A Hybrid Modelling Framework for Ecosystem-Based Climate Change Adaptation Using System Dynamics and Bayesian Networks

Abstract

The world is undoubtedly being threatened by the negative impacts of climate change. The degradation of the ecosystem, the loss of species and the endangerment of human health, livelihood and wellbeing are the main consequences of this ever-growing pressure. Coastal communities, particularly Small Island Developing States (SIDS), require extra attention due to their increased vulnerability and dependency on ecosystem services. Services provide by coral reefs are among the most fragile ecosystems that provide essential services to local SIDS communities. Adaptation is a commonly accepted method by both international and local governments and authorities to tackle this phenomenon; adaptation refers to moderating the adverse effects of climate change through a wide range of actions to protect, accommodate or retreat. However, some adaptation actions and policies are not being adopted in a comprehensive approach, causing negative impacts on each other or possibly resulting in the failure of the desired and designed effectiveness. Thus, it is essential to use a holistic approach to identify adaptation solutions that are economically and practically feasible and realistic without compounding additional pressures on natural systems. The ecosystem-based approach is the key to dealing with common adaptation challenges and to addressing the needs of SIDS local communities. However, planning for SIDS communities under rapidly changing, uncertain non-climatic and climatic conditions requires following a practical approach capable of fulfilling the general adaptation planning requirements as well as specific characteristics of SIDS traditional communities. Thus, the needs and features of successful adaptation planning were studied through a systematic literature review to create a practical and effective planning approach. A total of 650 relevant papers were initially nominated and reviewed; however, this number was reduced to 116 papers for thorough revision and detailed analysis. First, it was found that an integrative stepwise planning approach is required to integrate the results of multidisciplinary analyses and assessments and stakeholders' knowledge and opinions. Next, three crucial dimensions of a fully integrated climate change adaptation planning process—integration in assessment, modelling and adaptive responses—were identified. Adopting this novel approach, the multi-layered integrative climate change adaptation planning approach, is more likely to yield better climate change adaptation planning outcomes over the long-term. In accordance with the proposed multi-layered integrative climate change adaptation planning approach, a hybrid dynamic modelling framework was developed to assess the health and resilience of coral reefs under different climate change scenarios and their consequential impacts on human wellbeing in Port Resolution, Tanna Island, Vanuatu. This framework follows a structured process and employs suitable techniques capable of dealing with different challenges, including the complexity and dynamicity of socioeconomic and environmental systems and impacts of trans-discipline variables. This multi-layered integrative approach employed structural analysis, fuzzy cognitive mapping (FCM), Bayesian networks (BN) and system dynamics (SD) techniques. Each of these techniques features its own benefits and limitations, and integrating these modelling tools can maximise their respective advantages by compensating for another's limitations. First, the principal influential factors in coral reef health and ecosystem services were identified, and their causal relationships were subsequently mapped using the participatory FCM technique. As a result of structural and FCM analyses, the following outcomes were achieved: (i) system variables were identified and grouped under different categories including marine ecology, climatic, community and socioeconomic variables; (ii) all variables were assessed based on their level of influence on other variables; (iii) the interrelationships of all variables were mapped based on expert knowledge; and (iv) a preliminary scenario-based analysis was performed, and the role and significance of the factors in the time horizon of the study were determined. Next, the long-term perspective of the future health and resilience condition of coral reefs under different sets of management interventions was explored using the BN technique. The BN model was conceptualised using the results of the previously completed step (i.e., FCM). The BN technique was used to incorporate existing data and experts' knowledge and to predict the future conditions of coral reefs under different scenario settings. Finally, the SD modelling step investigated the nexus between environmental and economic values under different combinations of management or adaptation strategies over a long-term period, which is 50 years or by 2070. As an innovative approach, the SD model was parameterised from the outcome of the BN modellings, in which the existing data and information were insufficient to quantify the model. Furthermore, comparing the results of modelling outcomes and their respective sensitivity analyses supported the model behaviour testing process of the final SD model. While each research stage has its own specific practical, methodological and scientific contribution, the main findings of this PhD research are: (1) sustainable management or adaptation planning of coastal coral reefs should be studied from a multidisciplinary socio-ecological lens; (2) identifying, assessing and prioritising all potential adaptive responses, including engineering, social and regulatory, through an integrated vulnerability assessment and decision-making process with all of their subsets is the key to success; (3) immediate actions to preserve coral reef health and resilience are required to protect the current flow of ecosystem services; (4) local management interventions are not likely to protect coral reefs under the worst-case climate change scenario; and (5) the steady and integrated implementation of management strategies alongside global mitigation efforts to minimise the impacts of climate change could protect the long-term flow of economic benefits and maintain functional coral cover despite economic loss over a short-term period. The predominant output of this study is a novel hybrid BN-SD modelling framework to support ecosystem-based climate change adaptation planning.