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

Abstract

Irrigation uses the majority (69%) of fresh groundwater withdrawals in the United States (DeSimone et al., 2015;Dieter et al., 2018). In many aquifers supporting irrigated agriculture, heavy pumping has resulted in unsustainable water-level declines, threatening the economy and environment (Deines et al., 2020;Huggins et al., 2022;Scanlon et al., 2012). As groundwater is a limited resource, how to mitigate these declines to extend the usable lifetime of heavily stressed aquifers is a pressing question (Bierkens & Wada, 2019;Butler et al., 2020b;Castilla-Rho et al., 2019;Gleeson et al., 2020). In semi-arid environments with little access to surface water, groundwater conservation programs that seek to reduce pumping are one of the only viable options to decrease groundwater declines in the near to moderate term (Butler et al., 2020a;Deines et al., 2019;Hu et al., 2010).The fundamental premise of groundwater conservation is to reduce outflows from the aquifer by reducing pumping. However, it is not clear how the effectiveness of such conservation initiatives might change in the future as the hydrological system in areas with groundwater conservation adjusts to the observed pumping reductions (Butler et al., 2020a;Deines et al., 2021;Foster et al., 2017). For example, the transit time for water at the land surface to percolate downward and become groundwater recharge can vary dramatically over the High Plains aquifer due to variations in unsaturated zone thickness and vertical hydraulic conductivity (K Z ), with estimates ranging from decades to centuries (

Estimating irrigation water use from remotely sensed evapotranspiration data: Accuracy and uncertainties across spatial scales

“…High irrigation efficiency suggests that irrigation water withdrawals and applications should be approximately equal to each other and ET-based approaches may be particularly effective for calculating irrigation volumes in this setting. Additionally, due to numerous past studies of groundwater use in the SD-6 LEMA (Deines et al, 2021;Deines, Kendall, Butler, et al, 2019;Dhungel et al, 2020;Drysdale & Hendricks, 2018;Glose et al, 2022;Whittemore et al, 2023), we have a high degree of confidence in the accuracy of the irrigation withdrawal data for the SD-6 LEMA.…”

Identifying hydrologic signatures associated with streamflow depletion caused by groundwater pumping

“…This implies that even streams that appear unimpaired during a wet period may exhibit noticeable changes in hydrologic signatures during a dry period. Not only do dry conditions enhance the visibility of stream depletion impacts, but dry conditions are typically associated with increased groundwater use and well installations (Glose et al, 2022; Zipper, Helm Smith, et al, 2017) and stressed surface water resources (Van Loon, Gleeson, et al, 2016). This suggests that a waterway with unmeasurable streamflow depletion impacts during a wetter period may still experience streamflow depletion as a prominent factor that intensifies hydrologic drought (He et al, 2017; Van Loon, Stahl, et al, 2016).…”

Net Inflow: An Important Target on the Path to Aquifer Sustainability

“…However, trends in net inflow should eventually arise from both natural (e.g., climate‐induced changes in recharge) and anthropogenic (e.g., changes in pumping) forcings. Although we have not observed net inflow trends in the SD‐6 LEMA (Figure 2a), we expect that the pumping reductions will eventually lead to a decrease in I as a result of reductions in irrigation return flow, changes in lateral hydraulic gradients, and so on (Butler et al 2020b; Glose et al 2022). The reductions in I would be revealed on Δ WL vs. Q plots by a downward shift in the data points (i.e., the same pumping would produce a greater water‐level decline).…”