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1. Peak grain forecasts for the US High Plains amid withering waters

   https://doi.org/10.1073/pnas.2008383117  

   Mrad, Assaad; Katul, Gabriel G.; Levia, Delphis F.; Guswa, Andrew J.; Boyer, Elizabeth W.; Bruen, Michael; Carlyle-Moses, Darryl E.; Coyte, Rachel; Creed, Irena F.; van de Giesen, Nick; et al (October 2020, Proceedings of the National Academy of Sciences)

   null (Ed.)

   Irrigated agriculture contributes 40% of total global food production. In the US High Plains, which produces more than 50 million tons per year of grain, as much as 90% of irrigation originates from groundwater resources, including the Ogallala aquifer. In parts of the High Plains, groundwater resources are being depleted so rapidly that they are considered nonrenewable, compromising food security. When groundwater becomes scarce, groundwater withdrawals peak, causing a subsequent peak in crop production. Previous descriptions of finite natural resource depletion have utilized the Hubbert curve. By coupling the dynamics of groundwater pumping, recharge, and crop production, Hubbert-like curves emerge, responding to the linked variations in groundwater pumping and grain production. On a state level, this approach predicted when groundwater withdrawal and grain production peaked and the lag between them. The lags increased with the adoption of efficient irrigation practices and higher recharge rates. Results indicate that, in Texas, withdrawals peaked in 1966, followed by a peak in grain production 9 y later. After better irrigation technologies were adopted, the lag increased to 15 y from 1997 to 2012. In Kansas, where these technologies were employed concurrently with the rise of irrigated grain production, this lag was predicted to be 24 y starting in 1994. In Nebraska, grain production is projected to continue rising through 2050 because of high recharge rates. While Texas and Nebraska had equal irrigated output in 1975, by 2050, it is projected that Nebraska will have almost 10 times the groundwater-based production of Texas. 

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2. Conserving groundwater: Why irrigators chose to tax themselves

   https://doi.org/10.1525/elementa.2024.00081  

   Smith, Steven M; Andersson, Krister (January 2025, Elem Sci Anth)

   At the turn of the century, irrigators in San Luis Valley (SLV), Colorado confronted a reality of precipitously dropping water levels of their shared groundwater resource stemming from their collective overextraction. Rather than continuing with business as usual—risking further declines and potential state intervention—they decided to self-organize and agreed to adopt a pumping fee, substantially increasing the cost of water—one of their key agricultural inputs. This innovative approach to conservation departs from those commonly championed by many groundwater stakeholders, who tend to favor conservation policies that decrease—not increase—costs, such as subsidizing more efficient irrigation technology or paying farmers to fallow their land. Despite few empirical examples of the introduction of a pumping fee, there are sound economic reasons to consider this approach. In this article, we review the adoption of this home-made policy, discussing the process and reasoning behind the stakeholders’ choices, the economic theory that supports it, and some of the agricultural, hydrological, and social outcomes that have resulted from it. The case study illuminates the potential benefits of a groundwater fee but also highlights that policy choices are multifaceted and what works in one scenario does not imply it is a panacea. The article concludes with a discussion of a recent and surprising policy move: SLV farmers have decided to increase the primary groundwater pumping fee exponentially to $500 per acre-foot (10 times the original fee in 2009). We discuss how this new policy represents a shift from a Pigouvian tax structure to what resembles more of a cap-and-trade system. While the results of this latest policy innovation are still unknown, the eventual results promise to be instructive not only to SLV but also to other areas facing similar water scarcity issues. 

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3. Coupling a large-scale hydrological model (CWatM v1.1) with a high-resolution groundwater flow model (MODFLOW 6) to assess the impact of irrigation at regional scale

   https://doi.org/10.5194/gmd-15-7099-2022  

   Guillaumot, Luca; Smilovic, Mikhail; Burek, Peter; de Bruijn, Jens; Greve, Peter; Kahil, Taher; Wada, Yoshihide (January 2022, Geoscientific Model Development)

   Abstract. In the context of changing climate and increasing waterdemand, large-scale hydrological models are helpful for understanding andprojecting future water resources across scales. Groundwater is a criticalfreshwater resource and strongly controls river flow throughout the year. Itis also essential for ecosystems and contributes to evapotranspiration,resulting in climate feedback. However, groundwater systems worldwide arequite diverse, including thick multilayer aquifers and thin heterogeneousaquifers. Recently, efforts have been made to improve the representation ofgroundwater systems in large-scale hydrological models. The evaluation ofthe accuracy of these model outputs is challenging because (1) they areapplied at much coarser resolutions than hillslope scale, (2) they simplifygeological structures generally known at local scale, and (3) they do notadequately include local water management practices (mainly groundwaterpumping). Here, we apply a large-scale hydrological model (CWatM), coupledwith the groundwater flow model MODFLOW, in two different climatic,geological, and socioeconomic regions: the Seewinkel area (Austria) and theBhima basin (India). The coupled model enables simulation of the impact ofthe water table on groundwater–soil and groundwater–river exchanges,groundwater recharge through leaking canals, and groundwater pumping. Thisregional-scale analysis enables assessment of the model's ability tosimulate water tables at fine spatial resolutions (1 km for CWatM, 100–250 m for MODFLOW) and when groundwater pumping is well estimated. Evaluatinglarge-scale models remains challenging, but the results show that thereproduction of (1) average water table fluctuations and (2) water tabledepths without bias can be a benchmark objective of such models. We foundthat grid resolution is the main factor that affects water table depth biasbecause it smooths river incision, while pumping affects time fluctuations.Finally, we use the model to assess the impact of groundwater-basedirrigation pumping on evapotranspiration, groundwater recharge, and watertable observations from boreholes. 

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4. Groundwater is a hidden global keystone ecosystem

   https://doi.org/10.1111/gcb.17066  

   Saccò, Mattia; Mammola, Stefano; Altermatt, Florian; Alther, Roman; Bolpagni, Rossano; Brancelj, Anton; Brankovits, David; Fišer, Cene; Gerovasileiou, Vasilis; Griebler, Christian; et al (January 2024, Global Change Biology)

   Abstract Groundwater is a vital ecosystem of the global water cycle, hosting unique biodiversity and providing essential services to societies. Despite being the largest unfrozen freshwater resource, in a period of depletion by extraction and pollution, groundwater environments have been repeatedly overlooked in global biodiversity conservation agendas. Disregarding the importance of groundwater as an ecosystem ignores its critical role in preserving surface biomes. To foster timely global conservation of groundwater, we propose elevating the concept of keystone species into the realm of ecosystems, claiming groundwater as a keystone ecosystem that influences the integrity of many dependent ecosystems. Our global analysis shows that over half of land surface areas (52.6%) has a medium‐to‐high interaction with groundwater, reaching up to 74.9% when deserts and high mountains are excluded. We postulate that the intrinsic transboundary features of groundwater are critical for shifting perspectives towards more holistic approaches in aquatic ecology and beyond. Furthermore, we propose eight key themes to develop a science‐policy integrated groundwater conservation agenda. Given ecosystems above and below the ground intersect at many levels, considering groundwater as an essential component of planetary health is pivotal to reduce biodiversity loss and buffer against climate change. 

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5. Quantifying the Impact of Lagged Hydrological Responses on the Effectiveness of Groundwater Conservation

   https://doi.org/10.1029/2022WR032295  

   Glose, Thomas J.; Zipper, Sam; Hyndman, David W.; Kendall, Anthony D.; Deines, Jillian M.; Butler, Jr., James J. (July 2022, Water Resources Research)

   Abstract Many irrigated agricultural areas seek to prolong the lifetime of their groundwater resources by reducing pumping. However, it is unclear how lagged responses, such as reduced groundwater recharge caused by more efficient irrigation, may impact the long‐term effectiveness of conservation initiatives. Here, we use a variably saturated, simplified surrogate groundwater model to: (a) analyze aquifer responses to pumping reductions, (b) quantify time lags between reductions and groundwater level responses, and (c) identify the physical controls on lagged responses. We explore a range of plausible model parameters for an area of the High Plains aquifer (USA) where stakeholder‐driven conservation has slowed groundwater depletion. We identify two types of lagged responses that reduce the long‐term effectiveness of groundwater conservation, recharge‐dominated and lateral‐flow‐dominated, with vertical hydraulic conductivity (K_Z) the major controlling variable. When highK_Zallows percolation to reach the aquifer, more efficient irrigation reduces groundwater recharge. By contrast, when lowK_Zimpedes vertical flow, short term changes in recharge are negligible, but pumping reductions alter the lateral flow between the groundwater conservation area and the surrounding regions (lateral‐flow‐dominated response). For the modeled area, we found that a pumping reduction of 30% resulted in median usable lifetime extensions of 20 or 25 years, depending on the dominant lagged response mechanism (recharge‐ vs. lateral‐flow‐dominated). These estimates are far shorter than estimates that do not account for lagged responses. Results indicate that conservation‐based pumping reductions can extend aquifer lifetimes, but lagged responses can create a sizable difference between the initially perceived and actual long‐term effectiveness. 

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