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Aquifer overexploitation could significantly impact crop production in the United States because 60% of irrigation relies on groundwater. Groundwater depletion in the irrigated High Plains and California Central Valley accounts for ∼50% of groundwater depletion in the United States since 1900. A newly developed High Plains recharge map shows that high recharge in the northern High Plains results in sustainable pumpage, whereas lower recharge in the central and southern High Plains has resulted in focused depletion of 330 km3 of fossil groundwater, mostly recharged during the past 13,000 y. Depletion is highly localized with about a third of depletion occurring in 4% of the High Plains land area. Extrapolation of the current depletion rate suggests that 35% of the southern High Plains will be unable to support irrigation within the next 30 y. Reducing irrigation withdrawals could extend the lifespan of the aquifer but would not result in sustainable management of this fossil groundwater. The Central Valley is a more dynamic, engineered system, with north/south diversions of surface water since the 1950s contributing to ∼7× higher recharge. However, these diversions are regulated because of impacts on endangered species. A newly developed Central Valley Hydrologic Model shows that groundwater depletion since the 1960s, totaling 80 km3, occurs mostly in the south (Tulare Basin) and primarily during droughts. Increasing water storage through artificial recharge of excess surface water in aquifers by up to 3 km3 shows promise for coping with droughts and improving sustainability of groundwater resources in the Central Valley.

The Central Valley in California (USA) covers about 52,000 km 2 and is one of the most productive agricultural regions in the world. This agriculture relies heavily on surface-water diversions and groundwater pumpage to meet irrigation water demand. Because the valley is semi-arid and surface-water availability varies substantially, agriculture relies heavily on local groundwater. In the southern two thirds of the valley, the San Joaquin Valley, historic and recent groundwater pumpage has caused significant and extensive drawdowns, aquifer-system compaction and subsidence. During recent drought periods (2007–2009 and 2012-present), groundwater pumping has increased owing to a combination of decreased surface-water availability and land-use changes. Declining groundwater levels, approaching or surpassing historical low levels, have caused accelerated and renewed compaction and subsidence that likely is mostly permanent. The subsidence has caused operational, maintenance, and construction-design problems for water-delivery and flood-control canals in the San Joaquin Valley. Planning for the effects of continued subsidence in the area is important for water agencies. As land use, managed aquifer recharge, and surface-water availability continue to vary, long-term groundwater-level and subsidence monitoring and modelling are critical to understanding the dynamics of historical and continued groundwater use resulting in additional water-level and groundwater storage declines, and associated subsidence. Modeling tools such as the Central Valley Hydrologic Model, can be used in the evaluation of management strategies to mitigate adverse impacts due to subsidence while also optimizing water availability. This knowledge will be critical for successful implementation of recent legislation aimed toward sustainable groundwater use.

Understanding climate and human impacts on water storage is critical for sustainable water-resources management. Here we assessed climate and human drivers of total water storage (TWS) variability from Gravity Recovery and Climate Experiment (GRACE) satellites compared with drought severity and irrigation water use in 14 major aquifers in the United States. Results show that long-term variability in TWS tracked by GRACE satellites is dominated by interannual variability in most of the 14 major US aquifers. Low TWS trends in the humid eastern U.S. are linked to low drought intensity. Although irrigation pumpage in the humid Mississippi Embayment aquifer exceeded that in the semi-arid California Central Valley, a surprising lack of TWS depletion in the Mississippi Embayment aquifer is attributed to extensive streamflow capture. Marked storage depletion in the semi-arid southwestern Central Valley and south-central High Plains totaled ∼90 km 3 , about three times greater than the capacity of Lake Mead, the largest U.S. reservoir. Depletion in the Central Valley was driven by long-term droughts (⩽5 yr) amplified by switching from mostly surface water to groundwater irrigation. Low or slightly rising TWS trends in the northwestern (Columbia and Snake Basins) US are attributed to dampening drought impacts by mostly surface water irrigation. GRACE satellite data highlight synergies between climate and irrigation, resulting in little impact on TWS in the humid east, amplified TWS depletion in the semi-arid southwest and southcentral US, and dampened TWS deletion in the northwest and north central US Sustainable groundwater management benefits from conjunctive use of surface water and groundwater, inefficient surface water irrigation promoting groundwater recharge, efficient groundwater irrigation minimizing depletion, and increasing managed aquifer recharge. This study has important implications for sustainable water development in many regions globally.

Projected longer-term droughts and intense floods underscore the need to store more water to manage climate extremes. Here we show how depleted aquifers have been used to store water by substituting surface water use for groundwater pumpage (conjunctive use, CU) or recharging groundwater with surface water (managed aquifer recharge, MAR). Unique multi-decadal monitoring from thousands of wells and regional modeling datasets for the California Central Valley and central Arizona were used to assess CU and MAR. In addition to natural reservoir capacity related to deep water tables, historical groundwater depletion further expanded aquifer storage by ∼44 km3 in the Central Valley and by ∼100 km3 in Arizona, similar to or exceeding current surface reservoir capacity by up to three times. Local river water and imported surface water, transported through 100s of km of canals, is substituted for groundwater (≤15 km3 yr−1, CU) or is used to recharge groundwater (MAR, ≤1.5 km3 yr−1) during wet years shifting to mostly groundwater pumpage during droughts. In the Central Valley, CU and MAR locally reversed historically declining water-level trends, which contrasts with simulated net regional groundwater depletion. In Arizona, CU and MAR also reversed historically declining groundwater level trends in active management areas. These rising trends contrast with current declining trends in irrigated areas that lack access to surface water to support CU or MAR. Use of depleted aquifers as reservoirs could expand with winter flood irrigation or capturing flood discharges to the Pacific (0-1.6 km3 yr−1, 2000-2014) with additional infrastructure in California. Because flexibility and expanded portfolio options translate to resilience, CU and MAR enhance drought resilience through multi-year storage, complementing shorter term surface reservoir storage, and facilitating water markets.

In the present study, a 42-year record of rainfall and temperature from Airport and a 43-year rainfall record from Kizimbani meteorological station were analyzed to understand how these climatic variables are affecting groundwater supply on the Island of Zanzibar, Tanzania. Water table fluctuation (WTF) and rainfall data were examined for estimating groundwater recharge. The abstraction volume and recharge rate were used to estimate the water balance. Also, the different physicochemical parameters, such as chlorinity, nitrate, electrical conductivity (EC) and total dissolved solids (TDS) were examined to assess the impact of groundwater pumpage on water quality on the island of Zanzibar. Through the use of WTF method, the present study estimated the recharge rates, local sustainable yield (SY) and integrated water balance (IWB). Rainfall records showed that Zanzibar Island receives a total mean annual rainfall of 1673 mm out of which 7% (equivalent to 1.79 × 106 m3/y) recharges the groundwater. Temperature variations indicated an incremental trend accompanied by low rainfall. The average estimated SY was 0.72%, while the IWB showed a deficit of 39%. Furthermore, the total groundwater abstraction rate in the studied area was 2.49 × 106 m3/y, which was higher than the rate of recharge. This means that the groundwater resources are currently over-exploited and, if immediate action is not taken, the groundwater aquifers may be subjected to pollution, collapse and seawater intrusion. The effects of over-pumping were manifested by high levels of EC, chloride, TDS, total hardness and nitrate that showed an increasing trend with time.

This study addresses the challenges of and opportunities for achieving the ambitious greenhouse gas emissions reduction target of the fishery sector of the Republic of Korea, set at 96% by 2030. We also focus on the current status of land-based aquaculture and underground seawater resource development, quantitatively compare energy inputs for land-based fish cultivation, and evaluate the potential of underground seawater to reduce CO2 emissions. Since 2010, 762 underground seawater boreholes have been developed, yielding a cumulative daily pumpage of 125,780 m3. Jeollanam-do was found to have the highest daily pumpage, with an annual energy requirement of 131,205,613 Mcal. Despite the fact that the energy demands for underground seawater are higher in some months, it provides a 22.6% reduction in total annual energy consumption compared to surface water. The use of underground seawater for heating or cooling resulted in a 24.1% reduction in the required input energy. However, energy requirements increase due to the relatively high surface water temperature in some regions and seasons. This study also highlights the utilization of underground seawater in heating or cooling surface water via indirect applications using geothermal heat pumps. This innovative research broadens the methods of greenhouse gas mitigation, particularly in the agriculture, livestock, and fisheries industries.

Increasing artificial water recharge and restriction on groundwater pumpage have caused land displacements in Shanghai (China) to shift from subsidence to uplift. On the basis of field and laboratory data, the characteristics and mechanism of land subsidence and uplift are analyzed and discussed. Under the condition of long-term groundwater extraction, the deformation of aquifer and aquitard units consists of elastic, plastic, visco-elastic, and visco-plastic components. The recoverable elastic and visco-elastic deformation is only a small portion of the total deformation for both aquitard and aquifer units, especially when the groundwater level in the units is lower than the historically lowest values. When the groundwater level in aquifer and aquitard units rises, whether their expansion occurs immediately or not, depends on the changing modes of groundwater level they have experienced. Even aquifer units do not always rebound closely following the rise of groundwater level in them. The lagging of the occurrence of arrested land subsidence and uplift, clearly behind the rise of groundwater level in aquifer units, can be attributed to the visco-plastic deformation of all units and the consolidation deformation of aquitard units. Artificial recharge and limitation of pumpage are efficient measures for controlling land subsidence, but earlier actions are necessary to keep groundwater levels in all aquifer units above their historically lowest values all the time, if a more effective outcome is expected.

There is increasing concern about water constraints limiting oil and gas production using hydraulic fracturing (HF) in shale plays, particularly in semiarid regions and during droughts. Here we evaluate HF vulnerability by comparing HF water demand with supply in the semiarid Texas Eagle Ford play, the largest shale oil producer globally. Current HF water demand (18 billion gallons, bgal; 68 billion liters, bL in 2013) equates to ∼16% of total water consumption in the play area. Projected HF water demand of ∼330 bgal with ∼62 000 additional wells over the next 20 years equates to ∼10% of historic groundwater depletion from regional irrigation. Estimated potential freshwater supplies include ∼1000 bgal over 20 yr from recharge and ∼10 000 bgal from aquifer storage, with land-owner lease agreements often stipulating purchase of freshwater. However, pumpage has resulted in excessive drawdown locally with estimated declines of ∼100-200 ft in ∼6% of the western play area since HF began in 2009-2013. Non-freshwater sources include initial flowback water, which is ≤5% of HF water demand, limiting reuse recycling. Operators report shifting to brackish groundwater with estimated groundwater storage of 80 000 bgal. Comparison with other semiarid plays indicates increasing brackish groundwater and produced water use in the Permian Basin and large surface water inputs from the Missouri River in the Bakken play. The variety of water sources in semiarid regions, with projected HF water demand representing ∼3% of fresh and ∼1% of brackish water storage in the Eagle Ford footprint indicates that, with appropriate management, water availability should not physically limit future shale energy production.

In the Apalachicola-Chattahoochee-Flint (ACF) river basin in Alabama, Georgia, and Florida (USA), population growth in the city of Atlanta and increased groundwater withdrawal for irrigation in southwest Georgia are greatly affecting the supply of freshwater to downstream regions. This study was conducted to understand and quantify the effect of irrigation pumpage on the karst Upper Floridan Aquifer and river–aquifer interactions in the lower ACF river basin in southwest Georgia. The groundwater MODular Finite-Element model (MODFE) was used for this study. The effect of two drought years, a moderate and a severe drought year, were simulated. Comparison of the results of the irrigated and non-irrigated scenarios showed that groundwater discharge to streams is a major outflow from the aquifer, and irrigation can cause as much as 10 % change in river–aquifer flux. The results also show that during months with high irrigation (e.g., June 2011), storage loss (34 %), the recharge and discharge from the upper semi-confining unit (30 %), and the river–aquifer flux (31 %) are the major water components contributing towards the impact of irrigation pumpage in the study area. A similar scenario plays out in many river basins throughout the world, especially in basins in which underlying karst aquifers are directly connected to a nearby stream. The study suggests that improved groundwater withdrawal strategies using climate forecasts needs to be developed in such a way that excessive withdrawals during droughts can be reduced to protect streams and river flows.

This study demonstrates characteristics and mechanisms of deformation of an aquifer system in response to seasonal fluctuations of groundwater level when groundwater pumping has been strictly regulated after experiencing longtime land subsidence. Two boreholes with depth of 1226 m (G2 site) and 905 m (G3 site) were drilled at the Tianjin coastal region where severe land subsidence had occurred since the 1950s. Extensometer/piezometer groups installed at the G2 site illustrate synchronized variations of compaction and groundwater level since 2010 in the aquifer system between depth of 100–400 m which contributes most groundwater pumpage. Monitored land subsidence demonstrates that the shallow aquifer has become the main contributor to the land subsidence, and inelastic compaction still occurred in the aquifers where groundwater level has recovered. Pre-consolidation stresses show that clayey soils in depth < 100 m are under-consolidated, and deep clayey soils show the state of normal- to over-consolidation. The effects of the cyclic groundwater level oscillation on deformation were investigated using repeated loading and unloading tests. Void ratio changes in loading/unloading cycles illustrate that inelastic deformation rate decreases gradually and elastic deformation rate remains almost unchanged with increases of cyclic numbers. The deformation of soil samples from 100 to 400 m is mostly elastic for loading stress in the over-consolidation stress range. These findings suggest that groundwater dewatering in the shallow (depth < 100 m) aquifer will be the primary target to control land subsidence. Groundwater level fluctuations higher than pre-consolidation value in 100–400 m only lead to elastic and recoverable deformation even small residual permanent deformation may continue for a long time. The results improve the understanding of deformation in complex urban aquifers affected by groundwater level fluctuations and highlight the importance of city planning management for controlling land subsidence in coastal cities.