Floods in a Megacity

Geospatial Techniques in Assessing Hazards, Risk and Vulnerability

verfasst von: Ashraf Dewan

Verlag: Springer Netherlands

Buchreihe : Springer Geography

Enthalten in: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik" , Springer Professional "Wirtschaft"

Einloggen, um Zugang zu erhalten

Über dieses Buch

Flooding is one of the most devastating natural hazards in the world. Available records suggest that both flood frequency and severity are on the rise and this is likely to worsen in the context of climate change. As population, infrastructure and poverty grow rapidly in developing countries, particularly in urban agglomerations of 10 million people or more, floods could cause widespread devastation, economic damage and loss of life. Assessment of vulnerability and risk from naturally occurring phenomena is therefore imperative in order to achieve urban sustainability.

This book uses geospatial techniques to evaluate hazards, risk and vulnerability at a metropolitan scale in a data-scarce country. An empirical study was performed using remote sensing, GIS and census data. This research offers a new approach to mapping population, infrastructures and communities at risk which can greatly contribute to the deeper understanding of flood disasters in a rapidly expanding megacity. Examples shown in this book are from Dhaka Megacity, however, the techniques and methods can easily be implemented in medium to large cities of similar characteristics.

The book is essential reading for hazard researchers, geospatial scientists, disaster management professionals, geographers, urban planners, and social scientists.

Ashraf M. Dewan is currently a Lecturer in the Department of Spatial Sciences at Curtin University, Western Australia (on leave from his substantive position as Associate Professor in the Geography & Environment Department at the University of Dhaka, Bangladesh).

Inhaltsverzeichnis

Frontmatter

Chapter 1. Introduction

Abstract

This chapter presents trends in flood occurrences and associated damage since the 1950s in the context of the world, South Asia, and Bangladesh. The types of urban flooding and their causes are discussed to shed light on the increasing vulnerability of megacities to floods. The analyses reveal that floods and associated losses around the world have increased with time. However, while flood-related fatalities have decreased substantially, economic losses have increased, disproportionately affecting developing countries. Among the South Asian countries, India had the highest occurrence of floods, followed by Bangladesh. The vulnerability of megacities to floods, particularly in developing nations, is exacerbated due to rapid urban expansion, increasing concentration of population and property, rampant poverty, physical location, and poor-quality housing.

Ashraf M. Dewan

Chapter 2. Hazards, Risk, and Vulnerability

Abstract

Natural hazard terminologies with existing models of vulnerability, hazard, and risk are presented in this chapter. A conceptual framework has been developed based on hazard literature. The basic premise of the framework is based on Cutter’s place of hazard theory with inputs from recent literature. In the framework, hazard is viewed as a threat that has the potential to overwhelm people, property, and the environment. It is a pre-existing condition that can turn into a catastrophe depending on the influence of exogenous and endogenous factors. Exposure to hazard is treated as given and is an implicit element. The vulnerability element is perceived as the interactive effects of the social and physical aspects of a system (e.g., urban) regarding the causal process of hazards. Contrary to some conceptualizations, the framework views that the total vulnerability of a community depends on physical, social, and existing coping capacity attributes, and therefore, the calculation of the total vulnerability should consider these elements simultaneously. Risk is conceptualized as the product of hazard and vulnerability. To minimize the effects of disasters, it is imperative to take appropriate measures to reduce vulnerability rather than risk.

The utilization of geospatial techniques in flood risk management is separated into three categories: flood mapping, damage assessment, and evaluation of flood risk and vulnerability. Biophysical and socioeconomic data that are sourced from remote sensing, census geography, and other spatial databases are employed to evaluate flood-related risk in diverse environments. A variety of methods—comprising inductive, deductive, and multi-criteria evaluation—are used to determine flood vulnerability and risk as evidenced by the literature survey. It reveals that geospatial techniques can be utilized effectively in the entire spectrum of the disaster cycle, which can save lives and property from natural hazards such as flood, as well as support informed decision making during emergencies.

Ashraf M. Dewan

Chapter 3. Vulnerability of a Megacity to Flood: A Case Study of Dhaka

Abstract

This chapter illustrates the physical environment together with the built and socioeconomic characteristics of the megacity of Dhaka. An account of historical floods with damage statistics is discussed, revealing that flood loss in the city has increased over time. This is clearly attributed to unplanned and ill-structured development planning. A number of factors are accountable for the increase in flood vulnerability, including extreme population density, intense inequality in resource distribution, and dilapidated drainage systems. Although various adaptation strategies have been suggested for flood management, their success depends on a number of issues such as restricting urban expansion in flood-prone areas.

Ashraf M. Dewan

Chapter 4. Spatial and Temporal Distribution of Floods

Abstract

Flood mapping and monitoring was performed using both Landsat and Radarsat data from 1988 to 2009. Multi-temporal satellite data were digitally classified using a threshold algorithm to determine the spatial and temporal distribution of floods. In addition, flood depths were calculated using the highest water-level data with a DEM. Synthetic depth–damage curves were prepared for three housing categories and for major roads. Flood maps were evaluated using classified satellite images with ground truth data. It was found that 25% of the study area is flooded every year which could rise to more than 40% during abnormal events such as those that occurred in 1988 and 1998. Flood damage estimations revealed that the greatest damage occurred to katcha houses rather than semi-pucca and pucca houses. Variable accuracies were found for satellite-derived flood maps; however, the overall accuracy was highest for radar-based classifications.

Ashraf M. Dewan

Chapter 5. Modeling Flood Hazards

Abstract

Satellite-derived flood maps from 1988 to 2009 were used to construct a flood-affected frequency map of the study area. Similarly, a series of flood depth maps were used to generate a flood damage map for flood depth data. A flood hazard map was then developed by considering both the flood-affected frequency and flood depth data, simultaneously using a 2-D ranking matrix. The final flood hazard map was then combined with population and housing data to calculate the flood exposure for these two elements. The analysis revealed that 23% of the population is located in low- to high hazard zones, while 25% of human settlements are located in different flood hazard zones.

Ashraf M. Dewan

Chapter 6. Vulnerability and Risk Assessment

Abstract

Using census and spatial databases, this chapter demonstrates the assessment of flood vulnerability and risk zoning in the megacity of Dhaka. A place-based approach was adopted to evaluate flood vulnerability at the community level. A method comprising the AHP and the WLC was used to operationalize the conceptual model within a GIS framework. A number of biophysical variables were used to derive the physical vulnerability index (PVI). In addition, nine variables were extracted from diverse sources to derive the social vulnerability index (SVI). To determine the coping capacity of a community, five variables were employed and a coping capacity index (CCI) was developed. Using the PVI, SVI, and CCI, a composite vulnerability index (CVI) was prepared, which revealed that 28 and 14% of the population in the study area were located between high and very high vulnerable zones, respectively. Thirty-six percent were in katcha housing units, which are largely home to marginal people and were in the very high vulnerable zone, revealing the susceptibility of human settlements to floods. Flood hazard data were multiplied with the CVI to delineate the flood risk zone. A total of 18.5% of people lived in high and very high flood risk zones, which was further compounded by the number of females, young, elderly, and illiterate persons. At least 25.8% of housing units were located in these zones. The flood risk map developed in this study could be used as baseline information for the development of pertinent mitigation measures to ameliorate flood loss in the days ahead.

Ashraf M. Dewan

Chapter 7. Conclusions and Recommendations

Abstract

Flood has been singled out because it continues to be a matter of concern in many parts of the world, as suggested by various climate predictive models. Even though both rural and urban communities are equally prone to flood hazards, the literature suggests that the effect of floods is enormous in urban areas.

Ashraf M. Dewan

Backmatter

Titel: Floods in a Megacity
verfasst von: Ashraf Dewan
Verlag: Springer Netherlands
Electronic ISBN: 978-94-007-5875-9
Print ISBN: 978-94-007-5874-2
DOI: https://doi.org/10.1007/978-94-007-5875-9