Water Policy Center, Public Policy Institute of California, California, USA.
Center for Watershed Sciences, University of California, Davis, CA, USA.
J Environ Manage. 2020 Jun 15;264:110426. doi: 10.1016/j.jenvman.2020.110426. Epub 2020 Mar 20.
In regions experiencing aquifer depletion, planning for groundwater sustainability requires both accurate accounting of current groundwater budgets and an assessment of future conditions, with changes in recharge and pumping. Hydrologic variability, climate change effects on water flows, changing water infrastructure operations, and inherent uncertainties in modeling, challenge the plans to achieve groundwater sustainability. This paper examines the importance, magnitude, and policy implications of uncertainties in groundwater overdraft estimation for water management in California. We review water balance estimates from two regional-scale groundwater models-C2VSim and CVHM-for sub-regions within California's Central Valley, and examine the variability and uncertainty in historical and future estimates of groundwater overdraft. Assuming reductions in agricultural water use for sub-regions with overdraft, we estimate the probabilities of ending groundwater overdraft for different periods. We also obtain the economic costs associated with these reductions in agricultural production. Results from both groundwater models show significant inter-annual variability in flows affecting groundwater storage, and our model comparison highlights the uncertainty in water budget estimates for Central Valley sub-regions given the differences between models. The analysis of the probabilities of achieving sustainability at the sub-regional scale show that the average overdraft rate is important and that greater variance in annual groundwater storage increases uncertainties in ending overdraft, especially for shorter periods. Greater reductions in annual net water increases the reliability of achieving groundwater sustainability, but rising rapidly agricultural economic losses. Setting management thresholds below groundwater levels can ease meeting sustainability criteria, but also can introduce a false pathway to sustainability. Finally, we discuss policy implications for the design of local groundwater sustainability plans and state assessment and regulation of local plans.
在经历含水层枯竭的地区，规划地下水的可持续性需要准确核算当前的地下水预算，并评估未来的情况，包括补给和开采的变化。水文变异性、气候变化对水流的影响、不断变化的水基础设施运行情况以及建模固有的不确定性，都对实现地下水可持续性的计划构成了挑战。本文探讨了不确定性在加利福尼亚州地下水超采估计中的重要性、规模和政策影响，用于水资源管理。我们审查了两个区域规模地下水模型（C2VSim 和 CVHM）在加利福尼亚州中央谷内各子区域的水均衡估计，并考察了历史和未来地下水超采估计的变异性和不确定性。假设各子区域减少农业用水，我们估计不同时期结束地下水超采的概率。我们还获得了与这些农业生产减少相关的经济成本。两个地下水模型的结果都显示出影响地下水储存的流量的年际变异性，我们的模型比较突出了中央谷各子区域水预算估计的不确定性，因为模型之间存在差异。在子区域尺度上实现可持续性的概率分析表明，平均超采率很重要，年地下水储存的方差增加会增加结束超采的不确定性，特别是在较短的时期内。年度净水量的较大减少增加了实现地下水可持续性的可靠性，但农业经济损失迅速上升。将管理阈值设定在地下水位以下可以缓解可持续性标准的满足，但也可能引入一种虚假的可持续性途径。最后，我们讨论了设计当地地下水可持续性计划和州评估和监管当地计划的政策影响。
