Correlation between extreme rainfall and insurance claims due to urban flooding – case study Fredrikstad, Norway

Abstract

Abstract: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 during 2006−2012 in Fredrikstad, Norway. Data are analysed using Principal Component Analysis. The purpose has been to find characteristics of extreme rainfall and its influence on the extent of urban flooding. The number of claims seems to be peaked in the late summer period. Furthermore, the precipitation depth the week before an extreme rainfall seems to have significantly influence for the pay out from insurers, and thus the changing in runoff factor due to soil wetness is of importance. Compared to 25-year frequency rainfall with 30 min duration, relatively less intensive, but more stable and long-lasting rain seems to lead to more claims. Experiences from previous events may help to determine the level of flood risk when extreme rainfall is forecasted.

The relationship between precipitation and insurance data for floods in a Mediterranean region (northeast Spain)

“…Also our findings align with the results of previous studies (Spekkers et al, 2013;Zhou et al, 2013;Wobus et al, 2014;Torgersen et al, 2015) and further indicate that insurance databases are a promising source for flood damage assessment at local (Garrote et al, 2016;Le Bihan et al, 2017;Zischg et al, 2018;Zhou et al, 2013) and at regional scale (Barredo et al, 2012;Kim et al, 2012;Wobus et al, 2014;Zhou et al, 2017).…”

“…Linear regression has shown that 30 min precipitation is linked more closely with damages than 24 h precipitation, and also the logistic regression models present better results in terms of RA for the urban area considering higher-resolution data, with values higher than 0.8 in all cases. Therefore, we have been able to confirm that 30 min rainfall is a better predictor of the probability of large damages than daily rainfall in urban areas, and this result confirms previous studies such as that of Torgersen et al (2015), who found a significant relationship between insurance data and short-lasting rainfall when studying urban floods in Norway. In addition, Spekkers et al (2013) showed that high claim numbers associated with private property and content damage were significantly related to maximum rainfall intensity, based on a logistic regression, with rainfall intensity for 10 min to 4 h time windows.…”

The impact of intense rainfall on insurance losses in two Swedish cities

“…This study demonstrates a strong relationship between rainfall intensity and occurrence of insured flood losses in two Swedish cities during the summer months 2001–2015 and our findings confirm the results of several previous papers for example (Spekkers et al, ; Torgersen et al, ; Van Ootegem et al, ). We investigated the importance of sub‐daily and sub‐hourly rainfall intensity and found that the variable that had most influence on the number and the amount of insurance damages were maximum hourly rainfall amount each day.…”

“…Generally speaking, it seems to be considerable amounts of rainfall under a 60 min interval in combination with short periods of high‐intense precipitation that generate insurance damages. Only a few studies have previously been done in this field on sub‐hourly rainfall (Torgersen et al (); Sörensen and Mobini ().…”

“…Torgersen, Bjerkholt, Kvaal, and Lindholm () used insurance data and precipitation gauge data to analyse the relationship between extreme rainfall and insured flood damage for the period 2006–2012 in the city of Fredrikstad in south east Norway. The authors found a distinct peak of the a damage amount during the late summer months and the results further indicated that several hours of intense rainfall caused more damage than shorter, extreme rainfall events.…”