ursitti et al. 2018), as there are significant challenges with regard to the logistics, costs of installation and maintenance, acceptance by users, data collection, political will and enforcement (Molle and Closas 2021;Ursitti et al. 2018). Methods for estimating groundwater extraction that are more commonly utilised include simple water use coefficients (Lovelace 2009;Lowe et al. 2009b), or more complex agricultural/hydrological models that use satellite remote sensing to estimate crop or stock water demands (Cheema et al. 2014;Guerra et al. 2007;Singh et al. 2020;Kent et al. 2020). ...
Understanding the rate of extraction from bores (or wells) can be essential in estimating groundwater discharge at a regional scale and understanding pressures on sustainable use. The challenges in doing so include the impracticality of directly measuring extractions from all, or even a large proportion of, operating bores using flow meters, especially in rural and remote areas. This challenge may be addressed by metering a representative sample of bores and generalising results to develop estimation methods; however, even achieving this presents considerable obstacles. While the benefits of metering a subset of bores to progress groundwater science and management are recognised, the obstacles to implementing metering and guidance on overcoming them are not well documented. In the Surat Basin, Australia, most groundwater bores are used for stock watering and domestic purposes, with less than 0.1% metered. As part of a research program to understand regional groundwater extraction in this area, a voluntary bore metering program has been undertaken. In this paper the challenges that arose when recruiting participants, installing and maintaining flow metering equipment, and interpreting and using data collected are described. Lessons learnt during implementation of the program that can guide other voluntary metering of rural groundwater extractions are discussed.
... Groundwater is a significant urban and agricultural water source in California, accounting for nearly 40% of the total statewide water supply (DWR 2016b). Agricultural irrigation accounts for nearly 80% of California groundwater use (Newman et al. 2018). During extensive dry periods when surface water supplies are inadequate, groundwater provides up to 100% of the irrigation water supply in some areas (Freeman et al. 2010). ...
Agricultural water use is the leading cause of groundwater overdraft in California. However, agencies tasked with managing groundwater resources do not have access to accurate and reliable measurements of groundwater extraction. Previous studies identified a relationship between pump energy consumption and groundwater extraction and indicated that the efficiency lift method (ELM) can produce reliable estimates of groundwater extraction if based on reliable data. Recent advances in the availability of electricity and pump operating condition data have made the ELM viable for estimating large-scale groundwater extraction. This study considered the feasibility of using the ELM to estimate groundwater extractions from both individual wells and larger areas and identified the best data sources available for such estimates. Researchers found mean error rates of 5% at the individual well level and 3.3% for collections of wells when using the most specific data sources available, such as pump test reports and spatial groundwater level datasets. This research suggests that the ELM is a reasonable approach for estimating groundwater extraction on a large scale.
... Management goals and thresholds are customarily set by regulatory or permitting agencies in accordance with prevailing legal requirements (Groundwater Governance Project 2016), but sometimes arise in local collaborative planning or other contexts. For example, California's Sustainable Groundwater Management Act requires certain groundwater basins to establish a sustainable goal, sustainable yield, and measurable objectives and thresholds during groundwater management planning (Christian-Smith and Abhold 2015; Newman et al. 2018), whereas a sustainable yield goal was adopted locally for the Sierra Vista Subwatershed in Arizona through a collaborative response of 21 stakeholders to Section 321 of the National Defense Authorization Act (Upper San Pedro Partnership 2013). ...
... Clarity about who is responsible for monitoring, reporting, and implementation costs is key, and should include what funding sources or mechanisms will be used. Verification that funds are available, have been set aside, or are accounted for in bonding mechanisms, can increase incentives and certainty in the implementation of sustainable groundwater management (Cody et al. 2015;Newman et al. 2018;Fletcher et al. 2019). Some mechanisms for generating funds include administrative, water use, or replenishment fees for water districts (Newman et al. 2018) as well as seeking assistance from federal programs like the U.S. Department of Agriculture's Conservation Reserve Enhancement Program (Cody et al. 2015). ...
... Verification that funds are available, have been set aside, or are accounted for in bonding mechanisms, can increase incentives and certainty in the implementation of sustainable groundwater management (Cody et al. 2015;Newman et al. 2018;Fletcher et al. 2019). Some mechanisms for generating funds include administrative, water use, or replenishment fees for water districts (Newman et al. 2018) as well as seeking assistance from federal programs like the U.S. Department of Agriculture's Conservation Reserve Enhancement Program (Cody et al. 2015). For agencies, fee-based approaches to fund monitoring, reporting, and management may reduce uncertainties of future agency budgets to maintain the minimum provisions, and fees may be structured to provide incentives to benefit groundwater sustainability (Nie and Schultz 2012;Newman et al. 2018). ...
Groundwater is a critical resource not only for human communities but also for many terrestrial, riparian, and aquatic ecosystems and species. Yet groundwater planning and management decisions frequently ignore or inadequately address the needs of these natural systems. As a consequence, ecosystems dependent on groundwater have been threatened, degraded, or eliminated, especially in arid regions. There is growing acknowledgment that governmental protections for these ecological resources ar 10 e necessary, but current legal, regulatory and voluntary provisions are often inadequate. Groundwater management premised on “safe yield,” which aims to balance human withdrawals with natural recharge rates, typically provides little to no consideration for water needed by ecosystems. Alternatively, the “sustainable yield” concept aims to integrate social, economic and environmental needs for groundwater, but the complexity of groundwater systems creates substantial uncertainty about the impact that current or future groundwater withdrawals will have on ecosystems. Regardless of the legal or regulatory framework, guidance is needed to help ensure environmental water needs will be met, especially in the face of pressure to increase human uses of groundwater resources. In this paper, we describe minimum provisions for planning, managing, and monitoring groundwater that collectively can lower the risk of harm to groundwater‐dependent ecosystems and species, with a special emphasis on arid systems, where ecosystems and species may be especially reliant upon and sensitive to groundwater dynamics. This article is protected by copyright. All rights reserved.
... In 2014, California lawmakers passed the Sustainable Groundwater Management Act (SGMA), creating the state's first enforceable groundwater management guidelines and providing a framework for basin-level groundwater decision making [5,6,10]. Under SGMA, basins deemed high-or medium-priority must achieve long-term groundwater sustainability over a 20-year period, halt overdraft, and bring groundwater basins into balanced pumping and recharge [11][12][13]. ...
... The success of SGMA will depend on the accuracy of groundwater monitoring and modeling, but existing tools suffer from limited generalizability across basins and poor quantification of data and model uncertainty. Well-level spatial and temporal monitoring of depth-to-groundwater provides accurate readings proximal to the well, but well-level monitoring over large spatial regions or temporal periods requires costly large-scale data collection [10]. California's most comprehensive groundwater monitoring effort, the California Statewide Groundwater Elevation Monitoring Program (CASGEM), provides depth-to-groundwater measurements collected by the Department of Water Resources (DWR) and local monitoring parties [14,15]. ...
... This combination of model fidelity and transparency in prediction uncertainty make the Bayesian hierarchical modeling approach particularly useful for informing future sampling campaigns. Uniformly increasing spatial and temporal density of depth-togroundwater across an entire study area can be very costly [10]. However, one of CASGEM's goals is to identify and address data gaps in their groundwater monitoring program in accordance with Water Code section 10 933(a) [32]. ...
Groundwater is a critical freshwater resource for irrigation in the California Central Valley, particularly in times of drought. Groundwater depth has dropped rapidly in California’s overdrafted basins, but irregular monitoring across space and time limits the accuracy of the groundwater depth projections in the Groundwater Sustainability Plans required by the California Sustainable Groundwater Management Act (SGMA). This work constructs a Bayesian hierarchical model for predicting groundwater depth from sparse monitoring data in three Central Valley counties. We apply this model to generate 300 m resolution monthly groundwater depth estimates for drought years 2013–2015, and compare our smoothed groundwater depth map to smoothed rasterized maps published by the CA Department of Water Resources. Finally, we quantify uncertainty in groundwater depth predictions that are made by imputing missing well data and interpolating predictions across the study domain, which is helpful in directing future sampling efforts towards areas with high uncertainty. The BHM model accurately captures the spatiotemporal pattern in groundwater depth, as evidenced by 94.54% of withheld test samples’ true depth being covered by the 95% prediction interval drawn from the BHM posterior distribution. The model converged despite a very sparse dataset, demonstrating broad applicability for evaluating changes in regional groundwater depth as required by SGMA. Depth prediction intervals can also help prioritize future groundwater depth sampling activity and increase the utility of groundwater depth maps in total storage predictions by enabling sensitivity analysis.
... Reporting information obtained from metering is fundamental to make the information useful, but reporting is not necessarily required where metering is required (Nelson & Perrone 2016). Monitoring, metering, and reporting can be seen as resource intensive (requiring human and economic capital) or controversial (raising privacy concerns) (Newman et al. 2018). Remote sensing or satellite imagery are increasingly being used in places where localized information is not feasible to collect. ...
Groundwater is a crucial resource for current and future generations but is not being sustainably used in many parts of the world. The objective of this review is to provide a clear portrait of global-scale groundwater sustainability, systems and resources in the Anthropocene, in order to inspire a pivot towards more sustainable pathways. We examine groundwater from three different but related perspectives of sustainability science, natural resource governance and management, and Earth Systems science. We propose that groundwater sustainability can be defined with a direct link with observable data, governance and management as well as the crucial functions and services of groundwater. An Earth System approach highlights the connections between groundwater and the rest of the hydrosphere, biosphere, atmosphere and lithosphere, and how these connections are impacting, or impacted by, groundwater pumping. Regional differences in priorities, hydrology, politics, culture and economic contexts mean that different governance and management tools are important. But a global perspective can support higher level international policies in an increasingly globalised world, that require broader analysis of interconnections between regions and knowledge transfer between regions. 1.Groundwater is depleted or contaminated in some regions and ubiquitously distributed which, importantly, makes it broadly accessible, but also slow and invisible and therefore challenging to govern and manage.2.Groundwater is the largest store of unfrozen freshwater on Earth and is heterogeneously connected to a number of Earth System processes on different timescales.3.A coherent overarching framework of groundwater sustainability is more important for groundwater governance and management than the concepts of safe yield, renewability, depletion or stress.
... With the growing concern over aquifer depletion, groundwater allocation has become increasingly complex (Allin, 2008). A recent review of existing groundwater policies across western states confirmed that a variety of allocation approaches are in use, including the traditional prior appropriation approach, as well as new groundwater allocation techniques such as adjudicated pumping quotas and allocation per-irrigated acre (though these are only a small portion in California) (Newman, Howitt, & MacEwan, 2018). ...
Growing demand for groundwater, coupled with the projected threats to groundwater supplies and impacts, has led to an increased focus on policy options for groundwater management. Globally, agriculture is the largest human-use of water, making farmers a critical stakeholder for policy engagement. In California, the Sustainable Groundwater Management Act (SGMA), a comprehensive groundwater policy, was signed into law in 2014. Here we explore farmer perspectives of groundwater availability and groundwater management policy preferences through a mail survey of farmers (n = 137) in Yolo County, California, implemented in 2017. Overall, farmers expressed widespread concern for the five applicable ‘undesirable results’ considered under SGMA and the majority of farmers felt that these conditions were either occurring now or were likely to occur in the next ten years. The majority of farmers were supportive of individual or incentive-based policy options to address groundwater concerns (e.g. voluntary adoption of water management practices). However, a sizable group of farmers were also supportive of regulatory-based policy options (e.g. moratorium on drilling new wells). Multivariate regression models suggest that for both kinds of policies, individual support for SGMA positively predicts groundwater management policy support. However, for regulatory-based policies, subjective norms - a farmers’ belief that the majority of other farmers support SGMA—is also an important predictor of regulatory policy approaches along with a number of other factors. These results suggest that, should regulatory approaches for SGMA implementation be necessary, fostering subjective norms among farmers may be an important mechanism to achieving farmer support.
In groundwater modeling studies, accurate spatial and intensity identification of water sources and sinks is of critical importance. Precise construction data about wells (water sinks) are particularly difficult to obtain. The collection of well log data is expensive and laborious, and government records of historic well log data are often imprecise and incomplete with respect to the precise location or pumping rate. In many groundwater modeling studies, such as groundwater quality assessments, a precise representation of the horizontal and vertical distribution of well screens is required to accurately estimate contaminant breakthrough curves. The number of wells under consideration may be very large, for example, in the assessment of nonpoint source pollution. In this paper, we propose an imputation framework that allows for proper reconstruction of missing well data. Our approach exploits available information and tolerates data gaps and imprecisions. We demonstrate the value of this method for a subregion of the Central Valley aquifer (California, USA). We show that our framework imputes missing values that preserve statistical properties of available data and that remain consistent with the known spatial distribution of well screens and pumping rates in the three‐dimensional aquifer system.
Groundwater can play a critical role in improving livelihoods and adaptation to climate change but only if we manage the resource so that it is available when we need it most. Without action, we risk increasing our vulnerability to water scarcity.
Groundwater is a crucial resource for current and future generations, but it is not being sustainably used in many parts of the world. The objective of this review is to provide a clear portrait of global-scale groundwater sustainability, systems, and resources in the Anthropocene to inspire a pivot toward more sustainable pathways of groundwater use. We examine groundwater from three different but related perspectives of sustainability science, natural resource governance and management, and Earth System science. An Earth System approach thus highlights the connections between groundwater and the other parts of the system and how these connections are impacting, or are impacted by, groundwater pumping. Groundwater is the largest store of unfrozen freshwater on Earth and is heterogeneously connected to many Earth System processes on different timescales. We propose a definition of groundwater sustainability that has a direct link with observable data, governance, and management as well as the crucial functions and services of groundwater. ▪ Groundwater is depleted or contaminated in some regions; it is ubiquitously distributed, which, importantly, makes it broadly accessible but also slow and invisible and therefore challenging to govern and manage. ▪ Regional differences in priorities, hydrology, politics, culture, and economic contexts mean that different governance and management tools are important, but a global perspective can support higher level international policies in an increasingly globalized world that require broader analysis of interconnections and knowledge transfer between regions. ▪ A coherent, overarching framework of groundwater sustainability is more important for groundwater governance and management than the concepts of safe yield, renewability, depletion, or stress.
Full access link: http://www.annualreviews.org/eprint/WTVYRJAKSBWCHIQXCNVQ/full/10.1146/annurev-earth-071719-055251
