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1. Uncertainty of simulated groundwater recharge at different global warming levels: a global-scale multi-model ensemble study

   https://doi.org/10.5194/hess-25-787-2021  

   Reinecke, Robert ; Müller Schmied, Hannes ; Trautmann, Tim ; Andersen, Lauren Seaby ; Burek, Peter ; Flörke, Martina ; Gosling, Simon N. ; Grillakis, Manolis ; Hanasaki, Naota ; Koutroulis, Aristeidis ; et al ( January 2021 , Hydrology and Earth System Sciences)

   null (Ed.)

   Abstract. Billions of people rely on groundwater as being an accessible source of drinking water and for irrigation, especially in times of drought. Its importance will likely increase with a changing climate. It is still unclear, however, how climate change will impact groundwater systems globally and, thus, the availability of this vital resource. Groundwater recharge is an important indicator for groundwater availability, but it is a water flux that is difficult to estimate as uncertainties in the water balance accumulate, leading to possibly large errors in particular in dry regions. This study investigates uncertainties in groundwater recharge projections using a multi-model ensemble of eight global hydrological models (GHMs) that are driven by the bias-adjusted output of four global circulation models (GCMs). Pre-industrial and current groundwater recharge values are compared with recharge for different global warming (GW) levels as a result of three representative concentration pathways (RCPs). Results suggest that projected changes strongly vary among the different GHM–GCM combinations, and statistically significant changes are only computed for a few regions of the world. Statistically significant GWR increases are projected for northern Europe and some parts of the Arctic, East Africa, and India. Statistically significant decreases are simulated in southern Chile, parts of Brazil, central USA, the Mediterranean, and southeastern China. In some regions, reversals of groundwater recharge trends can be observed with global warming. Because most GHMs do not simulate the impact of changing atmospheric CO2 and climate on vegetation and, thus, evapotranspiration, we investigate how estimated changes in GWR are affected by the inclusion of these processes. In some regions, inclusion leads to differences in groundwater recharge changes of up to 100 mm per year. Most GHMs with active vegetation simulate less severe decreases in groundwater recharge than GHMs without active vegetation and, in some regions, even increases instead of decreases are simulated. However, in regions where GCMs predict decreases in precipitation and where groundwater availability is the most important, model agreement among GHMs with active vegetation is the lowest. Overall, large uncertainties in the model outcomes suggest that additional research on simulating groundwater processes in GHMs is necessary. 

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2. Developing a Multicriteria Decision Analysis Framework to Evaluate Reclaimed Wastewater Use for Agricultural Irrigation: The Case Study of Maryland

   https://doi.org/10.3390/hydrology8010004  

   Paul, Manashi ; Negahban-Azar, Masoud ; Shirmohammadi, Adel ; Montas, Hubert ( March 2021 , Hydrology)

   null (Ed.)

   Groundwater is the main source of irrigation and residential use in the Eastern Shore Maryland, which is experiencing challenges regarding overuse, saltwater intrusion, and diminishing productivity. The Chesapeake Bay is also facing the problem of water pollution due to pollutant loading from agricultural fields and wastewater treatment plants (WWTPs). Using recycled water for irrigation has the potential to alleviate the pressure on groundwater and reduce pollutant loading. The objective of this study was to develop a decision tool to explore the use of recycled water for agricultural irrigation in Maryland using Multicriteria Decision Analysis (MCDA) integrated with Geographical Information Systems (GIS). Four main evaluation criteria were included in the GIS-MCDA framework: agricultural land cover, climate, groundwater vulnerability, and characteristics of the WWTPs as sources of recycled water. Groundwater vulnerability zones were developed using the groundwater well density, water extraction data, and the aquifer information. Then, the most suitable areas for irrigation using recycled water were identified. About 13.5% and 32.9% of agricultural land was, respectively, found to be “highly” and “moderately” suitable for irrigation with recycled water when WWTPs were categorized based on their treatment process information. The results provide a useful decision tool to promote the use of recycled water for agricultural irrigation. 

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3. Evaluating the Impact of Future Seasonal Climate Extremes on Crop Evapotranspiration of Maize in Western Kansas Using a Machine Learning Approach

   https://doi.org/10.3390/land12081500  

   Igwe, Kelechi ; Sharda, Vaishali ; Hefley, Trevor ( August 2023 , Land)

   Data-driven technologies are employed in agriculture to optimize the use of limited resources. Crop evapotranspiration (ET) estimates the actual amount of water that crops require at different growth stages, thereby proving to be the essential information needed for precision irrigation. Crop ET is essential in areas like the US High Plains, where farmers rely on groundwater for irrigation. The sustainability of irrigated agriculture in the region is threatened by diminishing groundwater levels, and the increasing frequency of extreme events caused by climate change further exacerbates the situation. These conditions can significantly affect crop ET rates, leading to water stress, which adversely affects crop yields. In this study, we analyze historical climate data using a machine learning model to determine which of the climate extreme indices most influences crop ET. Crop ET is estimated using reference ET derived from the FAO Penman–Monteith equation, which is multiplied with the crop coefficient data estimated from the remotely sensed normalized difference vegetation index (NDVI). We found that the climate extreme indices of consecutive dry days and the mean weekly maximum temperatures most influenced crop ET. It was found that temperature-derived indices influenced crop ET more than precipitation-derived indices. Under the future climate scenarios, we predict that crop ET will increase by 0.4% and 1.7% in the near term, by 3.1% and 5.9% in the middle term, and by 3.8% and 9.6% at the end of the century under low greenhouse gas emission and high greenhouse gas emission scenarios, respectively. These predicted changes in seasonal crop ET can help agricultural producers to make well-informed decisions to optimize groundwater resources.

    

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4. River flow decline across the entire Arkansas River Basin in the 21st century

   https://doi.org/10.1016/j.jhydrol.2023.129253  

   Yang, Jia ; Zou, Chris ; Will, Rodney ; Wagner, Kevin ; Ouyang, Ying ; King, Chad ; Winrich, Abigail ; Tian, Hanqin ( March 2023 , Journal of Hydrology)

   The Arkansas River and its tributaries provide critical water resources for agricultural irrigation, hydropower generation, and public water supply in the Arkansas River Basin (ARB). However, climate change and other environmental factors have imposed significant impacts on regional hydrological processes, resulting in widespread ecological and economic consequences. In this study, we projected future river flow patterns in the 21st century across the entire ARB under two climate and socio-economic change scenarios (i.e., SSP2-RCP45 and SSP5-RCP85) using the process-based Dynamic Land Ecosystem Model (DLEM). We designed “baseline simulations” (all driving factors were kept constant at the level circa 2000) and “environmental change simulations” (at least one driving factor changed over time during 2001–2099) to simulate the inter-annual variations of river flow and quantify the contributions of four driving factors (i.e., climate change, CO2 concentration, atmospheric nitrogen deposition, and land use change). Results showed that the Arkansas River flow in 2080–2099 would decrease by 12.1% in the SSP2-RCP45 and 27.9% in the SSP5-RCP85 compared to that during 2000–2019. River flow decline would occur from the beginning to the middle of this century in the SSP2-RCP45 and happen throughout the entire century in the SSP5-RCP85. All major rivers in the ARB would experience river flow decline with the largest percentage reduction in the western and southwestern ARB. Warming and drying climates would account for 77%–95% of the reduction. The rising CO2 concentration would exacerbate the decline through increasing foliage area and ecosystem evapotranspiration. This study provides insight into the spatial patterns of future changes in water availability in the ARB and the underlying mechanisms controlling these changes. This information is critical for designing watershed-specific management strategies to maintain regional water resource sustainability and mitigate the adverse impacts of climate changes on water availability. 

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5. Sustainable Use of Groundwater May Dramatically Reduce Irrigated Production of Maize, Soybean, and Wheat

   https://doi.org/10.1029/2021EF002018  

   Lopez, Jose R. ; Winter, Jonathan M. ; Elliott, Joshua ; Ruane, Alex C. ; Porter, Cheryl ; Hoogenboom, Gerrit ; Anderson, Martha ; Hain, Christopher ( December 2021 , Earth's Future)

   Groundwater extraction in the United States (US) is unsustainable, making it essential to understand the impacts of limited water use on irrigated agriculture. To improve this understanding, we integrated a gridded crop model with satellite observations, recharge estimates, and water survey data to assess the effects of sustainable groundwater withdrawals on US irrigated agricultural production. The gridded crop model agrees with satellite‐based estimates of evapotranspiration (R² = 0.68), as well as survey data from the United States Department of Agriculture (R² = 0.82–0.94 for county‐level production and 0.37–0.54 for county‐level yield). Using the optimistic assumption that groundwater extraction equals effective aquifer recharge rate, we find that sustainable groundwater use decreases US irrigated production of maize, soybean, and winter wheat by 20%, 6%, and 25%, respectively. Using a more conservative assumption of groundwater availability, US irrigated production of maize, soybean, and winter wheat decreases by 45%, 37%, and 36%, respectively. The wide range of simulated losses is driven by considerable uncertainty in surface water and groundwater interactions, as well as accounting for the many aspects of sustainability. Our results demonstrate the vulnerability of US irrigated agriculture to unsustainable groundwater pumping, highlighting the difficulty of expanding or even maintaining irrigated food production in the face of climate change, population growth, and shifting dietary demands. These findings are based on reducing pumping by fallowing irrigated farmland; however, alternate pumping reduction strategies or technological advances in crop genetics and irrigation could produce different results.

    

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