Natural hazards cause enormous amounts of damage worldwide every year. Since 1994 more than 1.35 billion people have lost their lives and more than 116 million homes have been damaged. Understanding of disaster risk implies knowledge about vulnerability, capacity, exposure of persons and assets, hazard characteristics and the environment. Quantitative damage assessments are a fundamental part of disaster risk management. There are, however, substantial challenges when quantifying damage which depends on the diversity of hazards and the fact that one hazardous event can negatively impact a society in multiple ways. The overall aim of the thesis is to analyze the relationship between climate-related natural hazards and subsequent damage for the purpose of improving the prerequisite for quantitative risk assessments in the future. The thesis concentrates on two specific types of consequences due to two types of hazards, 1) damage to buildings caused by lake floods, and 2) loss of lives caused by quick clay landslides.  Several causal relationships were established between risk factors and the extent of damages. Lake water levels increased the probability of structural building damage. Private damage reducing measures decreased the probability of structural building damage. Extent of damage decreased with distance to waterfront but increased with longer flood duration while prewar houses suffered lower flood damage compared to others. Concerning landslides, the number of fatalities increased when the number of humans in the exposed population increased. The main challenges to further damage estimation are data scarcity, insufficient detail level and the fact that the data are rarely systematically collected for scientific purposes. More efforts are needed to create structured, homogeneous and detailed damage databases with corresponding risk factors in order to further develop quantitative damage assessment of natural hazards in a Nordic perspective.

Naturolyckor orsakar enorma mängder skador över hela världen varje år. Under åren 1994-2013 förlorade mer än 1,35 miljoner människor sina liv och mer än 116 miljoner hem skadades. Förståelse av risk för naturolyckor innebär kunskap om sårbarhet, kapacitet, exponering av personer och tillgångar, hot och miljö.

Kvantitativa skadebedömningar, som är en viktig del av riskbedömningar, omfattas av stora utmaningar som grundar sig i hotens mångfaldighet och det faktum att en naturolycka kan påverka ett samhälle negativt på många olika sätt. Det övergripande syftet med avhandlingen är att analysera förhållandet mellan naturkatastrofer och potentiellt påföljande skador i syfte att förbättra förutsättningarna för kvantitativa riskbedömningar i framtiden. Avhandlingen koncentrerar sig på två typer av naturolyckor med specifika konsekvenser, 1) skador på byggnader till följd av sjö-översvämningar, och 2) förlust av liv orsakat av lerskred. Flera orsakssamband mellan riskfaktorer och omfattning av skador har identifierats. Sjöarnas vattennivåer ökade sannolikheten att drabbas av strukturell byggnadsskada, samtidigt som privat initierade åtgärder minskande sannolikheten.. När avstånd mellan sjö och byggnad ökade minskade omfattningen av översvämningsskador, men ökade ju längre sjööversvämningen varade. Hus byggda före 1940 fick mindre skador jämfört med andra hus. Andelen dödsfall i samband med skred i kvicklera ökade när antal människor i den exponerade befolkningen ökade. Den största utmaningen i att förbättra dagens kvantitativa skadebedömningar är den rådande databristen vad gäller förluster och tillhörande riskfaktorer. Denna brist beror på otillgänglig skadedata, bristande detaljnivå på skadedata och tillhörande risk faktorer, och att uppgifterna sällan samlas systematiskt i syfte att studera kausalitet.

The overall aim of the thesis is to analyze the relationship between climate-related natural hazards and subsequent damage for the purpose of improving the prerequisite for quantitative risk assessments in the future. The thesis concentrates on two specific types of hazards with specific types of consequences, 1) damage to buildings caused by lake floods, and 2) loss of lives caused by quick clay landslides.  Several causal relationships were established between risk factors and the extent of damages. Lake water levels increased the probability of structural building damage. Private damage reducing measures decreased the probability of structural building damage. Extent of damage decreased with distance to waterfront but increased with longer flood duration while prewar houses suffered lower flood damage compared to others. Concerning landslides, the number of fatalities increased when the number of humans in the exposed population increased. The main challenges to further damage estimation are data scarcity, insufficient detail level and the fact that the data are rarely systematically collected for scientific purposes.

Quantitative risk assessments are a fundamental part of economic analysis and natural hazard risk management models. It increases the objectivity and the transparency of risk assessments and guides policymakers in making efficient decisions when spending public resources on risk reduction. Managing hazard risks calls for an understanding of the relationships between hazard exposure and vulnerability of humans and assets.

The purpose of this thesis is to identify and estimate causal relationships between hazards, exposure and vulnerability, and to evaluate the applicability of systematically collected data sets to produce reliable and generalizable quantitative information for decision support.

Several causal relationships have been established. For example, the extent of lake flood damage to residential buildings depends on the duration of floods, distance to waterfront, the age of the house and in some cases the water level. Results also show that homeowners private initiative to reduce risk, prior to or during a flood, reduced their probability of suffering building damage with as much as 40 percent. Further, a causal relationship has been established between the number of people exposed to quick clay landslides and landslide fatalities.

Even though several relationships were identified between flood exposure and vulnerability, the effects can only explain small parts of the total variation in damages, especially at object level. The availability of damage data in Sweden is generally low. The most comprehensive damage data sets in Sweden are held by private insurance companies and are not publicly available. Data scarcity is a barrier to quantitative natural hazard risk assessment in Sweden. More efforts should therefore be made to collect data systematically for modelling and validating standardized approaches to quantitative damage estimation.

Natural hazard damages have increased worldwide. Impacts caused by hydrological and meteorological hazards have increased the most. An analysis of insurance payments in Sweden showed that flood damages have been increasing in Sweden as well. With climate change and increasing populations we can expect this trend to continue unless efforts are made to reduce risk and adapt communities to the threats. Economic analysis and quantitative risk assessments of natural hazards are fundamental parts of a risk management process that can support policymakers' decisions on efficient risk reduction. However, in order to develop reliable damage estimation models knowledge is needed of the relationships between hazard exposure and the vulnerability of exposed objects and persons. This thesis has established causal relationships between residential exposure and flood damage on the basis of insurance data. I also found that private damage-reducing actions decreased the probability of damage to buildings with almost 40 percent. Further, a causal relationship has been established between the number of people exposed to quick clay landslides and fatalities. Even though several relationships have been identified between flood exposure and vulnerability, the effects can explain only small parts of the total variation in damages, especially at object level, and more effort is needed to develop quantitative models for risk assessment purposes.