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Global heat adaptation among urban populations and its evolution under different climate futures
(2022)
Heat and increasing ambient temperatures under climate change represent a serious threat to human health in cities. Heat exposure has been studied extensively at a global scale. Studies comparing a defined temperature threshold with the future daytime temperature during a certain period of time, had concluded an increase in threat to human health. Such findings however do not explicitly account for possible changes in future human heat adaptation and might even overestimate heat exposure. Thus, heat adaptation and its development is still unclear. Human heat adaptation refers to the local temperature to which populations are adjusted to. It can be inferred from the lowest point of the U- or V-shaped heat-mortality relationship (HMR), the Minimum Mortality Temperature (MMT). While epidemiological studies inform on the MMT at the city scale for case studies, a general model applicable at the global scale to infer on temporal change in MMTs had not yet been realised. The conventional approach depends on data availability, their robustness, and on the access to daily mortality records at the city scale. Thorough analysis however must account for future changes in the MMT as heat adaptation happens partially passively. Human heat adaptation consists of two aspects: (1) the intensity of the heat hazard that is still tolerated by human populations, meaning the heat burden they can bear and (2) the wealth-induced technological, social and behavioural measures that can be employed to avoid heat exposure. The objective of this thesis is to investigate and quantify human heat adaptation among urban populations at a global scale under the current climate and to project future adaptation under climate change until the end of the century. To date, this has not yet been accomplished. The evaluation of global heat adaptation among urban populations and its evolution under climate change comprises three levels of analysis. First, using the example of Germany, the MMT is calculated at the city level by applying the conventional method. Second, this thesis compiles a data pool of 400 urban MMTs to develop and train a new model capable of estimating MMTs on the basis of physical and socio-economic city characteristics using multivariate non-linear multivariate regression. The MMT is successfully described as a function of the current climate, the topography and the socio-economic standard, independently of daily mortality data for cities around the world. The city-specific MMT estimates represents a measure of human heat adaptation among the urban population. In a final third analysis, the model to derive human heat adaptation was adjusted to be driven by projected climate and socio-economic variables for the future. This allowed for estimation of the MMT and its change for 3 820 cities worldwide for different combinations of climate trajectories and socio-economic pathways until 2100. The knowledge on the evolution of heat adaptation in the future is a novelty as mostly heat exposure and its future development had been researched. In this work, changes in heat adaptation and exposure were analysed jointly. A wide range of possible health-related outcomes up to 2100 was the result, of which two scenarios with the highest socio-economic developments but opposing strong warming levels were highlighted for comparison. Strong economic growth based upon fossil fuel exploitation is associated with a high gain in heat adaptation, but may not be able to compensate for the associated negative health effects due to increased heat exposure in 30% to 40% of the cities investigated caused by severe climate change. A slightly less strong, but sustainable growth brings moderate gains in heat adaptation but a lower heat exposure and exposure reductions in 80% to 84% of the cities in terms of frequency (number of days exceeding the MMT) and intensity (magnitude of the MMT exceedance) due to a milder global warming. Choosing a 2 ° C compatible development by 2100 would therefore lower the risk of heat-related mortality at the end of the century. In summary, this thesis makes diverse and multidisciplinary contributions to a deeper understanding of human adaptation to heat under the current and the future climate. It is one of the first studies to carry out a systematic and statistical analysis of urban characteristics which are useful as MMT drivers to establish a generalised model of human heat adaptation, applicable at the global level. A broad range of possible heat-related health options for various future scenarios was shown for the first time. This work is of relevance for the assessment of heat-health impacts in regions where mortality data are not accessible or missing. The results are useful for health care planning at the meso- and macro-level and to urban- and climate change adaptation planning. Lastly, beyond having met the posed objective, this thesis advances research towards a global future impact assessment of heat on human health by providing an alternative method of MMT estimation, that is spatially and temporally flexible in its application.
The estimation of financial losses is an integral part of flood risk assessment. The application of existing flood loss models on locations or events different from the ones used to train the models has led to low performance, showing that characteristics of the flood damaging process have not been sufficiently well represented yet. To improve flood loss model transferability, I explore various model structures aiming at incorporating different (inland water) flood types and pathways. That is based on a large survey dataset of approximately 6000 flood-affected households which addresses several aspects of the flood event, not only the hazard characteristics but also information on the affected building, socioeconomic factors, the household's preparedness level, early warning, and impacts. Moreover, the dataset reports the coincidence of different flood pathways. Whilst flood types are a classification of flood events reflecting their generating process (e.g. fluvial, pluvial), flood pathways represent the route the water takes to reach the receptors (e.g. buildings). In this work, the following flood pathways are considered: levee breaches, river floods, surface water floods, and groundwater floods.
The coincidence of several hazard processes at the same time and place characterises a compound event. In fact, many flood events develop through several pathways, such as the ones addressed in the survey dataset used. Earlier loss models, although developed with one or multiple predictor variables, commonly use loss data from a single flood event which is attributed to a single flood type, disregarding specific flood pathways or the coincidence of multiple pathways. This gap is addressed by this thesis through the following research questions: 1. In which aspects do flood pathways of the same (compound inland) flood event differ? 2. How much do factors which contribute to the overall flood loss in a building differ in various settings, specifically across different flood pathways? 3. How well can Bayesian loss models learn from different settings? 4. Do compound, that is, coinciding flood pathways result in higher losses than a single pathway, and what does the outcome imply for future loss modelling?
Statistical analysis has found that households affected by different flood pathways also show, in general, differing characteristics of the affected building, preparedness, and early warning, besides the hazard characteristics. Forecasting and early warning capabilities and the preparedness of the population are dominated by the general flood type, but characteristics of the hazard at the object-level, the impacts, and the recovery are more related to specific flood pathways, indicating that risk communication and loss models could benefit from the inclusion of flood-pathway-specific information.
For the development of the loss model, several potentially relevant predictors are analysed: water depth, duration, velocity, contamination, early warning lead time, perceived knowledge about self-protection, warning information, warning source, gap between warning and action, emergency measures, implementation of property-level precautionary measures (PLPMs), perceived efficacy of PLPMs, previous flood experience, awareness of flood risk, ownership, building type, number of flats, building quality, building value, house/flat area, building area, cellar, age, household size, number of children, number of elderly residents, income class, socioeconomic status, and insurance against floods. After a variable selection, descriptors of the hazard, building, and preparedness were deemed significant, namely: water depth, contamination, duration, velocity, building area, building quality, cellar, PLPMs, perceived efficacy of PLPMs, emergency measures, insurance, and previous flood experience. The inclusion of the indicators of preparedness is relevant, as they are rarely involved in loss datasets and in loss modelling, although previous studies have shown their potential in reducing losses. In addition, the linear model fit indicates that the explanatory factors are, in several cases, differently relevant across flood pathways.
Next, Bayesian multilevel models were trained, which intrinsically incorporate uncertainties and allow for partial pooling (i.e. different groups of data, such as households affected by different flood pathways, can learn from each other), increasing the statistical power of the model. A new variable selection was performed for this new model approach, reducing the number of predictors from twelve to seven variables but keeping factors of the hazard, building, and preparedness, namely: water depth, contamination, duration, building area, PLPMs, insurance, and previous flood experience. The new model was trained not only across flood pathways but also across regions of Germany, divided according to general socioeconomic factors and insurance policies, and across flood events. The distinction across regions and flood events did not improve loss modelling and led to a large overlap of regression coefficients, with no clear trend or pattern. The distinction of flood pathways showed credibly distinct regression coefficients, leading to a better understanding of flood loss modelling and indicating one potential reason why model transferability has been challenging.
Finally, new model structures were trained to include the possibility of compound inland floods (i.e. when multiple flood pathways coincide on the same affected asset). The dataset does not allow for verifying in which sequence the flood pathway waves occurred and predictor variables reflect only their mixed or combined outcome. Thus, two Bayesian models were trained: 1. a multi-membership model, a structure which learns the regression coefficients for multiple flood pathways at the same time, and 2. a multilevel model wherein the combination of coinciding flood pathways makes individual categories. The multi-membership model resulted in credibly different coefficients across flood pathways but did not improve model performance in comparison to the model assuming only a single dominant flood pathway. The model with combined categories signals an increase in impacts after compound floods, but due to the uncertainty in model coefficients and estimates, it is not possible to ascertain such an increase as credible. That is, with the current level of uncertainty in differentiating the flood pathways, the loss estimates are not credibly distinct from individual flood pathways.
To overcome the challenges faced, non-linear or mixed models could be explored in the future. Interactions, moderation, and mediation effects, as well as non-linear effects, should also be further studied. Loss data collection should regularly include preparedness indicators, and either data collection or hydraulic modelling should focus on the distinction of coinciding flood pathways, which could inform loss models and further improve estimates. Flood pathways show distinct (financial) impacts, and their inclusion in loss modelling proves relevant, for it helps in clarifying the different contribution of influencing factors to the final loss, improving understanding of the damaging process, and indicating future lines of research.
Over the past decades, natural hazards, many of which are aggravated by climate change and reveal an increasing trend in frequency and intensity, have caused significant human and economic losses and pose a considerable obstacle to sustainable development. Hence, dedicated action toward disaster risk reduction is needed to understand the underlying drivers and create efficient risk mitigation plans. Such action is requested by the Sendai Framework for Disaster Risk Reduction 2015-2030 (SFDRR), a global agreement launched in 2015 that establishes stating priorities for action, e.g. an improved understanding of disaster risk. Turkey is one of the SFDRR contracting countries and has been severely affected by many natural hazards, in particular earthquakes and floods. However, disproportionately little is known about flood hazards and risks in Turkey. Therefore, this thesis aims to carry out a comprehensive analysis of flood hazards for the first time in Turkey from triggering drivers to impacts. It is intended to contribute to a better understanding of flood risks, improvements of flood risk mitigation and the facilitated monitoring of progress and achievements while implementing the SFDRR.
In order to investigate the occurrence and severity of flooding in comparison to other natural hazards in Turkey and provide an overview of the temporal and spatial distribution of flood losses, the Turkey Disaster Database (TABB) was examined for the years 1960-2014. The TABB database was reviewed through comparison with the Emergency Events Database (EM-DAT), the Dartmouth Flood Observatory database, the scientific literature and news archives. In addition, data on the most severe flood events between 1960 and 2014 were retrieved. These served as a basis for analyzing triggering mechanisms (i.e. atmospheric circulation and precipitation amounts) and aggravating pathways (i.e. topographic features, catchment size, land use types and soil properties). For this, a new approach was developed and the events were classified using hierarchical cluster analyses to identify the main influencing factor per event and provide additional information about the dominant flood pathways for severe floods. The main idea of the study was to start with the event impacts based on a bottom-up approach and identify the causes that created damaging events, instead of applying a model chain with long-term series as input and searching for potentially impacting events as model outcomes. However, within the frequency analysis of the flood-triggering circulation pattern types, it was discovered that events in terms of heavy precipitation were not included in the list of most severe floods, i.e. their impacts were not recorded in national and international loss databases but were mentioned in news archives and reported by the Turkish State Meteorological Service. This finding challenges bottom-up modelling approaches and underlines the urgent need for consistent event and loss documentation. Therefore, as a next step, the aim was to enhance the flood loss documentation by calibrating, validating and applying the United Nations Office for Disaster Risk Reduction (UNDRR) loss estimation method for the recent severe flood events (2015-2020). This provided, a consistent flood loss estimation model for Turkey, allowing governments to estimate losses as quickly as possible after events, e.g. to better coordinate financial aid.
This thesis reveals that, after earthquakes, floods have the second most destructive effects in Turkey in terms of human and economic impacts, with over 800 fatalities and US$ 885.7 million in economic losses between 1960 and 2020, and that more attention should be paid on the national scale. The clustering results of the dominant flood-producing mechanisms (e.g. circulation pattern types, extreme rainfall, sudden snowmelt) present crucial information regarding the source and pathway identification, which can be used as base information for hazard identification in the preliminary risk assessment process. The implementation of the UNDRR loss estimation model shows that the model with country-specific parameters, calibrated damage ratios and sufficient event documentation (i.e. physically damaged units) can be recommended in order to provide first estimates of the magnitude of direct economic losses, even shortly after events have occurred, since it performed well when estimates were compared to documented losses.
The presented results can contribute to improving the national disaster loss database in Turkey and thus enable a better monitoring of the national progress and achievements with regard to the targets stated by the SFDRR. In addition, the outcomes can be used to better characterize and classify flood events. Information on the main underlying factors and aggravating flood pathways further supports the selection of suitable risk reduction policies.
All input variables used in this thesis were obtained from publicly available data. The results are openly accessible and can be used for further research.
As an overall conclusion, it can be stated that consistent loss data collection and better event documentation should gain more attention for a reliable monitoring of the implementation of the SFDRR. Better event documentation should be established according to a globally accepted standard for disaster classification and loss estimation in Turkey. Ultimately, this enables stakeholders to create better risk mitigation actions based on clear hazard definitions, flood event classification and consistent loss estimations.
Natural hazards pose a threat to human health and life. In Germany, where the research for this thesis was conducted, numerous weather extremes occurred in the recent past that caused high numbers of fatalities and huge financial losses. The focus of this research is centred around two relevant natural hazards: heat stress and flooding. Preventing negative health impacts and deaths, as well as structural and monetary damage is the purpose of risk management and this requires citizens to adapt as well. Risk communication is implemented to foster people’s risk perception and motivate individual adaptation. However, methods of risk and crisis communication are often not evaluated in a structured manner. Much interdisciplinary research exists on both risk perception and adaptation, however, not much is known on the connection between the two. Furthermore, the existing research on risk communication is often not theory-driven and its impact on individual adaptation and risk perception is not thoroughly documented. This dissertation follows three research aims: (1) Compare psychological theories that contribute to natural hazard research. (2) Explore risk perception and adaptive behaviour by applying multiple methods. And (3) evaluate one risk communication method and one crisis communication method in a theory-driven manner to determine their impact on risk perception and adaptive behaviour. First, a literature review is provided on existing psychological theories which aim to explain the behaviour of individuals with regards to natural hazards. The three key theories included are the Protection Motivation Theory (PMT), the Protective Action Decision Model (PADM), and the Risk Information Seeking and Processing Model (RISP). Each of these are described and compared to each other with a focus on their explanatory power and practical significance in interdisciplinary research. Theoretical adaptations and possible extensions for future research are proposed for the presented approaches. Second, a multimethod field study on heat stress at an open-air event is presented. Face-to-face surveys (n = 306) and behavioural observations (n = 2750) were carried out at a horticultural show in Würzburg in summer 2018. The visitors’ risk perception, adaptive behaviour, and activity level were analysed and compared between hot days, summer days, and rainy days, applying correlation analyses, ANOVA, and multiple regression analyses. Heat risk perception was generally high, but most respondents were unaware of heat warnings on the day of their visit. During hot days the highest level of adaptation and lower activity levels were observed. Discrepancies between reported and observed adaptation emerged for different age groups.. Third, a telephone and web-based household survey on heat stress was conducted in the cities of Würzburg, Potsdam, and Remscheid in 2019 (n = 1417). The PADM served as the study’s theoretical framework. In multiple regression analyses the PADM factors of environmental and demographic context, risk communication, and psychological processes explained a substantial share of variance of protection motivation, protective response, and emotion-focused coping. Elements of crisis communication of a heat warning were evaluated experimentally. Results showed that understanding and adaptation intention was significantly higher in individuals that had received action recommendations alongside the heat warning. Fourth, the focus is set on a risk communication method of the flood context. A series of workshops on individual flood protection was carried out in six different settings. The participants (n = 115) answered a pretest-posttest questionnaire. Mixed-model analyses revealed significant increases in self-efficacy, subjective knowledge, and protection motivation. Stronger effects were observed in younger participants and those with lower levels of previous knowledge on flood adaptation as well as no flood experience. The findings of this thesis help to understand individual adaptation, as well as possible impacts of risk and crisis communication on risk perception and adaptation. The scientific background of this work is rooted in the disciplines of psychology and geosciences. The two theories PMT and PADM proved to be useful theoretical frameworks for the presented studies to suggest improvements in risk communication methods. A broad picture of individual adaptation is captured through a variety of methods of self-reports (face-to-face, telephone-based, web-based, and paper-pencil surveys) and behavioural observations, which recorded past and intended behaviour. Alongside with further methodological recommendations, the theory-driven evaluations of risk and crisis communication methods can serve as best-practice examples for future evaluation studies in natural hazard research but also other sciences dealing with risk behaviour to identify and improve effective risk communication pathways.
Traditional ways of reducing flood risk have encountered limitations in a climate-changing and rapidly urbanizing world. For instance, there has been a demanding requirement for massive investment in order to maintain a consistent level of security as well as increased flood exposure of people and property due to a false sense of security arising from the flood protection infrastructure. Against this background, nature-based solutions (NBS) have gained popularity as a sustainable and alternative way of dealing with diverse societal challenges such as climate change and biodiversity loss. In particular, their ability to reduce flood risks while also offering ecological benefits has recently received global attention. Diverse co-benefits of NBS that favor both humans and nature are viewed as promising a wide endorsement of NBS. However, people’s perceptions of NBS are not always positive. Local resistance to NBS projects as well as decision-makers’ and practitioners’ unwillingness to adopt NBS have been pointed out as a bottleneck to the successful realization and mainstreaming of NBS. In this regard, there has been a growing necessity to investigate people’s perceptions of NBS. Current research has lacked an integrative perspective of both attitudinal and contextual factors that guide perceptions of NBS; it not only lacks empirical evidence, but a few existing ones are rather conflicting without having underlying theories. This has led to the overarching research question of this dissertation, "What shapes people’s perceptions of NBS in the context of flooding?" The dissertation aims to answer the following sub-questions in the three papers that make up this dissertation: 1. What are the topics reflected in the previous literature influencing perceptions of NBS as a means to reduce hydro-meteorological risks? (Paper I) 2. What are the stimulating and hampering attitudinal and contextual factors for mainstreaming NBS for flood risk management? How are NBS conceptualized? (Paper II) 3. How are public attitudes toward the NBS projects shaped? How do risk-and place-related factors shape individual attitudes toward NBS? (Paper III) This dissertation follows an integrative approach of considering “place” and “risk”, as well as the surrounding context, by analyzing attitudinal (i.e., individual) and contextual (i.e., systemic) factors. “Place” is mainly concerned with affective elements (e.g., bond to locality and natural environment) whereas “risk” is related to cognitive elements (e.g., threat appraisal). The surrounding context provides systemic drivers and barriers with the possibility of interfering the influence of place and risk for perceptions of NBS. To empirically address the research questions, the current status of the knowledge about people’s perceptions of NBS for flood risks was investigated by conducting a systematic review (Paper I). Based on these insights, a case study of South Korea was used to demonstrate key contextual and attitudinal factors for mainstreaming NBS through the lens of experts (Paper II). Lastly, by conducting a citizen survey, it investigated the relationship between the previously discussed concepts in Papers I and II using structural equation modeling, focusing on the core concepts, namely risk and place (Paper III). As a result, Paper I identified the key topics relating to people’s perceptions, including the perceived value of co-benefits, perceived effectiveness of risk reduction effectiveness, participation of stakeholders, socio-economic and place-specific conditions, environmental attitude, and uncertainty of NBS. Paper II confirmed Paper I's findings regarding attitudinal factors. In addition, several contextual hampering or stimulating factors were found to be similar to those of any emerging technologies (i.e., path dependence, lack of operational and systemic capacity). Among all, one of the distinctive features in NBS contexts, at least in the South Korean case, is the politicization of NBS, which can lead to polarization of ideas and undermine the decision-making process. Finally, Paper III provides a framework with the core topics (i.e., place and risk) that were considered critical in Paper I and Paper II. This place-based risk appraisal model (PRAM) connects people at risk and places where hazards (i.e., floods) and interventions (i.e., NBS) take place. The empirical analysis shows that, among the place-related variables, nature bonding was a positive predictor of the perceived risk-reduction effectiveness of NBS, and place identity was a negative predictor of supportive attitude. Among the risk-related variables, threat appraisal had a negative effect on perceived risk reduction effectiveness and supportive attitude, while well-communicated information, trust in flood risk management, and perceived co-benefit were positive predictors. This dissertation proves that the place and risk attributes of NBS shape people’s perceptions of NBS. In order to optimize the NBS implementation, it is necessary to consider the meanings and values held in place before project implementation and how these attributes interact with individual and/or community risk profiles and other contextual factors. With the increasing necessity of using NBS to lower flood risks, these results make important suggestions for the future NBS project strategy and NBS governance.
Floods are among the most costly natural hazards that affect Europe and Germany, demanding a continuous adaptation of flood risk management. While social and economic development in recent years altered the flood risk patterns mainly with regard to an increase in flood exposure, different flood events are further expected to increase in frequency and severity in certain European regions due to climate change. As a result of recent major flood events in Germany, the German flood risk management shifted to more integrated approaches that include private precaution and preparation to reduce the damage on exposed assets. Yet, detailed insights into the preparedness decisions of flood-prone households remain scarce, especially in connection to mental impacts and individual coping strategies after being affected by different flood types.
This thesis aims to gain insights into flash floods as a costly hazard in certain German regions and compares the damage driving factors to the damage driving factors of river floods. Furthermore, psychological impacts as well as the effects on coping and mitigation behaviour of flood-affected households are assessed. In this context, psychological models such as the Protection Motivation Theory (PMT) and methods such as regressions and Bayesian statistics are used to evaluate influencing factors on the mental coping after an event and to identify psychological variables that are connected to intended private flood mitigation. The database consists of surveys that were conducted among affected households after major river floods in 2013 and flash floods in 2016.
The main conclusions that can be drawn from this thesis reveal that the damage patterns and damage driving factors of strong flash floods differ significantly from those of river floods due to a rapid flow origination process, higher flow velocities and flow forces. However, the effects on mental coping of people that have been affected by flood events appear to be weakly influenced by different flood types, but yet show a coherence to the event severity, where often thinking of the respective event is pronounced and also connected to a higher mitigation motivation. The mental coping and preparation after floods is further influenced by a good information provision and a social environment, which encourages a positive attitude towards private mitigation.
As an overall recommendation, approaches for an integrated flood risk management in Germany should be followed that also take flash floods into account and consider psychological characteristics of affected households to support and promote private flood mitigation. Targeted information campaigns that concern coping options and discuss current flood risks are important to better prepare for future flood hazards in Germany.