AbstractInland flood risk in the United States is most often conveyed through maps of 1% annual exceedance probability (AEP) or “100‐year” floodplains. However, monetary damages from flooding arise from a full distribution of events, including floods both larger and smaller than the 1% AEP event. Furthermore, floodplains are not static, since both the frequency and magnitude of flooding are likely to change in a warming climate. We explored the implications of a changing frequency and magnitude of flooding across a wide spectrum of flood events, using a sample of 376 watersheds in the United States where floodplains from multiple recurrence intervals have been mapped. Using an inventory of assets within these mapped floodplains, we first calculated expected annual damages (EADs) from flooding in each watershed under baseline climate conditions. We find that the EAD is typically a factor of 5–7 higher than the expected damages from 100‐year events alone and that much of these damages are attributable to floods smaller than the 1% AEP event. The EAD from flooding typically increases by 25–50% under a 1 °C warming scenario and in most regions more than double under a 3 °C warming scenario. Further increases in EAD are not as pronounced beyond 3 °C warming, suggesting that most of the projected increases in flood damages will have already occurred, for most regions of the country, by that time. Adaptations that protect against today's 100‐year flood will have increasing benefits in a warmer climate by also protecting against more frequent, smaller events.

中文翻译：

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预测美国河流洪水造成的年度预期损失的变化

摘要美国的内陆洪水风险通常通过 1% 年超标概率 (AEP) 或“100 年”洪泛区地图来传达。然而，洪水造成的金钱损失是由事件的完整分布引起的，包括大于和小于 1% AEP 事件的洪水。此外，洪泛区也不是静态的，因为随着气候变暖，洪水的频率和强度都可能发生变化。我们利用美国 376 个流域的样本，探索了各种洪水事件中洪水频率和强度变化的影响，其中已绘制了多个复发间隔的洪泛区地图。利用这些绘制的洪泛区内的资产清单，我们首先计算了基线气候条件下每个流域洪水造成的预期年度损失 (EAD)。我们发现，EAD 通常比 100 年事件的预期损失高出 5-7 倍，而且这些损失大部分可归因于小于 1% AEP 事件的洪水。在升温 1°C 的情况下，洪水造成的 EAD 通常会增加 25-50%，在大多数地区，在升温 3°C 的情况下，洪水造成的 EAD 会增加一倍以上。升温超过 3°C 后，EAD 的进一步增加并不那么明显，这表明到那时，对于该国大部分地区来说，预计的洪水损失增加大部分已经发生。在气候变暖的情况下，针对今天的一百年一遇的洪水采取的适应性措施也将通过防范更频繁、更小规模的洪水而带来更大的好处。