Simon Donner

Tarawa Atoll (Republic of Kiribati), located in the Central Pacific Ocean near the equator, is exposed to significant sea level and wave variability due to the El Niño / Southern Oscillation (ENSO) cycle. As significant wave height (Hs) and energy play a crucial role in inundation events, this thesis investigates ENSO’s impact on wave activity by analyzing the full offshore wave energy spectrum of two wave hindcasts between 1979 and 2018. When assessing the granularity needed to study an atoll’s wave variability, the high-resolution hindcast provided by the Pacific Community more accurately represented wave variations near the shorelines but underrepresented extreme waves compared to the hindcast acquired from the Collaboration for Australian Weather and Climate Research. The analysis focussed on the distinct effects of Central Pacific (CP), Eastern Pacific (EP), and mixed El Niño events, all exhibiting an overall directional change with increased wave energy due to trade wind changes and westerly wind bursts. During the boreal winter of EP El Niño events, positive anomalies were observed in waves originating from the north and northeast, predominantly approaching Tarawa’s less densely populated shorelines. Similarly, La Niña conditions exhibited increased wave activity from the east. South Tarawa’s densely populated lagoon-facing shorelines however were mainly impacted during CP and mixed El Niño events. By clustering extreme wave events, I found these to be more frequent during El Niño conditions, due in part to the higher likelihood of westerly wind bursts. Subsequently, I used Sheppard et al.’s (2005) wave attenuation model to estimate the propagation of average and extreme waves across the reef flat, revealing that the western lagoon-facing shoreline, typically characterized by reduced wave energy and wave set-up, is particularly susceptible to wind-generated waves during El Niño. The model runs also encompassed the potential impact of future sea level rise and reef degradation, providing a sensitivity analysis of how these forces will potentially act together in the future. By 2100, Hs along Tarawa’s lagoon-facing shoreline during El Niño-related westerly wind bursts is projected to increase by up to 89% and more than triple in wave energy under the SSP5-8.5 emission scenario.

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The increasing frequency and magnitude of extreme weather events are among the manifestations of anthropogenic climate change most notable to the public. Exposure to these events has been shown to heighten individuals’ concern about climate change, motivate personal-level climate actions, and enhance support for climate policies. However, the tendency towards single-action bias coupled with limited resources may lead individuals to prioritize either adaptation or mitigation actions in the wake of weather extremes. Until now, the effect of extreme weather events on climate action preferences remained largely underexplored. To address this research gap, this dissertation explored how news of extreme weather events affect individuals’ priorities concerning mitigation and adaptation actions. These priorities are explored both in terms of the intentions to undertake personal-level actions and support for governmental initiatives. To achieve this, a representative sample of the United States and Canadian population (N=1058) was recruited to participate in an experimental survey assessing the effect of exposure to news texts about record-breaking heatwaves, varied by geographical proximity and severity, on personal and collective-level climate action preferences. The results show that news about a weather extreme prompts individuals to prioritize personal- and governmental-level adaptation measures aimed at preparing for the effect of the type of event reported in the news article. This relationship is not affected by the geographical proximity or the presence of casualties associated with the portrayed heatwave. The findings suggest that extreme weather events present opportunities for policymakers to advance climate change adaptation initiatives and for climate change communicators to educate the public on effective adaptation actions that do not exacerbate emissions, while stressing the importance of emissions reduction actions.

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The recurrence of mass coral bleaching events and associated coral mortality driven by climate change in the past few decades has raised numerous questions about the future of coral reef ecosystems. Although these phenomena have been widely studied, our understanding of the geographical extent of these events has been limited. In this study, I present an updated version of the global mass coral bleaching database. The updated database provides the most comprehensive collection of global bleaching reports from 1963 to 2017, which were used to spatially model the probability of bleaching occurrence for 1985 through 2017 across the world’s warm-water coral reefs at a 0.05° x 0.05° resolution using indicator kriging. With this new spatially-explicit data, I provide a more accurate and up-to-date global and regional assessment of the extent of bleaching through the 1985-2017 period with a focus on the three global mass coral bleaching events that occurred in 1997-1998, 2009-2010, and 2014-2016. Results indicate that between 56% and 71% of the world’s coral reefs have experienced bleaching at least once during the assessed time period, with the greatest extents observed in the Southeast Asia, Australia, and Caribbean regions. High bleaching probabilities were more common towards the last decade of the period, and the most recent global bleaching event was assessed as up to 2.6 times more extensive than each of the first two. Results also show a positive relationship between the annual maximum Degree Heating Week, a measure of thermal stress, and high bleaching probability values. The updated database will help make global-scale analyses more robust, enhance real-time predictions, calibrate models for future projections, test for evidence of adaptive responses from corals and gain insights into the spatial-temporal trends of coral bleaching over time.

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Coral reefs support a high biodiversity, providing a natural, physical barrier from waves that protects coastal communities from shoreline erosion and inundation. The three-dimensional (3D) structural complexity of living coral communities provides frictional resistance as waves and currents pass over the reef. A shift in coral community assemblages towards small, weedy, stress-tolerant corals due to climate change and local human stressors may alter wave attenuation, threatening low-lying coastal regions facing sea-level rise. In this thesis, I investigated the effect of coral community composition on shoreline protection in Kiribati’s Tarawa and Abaiang Atolls by collecting fore reef and reef flat field data and creating 3D reconstructions of the fore reefs. I found that the 3D structure and contribution of certain coral growth forms to reef complexity varied depending on the complexity metric used. Surface rugosity and standard deviation of elevation were not significantly different between atolls, while the average terrain ruggedness was significantly greater at disturbed sites in South Tarawa dominated by the weedy species Porites rus. I show that the abundance of Porites rus and branching corals were positively related for all three complexity metrics, with the strongest positive association between Porites rus and terrain ruggedness. Lastly, I determined that South Tarawa reef flats, long mined of rocks for human use, have lower benthic roughness and receive higher offshore wave energy relative to North Tarawa. My research suggests that at current mean sea level, the difference in the diversity of coral growth forms on the fore reef across Tarawa and Abaiang have less effect on wave attenuation than other factors like coral cover, steepness of the fore reef, and benthic composition of the reef flat. Additionally, the most significant variation in wave runup will be due to parameters influencing fore reef slope and reef flat composition. As such, steeper fore reef slopes and smooth reef flats of South Tarawa are expected to dissipate less wave energy relative to reefs in North Tarawa and Abaiang. To summarize, my findings offer insights into possible trade-offs between reef resilience to climate change and shoreline protection, including shoreline vulnerabilities to sea-level rise around Kiribati.

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Both local and global threats are affecting the health of coral reefs worldwide. In addition to endangering the livelihoods and source of food for millions of people, threats to coral reefs may result in flattening reefs, which reduce habitat complexity and the ability of reefs to protect shorelines from erosion. This could be particularly detrimental to low-lying Pacific atolls like those found in the Republic of the Marshall Islands (RMI). I examined the influence of local human disturbance and heat stress on coral and algal community composition in Majuro and Arno Atolls in the RMI to explore how human disturbance affects coral and algal communities, and how to best characterize those communities. With a population of approximately 30,000 people, Majuro is home to the largest population of all of the RMI's 29 atolls and underwent extensive human modifications after American occupation during World War II. By contrast, Arno is home to fewer than 2,000 people and has remained relatively undisturbed. In June of 2016, I conducted benthic surveys at 25 sites along a gradient of human impacts across the two atolls. At each site at 10m depth, I measured percent cover of coral and algae genera and size-frequency of coral. I also utilized limited historical data to explore how reefs had recovered after a thermal stress event in 2014. In order to estimate human disturbance, I used the mean normalized difference vegetation index (NDVI) of the nearby coastline, which measures vegetation intensity. The coral and macroalgae composition of sites differed by atoll, mean NDVI, and wind and wave exposure, but not by sea surface temperature. The most degraded sites had low macroalgae cover and were dominated by turf algae, sponges, and cyanobacteria. One genus of macroalgae, Halimeda, was associated with sites that had low disturbance, while another, Hypnea, was correlated with higher disturbance. These results suggest that using macroalgae as an indicator of degradation may mask the influence of local human disturbance on reef community composition. Instead, it is important to consider identifying other indicator taxa and to measure coral and macroalgae cover to at least the genus level.

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Mass coral bleaching in recent years has become a recurring event and was suspected to have a relationship with El Niño events. Changes in the understanding of what constitutes an El Niño event prompted further research into the relationship with Caribbean sea surface temperatures due to their impact on corals.Multiple statistical tests were employed to profile the relationship between the individual event types and the Caribbean. Ultimately, a bootstrapping technique determined that Central Pacific El Niño events bear a relationship, while Eastern Pacific event types do not.An attempt to hindcast El Niño events in order to comment on the history of impacts upon the Caribbean was unsuccessful due to a lack of sufficient input data, but a model determining potential locations of data is presented.

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The rise of ocean temperatures globally has become a grave threat to coral reefs, as it is increasing the severity and frequency of mass coral bleaching events and post-bleaching coral mortality. The continued existence of productive coral reefs will rely on corals’ ability to undergo recovery. In 2010, Tobago’s coral reefs were exposed to severe heat stress leading to mass bleaching of up to 29-60% of colonies at observed sites. This study evaluated the impact of coral bleaching and recovery of coral communities across three major reef systems in Tobago that differ in their exposure to terrestrial runoff. Assessments were done on the 1) density and composition of coral juveniles to characterise the levels of recruitment, 2) sedimentation rates and composition to understand its potential impact on recovery, and 3) species’ size frequency distributions in 2010, 2011 and 2013 to examine temporal changes among population size structure. In 2013, low juvenile densities were observed (5.41 ± 6.31 m-²) at most reef sites, which were dominated by brooding genera while broadcasting genera were rare. Sediment material, measured in May and June (end of Tobago’s dry season) was mostly terrigenous and deposited at rates below coral stress threshold levels at most sites. Out of 27 species populations assessed between all sites, 4 populations mean colony size had significantly changed by the bleaching event, and only changed 5 populations over the two following years. The few populations that were significantly altered (mainly S. siderea and M. faveolata) after the bleaching saw a rise in small sized colonies, mostl likely as a result of colony fragmentation. This study highlights that recovery via sexually produced recruits among broadcasting species was limited. While sedimentation rates were low, it is likely they are significantly higher throughout the rainy season, thus a long-term sedimentation study is highly recommended. Most coral populations resisted significant alteration from heat stress in 2010. However, given that future thermal stress is projected to become more intense, this study shows that mass bleaching disturbance could lead to decline coral population’s mean colony size, which could affect coral recovery as smaller colonies are less fecund.

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The El Niño/ Southern Oscillation (ENSO) is known to influence the weather in western North America through teleconnections. Several studies have established a relationship between ENSO and forest fire occurrence. However, a recently discovered variant of ENSO, called Central Pacific El Niño, may cause a different teleconnection and forest fire pattern.Investigating and classifying past El Niño events and their possible influence on weather and forest fire patterns in western North America from 1981-2010 was the objective of this study.The analysis revealed that current El Niño classification methods are suboptimal and that a binary distinction leads to misclassification of events. It, however, confirms that the two types show a different warming pattern as well as different wind and precipitation patterns. These characteristics of the Central Pacific El Niño can cause different extra tropical teleconnections in western North America than the canonical El Niño. Variation of teleconnections within the events and the limited amount of events, however, complicate a clear conclusion. Further, other oscillations such as the Arctic Oscillation play a major role in impacting the climate in western North America. Exploratory analysis of natural forest fires of North America identified hot spots of annual area burned in central Alaska, north-west and central Canada and western United States. Further, singular value decomposition and spatial correlation analysis revealed a different teleconnection response in summer drought patterns over western North America related to the two types of El Niño. The drought pattern is significantly related with forest fire frequency and area burned in certain regions across western North America. A clear connection between the different El Niño types and the forest fire pattern however remains inconclusive.

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In this thesis I analyse the effects of the Kiribati Adaptation Project (KAP). The KAP is an early climate change adaptation project and it has been instrumental in the World Bank’s (the implementer of the KAP) expansion into the climate change agenda. I situate the KAP in the long, colonial, history of developmentalism and draw from critical development and policy studies to understand this project. Although climate change adaptation and development are contradictory in many senses, they have similarities: they are practiced by the same institutions, with the same project management techniques, and they are implemented through projects. I ask the following research questions:1. What work does climate change adaptation do as an organising principle for a project?2. How is climate change adaptation as a policy articulated into grounded practices?3. What are the unintended effects of a novel climate change adaptation project in an archetypical vulnerable place?To answer these research questions I draw from six weeks field work in Kiribati, where I met with KAP project managers and consultants, government officials and other interested onlookers. In chapter three, I observe that the KAP was focused on producing technical reports and technical expertise. I analyse why this is the case and what some of the effects of this are. By participating in the KAP, consultants, funders and other i-Matang relatives of the project gain expertise in the novel, and increasingly lucrative, arena of climate change adaptation. In chapter four, I analyse the ways in which i-Kiribati actors assemble and perform their vulnerability to climate change. Performances are an intentional strategy to gain recognition for the plight of the low-lying and fragile atoll nation. Officials and public servants have little choice but to perform their vulnerability; the Government of Kiribati depends on these finances, but this dependence is uncertain. The KAP is a key site, as it exemplifies the asymmetries of climate change adaptation and mitigation. The KAP expects to create local resilience in the face of an exogenous threat, in the place least able to be resilient, and least responsible for causing the threat.

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