Spatial Bias in Medium-Range Forecasts of Heavy Precipitation in the Sacramento River Basin: Implications for Water Management
Spatial Bias in Medium-Range Forecasts of Heavy Precipitation in the Sacramento River Basin: Implications for Water Management
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DOI：
10.1175/jhm-d-19-0226.1
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发表时间：
2020-07
影响因子：
3.8
通讯作者：
Z. Brodeur;S. Steinschneider
中科院分区：
文献类型：
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作者：
Z. Brodeur;S. Steinschneider
大气河流（AR）带来的强降水预报对于加州水库的防洪和供水管理变得越来越重要。本研究探讨的假设，中期预测的强降水在流域尺度表现出经常性的空间偏差，驱动相关的AR事件的中尺度和天气尺度特征。使用1984年至2019年的36年NCEP中期再预报，对萨克拉门托河流域的强降水事件进行了假设检验。对于每一个事件，我们集群降水预报误差在北美西部的提前时间范围从1到15天。综合水汽输送（IVT），500百帕位势高度，和登陆特性的AR的合成跨集群和前置时间诊断降水预报偏差的原因。我们调查的时间演变的预测误差，以表征其持续性在整个前置时间，并探讨预测IVT异常的准确性在不同领域的北美西海岸在强降水事件在萨克拉门托盆地。我们的研究结果确定了降水预报误差与预报天气尺度特征误差一致的经常性空间模式，特别是在长时间（5-15天）的领先地位。此外，我们发现的证据表明，AR登陆的预测远远超出了萨克拉门托盆地的纬度界限之前，在盆地内的强降水事件。这些结果表明，在设计预测型水库运行时，有可能使用太平洋-北美地区大尺度气候特征的中期预测，而不仅仅是流域尺度降水的局部预测。
Forecasts of heavy precipitation delivered by atmospheric rivers (ARs) are becoming increasingly important for both flood control and water supply management in reservoirs across California. This study examines the hypothesis that medium-range forecasts of heavy precipitation at the basin scale exhibit recurrent spatial biases that are driven by mesoscale and synoptic-scale features of associated AR events. This hypothesis is tested for heavy precipitation events in the Sacramento River basin using 36 years of NCEP medium-range reforecasts from 1984 to 2019. For each event we cluster precipitation forecast error across western North America for lead times ranging from 1 to 15 days. Integrated vapor transport (IVT), 500-hPa geopotential heights, and landfall characteristics of ARs are composited across clusters and lead times to diagnose the causes of precipitation forecast biases. We investigate the temporal evolution of forecast error to characterize its persistence across lead times, and explore the accuracy of forecasted IVT anomalies across different domains of the North American west coast during heavy precipitation events in the Sacramento basin. Our results identify recurrent spatial patterns of precipitation forecast error consistent with errors of forecasted synoptic-scale features, especially at long (5–15 days) leads. Moreover, we find evidence that forecasts of AR landfalls well outside of the latitudinal bounds of the Sacramento basin precede heavy precipitation events within the basin. These results suggest the potential for using medium-range forecasts of large-scale climate features across the Pacific–North American sector, rather than just local forecasts of basin-scale precipitation, when designing forecast-informed reservoir operations.