Trends in flood losses in Europe over the past 150 years

Abstract

Adverse consequences of floods change in time and are influenced by both natural and socio-economic trends and interactions. In Europe, previous studies of historical flood losses corrected for demographic and economic growth ('normalized') have been limited in temporal and spatial extent, leading to an incomplete representation of trends in losses over time. Here we utilize a gridded reconstruction of flood exposure in 37 European countries and a new database of damaging floods since 1870. Our results indicate that, after correcting for changes in flood exposure, there has been an increase in annually inundated area and number of persons affected since 1870, contrasted by a substantial decrease in flood fatalities. For more recent decades we also found a considerable decline in financial losses per year. We estimate, however, that there is large underreporting of smaller floods beyond most recent years, and show that underreporting has a substantial impact on observed trends.

Fig. 1

Trends in flood exposure. Percent of the population exposed to the 100-year river and coastal flood in Europe (a), including short-term projection to year 2020, and change in population exposed (b), in percentage points, to the 100-year flood (either river or coastal) in each country (1870–2016). Source of data: HANZE database with country borders from PBL

Fig. 2

Flood occurrences and fatalities. Total number of flood events and fatalities (unadjusted, reported values) between 1870 and 2016, a by month and b by country. Source of data: HANZE database with country borders from PBL

Fig. 3

Trends in flood losses per year. Comparison of unadjusted, reported values (dark colors) and normalized values, i.e., adjusted to 2011 levels of exposure (lighter colors), for a number of events; b area inundated; c fatalities; d persons affected; e financial value of losses with normalization by GDP; and f financial value of losses with normalization by wealth

Fig. 4

Trends in normalized flood losses per year. Comparison of losses with (lighter colors) and without gap-filling (dark colors) for a area inundated; b fatalities; c persons affected; d financial value of losses with normalization by GDP; and e financial value of losses with normalization by wealth

Fig. 5

Severity of floods. Annual number of flood events classified by severity into quintiles. Classification is based on normalized and gap-filled values of losses

Fig. 6

Flood losses in 30-year periods. Reported number of flood events and their consequences is summed per 30-year periods, with three types of adjustments: normalization, gap-filling of missing (normalized) loss data and estimation of underreporting of small flood events and normalized damages they caused, for a number of events; b area inundated; c fatalities; d persons affected; e financial value of losses with normalization by GDP; and f financial value of losses with normalization by wealth

Fig. 7

Validation of flood trends. a Trends in population and fixed assets living within 100-year flood hazard zone in England, using Environment Agency (EA) flood risk map and RAIN project map used in this study. b estimated persons affected (normalized) in England, compiled by intersecting EA historical flood outlines with HANZE-Exposure population grid, and compared with normalized reported persons affected from HANZE-Events. The trends were calculated using Poisson regression