Littérature scientifique sur le sujet « Deltaic megacity »

Achieving urban water security requires sustaining the trade-offs between the exploitation of water/environmental resources and ecosystem services. This achievement not only reduces the pollution and contamination in the environment, level of water stress, but also secures good ambient water quality and future for people’s well-being and livelihoods. Changes in land use and land cover and growth of impervious structures can immediately generate severe ecological and social issues and increase the level of natural or manmade risks, affecting the condition of ecosystem services within and in the vicinity of an urban region. As a result of these transformations and further exploitation, due to the growing anthropogenic pressure, surface water and groundwater quality can be deteriorated compared to ambient water quality standards (for both chemical and biological pollutants). Based on land use and land cover (LULC) data retrieved from remote sensing interpretation, we computed the changes of the ecosystem service values (ESV) associated with the LULC dynamics, water quality and, finally, urban water security during the pre- and post-monsoon periods of 2009, 2014 and 2019 in Kolkata, an Asian deltaic megacity, and its peri-urban wetlands named East Kolkata Wetlands (EKW). The area under wetlands reduced comprehensively in 2009–2019 due to the conversion of wetlands into various other classes such as urban settlement, etc. The quality of surface water bodies (such as rivers, lakes, canals and inland wetlands) deteriorated. The groundwater quality is still under control, but the presence of arsenic, manganese and other metals are a clear indication of urban expansion and related activities in the area. As a result, there was a change in the ESV during this timeframe. In the pre-monsoon period, there was an increase in total ESV from US$53.14 million in 2009 to US$53.36 million and US$59.01 million in 2014 and 2019, respectively. In the post-monsoon period, the ESV decreased from US$67.42 million in 2009 to US$64.13 and US$61.89 million in 2014 and 2019, respectively. These changes can be attributed to the peri-urban wetlands and the benefits or services arising out of them that contribute more than 50% of the total ESV. This study found that the area under wetlands has reduced comprehensively in the past 10 years due to the conversion of wetlands for various other uses such as urban expansion of the Kolkata City, but still, this peri-urban wetland supports the urban water security by providing sufficient ecosystem services. In conclusion, the transformation in extent of the water-related ecosystem is a crucial indicator of urban water security, which also measures the quantity of water contained in various water-related ecosystems. Quantitative analysis of the LULC change, hence, is important for studying the corresponding impact on the ecosystem service value (ESV) and water quality that helps in decision-making in securing urban water future and ecosystem conservation.

The United Nations Sustainable Development Goals (SDGs) and their corresponding targets are significantly interconnected, with many interactions, synergies, and trade-offs between individual goals across multiple temporal and spatial scales. This paper proposes a framework for the Integrated Assessment Modelling (IAM) of a complex deltaic socio-ecological system in order to analyze such SDG interactions. We focused on the Sundarban Biosphere Reserve (SBR), India, within the Ganges-Brahmaputra-Meghna Delta. It is densely populated with 4.4 million people (2011), high levels of poverty, and a strong dependence on rural livelihoods. It is adjacent to the growing megacity of Kolkata. The area also includes the Indian portion of the world’s largest mangrove forest––the Sundarbans––hosting the iconic Bengal Tiger. Like all deltaic systems, this area is subject to multiple drivers of environmental change operating across scales. The IAM framework is designed to investigate socio-environmental change under a range of explorative and/or normative scenarios and explore associated policy impacts, considering a broad range of subthematic SDG indicators. The following elements were explicitly considered: (1) agriculture; (2) aquaculture; (3) mangroves; (4) fisheries; and (5) multidimensional poverty. Key questions that can be addressed include the implications of changing monsoon patterns, trade-offs between agriculture and aquaculture, or the future of the Sundarbans’ mangroves under sea-level rise and different management strategies. The novel, high-resolution analysis of SDG interactions allowed by the IAM will provide stakeholders and policy makers the opportunity to prioritize and explore the SDG targets that are most relevant to the SBR and provide a foundation for further integrated analysis.

The Pearl River Delta (PRD) region has experienced rapid economic and population growth in the last three decades. The delta includes coastal megacities, such as Hong Kong. These low-lying urbanised coastal regions in the PRD are vulnerable to flood risks from unpredictable climatic conditions. These can result in increasing storm surges, rising sea level and intensified rainstorms causing coastal and inland flooding, all of which impact the delta. This paper has taken the coastal megacity of Hong Kong as a case, focusing on two study sites: Shenzhen River and Tai O town, chosen for their peculiar inland and coastal flood problems. A sustainable flood risk appraisal (SFRA) template was developed against which sustainable flood risk management (FRM) practices in these sites were benchmarked. Thirty-eight stakeholders were interviewed during this research in order to understand the current FRM practices, their barriers and their constraints. It was found that FRM in the case study currently focuses on hard engineering, while neglecting other important sustainability indicators. A SFRA practice that takes public participation, equity of flood preparedness and environmental friendly into account could be effective in achieving sustainable flood risk mitigation practices in Hong Kong and other coastal cities in the PRD.

Les deltas constituent des environnements combinant atouts et vulnérabilités. Milieux propices à la navigation, aux échanges maritimes et au commerce, fertiles pour l'agriculture, et riches en eau et biodiversité, leurs caractéristiques environnementales posent aussi des contraintes spécifiques. Au fur et à mesure que Bangkok s'est urbanisée et co-transformée avec son environnement deltaïque, la mégapole a dû gérer son exposition aux crues et aux marées, à l'érosion du littoral, à l'intrusion d'eau salée, à la pollution des eaux ainsi qu'à l'affaissement du sol et au problème d'alimentation en eau potable.Afin d'identifier les contraintes physiques et institutionnelles à une urbanisation durable, la thèse se donne comme objectif la compréhension des transformations conjointes ─ à la fois environnementales et sociopolitiques ─ induites par les enjeux de l'eau, à travers une analyse de la gouvernance 'en acte', manifestée par des processus de décision dans un contexte de pluralité d'acteurs, institutions, ramifications écologiques, échelles spatiales et administratives, normes, récits discursifs, représentations et imaginaires. Cette gouvernance multi-niveaux (on considère les interactions 'verticales' entre les acteurs globaux, l'État, la BMA (Bangkok Metropolitan Administration) et les collectivités locales) intersecte et se fond avec une gouvernance 'horizontale', qui associe des acteurs privés (industries, bureaux d'études, lobbies), la société civile (ONGs, collectifs), et le secteur académique.L'hypothèse centrale de cette thèse est que l'explicitation de la gouvernance, au prisme des processus décisionnels autour de projets et politiques publiques liés à l'eau, permet de rendre compte de la dimension anthropique des transformations environnementales et socio-politiques au service du maintien du développement et de la prospérité de la capitale face aux aléas du delta et aux impératifs économiques imposés par la compétition entre les mégapoles globales. Ces transformations sont explicitées à travers trois études de cas illustrant la formulation de problèmes publiques et leurs controverses : 1) la mise en valeur des berges de la rivière Chao Phraya à travers un projet de promenade ; 2) la gestion des eaux souterraines en lien avec le phénomène de subsidence ; 3) la protection de la capitale des inondations par des projets de canaux, extérieurs à la ville, permettant de dériver les débits de crue.L'eau par sa fluidité relie l'atmosphère, le sous-sol et les surfaces urbanisées aux habitants humains et non-humains du delta, et constitue un témoin matériel qui nous permet de saisir empiriquement la complexité des interactions hydro-sociales. La transformation environnementale de Bangkok n'est pas seulement la conséquence d'une urbanisation présentée comme incontrôlée ou inéluctable, elle est aussi le résultat de faisceaux d'intérêts politiques et financiers qui remodèlent constamment le flux et la distribution spatiale des bénéfices et des coûts associés à la transformation de l'environnement aquatique et du cycle hydrologique. L'analyse met en relief la faible autonomie décisionnelle de la BMA face à un État centralisé qui garde l'essentiel du pouvoir d'influence sur les politiques publiques, révèle l'importance centrale du monde universitaire dans les débats et prise de décision, fait ressortir le rôle du médium visuel dans l'enrôlement d'acteurs (processus d'imaginierie), et souligne la nature multi-scalaire de la composition des coalitions d'acteurs et de leurs reconfigurations
Deltas are environments that combine opportunities and vulnerabilities. They are ideal places for shipping, maritime trade and commerce, fertile for agriculture, and rich in water and biodiversity, but their environmental characteristics also pose specific constraints. As Bangkok has urbanised and co-evolved with its deltaic environment, the megalopolis has had to manage its exposure to floods and tides, coastal erosion, saltwater intrusion, water pollution, land subsidence and the supply of drinking water. In order to identify the physical and institutional constraints to sustainable urbanisation, this thesis aims to understand the joint transformations ─ both environmental and socio-political ─ induced by water challenges, through an analysis of governance 'in action', manifested by decision-making processes unfolding in a context of a plurality of actors, institutions, ecological ramifications, spatial and administrative scales, norms, narratives, representations and imaginaries. This multi-level governance (we consider the 'vertical' interactions between global players, the State, the BMA (Bangkok Metropolitan Administration) and local administrations) intersects and merges with 'horizontal' governance, which brings together private players (industries, consultancies, lobbies), civil society (NGOs, collectives) and the academic sector.The central hypothesis of this thesis is that the clarification of governance, through the analysis of decision-making processes around water-related projects and public policies, makes it possible to account for the environmental and socio-political transformations geared towards maintaining the capital's prosperity in the face of the hazards of the delta and the economic competition between global megacities. These transformations are explained through three case studies that illustrate the formulation of public problems and their controversies: 1) the enhancement of the banks of the Chao Phraya River through a promenade project; 2) the management of groundwater in relation to the phenomenon of land subsidence; 3) the protection of the capital from flooding through canals designed to divert flood flows away from the city.The fluidity of water links the atmosphere, the underground and urban surfaces to the human and non-human inhabitants of the delta, and constitutes a material witness that enables us to empirically grasp the complexity of hydro-social interactions. The environmental transformation of Bangkok is not only the consequence of urbanisation, presented as uncontrolled or inevitable, but also the result of a bundle of political and financial interests that are constantly reshaping the flow and spatial distribution of the benefits and costs associated with the transformation of the aquatic environment and the hydrological cycle. The analysis highlights the BMA's limited decision-making autonomy in the face of a centralised state that retains most of the power to influence public policy, reveals the central importance of the academic sector in debates and decision-making, highlights the role of visual media in enlisting stakeholders (the imagineering process), and underlines the multi-scalar nature of the composition of stakeholder coalitions and their reconfigurations