Flooding is assessed as the most important natural hazard in Europe, causing thousands of deaths, affecting millions of people and accounting for large economic losses in the past decade. Little is known about the damage processes associated with extreme rainfall in cities, due to a lack of accurate, comparable and consistent damage data. The objective of this study is to investigate the impacts of extreme rainfall on residential buildings and how affected households coped with these impacts in terms of precautionary and emergency actions. Analyses are based on a unique dataset of damage characteristics and a wide range of potential damage explaining variables at the household level, collected through computer-aided telephone interviews (CATI) and an online survey. Exploratory data analyses based on a total of 859 completed questionnaires in the cities of Münster (Germany) and Amsterdam (the Netherlands) revealed that the uptake of emergency measures is related to characteristics of the hazardous event. In case of high water levels, more efforts are made to reduce damage, while emergency response that aims to prevent damage is less likely to be effective. The difference in magnitude of the events in Münster and Amsterdam, in terms of rainfall intensity and water depth, is probably also the most important cause for the differences between the cities in terms of the suffered financial losses. Factors that significantly contributed to damage in at least one of the case studies are water contamination, the presence of a basement in the building and people's awareness of the upcoming event. Moreover, this study confirms conclusions by previous studies that people's experience with damaging events positively correlates with precautionary behaviour. For improving future damage data acquisition, we recommend the inclusion of cell phones in a CATI survey to avoid biased sampling towards certain age groups. ... Read more

Pluvial floods have caused severe damages to urban dwellings in Europe and elsewhere in recent years. With a predicted increase in extreme weather events as well as an ongoing urbanization, pluvial flood damage is expected to increase in the future. These type of flood events, caused by stormwater being unable to enter urban drainage systems or flowing out of urban drainage systems when capacity is exceeded, often happen with little warning and in areas which are often not obviously prone to flooding. Up to now little research was done on the adverse consequences of pluvial floods, as empirical damage data of pluvial flooding is scarce. In this study, results of two telephone surveys are discussed. The surveys comprise interviews with more than 500 flood-affected households in Germany (Münster and Greven) and the Netherlands (Amsterdam), related to the severe rain event of July 28th 2014. Respondents were asked a series of questions about the damage to their building structure and contents, as well as on topics such as early warning, emergency and precautionary measures, building properties and hazard characteristics. The questionnaire was developed with the aim to create a harmonized transnational pluvial flood damage survey that can potentially be extended to other European countries. New indicator variables have been developed to account for different national and regional standards in building structure, early warning, socio-economic data and recovery. The survey data from the German and Dutch case studies are compared with the goal to identify similarities and differences in damage reducing factors and recovery. Water level data and other hazard characteristics are used to form comparable groups out of the German and Dutch sample. Within these groups, regional distinctions in building topology and use are expected to have the strongest impact on differences between reported damage amounts of the two case studies. The newly collected data will be used in future studies to develop pluvial flood damage models. ... Read more

In het Impactproject ‘Samen met verzekeraars naar een regenbestendige stad’ hebben we de werelden van een verzekeraar, onderzoeker en gemeente/waterbeheerder bij elkaar gebracht. Amsterdam Rainproof, Waternet, Achmea en TU Delft zijn de samenwerking aangegaan om de impact van extreme regenval op bewoners in Amsterdam te analyseren en te verkennen hoe hierop te anticiperen om zo de waterschade te verminderen en het woongenot te vergroten. Het vertrekpunt van het Impactproject is de wateroverlast en schade die inwoners van Amsterdam, waaronder de klanten van Achmea, ondervonden als gevolg van extreme regenval. We willen hierbij in eerste instantie de manieren inzichtelijk maken waarop eigenaren van woningen, huurders, verzekeraars en Waternet alleen en in samenhang met elkaar kunnen anticiperen op een wolkbreuk om waterschade te verminderen. In tweede instantie willen we de werkwijze verbeteren waarmee betrokken organisaties informatie over schade inwinnen en delen. We hebben de schade van de wolkbreuk van 28 juli 2014 onderzocht door middel van een analyse van bestaande verzekeringsdata van Achmea verrijkt met andere openbare data, en meldingen van wateroverlast bij Waternet, de gemeente Amsterdam en de Brandweer. Daarnaast hebben we door middel van een bewonersenquête in Oud-Zuid en Oud-West gekeken naar de factoren die bijdragen aan waterschade en naar de werkelijk ervaren schade. Deze onderzoeken geven een beeld van de wateroverlast en schade die optreedt tijdens en na een wolkbreuk, en inzicht in de effectieve voorzorgsmaatregelen die genomen kunnen worden om schade te verminderen. Om de persoonsgegevens van alle betrokken bewoners in het onderzoeksgebied te beschermen hebben we gezorgd dat bij de aanpak van de onderzoeken informatie van verschillende bronnen (verzekeringsdata, meldingen bij Waternet) niet te combineren is op adresniveau, maar slechts op 6-cijferig postcode niveau. Individuele resultaten van de bewoners enquête heeft de TU Delft niet onderling gedeeld met Waternet en Achmea. In dit rapport zijn alleen geaggregeerde resultaten van de bewonersenquête terug te vinden; zonder verwijzing naar een individueel adres of persoon. ... Read more

The objective of this study was to identify the main failure mechanisms behind water-related building damage and to investigate to what extent these processes are related to characteristics of buildings and rainfall events. Results are based on the mining of property level insurance damage data, for a case study in Rotterdam, the Netherlands. This study has found that most frequent causes of water-related damage relate to roof leakages (28%), bursts of household water supply pipes (19%) and blocked household wastewater systems (18%). Cases of sewer flooding or depression filling were less present (2.4% and 0.6%), but showed stronger correlations with heavy rainfall events than any other failure mechanism. Classification tree analysis revealed that water discharges from neighbours is the main damage cause for high-rise buildings on days with no or minor rainfall (< 7.5 mm/h). Moreover, damage due to blocked household wastewater systems is associated with low-rise buildings younger than 50 years. ... Read more