Flooding in Dhaka, Bangladesh, and the challenge of climate change

Abstract

The country of Bangladesh is located in the Ganges-Brahmaputra-Meghna river delta, and faces multiple natural hazards, in particular flooding, and other challenges such as sea-level rise and a growing population. Dhaka, the capital of Bangladesh with a population of over 17 million people, is among the top five coastal cities most vulnerable to climate change, with over 30 % of the population living in slums. Effective disaster mitigation and adaptation requires an understanding how hazards such as flooding impact the population, e.g. in terms of mortality. If this link is understood, appropriate measures can be undertaken to assist the exponentially growing population in aquiring effective coping mechanisms. <br /> This thesis contributes to the understanding of the behavior of extreme water levels and their links to mortality by assessing the past and current situation in Dhaka. We hypothesize that water levels have changed in frequency, magnitude and duration during the past century, and that extreme water levels lead to an increase in mortality. We also believe that the impacts of climate change on flooding and thus livelihoods in a complex delta can not be treated isolated from other challenges of global change, and illustrate this by setting up a conceptual socio-hydrological causal network that assesses the interactions of natural and anthropogenic processes in a holistic way. <br /> We first analyzed daily water levels of the past 100 years in order to detect potential shifts in extremes. We also employ the enhanced Driving force - Pressure - State - Impact - Response framework compiled with an extensive literature review to explore the complex interactions between the hydrological system under climate change and anthropogenic impacts due to e.g. the construction of dams as well as a growing population. <br /> Our analysis suggests that water levels have indeed changed over the course of the past century. While the magnitude and duration of average flood events decreased, the frequency of extreme flood events has increased. Low water levels have also changed, with a significant decrease in the annual minimum water level most noticeable when we compare the time periods 1909 - 1939 and 1979 - 2009.<br /> The constructed socio-hydrological framework confirms that both natural and anthropogenic processes and their two-way feedbacks need to be included in a climate change impact assessment. The conceptual framework can put these impacts into perspective, allowing policy makers to know where available resources can be used effectively to increase resilience and reduce vulnerability.<br /> Climate change takes place over long stretches of time and thus enable the population of Bangladesh to adapt slowly. Resources such as social capital, which is one of the main tools for slum dwellers to be able to cope with flooding can be altered over time, and as such the system can be considered overall stable and resilient. However, transboundary water sharing issues during the dry season and other implications resulting from dam structures such as Farakka Barrage complicate a prognosis on how the rapidly growing population will be affected in the 21st century. This is particularly important in connection with our previous findings, which suggest that the Greater Dhaka population already experience a significant increase in mortality during droughts. Climate change can thus be seen as an anthropogenic amplification of the socio-hydrological challenges already faced by Bangladesh today.