Heavy rainfall: An underestimated environmental risk for buildings?

Abstract

Abstract. Although impacts of heavy rain on buildings in urban areas are often extensive, the public usually underestimates the negative consequences of that environmental risk compared e.g. to storm or hail events. However, the intensification of extreme weather events due to climate change as well as the rising physical vulnerability of assets are going to trigger the increase of impacts on the built environment. Heavy rain events are often highly localised that makes it difficult to estimate their probability and magnitude accurately. High intensity rain affects buildings both directly as well as indirectly.First, engineering surveys have already proven the broad variety and high physical vulnerability of building constructions that are directly and frequently affected by invading water during heavy rainfall events: flat roofs, roof terraces and balconies, connections between steep roofs and other building parts, soil-covered slabs of underground parking, soil-contacted basement walls and bottom plates as well as windows and external doors. It became evident that most damage is avoidable if exposed constructions become more resilient. Nevertheless, any adaptations require expertise on the demanding damage processes in order to explore deficiencies and to reduce physical vulnerability of building constructions exposed to heavy rainfall. In response to that challenge, the paper describes an engineering approach for the systematic classification of physical vulnerability criteria based on empirical research. A developed classification scheme allows the ex-ante examination of typical failure modes and the evaluation of negative consequences of heavy rainfall at individual building level. The topic is of high relevance, because the classification scheme may act as a capable tool for the prospective planning of adaptations towards more resilient buildings.Second, heavy rain may result in urban pluvial flooding due to sewer overflow that cause severe damage to buildings. A comprehensive study of the impacts and the consequences in Dresden (Germany), presented in the paper, revealed that the potential risks of flooding from sewers due to hydraulic overload can be estimated on building scale using the model approach IVART (Integrated Spatial Vulnerability and Risk Assessment Tool). Modelling results provide the basis to quantify the effectiveness and efficiency of flood resilience technologies.

Hydrological impacts of climate change on small ungauged catchments – results from a global climate model–regional climate model–hydrologic model chain

“…Floods in the western part of Norway (where Bergen is located) are mainly caused by heavy rainfall during the autumn season (Roald, 2008). The Norwegian Center for Climate Services report pointed out that rainfall-dominated floods are projected to increase by almost 60 % (with RCP8.5 scenario) towards the end of the century, and more frequent and stronger intense rainfall events may in the future present special challenges in small, steep rivers being fed by small upland catchments (Hanssen-Bauer et al, 2015). Vormoor et al (2015) found that autumn-winter events will become more frequent by 2099, which will lead to an intensification of the current autumn-winter flood regime for the coastal catchments in Norway.…”

“…statenskartverk.no/ (last access: 29 August 2019). The definition of small rural catchments is based on the report by Fleig and Wilson (2013) applying an upper area limit of 50 km 2 . The catchments were selected for this impact study because there are critical infrastructures (e.g., culverts, bridges, and buildings) at the outlet of the catchments which could be damaged by floods in the future period (2070-2100).…”

“…To assess the magnitude of a flood with a given probability, the flood frequency methods must be applied. A flood frequency analysis is important for flood hazard mapping, for which a flood of a certain return period (e.g., 200 years in Norway) is used for the flood zone mapping (Groen et al, 2012). To analyze changes in the magnitudes of a flood with a given return period (e.g., 200-year flood), flood frequency analysis is applied to the annual maximum series of the reference (1981-2011) and future period (2070-2100).…”

“…way, the average annual temperature and precipitation are expected to increase by 3.8 to 6.2 • C and 7 % to 27 %, respectively, by the end of the century using the RCP8.5 scenario (Hanssen-Bauer et al, 2015). The largest increase in precipitation is mostly expected during the autumn and winter months, which will in turn impact the magnitude and in some cases the seasonality of flood peaks.…”

“…These types of flood events are usually short in duration, but they are usually connected with severe damage (Menzel et al, 2006). Studies show that the probability and magnitude of hazardous heavyprecipitation events have been increasing in several European regions (e.g., Golz et al, 2016). Heavy localized precipitation could be caused by low-pressure systems (e.g., western Norway; Azad and Sorteberg, 2017) or by prevailing convective precipitation at hilly or mountainous areas.…”