Climate change implies changes in the frequency and magnitude of flood events. The influence of climate variability on flooding was evaluated by an analysis of sedimentary (palaeofloods) and documentary archives. A 500-year palaeoflood record at Montlleo River (657 km2 in catchment area), eastern Spain, revealed up to 31 palaeofloods with a range of discharges of 20–950 m3 s−1, and with at least five floods exceeding 740–950 m3 s−1. This information contrasts with the available gauged flood registers (since year 1971) with an annual maximum daily discharge of 129 m3 s−1. Our palaeoflood dataset indicates flood cluster episodes at (1) 1570–1620, (2) 1775–1795, (3) 1850–1890, and (4) 1920–1969. Flood rich periods 1 and 3 corresponded to cooler than usual (about 0.3 °C and 0.2 °C) climate oscillations, whereas 2 and 4 were characterised by higher inter-annual climatic variability (floods and droughts). This high inter-annual rainfall variability increased over the last 150 years, leading to a reduction of annual maximum flow. Flood quantiles (>50 years) calculated from palaeoflood+gauged data showed 30%–40% higher peak discharges than those using only instrumental records, whereas when increasing the catchment area (1500 km2) the discharge estimation variance decreased to ~15%. The results reflect the higher sensitivity of small catchments to changes on flood magnitude and frequency due to climate variability whereas a larger catchment buffers the response due to the limited extent of convective storms. Our findings show that extended flood records provide robust knowledge about hazardous flooding that can assist in the prioritization of low-regret actions for flood-risk adaptation to climate change.

中文翻译：

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地中海小集水区的极端洪水：对气候变率和变化的长期响应

气候变化意味着洪水事件频率和强度的变化。通过对沉积（古洪水）和文献档案的分析，评估了气候变化对洪水的影响。西班牙东部 Montlleo 河（集水区 657 平方公里）的 500 年古洪水记录显示多达 31 次古洪水，排放量范围为 20-950 m3 s-1，至少有 5 次洪水超过 740-950 m3 s-1。此信息与可用的测量洪水登记册（自 1971 年以来）形成对比，年最大日排放量为 129 m3 s-1。我们的古洪水数据集显示了 (1) 1570-1620、(2) 1775-1795、(3) 1850-1890 和 (4) 1920-1969 的洪水集群事件。洪水泛滥期 1 和 3 对应于比平时更冷（约 0.3 °C 和 0.2 °C）的气候振荡，而 2 和 4 的特点是年际气候变率较高（洪水和干旱）。在过去的 150 年中，这种年际降雨量的高变率有​​所增加，导致年度最大流量减少。根据古洪水+测量数据计算的洪水分位数（> 50 年）显示，峰值流量比仅使用仪器记录的流量高 30%–40%，而当增加集水区（1500 平方公里）时，流量估计方差降低到约 15%。结果反映了小流域对由于气候变异而引起的洪水量级和频率变化的更高敏感性，而较大的流域由于对流风暴的范围有限而缓冲了响应。