Probabilistic Modelling for Incorporating Uncertainty in Least Cost Path Results: a Postdictive Roman Road Case Study

AbstractThe movement of past peoples in the landscape has been studied extensively through the use of least cost path (LCP) analysis. Although methodological issues of applying LCP analysis in archaeology have frequently been discussed, the effect of DEM error on LCP results has not been fully assessed. Due to this, the reliability of the LCP result is undermined, jeopardising how well the method can confidently be used to model past movement. To strengthen the reliability of LCP results, this research proposes the use of Monte Carlo simulation as a method for incorporating and propagating the effects of error on LCP results. Focusing on vertical error, random error fields are calculated and incorporated into the documented and reproducible LCP modelling process using the R package leastcostpath. By graphically communicating the impact of vertical error using probabilistic LCPs, uncertainty in the results can be taken into account when interpreting LCPs. The method is applied to a Roman road case study, finding that the incorporation of vertical error results in the identification of multiple ‘least cost’ routes within the landscape. Furthermore, the deviation between the roman road and the probabilistic LCP suggests that the location of the roman road was influenced by additional factors other than minimising energy expenditure. This research finds that the probabilistic LCP derived using Monte Carlo simulation is a viable method for the graphical communication of the uncertainty caused by error within the input data used within the LCP modelling process. Therefore, it is recommended that probabilistic LCPs become the default approach when modelling movement using input data that contains errors.</jats:p

Climate-Based Emulator of Distant Swell Trains and Local Seas Approaching a Pacific Atoll

ABSTRACT: Wave-induced flooding is a major coastal hazard for the low-lying atolls of the Pacific. These flooding events are expected to increase over time, which may cause significant coastal damage in some locations. Coastal flooding analysis (forensic or forecasted) is particularly challenging in these small islands due to the co-occurrence of several swells and local seas propagating in a complex configuration of archipelagos. Therefore, assessing the contribution of swells and wind seas on the flooding hazards that threaten the atoll islands requires the spectral characterization of the wave climate, since integrated wave parameters do not accurately represent the wave conditions in these environments. On the other hand, the relative short records of wave conditions, represent only a small fraction of the possible range of combinations that could produce a wave-induced flooding event. For these reasons, we propose the analysis of all the spectral energy arriving toward a study site, by isolating and parameterizing each swell train. Then, taking into account the link with large-scale climatic patterns (i.e., El Niño Southern Oscillation), we present a new multi-modal seas emulator capable of generating infinitely long time series of synthetic individual swell trains and seas. This new climate-based emulator allows a better understanding of swell behavior in the Pacific, and the generation of multimodal wave conditions to populate the historical records as a key point to perform robust coastal flood risk assessments considering climate variability

Aerial Laser Scanning Data as a Source of Terrain Modeling in a Fluvial Environment: Biasing Factors of Terrain Height Accuracy

K

Inundation Exposure Assessment for Majuro Atoll, Republic of the Marshall Islands Using A High-Accuracy Digital Elevation Model

Majuro Atoll in the central Pacific has high coastal vulnerability due to low-lying islands, rising sea level, high wave events, eroding shorelines, a dense population center, and limited freshwater resources. Land elevation is the primary geophysical variable that determines exposure to inundation in coastal settings. Accordingly, coastal elevation data (with accuracy information) are critical for assessments of inundation exposure. Previous research has demonstrated the importance of using high-accuracy elevation data and rigorously accounting for uncertainty in inundation assessments. A quantitative analysis of inundation exposure was conducted for Majuro Atoll, including accounting for the cumulative vertical uncertainty from the input digital elevation model (DEM) and datum transformation. The project employed a recently produced and validated DEM derived from structure-from-motion processing of very-high-resolution aerial imagery. Areas subject to marine inundation (direct hydrologic connection to the ocean) and low-lying lands (disconnected hydrologically from the ocean) were mapped and characterized for three inundation levels using deterministic and probabilistic methods. At the highest water level modeled (3.75 ft, or 1.143 m), more than 34% of the atoll study area is likely to be exposed to inundation (68% chance or greater), while more than 20% of the atoll is extremely likely to be exposed (95% chance or greater). The study demonstrates the substantial value of a high-accuracy DEM for assessing inundation exposure of low-relief islands and the enhanced information from accounting for vertical uncertainty

The challenges of climate change adaptation for displaced communities : the Bikini community on Kili and Ejit Islands : a thesis presented in partial fulfilment of the requirements for the Master of International Development, School of People, Environment and Planning, Massey University

The displaced Bikini community on Kili and Ejit Islands are facing significant threats from sea level rise. This effect of climate change is just the latest devastation to face this community. In 1946, the Bikinians were coerced into leaving their homes on Bikini Atoll to allow the United States to conduct nuclear tests. Their forced relocation has led to the community suffering long term impacts associated with displacement as they are still unable to return home. The vulnerabilities faced by the Bikinians due to displacement are intensifying the Bikinians’ exposure and sensitivity to climate change. However, the Bikinians are not passive victims of displacement or climate change and have shown high levels of resilience to the disruptive impacts of these processes. The strategies first developed in response to their displacement must now consider climate change. Conversely, for their adaptation to climate change to be successful, these strategies must address the impacts of displacement as the underlying cause of Bikinian vulnerability. The threats of climate change for the community on Kili and Ejit are considerable. Despite having developed strategies to respond to the vulnerabilities they face, climate change will continue to make life on Kili and Ejit Islands difficult because of the underlying social, cultural, economic and environmental characteristics. There may be limits to the Bikinians’ ability to adapt and remain resilient. The Bikinians, already forced from their homes, have been highly mobile with most of their population residing on other islands within the Marshall Islands or in the United States. Climate change may force yet more Bikinians to consider migration as a form of adaptation. This study explores how the vulnerabilities the Bikinians endure because of their displacement contribute to vulnerabilities associated with climate change. This study analyses these issues and focuses on how Bikinians adapt and build resilience. In seeking to share the story of the Bikinians this study draws on bwebwenato (talk story) research methods with members of the Bikinian leadership, and an analysis of documents detailing their struggle for justice against their displacement, and their experience with climate change

Hidrogeomorfologia e efeitos da subida do nível do mar no Balneário Cassino, RS - Brasil

O Balneário Cassino está localizado sobre uma barreira costeira progradante, com evolução geológica associada à regressão marinha iniciada após o último máximo transgressivo Holocênico (barreira IV). A configuração geomorfológica do sítio físico estabelece uma alta suscetibilidade física a alagamentos e inundações, condição que será potencializada progressivamente devido às mudanças climáticas previstas pelo IPCC. Nesta pesquisa foi utilizado um conjunto de metodologias com enfoque geoespacial para identificar e quantificar as principais suscetibilidades associadas à hidrogeomorfologia da área de estudo, assim como os eventuais efeitos da subida do nível do mar no que tange as inundações diretas (intrusão marinha) e indiretas (emersão do nível freático). De forma geral, a barreira Holocênica apresenta uma macrodrenagem regulada pela combinação da orientação dos depósitos sedimentares, na forma de cordões litorâneos regressivos, e do nível da base costeiro. Através da análise de fluxos superficiais, foi identificada uma rede de drenagem mista formada por padrão paralelo e dendrítico. O padrão dendrítico tem predomínio quando na ocorrência de lençóis de areias transgressivos, substrato majoritário da área urbana, dando origem aos divisores de águas de microbacias costeiras. A reconstrução topográfica de alta resolução realizada por levantamento VANT e algorítimo SfM sobre a porção mais próxima da atual linha de costa e o emprego de abordagem bathtub, permitiu mapear o potencial de inundação dos terrenos baixos do Balneário Cassino com base nas cotas de subida do nível do mar propostas pelo IPCC. Assim, se constatou a alta suscetibilidade das áreas localizadas no reverso do cordão de dunas ativas e daquelas próximas as calhas dos canais de drenagem costeiros (sangradouros). Já o monitoramento do nível freático demonstrou a significativa contribuição dos pulsos de infiltração e recarga na variação da zona vadosa. De forma secundária, foi possível identificar a contribuição da energia de ondas e ventos do quadrante S na variação do mesmo. Os resultados também sugerem a estreita relação entre a profundidade do nível freático e a morfologia de cristas e cavas do substrato transgressivo. A modelagem de emersão das águas subterrâneas impulsionadas pela subida do nível do mar demonstrou que para além das inundações diretas, o Balneário Cassino apresenta alta suscetibilidade a inundações indiretas quando os períodos de estreitamento da zona vadosa (meses de maior recarga) são combinados com projeções de subida do nível do mar. Esses resultados demonstram a alta suscetibilidade do sítio em questão a eventos de alagamento e inundações e como esses fenômenos serão potencializados pelas atuais projeções de subida do nível do mar.The Cassino balneary is located on a coastal prograded barrier, with geological evolution associated with the marine regression that started after the last maximum Holocene transgressive (barrier IV). The geomorphological configuration of the physical site establishes a high physical susceptibility to floods and inundations, a condition that will be progressively enhanced due to the climate changes predicted by the IPCC. In this research, a set of methodologies with a geospatial approach was used to identify and quantify the main susceptibilities associated with the study area hydrogeomorphology, as well as the possible effects of sea-level rise in terms of direct (marine intrusion) and indirect (emergence of the water table) form. In general, the Holocene barrier presents a macrodrainage regulated by the combination of the sedimentary deposits orientation, in the form of relict foredune ridges, and the level of the coastal base. Through the surface flows analysis, a mixed drainage network formed by a parallel and dendritic pattern was identified. The dendritic pattern is predominant when transgressive sand sheets occur, a major substrate of the urban area, giving rise to the coastal basin dividers. The high resolution topographic reconstruction performed by UAV survey, the SfM algorithm on the closest part of the current coastline, and the use of a bathtub approach, allowed mapping the flood potential of the low lands of the Casino balneary based on the sea level rise quotas proposed by the IPCC. Thus, it was verified the high susceptibility of the areas located in the active dune cord reverse and of those close to the troughs of the coastal drainage streams (washouts). The monitoring of the phreatic level demonstrated the significant contribution of the infiltration and recharge pulses in the variation of the vadose zone. Secondarily, it was possible to identify the contribution of wave and wind energy in the S quadrant in its variation. The results also suggest the close relationship between the water table depth and the morphology of ridges and pits. The modeling of groundwater emergence driven by sea level rise demonstrated that in addition to direct flooding, Cassino balneary is highly susceptible to indirect flooding when periods of vadose zone narrowing (months of highest recharge) are combined with projections of sea-level rise. These results demonstrate the high susceptibility of the site in question to flooding and inundation events and how the current projections of sea-level rise will enhance these phenomena