The challenge of unprecedented floods and droughts in risk management

Risk management has reduced vulnerability to floods and droughts globally1,2, yet their impacts are still increasing3. An improved understanding of the causes of changing impacts is therefore needed, but has been hampered by a lack of empirical data4,5. On the basis of a global dataset of 45 pairs of events that occurred within the same area, we show that risk management generally reduces the impacts of floods and droughts but faces difficulties in reducing the impacts of unprecedented events of a magnitude not previously experienced. If the second event was much more hazardous than the first, its impact was almost always higher. This is because management was not designed to deal with such extreme events: for example, they exceeded the design levels of levees and reservoirs. In two success stories, the impact of the second, more hazardous, event was lower, as a result of improved risk management governance and high investment in integrated management. The observed difficulty of managing unprecedented events is alarming, given that more extreme hydrological events are projected owing to climate change3

Panta Rhei benchmark dataset: socio-hydrological data of paired events of floods and droughts

As the adverse impacts of hydrological extremes increase in many regions of the world, a better understanding of the drivers of changes in risk and impacts is essential for effective flood and drought risk management and climate adaptation. However, there is currently a lack of comprehensive, empirical data about the processes, interactions and feedbacks in complex human-water systems leading to flood and drought impacts. Here we present a benchmark dataset containing socio-hydrological data of paired events, i.e., two floods or two droughts that occurred in the same area. The 45 paired events occurred in 42 different study areas and cover a wide range of socio-economic and hydro-climatic conditions. The dataset is unique in covering both floods and droughts, in the number of cases assessed, and in the quantity of socio-hydrological data. The benchmark dataset comprises: 1) detailed review style reports about the events and key processes between the two events of a pair; 2) the key data table containing variables that assess the indicators which characterise management shortcomings, hazard, exposure, vulnerability and impacts of all events; 3) a table of the indicators-of-change that indicate the differences between the first and second event of a pair. The advantages of the dataset are that it enables comparative analyses across all the paired events based on the indicators-of-change and allows for detailed context- and location-specific assessments based on the extensive data and reports of the individual study areas. The dataset can be used by the scientific community for exploratory data analyses e.g. focused on causal links between risk management, changes in hazard, exposure and vulnerability and flood or drought impacts. The data can also be used for the development, calibration and validation of socio-hydrological models. The dataset is available to the public through the GFZ Data Services (Kreibich et al. 2023, link for review: https://dataservices.gfz-potsdam.de/panmetaworks/review/923c14519deb04f83815ce108b48dd2581d57b90ce069bec9c948361028b8c85/).</p

Just or Unjust : Assessment of rainfall-related flood damage in a Swedish context

Climate change has led to an increase in heavy summer rainfalls, and climate projections for Sweden indicate that there will be more sudden rainfall in the future. While the exact locations and time for this rainfall are unknown, it is known that there will be damages to buildings, cars, and people when the rainfall occurs. It is thus important to evaluate past events to understand the resulting flood damage, with an emphasis on the people who suffer from it, and the procedures for damage claims. Moreover, with more and more people living in cites, there is also an increasing diversity in the socioeconomic conditions that determine residents’ capacity to manage losses.This thesis examines flood damage claims for 1992-2019 in Malmö, Sweden in detail, including the extreme cloudburst event on 31 August 2014. In terms of population, Malmö is Sweden’s third largest city, and historically, there have been recurring problems with rainfall-related flooding there. The socioeconomic conditions of Malmö’s residents are diverse, making it an interesting and important case for the study of urban flood damage management. This requires an analysis of both the technical aspects of the flooding process and of how different groups are affected. Key aspects for evaluating this in this thesis are residents’ coping capacity for flood damage costs; how damage claims compensation is handled; and an evaluation of equity in flood damage management.The majority of homeowners in Sweden have home insurance, and there is no separate flood insurance. Therefore, some part of the damage cost is usually covered by the insurance company, but homeowners' losses also comprise their deductible portion as well as the reductions that are not covered by the insurance companies. The impact of these costs on residents will differ based on the resident’s socioeconomic conditions. This thesis investigates the effect of income, education, and immigration status on flood vulnerability in different neighbourhoods in Malmö. A main result is that flood damage costs are higher in low-income neighbourhoods in which there are high rates of immigrants and lower levels of education.A natural and technical explanation for the differences in outcome between residents lies in what causes flood damage and why some areas are more prone to flood damage. One main risk factor is the difference between combined and separated sewer system connections. Houses connected to a combined sewer system are at a higher risk of basement flooding each time the rainfall exceeds the capacity of the sewer pipe. The results showed that, historically, there are more and repeated flood damage claims for houses connected to combined than separated sewer systems. It was also found that a higher percentage of homes connected to separated sewer systems received compensation compared to homes connected to combined systems.The current legal practice in Sweden entails that the water and wastewater utility must assume full responsibility for homes in which basements have been flooded via sewer overflow and that are connected to separated sewer systems. On the other hand, the water and wastewater utility has only a partial responsibility for homes connected to combined sewer systems; in these cases, the municipality must investigate the capacity of the pipeline in question to decide where the responsibility lies. This explains why there was a high percentage of rejected flood damage claims in this category during the August 2014 event. Ironically however, all houses connected to combined sewer systems are at greater risk of flooding, as the system collects both rainfall and wastewater. This means that people in areas with combined sewer systems are both more exposed to flood damage and not compensated to the same degree for their damage claims as people whose houses are connected to separate sewer systems.Based on the results, the equity of damage compensation from the water and wastewater utility in the Swedish system is questioned. Why is flood damage liability based on the type of sewer system, and why does the system favour owners of buildings that already have a lower risk of flooding? The results in this thesis show that there is a need for an assessment of inequities in the Swedish urban flood management system under the present laws and regulations. The next step should be to investigate how support can be strengthened for those who suffer the most from flood damage. There are many potential systems for dealing with compensation to houseowners that are affected by urban flooding. Irrespective of the compensation system, it is important to consider the consequences on different groups and use that information to develop systems based on a perspective of justice

Pluvial, urban flood mechanisms and characteristics – Assessment based on insurance claims

Pluvial flooding is a problem in many cities and for city planning purpose the mechanisms behind pluvial flooding are of interest. Previous studies seldom use insurance claim data to analyse city scale characteristics that lead to flooding. In the present study, two long time series (∼20 years) of flood claims from property owners have been collected and analysed in detail to investigate the mechanisms and characteristics leading to urban flooding. The flood claim data come from the municipal water utility company and property owners with insurance that covers property loss from overland flooding, groundwater intrusion through basement walls and flooding from the drainage system. These data are used as a proxy for flood severity for several events in the Swedish city of Malmö. It is discussed which rainfall characteristics give most flooding and why some rainfall events do not lead to severe flooding, how city scale topography and sewerage system type influence spatial distribution of flood claims, and which impact high sea level has on flooding in Malmö. Three severe flood events are described in detail and compared with a number of smaller flood events. It was found that the main mechanisms and characteristics of flood extent and its spatial distribution in Malmö are intensity and spatial distribution of rainfall, distance to the main sewer system as well as overland flow paths, and type of drainage system, while high sea level has little impact on the flood extent. Finally, measures that could be taken to lower the flood risk in Malmö, and other cities with similar characteristics, are discussed

Urban flood damage claim analyses for improved flood damage assessment

Urban flood damage leads to major costs for private house owners, insurance companies, and water and wastewater utilities. Analysis of flood damage claims can be used to improve the understanding of the details of flood damage characteristics and reasons for drainage system failures. However, few studies have used data of this kind to investigate urban flood characteristics. We examined 3113 damage claim cases over 30 years (1992–2019) for the city of Malmö, Sweden. We quantified the distribution and frequency of both major and minor flood damages over this period. Our analysis showed that most floods occur in August, but we could not find any significant trend in the count of damage claims between 1992 till 2019. The main drivers of flood damages were rainfall and failure mechanisms in the drainage system. In total, 24.5% of properties suffered from repeated flood damages, 44% originating from combined sewer system connection and 17% from the separated sewer system. This highlights the importance of sewer system types in flood damage claims. In addition, there was an uneven claim count between insurance companies and owners per event. About 42% of insurance company claims were not accompanied by the owner's deductible claims. Our results highlight the need to further investigate the reason behind this difference and ways for better future planning to minimize the damage from flood events

Systemic Inequity in Urban Flood Exposure and Damage Compensation

Urban flooding is a growing concern in Northern Europe. While all countries in this region invest substantial resources into urban flood risk management, all property owners have unequal opportunity to have their flood risk managed. This paper presents the notion of equity in the urban flood risk management, focusing on urban flood exposure and compensation after sewage surcharge on the 31 August 2014 cloudburst over Malmö in Sweden. All damage claims and the procedures assessing them were analysed based on the type of sewer system (combined or separated) that affected the properties. The results demonstrated considerable systemic inequity in both flood exposure and damage compensation. The owners of properties connected to combined systems were four times more likely to make a damage claim, while having their damage claims approved just over half as often, compared with owners of properties connected to separated sewage systems. Considering the multifaceted nature of both inequities and their possible resolution, current praxis is not sufficient for the management of future urban drainage systems; not only concerning changing climatic conditions but also concerning social condition

Resource Decline in Higher Education – Perceptions and Consequences

Teaching students is one of the main tasks of LTH, as thousands of students engage on their engineering studies at the faculty every year. The funding for teaching these students is an essential source of income for LTH, but in recent years there has been an increased worry for diminishing financing for lecturing at the faculty.This study aims to investigate how lecturers perceive the development and what practical measures they have taken in their courses to counteract it. Interviews with ten lecturers at the department of Building and Environmental technology were performed. Many different practical strategies for dealing with the situation were documented during the interviews. The strategies are mainly focusing on making the students do more of the work on their own, e.g. working with the course literature. But the approaches to the problem varied greatly, as some lecturers tried to change as little as possible in order to save time, and others who saw a need for restructuring the entire educational program

Analysis of pluvial flood damage costs in residential buildings : A case study in Malmö

Pluvial flood damage to residential buildings causes a significant part of direct tangible flood losses. In this study, we investigate the non-hazard variables and sewer system types in relation to damage costs in the city of Malmö, Sweden. A comprehensive data set of around 1000 records of direct damage to residential buildings from a cloudburst event on 31 August 2014 in Malmö, Sweden has been analysed at property scale with no lumping together of data. The results show that properties connected to combined sewer systems are much more exposed to pluvial flood damage than properties connected to separated sewer systems, with the ratio of the number of claims being close to three. The analysis of building-specific variables shows no clear statistical relationships to the damage costs. To further the understanding of damage costs caused by urban pluvial flooding, it is necessary to extend the group of explanatory variables to include information about the socio-economic background of households, the actual value of assets in basements and the precautionary measures taken by house owners

Natural hazard insurance outcomes at national, regional and local scales : A comparison between Sweden and Portugal

This study addresses the role of natural hazard insurance in two European countries with different insurance markets and socioeconomic conditions: Sweden and Portugal. The analyses were conducted at the national, regional (Southern Sweden and Lisbon Metropolitan Area - LMA), and local (Malmö and Lisbon cities) scales. Most damage caused by weather and climate-related (WCR) hazards during the 1980-2019 period was not covered by insurance companies in Sweden (71%) and Portugal (91%). An insurance affordability analysis was performed using income for the national and regional scales. Unaffordability is higher in Southern Sweden than in LMA, implying that better socioeconomic conditions do not necessarily mean a higher average capacity to pay for insurance. At the local scale, urban flooding was analysed for Malmö (1996-2019) and Lisbon (2000-2011) using insurance databases, in which the most relevant 21st century rainfall events for each city are included (2014 and 2008, respectively). The influence of terrain features on flooding claims and payouts was determined using Geographic Information Systems (GIS) spatial analyses. The flat Malmö favours ponding and extensive flooding, while the distance to the drainage network and flow accumulation are key factors to promote flooding along valley bottoms in the hilly Lisbon. Flooding hotspots tend to result from a combination of higher depths/lower velocities (accumulation of floodwaters and ponding) and not from a pattern of lower depths/higher velocities (shallow overland flow). More detailed data on insurance, flooding, and socioeconomic conditions, at regional and mainly local scales, is needed to improve affordability and urban flooding risk assessments