Identification of a change in climate state using regional flood data

摘要

Flood frequency analysis typically assumesthat annual floods arise from a single distribution and are independent.However, there is significant evidence for the existence of persistent climatemodes. Timescales associated with climate variability range from inter-annualthrough to longer, multi-decadal time scales. In the case of the Australianclimate, previous studies of the Indian and Pacific Oceans have indicated markedmulti-decadal variability in both mean Sea Surface Temperatures (SST) andtypical circulation patterns. In this light, data from 40 stream gauges aroundNew South Wales are examined to determine whether flood frequency data areindeed independent and distributed identically. Given likely correlation inflood records between gauges, an assessment of the regional significance ofobserved changes in flood frequency is required. To achieve this, floodobservations are aggregated into a regional index. A simple non-parametric testis then employed to identify the timing and magnitude of any change in meanannual flood. Finally, it is shown that the identified change in flood frequencycorresponds directly to an observed shift in SST and mean circulation. Theseresults demonstrate the role of natural variability in climate parameters andthe need for an improved conceptual framework for flood frequency estimation. style="line-height: 20px;">Keywords: Floods, flood frequency, climate variability, IPO, PDO, climate change