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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. Individuals and human behavior play a crucial role in driving CHANS' dynamics.Modeling individuals shows how CHANS' dynamics impact these individuals differently.Assumptions on human behavior have considerable effects on model results.Education and information diffusion can have critical roles in water conservation.

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 (Tmax) ≥ 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.

Peak groundwater depletion from overtapping aquifers beyond recharge rates occurs as the depletion rate increases until a peak occurs followed by a decreasing trend as pumping equilibrates towards available recharge. The logistic equation of Hubbert's study of peak oil is used to project measurements at a set of observation wells, which provide estimates of saturated thickness and changes in groundwater storage from 1930 to 2110. The annual rate of depletion in High Plains Aquifer of the central USA is estimated to have peaked at 8.25 × 109 m3/yr in 2006 followed by projected decreases to 4.0 × 109 m3/yr in 2110. The timing of peaks follows a south–north progression, with peaks occurs in 1999 for Texas, 2002 for New Mexico, 2010 for Kansas, 2012 for Oklahoma and 2023 for Colorado; peaks do not occur before 2110 for Nebraska, South Dakota and Wyoming. The manifestation of peak groundwater depletion contributes towards the more comprehensive understanding necessary to assess potential vulnerabilities in the water-food nexus posed by aquifer depletion.

Future extreme precipitation (EP, daily rainfall amount over certain thresholds) is projected to increase with global climate change; however, its effect on groundwater recharge has not been fully explored. This study specifically investigates the spatiotemporal dynamics of groundwater recharge and the effects of extreme precipitation (daily rainfall amount over the 95th percentile, which is tagged by ranking the percentiles in each season for a base period) on groundwater recharge from 1950 to 2010 over the Northern High Plains (NHP) Aquifer using the Soil Water Balance Model. The results show that groundwater recharge significantly (p

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 &minus, 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&ndash, 65% within the study area during summer months and between 20&ndash, 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.

The major driver of water-level changes in many heavily stressed aquifers is irrigation pumping, which is primarily a function of meteorological conditions (precipitation and potential evapotranspiration). Correlations among climatic indices, water-level changes, and pumping can thus often be used to assess the impact of climatic and anthropogenic stresses. The power of this simple, first-order approach, which captures the primary excitation–response relationships driving aquifer behavior, is demonstrated for the High Plains aquifer in the central United States (Kansas). Regional correlations between water-level changes and climatic indices indicate that a repeat of the most severe drought on record would more than double water-level decline rates. More importantly, correlations between water-level changes and reported pumping reveal that practically feasible pumping reductions should stabilize water levels, at least temporarily, over much of the aquifer in Kansas. This example illustrates that wh...

The volume of groundwater stored in the subsurface in the United States decreased by almost 1000 km 3 during 1900–2008. The aquifer systems with the three largest volumes of storage depletion include the High Plains aquifer, the Mississippi Embayment section of the Gulf Coastal Plain aquifer system, and the Central Valley of California. Depletion rates accelerated during 1945–1960, averaging 13.6 km 3 /year during the last half of the century, and after 2000 increased again to about 24 km 3 /year. Depletion intensity is a new parameter, introduced here, to provide a more consistent basis for comparing storage depletion problems among various aquifers by factoring in time and areal extent of the aquifer. During 2001–2008, the Central Valley of California had the largest depletion intensity. Groundwater depletion in the United States can explain 1.4% of observed sea-level rise during the 108-year study period and 2.1% during 2001–2008. Groundwater depletion must be confronted on local and regional scales to help reduce demand (primarily in irrigated agriculture) and/or increase supply.

Groundwater pumping for agriculture is a major driver causing declines of global freshwater ecosystems, yet the ecological consequences for stream fish assemblages are rarely quantified. We combined retrospective (1950–2010) and prospective (2011–2060) modeling approaches within a multiscale framework to predict change in Great Plains stream fish assemblages associated with groundwater pumping from the United States High Plains Aquifer. We modeled the relationship between the length of stream receiving water from the High Plains Aquifer and the occurrence of fishes characteristic of small and large streams in the western Great Plains at a regional scale and for six subwatersheds nested within the region. Water development at the regional scale was associated with construction of 154 barriers that fragment stream habitats, increased depth to groundwater and loss of 558 km of stream, and transformation of fish assemblage structure from dominance by large-stream to small-stream fishes. Scaling down to subwatersheds revealed consistent transformations in fish assemblage structure among western subwatersheds with increasing depths to groundwater. Although transformations occurred in the absence of barriers, barriers along mainstem rivers isolate depauperate western fish assemblages from relatively intact eastern fish assemblages. Projections to 2060 indicate loss of an additional 286 km of stream across the region, as well as continued replacement of large-stream fishes by small-stream fishes where groundwater pumping has increased depth to groundwater. Our work illustrates the shrinking of streams and homogenization of Great Plains stream fish assemblages related to groundwater pumping, and we predict similar transformations worldwide where local and regional aquifer depletions occur.

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.

The impacts of climate extremes and water use on groundwater storage across large aquifers can be quantified using Gravity Recovery and Climate Experiment (GRACE) satellite monitoring. We present new methods to improve estimates of changes in groundwater storage by incorporating irrigation soil moisture corrections to common data assimilation products. These methods are demonstrated using data from the High Plains Aquifer (HPA) for 2003 to 2013. Accounting for the impacts of observed and inferred irrigation on soil moisture significantly improves estimates of groundwater storage changes as verified by interpolated measurements from ~10,000 HPA wells. The resulting estimates show persistent declines in groundwater storage across the HPA, more severe in the southern and central HPA than in the north. Groundwater levels declined by an average of approximately 276 ± 23 mm from 2003 to 2013, resulting in a storage loss of 125 ± 4.3 km3, based on the most accurate of the three methods developed here.

We examine the effects of energy prices on groundwater extraction using an econometric model of a farmer's irrigation water pumping decision that accounts for both the intensive and extensive margins. Our results show that energy prices have an effect on both types of margins. Increasing energy prices would affect crop selection decisions, crop acreage allocation decisions, and farmers' demand for water. Our estimated total marginal effect, which sums the effects on the intensive and extensive margins, suggests that a $1 per million btu increase in the energy price would decrease water extraction by an individual farmer by 5.89 acre‐feet per year, a decrease of 3.6 percent of the average annual extraction rate. Our estimated elasticity of water extraction with respect to energy price is −0.26.

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 (WFarea) of the major irrigated crops alfalfa, corn, cotton, sorghum, soybean and wheat has been determined as 45.72 km3 year−1 (54 % blue, 46 % green). Clustering the HPA by groundwater decline, blue WFarea and green WFarea 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 km3 year−1) of the total blue WFarea. WFcrop (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 WFcrop and the largest fraction of green water consumption occur (67 %).

Groundwater studies face computational limitations when providing local detail (such as well drawdown) within regional models. We adapt the Analytic Element Method (AEM) to extend separation of variable solutions for a rectangle to domains composed of multiple interconnected rectangular elements. Each rectangle contains a series solution that satisfies the governing equations and coefficients are adjusted to match boundary conditions at the edge of the domain and continuity conditions across adjacent rectangles. A complete mathematical implementation is presented including matrices to solve boundary and continuity conditions. This approach gathers the mathematical functions associated with head and velocity within a small set of functions for each rectangle, enabling fast computation of these variables. Benchmark studies verify that conservation of mass and energy conditions are accurately satisfied using a method of images solution, and also develop a solution for heterogeneous hydraulic conductivity with log normal distribution. A case study illustrates that the methods are capable of modeling local detail within a large-scale regional model of the High Plains Aquifer in the central USA and reports the numerical costs associated with increasing resolution, where use is made of GIS datasets for thousands of rectangular elements each with unique geologic and hydrologic properties, Methods are applicable to interconnected rectangular domains in other fields of study such as heat conduction, electrical conduction, and unsaturated groundwater flow.