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Using ensemble reforecasts to generate flood thresholds for improved global flood forecasting
Journal of Flood Risk Management ( IF 4.1 ) Pub Date : 2020-08-27 , DOI: 10.1111/jfr3.12658
Ervin Zsoter 1, 2 , Christel Prudhomme 1, 3, 4 , Elisabeth Stephens 2 , Florian Pappenberger 1 , Hannah Cloke 2, 5, 6, 7
Affiliation  

Global flood forecasting systems rely on predefining flood thresholds to highlight potential upcoming flood events. Existing methods for flood threshold definition are often based on reanalysis datasets using a single threshold across all forecast lead times, such as in the Global Flood Awareness System. This leads to inconsistencies between how the extreme flood events are represented in the flood thresholds and the ensemble forecasts. This paper explores the potential benefits of using river flow ensemble reforecasts to generate flood thresholds that can deliver improved reliability and skill, increasing the confidence in the forecasts for humanitarian and civil protection partners. The choice of dataset and methods used to sample annual maxima in the threshold computation, both for reanalysis and reforecast, is analysed in terms of threshold magnitude, forecast reliability, and skill for different flood severity levels and lead times. The variability of threshold magnitudes, when estimated from the different annual maxima samples, can be extremely large, as can the subsequent impact on forecast skill. Reanalysis‐based thresholds should only be used for the first few days, after which ensemble‐reforecast‐based thresholds, that vary with forecast lead time and can account for the forecast bias trends, provide more reliable and skilful flood forecasts.

中文翻译:

使用整体重预报生成洪水阈值,以改善全球洪水预报

全球洪水预报系统依靠预定义洪水阈值来突出潜在的即将发生的洪水事件。现有的洪水阈值定义方法通常基于在所有预测提前期上使用单个阈值的重新分析数据集,例如在全球洪水意识系统中。这导致在洪水阈值中如何表示极端洪水事件与整体预报之间存在不一致。本文探讨了使用河流流量整体预报产生洪水阈值的潜在好处,这些阈值可以提供更高的可靠性和技能,从而增加了对人道主义和民防合作伙伴预测的信心。选择用于阈值计算中的年度最大值的数据集和方法,用于重新分析和重新预测,根据阈值大小,预测的可靠性以及针对不同洪灾严重程度级别和交付时间的技能进行了分析。从不同的年度最大值样本进行估算时,阈值幅度的变异性可能会非常大,随后对预测技能的影响也会如此。基于重新分析的阈值仅应在前几天使用,此后,基于集合预测的阈值会随预测提前期而变化,并且可以解释预测偏差趋势,从而提供更加可靠和熟练的洪水预测。
更新日期:2020-08-27
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