Global Megacities and Frequent Floods: Correlation between Urban Expansion Patterns and Urban Flood Hazards

Abstract

With climate change causing increased extreme weather events, megacities worldwide are experiencing unprecedentedly devastating floods and recurring flood damage. Investigating global megacities’ increased disposition to flooding will aid in developing sustainable flood-risk-management frameworks. Many studies have been conducted on the association between land-cover types and flood consequences, but few on investigating urban expansion patterns’ correlation with flood hazard and risk. This study examines the correlation between urban expansion patterns and increased flood hazards. Twelve megacities throughout the world were selected for this study. After exploring the possibility of the megacities having experienced flooding, we qualified their patterns of urban expansion and their potential to influence the elements of flood risk. Our results revealed that edge expansion and leapfrogging patterns had a strong positive correlation with statistical significance with flood hazard, while infilling had a weak positive correlation that showed no statistical significance with flood hazard. Further, we found that the megacities have all experienced devastating floods in the past two decades. Flood risk frameworks need to account for the impact of these patterns, and future urban planning designs and policies need to incorporate flood risk frameworks that account for patterns of urban expansion.

The Resilience of the Built Environment to Flooding: The Case of Alappuzha District in the South Indian State of Kerala

“…Urbanisation and land-use changes are significant factors contributing to hazard, exposure, and vulnerability (H-E-V), owing to their impact on urban surface hydrological characteristics [40,41]. Urban expansion patterns and types, such as edge expansion and leapfrogging, can affect the risk level, as infilling has a weaker positive correlation with flood hazards [42]. Construction activities affect surface infiltration, evapotranspiration, and runoff, exacerbating the frequency and duration of urban flooding [43].…”

“…Different land-use scenarios (natural, economic, and sustainable development) showed that the land-use pattern under the sustainable development scenario is the most conducive to reducing the flood risk [40,41]. In addition, the spatial distribution of water-bearing surfaces, such as the presence of natural or artificial lakes, can significantly influence the flood levels in urban areas and increase risk [42,46]. In addition, the built environment can alter natural waterways and drainage patterns, leading to increased flood hazards.…”

“…The implementation of low-impact development (LID) practices, including "rain gardens (RG), green roofs (GR), vegetated swales, infiltration trench (IT), bioretention (BR), rain barrels (RB), permeable pavement (PP), and their combinations", has been shown to mitigate inundation to some extent, particularly under rainfall events of smaller magnitude [47]. The concept of "sponge cities" in China illustrates an approach to urban design that integrates water management into the urban development, aiming to mitigate flood risk through permeable pavements and other low-impact development strategies [42].…”

Revisiting Urban Resilience: A Systematic Review of Multiple-Scale Urban Form Indicators in Flood Resilience Assessment

“…Additionally, cities can leverage technology, such as real-time monitoring and communication systems, to provide timely warnings and updates to residents about evacuation routes and flood risks [152,282,283]. Proximity to water bodies significantly impacts FR, as areas near rivers, lakes, or coastlines are more susceptible to inundation and flood risks [268,[284][285][286]. While proximity to water bodies may offer recreational and economic opportunities, it also increases the vulnerability of communities to flooding events.…”

A Risk-Based Multicriteria Approach for Assessing and Monitoring Flood Disasters Under Heavy Precipitation

“…Another well-known problem related to floods is accelerated and unplanned urbanization, which aggravates flood problems, especially in large cities (Daksiya, Mandapaka, and Lo 2021). Idowu and Zhou (2023) found that all the twelve megacities worldwide investigated in their study have experienced devastating floods in the past two decades, therefore, evidencing the need to incorporate in flood risk management (FRM) the accounting of urban expansion patterns together with climate changes. FRM involves several actions and decisions for disaster preparedness, warning, and response.…”