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In this paper, the feasibility of managed aquifer recharge (MAR) for southwestern Kansas was investigated. Multiple sources of water for MAR were investigated, including rainfall-runoff from fields, use of low-flow or ephemeral rivers and streams, and use of a large regional river. Use of the Arkansas River was found to be the most viable source of water. Construction of infiltration basins in existing sand mines was found to be the best MAR alternative in this region. The requirement for the reclamation of sand mines set out by the State of Kansas fits the requirements of infiltration basins, and there exists a local ditch system that can convey Arkansas River flows to the basins with little need of new construction. The salinity of the Arkansas River is of concern. The negative impact of this could be reduced by selecting salt-tolerant crops. This investigation is relevant throughout the State of Kansas, leading to the possibility that another region would have more suitable conditions. [ABSTRACT FROM AUTHOR]

Irrigated agriculture is the dominant user of water globally, but most water withdrawals are not monitored or reported. As a result, it is largely unknown when, where, and how much water is used for irrigation. Here, we evaluated the ability of remotely sensed evapotranspiration (ET) data, integrated with other datasets, to calculate irrigation water withdrawals and applications in an intensively irrigated portion of the United States. We compared irrigation calculations based on an ensemble of satellite-driven ET models from OpenET with reported groundwater withdrawals from hundreds of farmer irrigation application records and a statewide flowmeter database at three spatial scales (field, water right group, and management area). At the field scale, we found that ET-based calculations of irrigation agreed best with reported irrigation when the OpenET ensemble mean was aggregated to the growing season timescale (bias = 1.6–4.9 %, R2 = 0.53–0.74), and agreement between calculated and reported irrigation was better for multi-year averages than for individual years. At the water right group scale, linking pumping wells to specific irrigated fields was the primary source of uncertainty. At the management area scale, calculated irrigation exhibited similar temporal patterns as flowmeter data but tended to be positively biased with more interannual variability. Disagreement between calculated and reported irrigation was strongly correlated with annual precipitation, and calculated and reported irrigation agreed more closely after statistically adjusting for annual precipitation. The selection of an ET model was also an important consideration, as variability across ET models was larger than the potential impacts of conservation measures employed in the region. From these results, we suggest key practices for working with ET-based irrigation data that include accurately accounting for changes in soil moisture, deep percolation, and runoff; careful verification of irrigated area and well-field linkages; and conducting application-specific evaluations of uncertainty.

In the United States, agriculture is responsible for the majority of consumptive water use. To reduce consumptive use in water scarce regions, policymakers have implemented a number of costly interventions. These interventions range from land retirement to subsidies that encourage the adoption of efficient irrigation technologies. In nonagricultural contexts, costly policy interventions have been complemented by low‐cost interventions inspired by behavioral economics. Whether these behavioral interventions are effective in the context of commercial farming is not well understood. In a preregistered, randomized field intervention, we estimate the impact of social (peer) comparisons on agricultural groundwater users in Colorado and Kansas. More than three thousand irrigators were randomized to receive either an annual peer comparison or no comparison. The peer comparison contrasted each irrigator's groundwater use to the distribution of use by neighboring irrigators. The comparison intervention reduced average annual groundwater use by 4.05% [95% CI (−5.87%, − 2.21%)], resulting in an aggregate reduction of more than 21,000 acre‐feet per year at a cost less than $1.31 per acre‐foot conserved. The estimated treatment effect was larger among irrigators with lower pre‐intervention water use. In the 3‐year experiment, we observed no evidence that the treatment effect substantially attenuated over time. We did, however, detect within‐irrigator spillovers in the treatment group: groundwater use also declined among wells that were not included in the peer comparisons (peer comparisons included a maximum of three wells). The results imply that social comparisons can be a cost‐effective tool, alongside other policy interventions, aimed at reducing agricultural water use. [ABSTRACT FROM AUTHOR]

Groundwater transit time distributions (TTDs) describe the spectrum of flow‐weighted apparent ages of groundwater from aquifer recharge to discharge. Regional‐scale TTDs in stream baseflow are often estimated from numerical models with limited calibration from groundwater sampling and suggest much younger groundwater discharge than has been observed by discrete age‐dating techniques. We investigate both local and regional‐scale groundwater TTDs in the Upper Middle Loup watershed (5,440 km2) overlying the High Plains Aquifer in the Nebraska Sand Hills, USA. We determined flow‐weighted apparent ages of groundwater discharging through the streambed at 88 discrete points along a 99 km groundwater‐dominated stream segment using 3H, noble gases, 14C, and groundwater flux measurements at the point‐scale (<7.6 cm diameter). Points were organized in transects across the stream width (3–10 points per transect) and transects were clustered in five sampling areas (10–610 m in stream length) located at increasing distances along the stream. Groundwater apparent ages ranged from 0 to 8,200 years and the mean groundwater transit time along the 99 km stream is >3,000 years. TTDs from upstream sampling areas were best fit by distributions with a narrow range of apparent ages, but when older groundwater from downstream sampling areas is included, the regional TTD is scale dependent and the distribution is better described by a gamma model (α ≈ 0.4) which accommodates large fractions of millennial‐aged groundwater. Observations indicate: (a) TTDs can exhibit spatial variability within a watershed and (b) watersheds can discharge larger fractions of old groundwater (>1,000 years) than commonly assumed. Plain Language Summary: The transit time distribution (TTD) of an aquifer describes the complete spectrum of groundwater transit times from the water table to discharge at an outlet such as a stream. TTDs indicate how susceptible aquifers may be to contamination, drought, or pumping. Despite their importance, TTDs are difficult to quantify and many approaches either overestimate the relative fraction of young groundwater discharge or have been conducted in small systems (areas <1,000 km2 or stream lengths <10 km). We measured the flow‐weighted transit time of groundwater through the streambed at 88 points along a 99 km stream in the Upper Middle Loup watershed (5,440 km2) in Nebraska, USA to estimate TTDs of the underlying High Plains Aquifer at various spatial scales. Transit times ranged from 0 to 8,200 years and the mean transit time is >3,000 years along the entire study stream with substantially older groundwater discharge downstream. Upstream TTDs were well‐fit by distributions with larger fractions of young groundwater (<15 years), but TTDs for the entire study stream were better fit by distributions that accommodate large fractions of millennial‐aged groundwater. Our findings suggest that TTDs can vary within a watershed and ancient groundwater may be a significant component of modern streamflow. Key Points: Groundwater age and flux along a 99 km stream overlying the High Plains Aquifer, USA yield transit time distributions (TTD) and meanGroundwater ages ranged from 0 to 8,200 years with mean age >3,000 years and increasing apparent age of baseflow downstreamTTD evolution with stream distance suggests streams overlying regional systems may intersect large fractions of millennial‐aged groundwater [ABSTRACT FROM AUTHOR]

The continuing depletion of the world's aquifers has given rise to a profound intergenerational inequity, as prospects for future generations have been diminished through the actions of the current and earlier ones. We explore what can be done to confront this depletion-induced inequity, propose a theological framework that supports efforts to address it, and consider possible roles that the pastoral community could play in charting paths to a more sustainable future. [ABSTRACT FROM AUTHOR]

Understanding groundwater resource dynamics is limited by the sparsity of observations of water levels, pumping rates, and hydraulic properties relative to their spatiotemporal heterogeneity. To address some of this complexity, we proposed a new highly parameterized linear inverse method to quantify water table change and groundwater depletion rate in unconfined aquifers that does not require initial or boundary conditions. The method requires linearization, and we tested the performance of six proposed water table functions with three coordinate systems with synthetic models, finding that water table functions by the dimensionless method achieve the lowest errors. Our inverted water table changes and depletion rates remained stable and accurate with head measurement error of 5%. However, inversions became less accurate when head observations contained large temporal gaps. Next, we applied the inversion for water table changes and depletion rates in the Texas High Plains Aquifer (HPA) and the HPA during 2000–2015. To address sparse water levels and uncertain hydraulic conductivity measurements, two modifications were made to improve data constraints for inversion: (a) calculating winter‐time water levels for wells with >1 head observation by linear interpolation and (b) using hydraulic conductivity geostatistical realizations. The inverted water table change and depletion rate expected mean values and uncertainties were reasonable compared to the known pumping records of the Texas HPA. With relatively minor data curation, the new inverse method can quantify spatiotemporally continuous water table change, depletion rates, and their uncertainty for heterogeneous aquifers with temporally sparse and noisy water level observations. Plain Language Summary: Groundwater pumping is causing shallow groundwater levels, or the water table, to lower in unsustainable ways. Because groundwater observations are typically sparse and uncertain, so we do not always know where water tables are dropping or how fast they drop. In this study, we introduced a new mathematical method of accurately estimating water table changes and the related losses in groundwater storage while not needing to know all of the uncertain properties of the ground. We tested this method for make‐up cases and cases of the High Plains Aquifer in the central United States. The results demonstrate that the method is both fast and accurate and can be applied for other aquifers. Key Points: New highly parameterized linear inverse method was developed for unconfined aquifers with unknown initial and boundary conditionsSynthetic and field inversions demonstrate accurate and reasonable results with spatiotemporally sparse and uncertain head observationsThe new inverse method yielded accurate water table change and depletion rates despite large uncertainty in hydraulic conductivity [ABSTRACT FROM AUTHOR]

The High Plains aquifer (HPA) is the primary water source for agricultural irrigation in the US Great Plains. The water levels in many locations of the aquifer have declined steadily over the past several decades because the rate of water withdrawals exceeds recharge, which has been a serious concern to the water resources management in the region. We evaluated temporal trends and variations in agricultural water use and hydroclimatic variables including precipitation, air temperature, reference evapotranspiration, runoff, groundwater level, and terrestrial water storage across the HPA region for different periods from 1985 to 2020 at the grid, county, or region scale. The results showed that water withdrawals decreased from 21.3 km3/year in 1985 to 18.2 km3/year in 2015, while irrigated croplands increased from 71,928 km2 in 1985 to 78,464 km2 in 2015 in the entire HPA. The hydroclimatic time‐series showed wetting trends in most of the northern HPA, but drying and warming trends in the southern region from 1985 to 2020. The groundwater level time‐series indicated flat trends in the north, but significant declining in the central and southern HPA. Trends in irrigation water withdrawals and irrigation area across the HPA were controlled by the advancement of irrigation systems and technologies and the management of sustainable water use, but also were affected by dynamical changes in the hydroclimatic conditions. [ABSTRACT FROM AUTHOR]

Substantial storage reductions by irrigation pumping in many of the world’s major aquifers jeopardize future food production. As a result, new conservation measures are being utilized to reduce pumping and extend aquifer lifespans. The key question is how effective are these practices in attaining true water conservation (i.e., water use reduction) for a given area? Relationships between pumping and precipitation help provide an answer, as precipitation explains most of the variation in annual irrigation water use for aquifers in semi-arid to sub-humid climates when surface water supplies are limited. Our objective is to utilize correlations between radar precipitation and irrigation groundwater use at a range of spatial scales to assess the effectiveness of conservation approaches in the High Plains aquifer in the central USA. Linear regressions between pumping and precipitation for a conservation area established in 2013 in northwest Kansas indicate that water use and water use per irrigated area were over 27 % less and 25 % less, respectively, during 2013–2021 compared to the same climatic conditions during 2005–2012. Similar regressions found over a 38 % reduction and 23 % reduction in irrigation water use and use per irrigated area, respectively, during 2018–2021 compared to the same conditions during 2005–2017 in a west-central Kansas county with conservation areas. A decrease in irrigated area accounted for most of the difference between these reductions. Higher R2 values after conservation area establishment imply that irrigation tracks precipitation better due to use of soil moisture sensors and other measures as part of increased irrigation efficiency and enhanced water management. The precipitation and water use relationships, which are statistically significant for a wide range of spatial scales, have great potential for assessing the effectiveness of conservation practices in areas with high-quality water use and precipitation data.

Irrigated agriculture is the dominant user of water globally, but most water withdrawals are not monitored or reported. As a result, it is largely unknown when, where, and how much water is used for irrigation. Here, we evaluated the ability of remotely sensed evapotranspiration (ET) data, integrated with other datasets, to calculate irrigation water withdrawals and applications in an intensively irrigated portion of the United States. We compared irrigation calculations based on an ensemble of satellite-driven ET models from OpenET with reported groundwater withdrawals from hundreds of farmer irrigation application records and a statewide flowmeter database at three spatial scales (field, water right group, and management area). At the field scale, we found that ET-based calculations of irrigation agreed best with reported irrigation when the OpenET ensemble mean was aggregated to the growing season timescale (bias = 1.6–4.9 %, R2 = 0.53–0.74), and agreement between calculated and reported irrigation was better for multi-year averages than for individual years. At the water right group scale, linking pumping wells to specific irrigated fields was the primary source of uncertainty. At the management area scale, calculated irrigation exhibited similar temporal patterns as flowmeter data but tended to be positively biased with more interannual variability. Disagreement between calculated and reported irrigation was strongly correlated with annual precipitation, and calculated and reported irrigation agreed more closely after statistically adjusting for annual precipitation. The selection of an ET model was also an important consideration, as variability across ET models was larger than the potential impacts of conservation measures employed in the region. From these results, we suggest key practices for working with ET-based irrigation data that include accurately accounting for changes in soil moisture, deep percolation, and runoff; careful verification of irrigated area and well-field linkages; and conducting application-specific evaluations of uncertainty. [Display omitted] • Compared ET-based irrigation volumes to reported water use data at multiple scales. • ET-based irrigation volumes and reports agreed best at field scale. • Uncertainties include water balance closure and linking irrigated area to wells. • Variation among ET models is substantial relative to irrigation management actions. • ET-based irrigation tracking is promising but application-relevant uncertainties exist. [ABSTRACT FROM AUTHOR]

We use GPS data to image vertical crustal velocities in the vicinity of the Great Plains physiographic province of the United States. In the southern Great Plains, we find crustal uplift of up to 2 mm/year in an area approximately 670 km × 280 km. This signal is spatially correlated with the area of greatest groundwater decline in the southern High Plains aquifer. To determine the uplift mechanism and its possible relation to aquifer depletion, we investigate changes in aquifer water content. Gravity data coupled with an elastic model show the uplift rate is consistent with hydrological unloading from anthropogenic aquifer depletion exacerbated by severe drought. Our model that encompasses two regions of greatest groundwater decline indicates a water volume loss of −5.1 km3/year is sufficient to match the observed signal. In other large aquifers, vertical crustal motions associated with groundwater depletion are often dominated by near‐field subsidence. Our results challenge the perception that vertical motions driven by aquifer depletion necessarily equate to near‐field subsidence. In the High Plains system, depletion causes near‐field uplift because of the combination of mass removal and the style of geologic reservoir. As current climate change models predict aggravated drought conditions in the southern Great Plains in the coming decades, we expect to see an increasing rate of uplift caused by groundwater depletion unless there is offsetting recharge or changes in water resource management. Plain Language Summary: We use high‐precision data from hundreds of GPS stations in the Great Plains region of the United States to create a map of vertical land motion in the area. In the southern portion of the map, the land is moving up at a rate of almost 2 mm/year, which contrasts the downward motion of the surrounding area. The location of the uplift appears related to the southern portion of the High Plains aquifer. We study climate, water, and GPS trends over time to understand if the upward movement is connected to dropping aquifer levels. The data show that uplift is in response to water level declines caused by increased human reliance on groundwater from drought and drying climate patterns. Though groundwater pumping over time typically suggests land subsidence, the water in the aquifer is at atmospheric pressure, and does not experience the pressure differential within an aquifer reservoir that causes the ground to go down. Our results challenge the perception that vertical land motions driven by aquifer depletion necessarily equate to land subsidence. Key Points: A GPS vertical velocity field with GIA removed reveals approximately 2 mm/year of uplift spatially correlated with the southern High Plains aquiferUplift is consistent with seasonal and anthropogenic‐driven hydrological unloading further aggravated by climate changeThe sign of vertical land motion from aquifer depletion depends on aquifer confinement style and land does not necessarily subside [ABSTRACT FROM AUTHOR]

Global food security is threatened by aquifer depletion in arid and semi-arid regions. Ensuring aquifer sustainability while minimizing farmers' costs requires effective groundwater management policies, which are informed by hydro-economic models. However, the reliability of these models is typically compromised by oversimplifications. This study introduces a hydro-economic modeling framework (ABM-MODFLOW), applied in the U.S. High Plains, overcoming previous models' shortcomings. It employs an interdisciplinary approach, simulating real-world farming decisions and the resultant impacts on groundwater systems. Model validation indicates satisfactory performance in reproducing historical data and trends, outperforming the standalone groundwater model. Results show that agents with high irrigation capacities and fine soils earn the highest profits, whereas those with low irrigation capacities and coarse soils achieve the lowest profits. This modeling framework provides an advanced approach for simulating interactions between human decisions, crops, and groundwater in heavily stressed aquifers globally, supporting the development of effective groundwater management policies. • Hydro-economic models of groundwater systems are often oversimplified. • These hydro-economic models also lack robust model validation. • A hydro-economic model is developed via interdisciplinary collaboration. • Developed hydro-economic model undergoes comprehensive validation. • Model effectively simulates coevolution of human decisions, crops, and groundwater. [ABSTRACT FROM AUTHOR]

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In many regions of the world, energy costs associated with extraction represent the only explicit price for groundwater use. Therefore, energy pricing policies can significantly influence the use of scarce groundwater resources. This article leverages unique well‐level data on groundwater use, electricity prices, and pumping efficiency from the Republican River Basin of Colorado to estimate producer responses to changes in marginal energy prices. Empirical parameter estimates are used to simulate a change in energy pricing policy from existing decreasing block rate structures to a revenue‐neutral uniform marginal price. The simulation results reveal that, on average, uniform energy pricing leads to an 11% decrease in groundwater use than would occur under a decreasing block rate pricing regime. However, a transition to uniform energy pricing diminishes short‐run producer welfare. More broadly, the results illustrate how energy pricing has important implications for groundwater management and informs a more comprehensive understanding of how priced inputs influence the use of unpriced natural resources. [ABSTRACT FROM AUTHOR]

Warming temperatures increase the evapotranspiration demand of crops, leading to an increase in irrigation and exacerbating water scarcity. Previous research relies on models of irrigation water requirements to understand the potential impacts of climate change, but these models have significant uncertainty and ignore the risk-averse behavior of irrigators. Here we develop regression models to estimate how changes in vapor pressure deficit and precipitation affect groundwater withdrawals for corn, soybeans, and wheat using well-level data from the Kansas portion of the High Plains Aquifer. Withdrawals are expected to increase for all three crops, with the largest increase for soybeans. Even after accounting for the CO _2 improvements in transpiration efficiency, we find that total withdrawals are expected to increase by 5.9% (7.6%) by mid-century under RCP 4.5 (8.5). The increase in withdrawals is expected to accelerate the decline in aquifer water levels and is therefore important to consider when projecting future aquifer conditions.

• Incentivizing the adoption of efficient irrigation technology is a common, yet largely unsuccessful, approach to sustainably managing water. • A local collaborative governance approach in Kansas has resulted in reduced groundwater withdrawals with the support of producers. • To scale up this policy strategy, lawmakers should seek to replicate its success on a local level rather than expanding to larger geographic areas. Sustainable water management is increasingly essential on local to global scales, especially in regions where water scarcity is causing immediate environmental, social, and economic harm. While academics and politicians agree on the need to reduce pressure on critical water resources, the path toward that goal is not clear. Here, we present an interdisciplinary evaluation of two distinct policy approaches toward water conservation to determine whether they reduced the depletion rate of the High Plains Aquifer in the Central United States. Several studies have demonstrated, and our findings support, that subsidizing the purchase of more efficient irrigation technology failed to reduce water consumption. However, a structural approach in which state-facilitated, but locally-derived, limits were placed on water consumption did successfully reduce groundwater extraction with the support of local agricultural producers. We analyze these results using a political, sociological, and economic theoretical framework and conclude that to build upon the success of this collaborative governance model, states should seek to replicate localized groups rather than expanding management boundaries to incorporate larger geographic areas. [ABSTRACT FROM AUTHOR]

High Plains Aquifer is one of the most important aquifers in the United States, accounting for one-fourth of total annual freshwater withdrawal, and one-fifth of crop production of some major crops. But the area above this aquifer has not been extensively researched for determining the risk of groundwater pollution. Therefore, this study was undertaken to determine the groundwater pollution potential using DRASTIC model in a Geographic Information System (GIS) environment, ESRI ArcGIS. Instead of difficulty of obtaining data, it was possible to run the DRASTIC model in ArcGIS for this aquifer. The results indicated that large portions of southwestern Texas, central Kansas, eastern Colorado, eastern Wyoming, western and north-western Nebraska were highly vulnerable to groundwater pollution whereas Oklahoma had lowest vulnerability. [Fundam Appl Agric 2019; 4(3.000): 933-942]

Study region: Nebraska National Forest in the High Plains Aquifer, Nebraska Sand Hills, U.S.A. Study focus: This research aimed to investigate the effects of grassland conversions to forest on recharge rates in a century-old experimental forest. The DiffeRential Evolution Adaptive Metropolis (DREAMZS) global optimization algorithm was used to calibrate the effective soil hydraulic parameters from observed soil moisture contents for 220 cm deep uniform soil profiles. The historical recharge rates were then estimated by applying the numerical model HYDRUS 1-D for simulation of two plots representing grasslands and dense pine forest conditions. New hydrological insights: The results indicate that conversion from grasslands to dense pine forests led to vegetation induced changes in soil hydraulic properties, increased rooting depth, and greater leaf area index, which together altered the water budget considerably. The impacts of land use change, expressed in percent of gross precipitation, include a 7% increase in interception associated with an increase in leaf area index, a nearly 10% increase in actual evapotranspiration, and an overall reduction of groundwater recharge by nearly 17%. Simulated average annual recharge rates decreased from 9.65 cm yr−1 in the grassland to 0.07 cm yr−1 in the pine plot. These outcomes highlight the significance of the grassland ecology for water resources, particularly groundwater recharge, in the Nebraska Sand Hills and the overall sustainability and vitality of the High Plains Aquifer.

The Ogallala Aquifer underlies 45 million ha, providing water for approximately 1.9 million people and supporting the robust agriculture economy of the US Great Plains region. The Ogallala Aquifer has experienced severe depletion, particularly in the Southern Plains states. This paper presents policy innovations that promote adoption of irrigation technology, and management innovations. Innovation in Kansas water policy has had the dual effects of increasing the authority of the state to regulate water while also providing more flexibility and increasing local input to water management and regulation. Technology innovations have focused on improved timing and placement of water. Management innovations include soil water monitoring, irrigation scheduling, soil health management and drought-tolerant varieties, crops, and cropping systems. The most noted success has been in the collective action which implemented a Local Enhanced Management Area (LEMA), which demonstrated that reduced water pumping resulted in low to no groundwater depletion while maintaining net income. Even more encouraging is the fact that irrigators who have participated in the LEMA or other conservation programs have conserved even more water than their goals. Innovative policy along with creative local–state–federal and private–public partnerships are advancing irrigation technology and management. Flexibility through multi-year allocations, banking of water not used in a given year, and shifting water across multiple water rights or uses on a farm are promising avenues to engage irrigators toward more sustainable irrigation in the Ogallala region.

Groundwater aquifers support agricultural production in many parts of the world. Rapidly declining aquifer levels can have significant negative implications for the sustainability of irrigated agriculture. In this paper, we study the effects of declining well capacities on the downside risk of irrigated agricultural production, defined as the standard deviation of profits that are below the average profit. We simulate seasonal crop yield and profits for three different crops, namely, maize, wheat, and grain sorghum and five different soil types for Finney County in Kansas which overlies the high plains aquifer under current climatic conditions and under the projected climate change scenario with RCP4.5. We find that lower well capacities not only result in lower average profits for all three crops, but they also result in an increase in downside risk. However, we also find that there is significant heterogeneity in downside risk across different crops and soil types. Our results highlight the importance of downside risk for the sustainability of irrigated production under declining aquifer levels and climate change. [ABSTRACT FROM AUTHOR]

The question of how much longer groundwater can support large‐scale agricultural production is one of global significance. Many of the world's regional aquifers supporting irrigated agriculture are on a trajectory toward resource depletion. In the absence of alternative water supplies, the only viable near‐term (few to several decades) option for redirecting these heavily stressed systems on to more sustainable paths is to reduce pumping. The key issues therefore become how much should pumping be reduced to significantly extend an aquifer's lifetime and what is the likelihood of attaining a sustainable condition. We have developed a water‐balance approach to glean insights into these issues and chart pathways toward more sustainable states. An aquifer's response to pumping reductions heavily depends on the net inflow component of an aquifer's water budget, both in terms of its magnitude and how it decreases with time in response to reductions. If a reduction leads to a pumping rate that is above net inflow, the aquifer lifespan can often be extended by a factor of two or more, but depletion will be the final outcome. In contrast, if a reduction results in a pumping rate more than 10% below net inflow, a lengthy period of apparent sustainability will result. In that case, the aquifer lifespan may be extended long enough so that other options, such as large‐scale water transfers or development of more sustainable crop mixes, become viable. These concepts are demonstrated using examples based on an ongoing experiment in pumping reductions in the High Plains aquifer. Key Points: A new approach for gleaning insights into the pumping reductions required to redirect heavily stressed aquifers on to more sustainable pathsAn aquifer's response to pumping reductions heavily depends on the net inflow, both its magnitude and how it changes with timeStrategies for significantly extending aquifer lifespans are evaluated using data from an ongoing field experiment in pumping reductions [ABSTRACT FROM AUTHOR]

The sustainability of groundwater resources for agricultural and domestic use is dependent on both the groundwater recharge rate and the groundwater quality. The main purpose of this study was to improve the understanding of the timing, or seasonality, of groundwater recharge through the use of stable isotopes. Based on 768 groundwater samples collected from aquifers underlying natural resources districts in Nebraska, the isotopic composition of groundwater (δ2H and δ18O) was compared with that of precipitation by (a) mapping the isotopic composition of groundwater samples and (b) mapping a seasonality index for groundwater. Results suggest that for the majority of the state, groundwater recharge has a nongrowing season signature (October–April). However, the isotopic composition of groundwater suggests that in some intensively irrigated areas, human intervention in the water cycle has shifted the recharge signature towards the growing season. In other areas, a different human intervention (diversion of Platte River water for irrigation) has likely produced an apparent but possibly misleading nongrowing season recharge signal because the Platte River water differs isotopically from local precipitation. These results highlight the need for local information even when interpreting isotopic data over larger regions. Understanding the seasonality of recharge can provide insight into the optimal times to apply fertilizer, specifically in highly conductive soils with high leaching potential. In areas with high groundwater nitrate concentrations, this information is valuable for protecting the groundwater from further degradation. Although previous studies have framed nongrowing season recharge within the context of future climate change, this study also illustrates the importance of understanding how historical human intervention in the water cycle has affected groundwater recharge seasonality and subsequent implications for groundwater recharge and quality. [ABSTRACT FROM AUTHOR]

Assimilating terrestrial water storage observations from the Gravity Recovery and Climate Experiment (GRACE) mission into land surface models (LSMs) provides an opportunity to disaggregate and downscale GRACE information to finer scales and improve water component estimates in LSMs. However, the performance of GRACE data assimilation (GRACE‐DA) is limited by the lack of representation of human activities in most LSMs. To simultaneously improve GRACE‐DA and reduce the uncertainties in the modeled anthropogenic processes, we assimilate mascon‐based GRACE terrestrial water storage into the Noah‐Multiparameterization LSM that includes groundwater extraction for irrigation. Simulations with and without GRACE‐DA and with and without groundwater pumping for irrigation are performed to study the isolated and combined effects of groundwater irrigation and GRACE‐DA on water and energy fluxes over the High Plains Aquifer (HPA). The results reveal that the DA‐only simulation may erroneously distribute increments across water storage components and affect the related fluxes through biased feedbacks, while the irrigation‐only simulation may overestimate groundwater decline due to shortcomings in the irrigation and groundwater parameterizations. Assimilating GRACE when irrigation is simulated produces the best overall performance for water storage trends over the northern HPA. For the southern HPA, GRACE assimilation with irrigation performs similarly to irrigation‐only simulation for water storage components and evapotranspiration. GRACE assimilation also improves results in nonirrigated regions and can potentially alleviate the overestimation of groundwater trends in regions with greater irrigation uncertainties. This study highlights the potential to advance hydrological data assimilation in the context of anthropogenic water consumption and land‐atmosphere interactions. Key Points: GRACE TWS data are assimilated into the Noah‐MP land surface model that includes groundwater extraction for irrigationAssimilating GRACE without irrigation produces biased increments, while simulating irrigation without GRACE may exacerbate model errorCombining GRACE‐DA and irrigation shows the overall best performance for water storage components and evapotranspiration [ABSTRACT FROM AUTHOR]

Groundwater storage in the High Plains aquifer has been steadily decreasing for 50 or more years due to withdrawals for irrigation. This trend has been documented in annually published United States Geological Survey reports of water level changes in the High Plains aquifer, but assessments of groundwater storage changes in other parts of the world are incomplete. NASA's gravity recovery and climate experiment (GRACE) soon may provide an alternative means for monitoring groundwater changes, via satellite remote sensing. That terrestrial water storage changes are likely to be detectable by GRACE satellites has been demonstrated by prior studies. This investigation builds on those studies by evaluating the potential for isolating changes in the groundwater component of terrestrial water storage. In the High Plains, the magnitude of annual groundwater storage changes averaged 19.8 mm between 1987 and 1998. Uncertainty in deriving estimates of High Plains aquifer storage changes from GRACE observations will arise mainly from the removal, via land surface modeling, of the effects of soil moisture changes from the gravity signal. Total uncertainty is predicted to be about 8.7 mm. © 2002 Elsevier Science B.V. All rights reserved.

We investigate the role of peer effects in the diffusion of an important water‐saving irrigation technology: low energy precise application (LEPA). Using detailed irrigation behavior data for growers in the High Plains Aquifer region of Kansas covering 1990–2014, we find clear evidence of peer influence in adoption of LEPA, net of environmental factors. Specifically, an additional neighboring LEPA installation within 1 km increases the probability of adoption by about 0.3 percentage points, on average, and this effect diminishes with distance. Our empirical estimates indicate that in the absence of peer effects, LEPA adoption would have been about 10% lower (1,000–1,600 fewer installations) per year. In addition, we find that growers install LEPA in response to higher energy prices. [ABSTRACT FROM AUTHOR]

The High Plains Aquifer (HPA) underlies parts of eight states and 208 counties in the central area of the United States (U.S.). This region produces more than 9% of U.S. crops sales and relies on the aquifer for irrigation. However, these withdrawals have diminished the stock of water in the aquifer. In this paper, we investigate the aggregate county‐level effect on the HPA of groundwater withdrawal for irrigation, of climate variables, and of energy price changes. We merge economic theory and hydrological characteristics to jointly estimate equations describing irrigation behavior and a generalized water balance equation for the HPA. Our simple water balance model predicts, at average values for irrigation and precipitation, an HPA‐wide average decrease in the groundwater table of 0.47 feet per year, compared to 0.48 feet per year observed on average across the HPA during this 1985–2005 period. The observed distribution and predicted change across counties is in the (−3.22, 1.59) and (−2.24, 0.60) feet per year range, respectively. The estimated impact of irrigation is to decrease the water table by an average of 1.24 feet per year, whereas rainfall recharges the level by an average of 0.76 feet per year. Relative to the past several decades, if groundwater use is unconstrained, groundwater depletion would increase 50% in a scenario where precipitation falls by 25% and the number of degree days above 36°C doubles. Editor's note: This paper is part of the featured series on Optimizing Ogallala Aquifer Water Use to Sustain Food Systems. See the February 2019 issue for the introduction and background to the series. Research Impact Statement: Results show the average net effect of irrigation in the High Plains Aquifer is a reduction in groundwater level of 0.47 feet per year. Climate change could significantly increase the rate of change. [ABSTRACT FROM AUTHOR]

This study provides an estimate of the gross value of irrigation water from the U.S. High Plains Aquifer. We estimate a yield function for aggregated crop biomass production, based on county-level observations for 1960–2007. This study found that irrigation increases total biomass yield in this region by an average of 51%. We estimate the average gross annual value of irrigation as of 2007 to be $196 per acre, for a total of about $3 billion across the aquifer. We also estimate that on average across the aquifer, exposure to 24 hours of temperatures above 33°C (one degree day) reduces biomass yield by 3%, with a value in 2007 of about $10 per acre. [ABSTRACT FROM AUTHOR]

Irrigated agriculture is a major economic contributor of the High Plains Region and it primarily relies on the High Plains Aquifer as a source of water. Over time, areas of the High Plains Aquifer have experienced drawdowns limiting its ability to supply sufficient water to sustain fully irrigated crop production. This among other reasons, including variable climatic factors and differences in state water policy, has resulted in some areas adopting and practicing deficit irrigation management. Considerable research has been conducted across the High Plains Aquifer region to identify locally appropriate deficit irrigation strategies. This review summarizes and discusses research conducted in Nebraska, Colorado, Kansas, and Texas, as well as highlights areas for future research. Editor's note: This paper is part of the featured series on Optimizing Ogallala Aquifer Water Use to Sustain Food Systems. See the February 2019 issue for the introduction and background to the series. Research Impact Statement: It is imperative appropriate irrigation management strategies are developed to extend the usable life of the High Plains Aquifer. Past research findings and future research needs are discussed. [ABSTRACT FROM AUTHOR]

Substantial storage reductions by irrigation pumping in many of the world's major aquifers jeopardize future food production. As a result, new conservation measures are being utilized to reduce pumping and extend aquifer lifespans. The key question is how effective are these practices in attaining true water conservation (i.e., water use reduction) for a given area? Relationships between pumping and precipitation help provide an answer, as precipitation explains most of the variation in annual irrigation water use for aquifers in semi-arid to sub-humid climates when surface water supplies are limited. Our objective is to utilize correlations between radar precipitation and irrigation groundwater use at a range of spatial scales to assess the effectiveness of conservation approaches in the High Plains aquifer in the central USA. Linear regressions between pumping and precipitation for a conservation area established in 2013 in northwest Kansas indicate that water use and water use per irrigated area were over 27 % less and 25 % less, respectively, during 2013–2021 compared to the same climatic conditions during 2005–2012. Similar regressions found over a 38 % reduction and 23 % reduction in irrigation water use and use per irrigated area, respectively, during 2018–2021 compared to the same conditions during 2005–2017 in a west-central Kansas county with conservation areas. A decrease in irrigated area accounted for most of the difference between these reductions. Higher R2 values after conservation area establishment imply that irrigation tracks precipitation better due to use of soil moisture sensors and other measures as part of increased irrigation efficiency and enhanced water management. The precipitation and water use relationships, which are statistically significant for a wide range of spatial scales, have great potential for assessing the effectiveness of conservation practices in areas with high-quality water use and precipitation data. • Precipitation–water use relationships reveal if groundwater is being conserved. • Areas in a heavily stressed aquifer have reduced groundwater use by >20 %. • Reductions are due to increased irrigation efficiency and decreased irrigated area. • The impact of increased efficiency and decreased area can be separately quantified. [ABSTRACT FROM AUTHOR]

A bivariate kernel density estimation (KDE) method was utilized to develop a stochastic framework to assess how agricultural droughts are related to unfavorable meteorological conditions. KDE allows direct estimation of the bivariate cumulative density function which can be used to extract the marginal distributions with minimal subjectivity. The approach provided excellent fits to bivariate relationships between the standardized soil moisture index (SSMI) computed at three- and six-month accumulations and standardized measures of precipitation (P), potential evapotranspiration (PET), and atmospheric water deficit (AWD = P − PET) at 187 stations in the High Plains region of the US overlying the Ogallala Aquifer. The likelihood of an agricultural drought given a precipitation deficit could be as high as 40–65% within the study area during summer months and between 20–55% during winter months. The relationship between agricultural drought risks and precipitation deficits is strongest in the agriculturally intensive central portions of the study area. The conditional risks of agricultural droughts given unfavorable PET conditions are higher in the eastern humid portions than the western arid portions. Unfavorable PET had a higher impact on the six-month standardized soil moisture index (SSMI6) but was also seen to influence three-month SSMI (SSMI3). Dry states as defined by AWD produced higher risks than either P or PET, suggesting that both of these variables influence agricultural droughts. Agricultural drought risks under favorable conditions of AWD were much lower than when AWD was unfavorable. The agricultural drought risks were higher during the winter when AWD was favorable and point to the role of soil characteristics on agricultural droughts. The information provides a drought atlas for an agriculturally important region in the US and, as such, is of practical use to decision makers. The methodology developed here is also generic and can be extended to other regions with considerable ease as the global datasets required are readily available.

Depletion of aquifers across the globe is challenging our ability to maintain critically needed agricultural production and provide potable water supplies for millions. In most cases, the only option to decrease the rate of depletion is to reduce the pumping of groundwater. Although implementation of large-scale pumping reductions in the absence of alternative water sources has proven difficult, recent work has shown that locally based, stakeholder-driven initiatives, coupled with regulatory oversight, can be a promising path forward. A critical question is how much must pumping be reduced to have a significant impact on decline rates. Data limitations and modeling uncertainties, however, have frustrated efforts to answer this question with reliable estimates of the needed reductions. We address this situation using a variant of the water-balance equation to identify a key factor, the misestimation of specific yield, that is limiting our ability to assess the impact of proposed pumping reductions. We find that common modeling practices can lead to large overestimates of the required pumping reductions, thereby inadvertently discouraging conservation efforts. We demonstrate the importance of this general finding using data from the High Plains Aquifer in the central United States where common practices have led to overestimates of required pumping reductions by a factor of three to six. We introduce a new metric, the coefficient of variation of net inflow, to help identify such conditions. The reliability of estimates of the impact of pumping reductions can be greatly improved when the constraints imposed by this new metric are combined with a recently proposed method for estimation of specific yield from field data. The ramifications of these findings are far reaching, as defensible estimates of the impact of proposed pumping reductions are an essential element of efforts to chart more sustainable paths for the world’s heavily stressed aquifers.

Relating Gravity Recovery and Climate Experiment (GRACE)‐derived terrestrial water storage anomaly (aTWS) variations to in situ groundwater data is important to understanding GRACE data utility. Here GRACE‐derived annual changes in aTWS (ΔTWS) from National Aeronautics and Space Administration's Jet Propulsion Laboratory and Goddard Space Flight Center are compared to annual changes in saturated groundwater volumes (ΔGW) in the High Plains aquifer (HPA) and overlying alluvial aquifers in Kansas. Regression analysis suggests that trends in ΔTWS are strongly related to trends in ΔGWalluvial and weakly related to trends in ΔGWHPA, although the magnitude of ΔTWS is much larger than ΔGWalluvial and is similar to ΔGWHPA. Unlike alluvial aquifers, a thick vadose zone overlies the HPA. Estimates of changes in vadose zone water content (ΔVZ) using GRACE products are similar in magnitude to annual variations in North American Land Data Assimilation soil moisture data, suggesting an unexpected dominance of ΔVZ in ΔTWS despite significant groundwater depletion. Results demonstrate that water storage changes in shallow alluvial aquifers, the root zone, the deep vadose zone, and the HPA itself are all significant in the HPA region of Kansas. Consequently, GRACE observations cannot, alone, be taken to reflect variations in saturated zone groundwater storage in the HPA, or other large, heavily used aquifers subject to substantial groundwater depletion, when deep unsaturated zones exist. GRACE can best provide guidance on regional aquifer storage changes where water storage changes in the vadose zone and perched or adjacent aquifers are well constrained. Key Points: GRACE terrestrial water storage observations cannot, alone, be taken to reflect groundwater storage variations in the High Plains aquiferWater storage changes in shallow aquifers, the shallow and deep vadose zone, and the High Plains aquifer itself are all significantGRACE is best suited for estimating regional aquifer storage changes where vadose zone and shallow aquifer storage changes are well known [ABSTRACT FROM AUTHOR]

Monitoring is a key component of risk management at geologic carbon storage (GCS) sites, serving both to help operators understand and manage site performance, and to assure the public and other stakeholders that effective containment is maintained and impacts avoided. Potential leakage of CO 2 and/or brine through wellbores, faults, and fractures to potable groundwater resources is a primary risk concern at onshore GCS sites. In this paper, we present an adaptive methodology for leakage risk-based monitoring design. The methodology uses a risk event tree to predict the likelihood of leakage occurrence, with detection probabilities of risk events estimated for multiple monitoring plans. The overall detection probability of a proposed monitoring plan incorporates baseline data, stochastically simulated leakage events, and the likelihood that a set of technologies will detect the changes in baseline conditions induced by the simulated leakage events. The adaptive monitoring design methodology is demonstrated with a representative case study of CO 2 and brine leaking from a well to a potable groundwater aquifer using simulated data at the High Plains aquifer in the United States. Groundwater quality parameters, pH, total dissolved solids and benzene concentrations, were used to calculate the corresponding detection probabilities of conventional groundwater sampling and fixed sensor monitoring for selected leakage scenarios. The overall detection probability considering all monitoring information was then calculated to evaluate proposed monitoring plan designs. Finally, a simple optimization problem to maximize detection probability with constrained monitoring resources was presented as an application example to close the loop of monitoring and modeling. [ABSTRACT FROM AUTHOR]

The only means of moderating alarming depletion rates in many of the world’s major aquifers is to reduce pumping. We apply a new water-balance approach to assess the impact of pumping reductions in a portion of the High Plains aquifer in the United States. Although projected aquifer responses to pumping reductions vary, practically achievable reductions would have a large impact throughout the area. These findings demonstrate that modest pumping reductions could greatly enhance prospects for groundwater-supported irrigation in the High Plains aquifer and similar aquifers elsewhere. [ABSTRACT FROM AUTHOR]

Understanding the controls of agriculture and climate change on recharge rates is critically important to develop appropriate sustainable management plans for groundwater resources and coupled irrigated agricultural systems. In this study, several physical (total potential ( ψ T ) time series) and chemical tracer and dating ( 3 H, Cl − , Br − , CFCs, SF 6 , and 3 H/ 3 He) methods were used to quantify diffuse recharge rates beneath two rangeland sites and irrigation recharge rates beneath two irrigated corn sites along an east-west (wet-dry) transect of the northern High Plains aquifer, Platte River Basin, central Nebraska. The field-based recharge estimates and historical climate were used to calibrate site-specific Hydrus-1D models, and irrigation requirements were estimated using the Crops Simulation Model (CROPSIM). Future model simulations were driven by an ensemble of 16 global climate models and two global warming scenarios to project a 2050 climate relative to the historical baseline 1990 climate, and simulate changes in precipitation, irrigation, evapotranspiration, and diffuse and irrigation recharge rates. Although results indicate statistical differences between the historical variables at the eastern and western sites and rangeland and irrigated sites, the low warming scenario (+1.0 °C) simulations indicate no statistical differences between 2050 and 1990. However, the high warming scenarios (+2.4 °C) indicate a 25% and 15% increase in median annual evapotranspiration and irrigation demand, and decreases in future diffuse recharge by 53% and 98% and irrigation recharge by 47% and 29% at the eastern and western sites, respectively. These results indicate an important threshold between the low and high warming scenarios that if exceeded could trigger a significant bidirectional shift in 2050 hydroclimatology and recharge gradients. The bidirectional shift is that future northern High Plains temperatures will resemble present central High Plains temperatures and future recharge rates in the east will resemble present recharge rates in the western part of the northern High Plains aquifer. The reductions in recharge rates could accelerate declining water levels if irrigation demand and other management strategies are not implemented. Findings here have important implications for future management of irrigation practices and to slow groundwater depletion in this important agricultural region. [ABSTRACT FROM AUTHOR]

Water is an essential natural resource. Among many stressors, altered climate is exerting pressure on water resource systems, increasing its demand and creating a need for vulnerability assessments. The overall objective of this study was to develop a novel tool that can translate a theoretical concept (vulnerability of water resources (VWR)) to an operational framework mainly under altered temperature and precipitation, as well as for population change (smaller extent). The developed tool had three stages and utilized a novel systems thinking approach. Stage-1: Translating theoretical concept to characteristics identified from studies; Stage-2: Operationalizing characteristics to methodology in VWR; Stage-3: Utilizing the methodology for development of a conceptual modeling tool for VWR: WR-VISTA (Water Resource Vulnerability assessment conceptual model using Indicators selected by System’s Thinking Approach). The specific novelties were: 1) The important characteristics in VWR were identified in Stage-1 (target system, system components, scale, level of detail, data source, frameworks, and indicator); 2) WR-VISTA combined two vulnerability assessments frameworks: the European’s Driver–Pressure–State–Impact–Response framework (DPSIR) and the Intergovernmental Panel on Climate Change’s framework (IPCC’s); and 3) used systems thinking approaches in VWR for indicator selection. The developed application was demonstrated in Kansas (overlying the High Plains region/Ogallala Aquifer, considered the “breadbasket of the world”), using 26 indicators with intermediate level of detail. Our results indicate that the western part of the state is vulnerable from agricultural water use and the eastern part from urban water use. The developed tool can be easily replicated to other regions within and outside the US. [ABSTRACT FROM AUTHOR]

Trends in monthly evapotranspiration (ET) rates across Nebraska, the most intensely irrigated state within the US, were calculated by the calibration-free version of the nonlinear complementary relationship of evaporation over the 1979–2015 period utilizing North American Regional Reanalysis (NARR) net radiation, 10-m wind velocity, as well as Parameter Regression Independent Slope Model (PRISM) air- and dew-point temperature data. State-averaged modeled ET rates rose by 5.5 mm decade −1 due to the presence of wide-spread large-scale irrigation projects in accordance with a 2.4 mm decade −1 increase in PRISM precipitation ( P ) and a simultaneous −2.8 mm decade −1 drop in United States Geological Survey’s state-averaged annual streamflow rates, raising the state-wide ET to P ratio from 0.89 to 0.91 over the modeled time-period. ET rates over irrigated crops increased by 7 mm decade −1 despite a −4.4 mm decade −1 drop in precipitation rates. A similar increase in ET rates (6 mm decade −1 ) required 8.1 mm decade −1 increase in precipitation rates across the non-irrigated Sand Hills of Nebraska. Published NARR ET rates are unable to pick up this unusual regional trend. Since an increase in precipitation rates should normally decrease the ET ratio, as predicted by the Budyko curve, this study yields evidence on how dramatically sustained large-scale irrigation can alter the regional hydrologic cycle not only through a) trivially depleting streamflow rates and/or lowering groundwater table levels; b) suppressing precipitation locally (while enhancing it a long distance downwind), but also; c) reversing the trajectory of the regional ET ratio under generally increasing trends of precipitation. [ABSTRACT FROM AUTHOR]

We used Landsat imagery to examine surface-water dynamics over the past 27 years in 39 salt lakes (salinas) of the Southern High Plains of the U.S. These groundwater- and precipitation-fed wetlands are regionally unique habitats with high salt concentrations and halophytic biota that may be vulnerable to hydrological changes from groundwater extraction for agriculture coupled with drought. We documented amounts and occurrences of water within the 39 salinas, comparing summer and winter (representing periods of high and low groundwater demand, respectively) in 1986-2013. During this span in our study area, total and irrigated cropland acreage increased, and the saturated thickness of the Ogallala Aquifer decreased by ~18.3%. There was variation in inundation frequency by salina, with two never holding water during our study. A third of the salinas went dry at least once, slightly more in summer than winter. Occurrence of water was not simply a function of basin size or to depth to the aquifer. These wetlands are being impacted by human changes to the landscape that are diminishing groundwater inputs, effectively creating novel wetlands that are now primarily supplied by precipitation rather than groundwater, with altered hydrological and ecological traits that may exacerbate regional vulnerability to climate change. [ABSTRACT FROM AUTHOR]

In the Central United States, the Arkansas darter ( Etheostoma cragini) is listed as a threatened fish species by the State of Kansas. Survival of the darter is threatened by loss of habitat caused by changing streamflow conditions, in particular flow depletion. Future management of darter populations and habitats requires an understanding of streamflow conditions and how those conditions may have changed over time in response to natural and anthropogenic factors. In Kansas, streamflow alteration was assessed at 9 U.S. Geological Survey streamgages in 6 priority basins with no pronounced long-term trends in precipitation. The assessment was based on a comparison of observed (O) and predicted expected (E) reference conditions for 29 flow metrics. The O/E results indicated a likely or possible diminished flow condition in 2 basins; the primary cause of which is groundwater-level declines resulting from groundwater pumping for irrigated agriculture. In these 2 basins, habitat characteristics adversely affected by flow depletion may include stream connectivity, pools, and water temperature. The other 4 basins were minimally affected, or unaffected, by flow depletion and therefore may provide the best opportunity for preservation of darter habitat. Through the O/E analysis, anthropogenic streamflow alteration was quantified and the results will enable better-informed decisions pertaining to the future management of darters in Kansas. [ABSTRACT FROM AUTHOR]

In models of coupled human and natural systems (CHANS), the role of individuals and human behavior is often overlooked as data are scarce and assumptions hard to verify. To assess this role, we couple an agent-based model simulating farmers' behavior and a groundwater model and apply the models to the case of groundwater-fed irrigation in a river basin in the High Plains Aquifer region. Results show the crucial role of human behavior in driving the interactions between these coupled systems. Conversely, individuals are impacted by the systems’ dynamics in different ways depending on physical, economic and social characteristics. The findings provide implications for local policy making and education and demonstrate that assumptions on human behavior could be treated as an additional source of uncertainty. This work suggests that modeling individuals and human behavior can be an important step to simulate and understand the dynamics of CHANS in a holistic way. [ABSTRACT FROM AUTHOR]

Crop failure temperatures (CFTs) are critical temperature thresholds for plants beyond which plant tissue has a high potential of being damaged. Climatic changes resulting in fewer or more CFTs have important implications for agriculture. Examining CFT trends can provide information that will assist plant breeders and agricultural producers to develop new adaptation strategies for crop and livestock selection, and thereby safeguard the general food supply. Six CFTs temperatures [maximum temperatures (T max ) ≥ 30 °C, 32 °C, 34 °C, 35 °C, 39 °C and 40 °C] were considered in this study. The variability frequency and intensity of CFTs were analyzed over both short-term (four time-periods; initiation of recordkeeping up to 1920, 1921–1950, 1951–1980, and 1981–2009) and long-term (100-year) time-periods, using data from 23 weather stations spread across Kansas, USA. Results indicated that ∼75% of long-term trend values across all CFTs and locations decreased, one remained the same (less than 1%), and ∼25% had positive trend values. About 91% of long-term trend values fell between 1 and −1 day/decade. Overall, the range in the number CFT days was greatest at 30 °C and steadily decreased as CFT increased, with a 10-fold decrease in the range of the number of CFT days at 40 °C CFT. However, 53% of all 30-year trend lines with absolute slope values of >6 days/decade occurred during the 1981–2009 time-period. The greatest changes in slope were also recorded during this time-period, with 9 slopes greater than 10 days/decade. Thus, the greatest changes in number of CFT days, along with the greatest number of sites experiencing decreases in CFT days occurred during the most recent time-period. Eastern Kansas had the most and largest decreases in CFT days across all CFTs. [ABSTRACT FROM AUTHOR]

Climate, groundwater extraction, and surface water flows have complex nonlinear relationships with groundwater level in agricultural regions. To better understand the relative importance of each driver and predict groundwater level change, we develop a new ensemble modeling framework based on spectral analysis, machine learning, and uncertainty analysis, as an alternative to complex and computationally expensive physical models. We apply and evaluate this new approach in the context of two aquifer systems supporting agricultural production in the United States: the High Plains aquifer (HPA) and the Mississippi River Valley alluvial aquifer (MRVA). We select input data sets by using a combination of mutual information, genetic algorithms, and lag analysis, and then use the selected data sets in a Multilayer Perceptron network architecture to simulate seasonal groundwater level change. As expected, model results suggest that irrigation demand has the highest influence on groundwater level change for a majority of the wells. The subset of groundwater observations not used in model training or cross-validation correlates strongly (R > 0.8) with model results for 88 and 83% of the wells in the HPA and MRVA, respectively. In both aquifer systems, the error in the modeled cumulative groundwater level change during testing (2003-2012) was less than 2 m over a majority of the area. We conclude that our modeling framework can serve as an alternative approach to simulating groundwater level change and water availability, especially in regions where subsurface properties are unknown. [ABSTRACT FROM AUTHOR]

Cimarron County, Oklahoma and Union County, New Mexico, neighboring counties in the Southern High Plains, are part of a vital agricultural region in the United States. This region experiences extended periods of cyclical drought threatening its ability to produce, creating an incentive for extensive center pivot irrigation (CPI). Center pivots draw from the rapidly depleting High Plains Aquifer System. As a result, the prospect of long-term sustainability for these agricultural communities is questionable. We use Remote Sensing and Geographic Information Systems to quantify growth in land irrigated by CPI between the 1950s and 2014, and key informant interviews to explore local perspectives on the causes and impact of such growth. In Cimarron County, OK, CPI increased by the mid-1980s, and has continually increased since. Results suggest adaptation to drought, a depleting aquifer, high corn prices, and less rigid groundwater regulations contribute to CPI growth. Conversely, CPI in Union County, NM, increased until 2010, and then declined. Results also suggest that drought-related agricultural changes and more aggressive well drilling regulations contribute to this decrease. Nevertheless, in both counties, there is a growing concern over the depleting aquifer, the long-term sustainability of CPI, and the region's economic future. [ABSTRACT FROM AUTHOR]

Severe groundwater depletion of the High Plains aquifer (HPA) demands sustainable utilization of water resources to ensure continued freshwater supply in the region. Considering the period 1990-2012, the region's average water footprint (WF) of the major irrigated crops alfalfa, corn, cotton, sorghum, soybean and wheat has been determined as 45.72 km year (54 % blue, 46 % green). Clustering the HPA by groundwater decline, blue WF and green WF allowed for spatial differentiation of hotspots. We show that two clusters, classified as 'significant' and 'severe,' cover 20 % of the irrigated land, yet consume 32 % (7.94 km year) of the total blue WF. WF (blue and green water consumption per unit yield) is highest in the cluster 'severe,' paired with the largest fraction of blue water consumption (66 %). In contrast, green water satisfies crop water demands in the northern subregion, where the lowest WF and the largest fraction of green water consumption occur (67 %). [ABSTRACT FROM AUTHOR]