More flood disasters in New Zealand Graeme M. Smart and Alistair I. McKerchar

摘要

Most New Zealanders reside in coastal regions and many communities are situated on active floodplains. In the last decade there have been many storm events with rainfall annual exceedance probabilities of 1/150 or rarer and there have been many flood-related disasters. Insurance claim statistics suggest that the frequency of floods is increasing. Such statistics are a concern for local government authorities, insurance companies and populations in low-lying areas. Some underlying physical and hydrologic causes of the flood disasters are investigated. It is found that the present numbers of rare rainfall events are not unexpected and there does not appear to be any significant trend evident in the occurrence of river floods. For the areas studied, the river floods appear to cluster in certain decades. The clusters do not occur at the same time in different parts of the country and high rainfalls (required to cause floods) in the southwest of New Zealand are associated with El Nino conditions. Recently there has been more flooding in the north, which is where more of the population lives. The general increase in population has also seen more houses built in locations prone to flooding. Thus the increase in flood-related insurance claims is attributed to more floods in populated areas and to more people getting in the way of floods, rather than to any increase in the number of floods that have occurred. Wise regulation of future infrastructure development will be required to prevent more flood disasters in the years to come.