CORRELATION BETWEEN EXTREME RAINFALL AND INSURANCE CLAIMS DUE TO URBAN FLOODING – CASE STUDY FREDRIKSTAD, NORWAY

摘要

During the last decades an increase in extreme rainfall has led to more urban flooding.This study is based on insurance claims of damages caused by heavy rain during2006?2012 in Fredrikstad, Norway. Data are analysed using Principal ComponentAnalysis. The purpose has been to find characteristics of extreme rainfall and itsinfluence on the extent of urban flooding. The number of claims seems to be peaked inthe late summer period. Furthermore, the precipitation depth the week before anextreme rainfall seems to have significantly influence for the pay out from insurers, andthus the changing in runoff factor due to soil wetness is of importance. Compared to25-year frequency rainfall with 30 min duration, relatively less intensive, but morestable and long-lasting rain seems to lead to more claims. Experiences from previousevents may help to determine the level of flood risk when extreme rainfall is forecasted.