Balancing Flood Risk and Water Supply in California: Policy Search Integrating Short‐Term Forecast Ensembles With Conjunctive Use
Balancing Flood Risk and Water Supply in California: Policy Search Integrating Short‐Term Forecast Ensembles With Conjunctive Use
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DOI：
10.1029/2018wr023177
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发表时间：
2018-10
影响因子：
5.4
通讯作者：
M. Nayak;J. Herman;S. Steinschneider
中科院分区：
文献类型：
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作者：
M. Nayak;J. Herman;S. Steinschneider
短期天气预报有可能改善水库的防洪和供水目标，特别是在目前依赖固定季节性洪水池来减轻风险的地区。基于预测的政策的成功开发应该整合现代预测产品的不确定性，以创建可以在样本外时期进行测试的明确规则。本研究探讨了此类运营政策在保持防洪的同时提高供水效率的潜力，将最先进的天气预报与下游联合使用相结合，将多余的洪水释放转移到地下水储存中。由于可用的天气后报是相对较短的（10-20年），我们提出了一个新的统计框架，以发展合成预测在较长时期的历史记录。操作规则的训练与最近开发的政策搜索框架中，决策规则结构为二叉树。以加州的福尔松水库为例，针对不同的预报技巧和联合使用能力，为一系列情景制定了政策。结果表明，联合使用和短期天气预报的组合可以通过允许存储保持高水平直到预报触发释放来大大改善供水和防洪目标。此外，联合使用能力的增加降低了预报技能的重要性，因为在汛期，地表水储存可以转移到地下水，而不会失去供水。该分析有助于为加州和其他洪水水文气候相似地区的大型多用途水库制定基于预测的运行策略。
Short‐term weather forecasts have the potential to improve reservoir operations for both flood control and water supply objectives, especially in regions currently relying on fixed seasonal flood pools to mitigate risk. The successful development of forecast‐based policies should integrate uncertainty from modern forecast products to create unambiguous rules that can be tested on out‐of‐sample periods. This study investigates the potential for such operating policies to improve water supply efficiency while maintaining flood protection, combining state‐of‐the‐art weather hindcasts with downstream conjunctive use to transfer surplus flood releases to groundwater storage. Because available weather hindcasts are relatively short (10–20 years), we propose a novel statistical framework to develop synthetic forecasts over longer periods of the historical record. Operating rules are trained with a recently developed policy search framework in which decision rules are structured as binary trees. Policies are developed for a range of scenarios with varying forecast skill and conjunctive use capacity, using Folsom Reservoir, California, as a case study. Results suggest that the combination of conjunctive use and short‐term weather forecasts can substantially improve both water supply and flood control objectives by allowing storage to remain high until forecasts trigger a release. Further, increased conjunctive use capacity reduces the importance of forecast skill, since surface storage can be moved to groundwater during the flood season without losing water supply. This analysis serves the development of forecast‐based operating policies for large, multipurpose reservoirs in California and other regions with similar flood hydroclimatology.