Accurate estimation of design floods is necessary for developing effective flood‐management strategies. Climate change (CC) studies on floods generally consider alterations in mean runoff using ensembles compared to a base period. In this study, we examined the plausibility and implications of applying individual climate model‐generated flows versus their ensembles to estimate peak floods (magnitude and timing of occurrence), using Budhigandaki River Basin of Nepal as a case study. Annual maximum one‐day floods were derived for four future climate scenario projections (cold‐dry, cold‐wet, warm‐wet, and warm‐dry) from simulated daily flow series. Future floods of six return periods estimated for the individual climate scenarios were compared with their “Ensemble” (combiner for the ensemble series is the arithmetic mean of daily floods), “Average,” and ‘Baseline.” Results showed that magnitudes of the flood peaks are such that those estimated using “Ensemble” < “Average” < individual series. We conclude that ensemble series should not be used for flood estimation because of the averaging effect. Designers should consider at the least the “Average” instead of the “Ensemble” series while designing climate‐resilient flood structures. Furthermore, the occurrences of flood peaks are likely to be confined within the monsoon season for the “Ensemble” but spread out in the other months for the individual climate scenarios. This could have direct implications on the availability and mobilization of resources as well as the need for a year‐round operational early warning system for flood risk management.

中文翻译：

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质疑在未来峰值洪水预测中使用集合与单独气候模型产生的流量：合理性和影响

准确估计设计洪水对于制定有效的洪水管理策略是必要的。关于洪水的气候变化（CC）研究通常考虑使用集合与基期相比平均径流的变化。在本研究中，我们以尼泊尔布迪甘达基河流域为案例研究，研究了应用单个气候模型生成的流量与其集合来估计洪峰（发生的强度和时间）的合理性和影响。针对四种未来气候情景预测得出了年度最大单日洪水（冷干,冷湿,温湿型， 和暖干）来自模拟每日流量系列。将针对各个气候情景估计的六个重现期的未来洪水与其“整体”（整体系列的组合是每日洪水的算术平均值）、“平均值”和“基线”进行比较。结果表明，洪峰的震级是使用“整体”<“平均”<单个序列估计的。我们得出的结论是，由于平均效应，集合序列不应用于洪水估计。设计师在设计耐气候洪水结构时至少应考虑“平均”系列，而不是“整体”系列。此外，对于“整体”来说，洪峰的出现可能仅限于季风季节，但对于个别气候情景来说，洪峰的出现可能会分散在其他月份。这可能对资源的可用性和调动以及洪水风险管理全年运行预警系统的需求产生直接影响。