Climate change is an omnipresent issue in politics, industry, science, and society. Scientist knew of its existence for several decades, but only recently has the perception of it shifted from a solely environmental problem to a matter of international security. Climate change is thought to impact the likelihood of extreme weather events, intensity of droughts, rising sea levels and more. In this way climate change contributes to ongoing conflicts around the world by destroying resources or forcing people out of habitats, creating tensions among groups of people. As the impacts of climate change are being felt more directly, calls for bolder climate action are getting louder. At the same time, there is also resistance by climate skeptics in industry, government, and among voters. Although most people appear aware and concerned with the development of climate change, the attitude towards climate action is extremely broad. Political rhetoric and disinformation in the media compound the disagreement on climate change, causing polarization. Although some polarization is beneficial for democratic deliberation and for mobilizing voters, if polarization divides the electorate into mutually distrustful groups, it can trap societies in a stifling gridlock or gradually erode democratic institutions. These pernicious effects are what necessitates closer study to monitor societal polarization, prevent conflict and improve climate action efforts. Social media offers huge amounts of textual data to study discourse on climate change, which this study leverages to make first steps in understanding what topics make up the public discourse, how it varies across linguistic regions (English, German, Dutch) and how it changes considering climate-related events, namely floods and a climate protest. Using both topic modelling and sentiment analysis on Twitter data, it could be identified that activity spiked around major events: namely the 2019 Climate Strike and the 2021 Flood in Western Europe. However, reaction to events appears to be mainly regional with reaction to floods seen only in the Dutch and German tweets. The English Twittersphere seemed to be mainly skewed towards events in America. Polarization appeared low as most tweets were neutral. Examining only tweets with high sentiment, a different behavior was detected in terms of news coverage as there existed more high negative sentiment tweets, but almost no high positive sentiment tweets. During the 2019 Global Climate Strike, extreme sentiment tweets went both positive and negative, possibly indicating more intense discourse and a more polarized atmosphere. Overall, results show that conflict-triggering climate events are very likely to be domestic events. Thus, from a security perspective, it suggests on the short-term to focus on the monitoring of domestic actors. On the long-term however, policies need to be implemented which address underlying factors that make society susceptible to polarization, such as socioeconomic inequalities and exclusion, disinformation in media or corruption. Lastly, from an academic perspective, more research on other dimensions of polarization needs to be conducted. Polarization is a complex phenomenon, whose full implications cannot be captured by the sentiment metrics. Thus, research moving forward should strive towards a more refined multi-method approach to further investigate climate change polarization and its conflict potential. A better understanding could benefit practitioners in many areas such as security and social policy, for strategic planning regarding climate change.

Climate change intensifies the frequency and severity of floods - the most devastating and costly climate-induced hazard. Government adaptations such as dikes or beach nourishments are important, yet insufficient in the face of worsening hazards. They reduce the hazard probability, but the local actions at the household level determine the extent of damages and inequalities in its distributional impacts on various societal groups. To design effective policies and risk reduction strategies it is critical to quantify the speed and scope of the household adaptation uptake and the resulting damage prevention. This is especially the case for distributional impacts (i.e., how different societal household groups adapt), which are often neglected. Quantifying both aggregate and distributional impacts of household climate change adaptation (CCA) on flood risk fosters the design of tailored flood risk management policies which allocate resources to the societal groups that need them most. This thesis presents a state-of-the-art agent-based flood model in downtown Shanghai, China to understand the role of household CCA in reducing coastal flood risk both in its aggregate and distributional impacts. To model the households’ exposure to climate-induced floods we overlayed the geolocations of 18.039 residential buildings with 21 inundation maps that depict dike failures and dike overtopping under different climate-change scenarios. We further parameterized households using context-specific micro-level survey data from Shanghai and depicted households’ adaptation decisions using an extended version of the Protection Motivation Theory. Our results show that autonomous household adaptation (adaptation without government policy) to climate change plays an essential role in reducing flood damage in downtown Shanghai. However, despite the considerable adaptation uptake, the residual damages increase over time due to the effects of sea level rise and land subsidence. This shows that autonomous household adaptation alone is insufficient to keep pace with the increasing severity of climate-related flooding, as it is constrained by barriers in the form of adaptation measure costs and regulations. Thus, additional policies are needed to overcome these barriers. These policies should take into account differences in adaptation behaviour and damage prevention among societal household groups. Specifically, our results indicate that households with lower worry, self-efficacy, and income adapt measurably slower to climate-induced floods, which makes these household groups significantly more vulnerable to flooding.

Climate is changing. It is widely accepted that irrespective of the emission reductions efforts, adaptation to the already committed climate change is a must in the coming decades. Flooding is one of the most devastating climate-induced hazards, calling for adaptation across scales: from government-led adaptation (e.g. dikes), to personal household-led adaptation. There are numerous private adaptation measures, both structural and non-structural, that households can autonomously take to reduce damages and speed up own recovery, in case of the adverse event does occur. Worldwide household surveys provide the empirical evidence suggesting that the appraisal of fear, perceptions of own coping abilities and social influences affect individual decision to adapt. Especially the latter appear as a strong determinant of household-led adaptation. Yet, the role of social networks has not been studied systematically, let alone the exploration of the interplay between private households' adaptation and public policies in the presence of social influences. To increase the understanding of social networks' impact on private flood adaptation under various public policies, an empirical agent-based model is built. In addition to empirical flood maps, I employ Protection Motivation Theory and households' survey data from Houston (Texas, USA) to capture the household’s adaptation decisions, which are subject to social influence. To represent a range of social networks, I explore the effect of three random networks - Erdös-Renyi random network, Barabasi-Albert scale-free network, Watts-Strogatz small-world network -- on the diffusion of flood preparedness. These three networks could serve as a proxy of diverse types of social relationships that vary across cultures, with some being hierarchical and others egalitarian. Furthermore, I test how the diffusion of private adaptation among households evolves under four generic public policy strategies: protection by publicly-funded infrastructure, market-based policy such as subsidy, information policy and regulatory policy. The thesis findings reveal that the type of social networks influence success of private adaptation decisions significantly. Notably, the effect of social norms depends on the network configuration, where more homogeneous networks lead to higher private adaptation uptake. Furthermore, the thesis quantifies the interaction effects between social networks and policies designed to support private climate change adaptation, for example communication campaigns affecting individual risk perceptions that in turn drive household-led adaptation. Therefore, information policies can be very effective in steering public opinions and, hence, the uptake of households' adaptation measures. Moreover, I find that in the presence of social networks, public adaptation policies interact with each other: a combination of subsidies with communication exhibit synergistic effects on the flood damage reduction from private adaptation. Policies that do not interact with households' perceptions, like infrastructure projects or laws, can be considered more robust - less sensitive to social networks. To conclude, networks can shape the success of climate change adaptation policies and should be accounted for in their design. Further research should focus on the endogenous evolution of social networks and the model behavior under changing flooding conditions and what this complex adaptive system's dynamics means for future cross-scale adaptation efforts.

Climate change is happening and has an increasingly great impact on nature, ecosystems, biodiversity and human society. To reduce adverse consequences of hazards for current and future generations, one must understand how adaptation behavior of civil societies could develop itself over time, interact with its environment and effect its ecosystem. As the emergence of adaptation behavior is complex, differs locally and is influenced by lots of cultural, socio, environment and political factors, there are a lot of missing places on which more research on the emergence of adaptation behavior of civil societies can be done. This EPA master thesis will study is the emergence of adaptation behavior on a case-study about flood adaptation behavior in Jakarta. A modeling approach will be used to analyze the cumulative impact of autonomous bottom-up household adaptation decisions according to the Protection Motivation Theory on the overall flood resilience of Jakarta. The model will be used to explore the effect of policy interventions on household adaptation decisions, to ultimately give an advice on how to achieve a more resilient flood response. The results of this study aim to provide a better understanding on human behavior and its interactions within Jakarta’s environmentally complex situation, what could be of help for the government of Jakarta in the development of long-term flood adaptation strategies.

Floods appear in many of the world's oldest stories (i.e. Noah and the Arc in the Abrahamic religions, Manu in Hinduism, and the Gun-Yu myth in Chinese mythology). When observed historically, they often have an element of mysticism about them, symbolizing eradication and rebirth. In the present, however, there is little that is mystical about the devastation brought on by floods as they cause more destruction annually than any other hazard. With much of the modern development taking place along the coast or near riverways, assets and livelihoods are increasingly concentrated in exposed areas. By-products of climate change such as sea level rise and extreme precipitation events increasingly devastate these regions; with the projection that the risk of floods will continue to increase in the future. Top-down, government-led adaptation to floods on its own cannot contend with growing risk; rendering household participation essential. Governments, risk modelers, scientists, and other interest groups (i.e. NGOs) need a solid understanding of household behavior in order to formulate strategies and engage stakeholders across scales to address climate-induced risks. This dissertation devotes its attention to better understanding households' perceptions, intentions, and behavioral drivers and their dynamics, concerning floods in various social, geographical, cultural, and environmental contexts. More concretely, the principal research objective of this dissertation is: To progress toward an understanding of how households perceive, are affected by, and adapt to floods in various contexts over time. Following a comprehensive review and analysis of prior empirical research on household flood adaptation, this dissertation presents the analysis of a panel survey carried out between 2020-2021 aimed at collecting data to tackle the aforementioned objective. Focusing on large urban centers in the United States, China, Indonesia, and the Netherlands I use various statistical techniques and methods to analyze the survey data and study a range of aspects from household perceptions as they concern floods and climate change, to reported adaptation behavior. The survey solicits information on 18 adaptation measures that range from inexpensive, actions that do not require considerable effort (i.e. having an emergency preparedness kit, emergency coordination with one's neighbor, etc.), to costly measures that require a substantial time investment (i.e. elevating one's home, waterproofing one's windows, etc.) In analyzing how household adaptation decisions are influenced, depending on the extit{type} of measure and the context in which the household resides, this dissertation offers insight into which socio-behavioral drivers and barriers of household adaptation are generic and those which may vary depending on the institutional and environmental conditions. A household's perceived ability to cope, and the emotion, ``worry,'' plays a substantial role in driving household adaptation intention. In contrast, the financially calculated risk-based drivers: the perceived probability of a flood happening and the perceived damage should a flood occur, generally have a more subdued effect on household adaptation intentions. This is related to the fact that not all households have sufficient capacity or awareness to subjectively assess the probability and damage of a potential flood. Individual risk-uncertainty - a trait more frequently found in populations historically more vulnerable to floods (i.e. women and lower educated) has a large detrimental effect on households' intention to pursue flood adaptation measures. While internal perceptions are critical to consider, external factors can have an equally potent role in affecting household adaptation behavior. I examine the effect of context at multiple scales in this dissertation, assessing the role of social expectations, perceptions of government measures, and national culture on household adaptation decisions. Households use their observations of what others (i.e. their social network, the government) are doing with respect to flood adaptation, to inform their decisions. The degree to which both external and internal factors influence household adaptation decisions can differ based on the cultural and geographical context. Various factors have a weaker or stronger influence and at times even the opposite effect on adaptation behavior, depending on where the household resides. While internal and external perceptions are requisite considerations in understanding household behavior, it is likewise crucial to account for experiences and the co-benefits of various household adaptive actions. The effects of prior flood experiences and the benefits of taking adaptations together are additional key considerations when studying household flood adaptation, due to the economic benefits that can arise from undertaking measures together. Furthermore, prior experience with floods can motivate adaptation behavior, but substantial financial damage from a flood impedes a household's adaptation intention; as their focus is on recovery, not adapting. The findings in this dissertation are of use to scientists, modelers, risk specialists, and policymakers; whether they are designing models, a communication strategy, or a policy aimed at encouraging household action. With the effects of climate change increasingly affecting communities across the globe, households are having to contend with hazards that are more extreme and frequent than in the living memory of humanity. Unless immediate action is taken across scales, the harrowing effects of climate change are expected to increasingly threaten extensive populations globally. This dissertation provides insights into how households think, perceive, behave, and learn over time concerning one of the most deadly and damaging hazards: floods. @en