Urban infrastructure inundation risk from permanent sea-level rise scenarios in London (UK), Bangkok (Thailand) and Mumbai (India): A comparative analysis

Abstract

Due to anthropogenically created climate change, global cities are facing inundation by rising sea levels. This study aimed to fill knowledge gaps in understanding the exposure of urban infrastructure such as roads, railways, buildings and parks to sea-level rise (SLR) scenarios, and how this would affect local populations. Three economic hubs, namely London (United Kingdom), Bangkok (Thailand) and Mumbai (India) were chosen for comparison due to their coastal locations and regionally concentrated asset wealth with dense populations and economic influence regionally.

The data sources for this research study included three digital elevation models (DEMs); two traditionally used globally available datasets from the Japanese Aerospace Exploration Agency and United States Geological Survey (1 arc-second spatial resolution), and a recently released elevation model by ClimateCentral (3 arc-second spatial resolution). Vector data for the urban infrastructural layers was sourced from navigational supplier HERE, while raster population data was sourced from WorldPop (3 arc-second spatial resolution). A modified bathtub-fill modelling method approach was then applied within GIS applications to model landward-creeping SLR (high-risk: 1 metre, medium-risk: 3 metres and low-risk: 5 metres) using the three DEMs, resulting in the extraction of the total lengths, areas and counts of the infrastructural layers and populations that intersected these flooded areas. Risk index maps were built for the cities' districts to understand where the greatest risks lie, while hypotheses for the inter-relationship between the cities and their infrastructure were tested using non-parametric Kruskal-Wallis independent tests.

From this method, the results showed that in a 1m (high-risk) scenario, Mumbai is consistently the most vulnerable city with between 6-10% of the city's area (particularly the central business district) showing flooding. Bangkok is at lower risk at 4-6% inundation of the city's area (in lower density suburbs), while approximately 2% of London's area (mainly in industrial riverside locations) is at risk. In the medium- and low-risk scenarios, Bangkok is the most vulnerable with 16-51% and 57-92% of its area showing flooding respectively. A 1m SLR shows greatest threat to Mumbai's functionality as a city as all infrastructural elements and up to 24% of the local population will be impacted on a day-to-day basis. On the other hand, a 3 and 5 metre SLR would impact up to 52% and 96% of Bangkok's population respectively.

Although this study gives a geographic indication of the SLR impact on these three cities, budgetary and network constraints precluded the sourcing of high-resolution elevation model data from ClimateCentral as well as locally sourced flood defence structure and hydrological input data. Accuracy within the findings in future studies would increase from inputs such as LiDAR elevation data, socio-economic asset values for the cities' urban infrastructure and multi-criteria hydrological information. In this way, researchers and municipalities would be better informed on the vulnerability to their cities, and use this to build resilience and mitigative efforts against SLR over the coming decades.

Popular Abstract

Since the 1950s, it has been known that human industrial activities are changing the Earth’s natural climate. This is predicted to melt the planet’s ice and warm up the atmosphere, leading to a rise in sea levels and changing weather patterns around the globe. Geographic information sciences (GIS) uses tools to understand locational data captured by satellites and researchers and show where patterns and changes over time. This study aimed to better understand how urban landscapes will be impacted by sea-level rise (SLR), since past studies focusing on SLR gave this field limited coverage. Flooding of urban elements such as roads, railways, buildings and parks will impact people living locally and determine how well a coastal city can function. Three cities with similar physical designs, populations and economic influence were examined and compared: London (United Kingdom), Bangkok (Thailand) and Mumbai (India).

Three sets of digital geographic data for the three cities’ current elevations above sea level were analysed using GIS software, together with data for population, hydrological and urban elements. Using the three elevation data types (two traditional and one new dataset), SLR scenarios of 1- (1m), 3- (3m) and 5-metres (5m) above present day sea levels were simulated, and urban elements and populations within flooded zones were compared. Statistics of the proportion of elements expected to flood in coming decades were calculated, and risk index maps showed which parts of the cities are at greatest risk.

It was found that with a 1m SLR, Mumbai is the city at highest risk with the most land area and urban elements facing flooding (6-10% of its area and up to 24% of its population). Bangkok is at a slightly lower risk, where 4-6% of the city would be flooded, and London is at least risk with 2% area flooded. As sea levels rise further, Bangkok is at greater risk, with 16-51% of the city facing flooding in a 3m SLR scenario and 57-92% flooding in a 5m SLR scenario. From the three elevation datasets used, the newest one (created to have less errors than the traditional datasets) showed the larger areas at risk of flooding, especially with SLR greater than 1m. The model shows that up to 52% and 96% of Bangkok’s population would be impacted respectively, meaning that this city would be unliveable if the sea around it rose by even 3 metres!

Although Mumbai would remain liveable, most of its city centre assets would need relocating or protecting as a priority. This is crucial for both cities’ authorities as they currently have limited strategies in place to manage future climate change. This study visualises which areas of these cities need greater attention. With time global elevation data and local water data will become available and help create more detailed results. This way, people can better understand which parts of their cities are at risk of permanent flooding, and be prepared for the rising sea levels around them.

• author: Pace, Shawn
• supervisor: Andreas Persson
• organization: Dept of Physical Geography and Ecosystem Science
• course: GISM01 20211
• year: 2021
• type: H2 - Master's Degree (Two Years)
• subject: Earth and Environmental Sciences
• keywords: Geography, GIS, Climate Change, Sea-Level Rise, Urban Infrastructure, DEM, London, Mumbai, Bangkok
• publication/series: Master Thesis in Geographical Information Science
• report number: 130
• language: English
• id: 9042597
• date added to LUP: 2021-03-29 15:21:32
• date last changed: 2021-03-29 15:21:32