BONNER METEOROLOGISCHE ABHANDLUNGEN Heft 82 (2018) (ISSN 0006-7156) Herausgeber: Andreas Hense Insa Thiele-Eich FLOODING IN DHAKA,BANGLADESH, AND THE CHALLENGE OF CLIMATE CHANGE BONNER METEOROLOGISCHE ABHANDLUNGEN Heft 82 (2018) (ISSN 0006-7156) Herausgeber: Andreas Hense Insa Thiele-Eich FLOODING IN DHAKA,BANGLADESH, AND THE CHALLENGE OF CLIMATE CHANGE Flooding in Dhaka, Bangladesh, and the challenge of climate change DISSERTATION ZUR ERLANGUNG DES DOKTORGRADES (DR. RER. NAT.) DER MATHEMATISCH-NATURWISSENSCHAFTLICHEN FAKULTÄT DER RHEINISCHEN FRIEDRICH-WILHELMS-UNIVERSITÄT BONN vorgelegt von Dipl.-Meteorologin Insa Thiele-Eich aus Heidelberg Bonn, Juli 2017 Diese Arbeit ist die ungekürzte Fassung einer der Mathematisch-Naturwissenschaft- lichen Fakultät der Rheinischen Friedrich-Wilhelms-Universität Bonn im Jahr 2017 vorgelegten Dissertation von Insa Thiele-Eich aus Heidelberg. This paper is the unabridged version of a dissertation thesis submitted by Insa Thiele-Eich born in Heidelberg to the Faculty of Mathematical and Natural Sciences of the Rheinische Friedrich-Wilhelms-Universität Bonn in 2017. Anschrift des Verfassers: Address of the author: Insa Thiele-Eich Meteorologisches Institut der Universität Bonn Auf dem Hügel 20 D-53121 Bonn 1. Gutachter: Prof. Dr. Clemens Simmer, Rheinische Friedrich-Wilhelms-Universität Bonn 2. Gutachter: Prof. Dr. Mariele Evers, Rheinische Friedrich-Wilhelms-Universität Bonn Tag der Promotion: 10. Oktober 2017 Erscheinungsjahr: 2018 Flooding in Dhaka, Bangladesh, and the challenge of climate change 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. 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. 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. 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. 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 as- sessment. 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. 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. Contents Abstract I List of Figures VII List of Tables IX 1 Introduction 1 1.1 Current situation . .2 1.1.1 Flooding and its impact on the livelihood in Dhaka City . .2 1.1.2 Impact of water levels on health and mortality . .2 1.1.3 Climate change in Bangladesh . .4 1.1.4 The need for a socio-hydrological framework . .5 1.2 Scientific objectives . .6 2 Socio-economy, climate and hydrology of Bangladesh 9 2.1 Socio-economic aspects of global change . 10 2.2 Climate of Bangladesh . 11 2.3 Rivers in the Ganges-Brahmaputra-Meghna delta . 13 2.3.1 Farakka Barrage . 17 2.3.2 Low flow . 18 2.3.3 High flow . 20 3 Data and methods 21 3.1 Data . 21 3.1.1 Temperature and precipitation . 21 3.1.2 Hydrological data . 21 III IV Contents 3.1.3 Mortality data . 26 3.2 Methods . 26 3.2.1 Generalized linear models . 27 3.2.2 Distributed lag non-linear models . 32 3.2.3 Block maxima approach - Extreme value theory . 34 3.2.4 The enhanced Driving force - Pressure - State - Impact - Re- sponse framework . 35 3.2.5 Software . 36 4 Water levels in the megacity Dhaka 37 4.1 Assessment of historic changes in frequency, magnitude and duration of water levels . 37 4.2 Mortality during floods of 2004 and 2007 . 49 4.2.1 Flood event of 2004 . 49 4.2.2 Flood event of 2007 . 50 4.3 Connection of flooding in Dhaka with mortality . 50 5 A socio-hydrological framework for Bangladesh 55 5.1 Key indicators for socio-hydrological processes in Bangladesh . 56 5.1.1 Driving force: climate change . 59 5.1.2 Driving force: population growth . 59 5.1.3 Driving force: higher health standards . 61 5.1.4 Driving force: international dam construction . 61 5.1.5 Driving force: shrinking space of democracy . 62 5.2 An application of the framework: studying mortality . 64 6 Discussing flooding in the context of climate change 67 A Indicators included in enhanced Driving force - Pressure - State - Impact - Response framework 79 A.1 Indicators for natural processes . 79 A.1.1 Atmosphere . 79 A.1.2 Soil and geology . 83 Contents V A.1.3 Hydrology . 85 A.1.4 Vegetation . 89 A.2 Natural hazards . 90 A.2.1 Atmospheric . 90 A.2.2 Land . 92 A.2.3 Hydrological . 95 A.3 Indicators for anthropogenic processes . 96 A.3.1 Demography . 96 A.3.2 Socio-economics . 96 A.3.3 Climate change . 98 A.3.4 Water management . 98 A.3.5 Agriculture . 100 A.4 Technical failures . 102 A.5 Implications . 105 A.5.1 Country-wide implications . 105 A.5.2 Individual implications . 106 Bibliography 108 List of Figures 1.1 Major river systems of Bangladesh . .3 2.1 The Ganges-Brahmaputra-Meghna catchment . 10 2.2 The city of Dhaka . 12 2.3 Climate in Bangladesh . 14 2.4 Hydrological year of the Ganges, Brahmaputra and Meghna rivers . 16 2.5 Dry season flow downstream from Farakka Barrage . 18 2.6 Average annual area inundated in Bangladesh . 19 3.1 Precipitation stations in Bangladesh . 22 3.2 Statistics for four water level stations surrounding Dhaka . 24 3.3 Logistic regression for four water level stations in Dhaka . 25 4.1 Annual boxplots for water level station Dhaka, 1909 - 2009 . 38 4.2 Annual boxplots for four water level stations surrounding Dhaka, 1950 - 2009 ..................................... 38 4.3 Number of days above danger level NODdl for Dhaka, 1909 - 2009 . 39 4.4 Number of days above danger level NODdl for four water level stations surrounding Dhaka, 1950 - 2009 . 40 4.5 Correlation between the NODdl of the four water level stations surround- ing Dhaka . 42 4.6 Logistic regression modelling of the probability of one station being above danger level depending on the water levels of the other stations . 43 4.7 Duration of flooding in Dhaka, 1909 - 2009 . 44 4.8 Duration of flooding at the four water level stations surrounding Dhaka, 1950 - 2009 . 45 4.9 Running variance for the annual maximum water level in Dhaka . 46 VII VIII List of Figures 4.10 Annual maximum water levels in Dhaka . 47 4.11 Annual minimum water levels in Dhaka . 48 4.12 Mortality during floods of 2004 and 2007 . 50 4.13 Contour plot of relative risk of mortality . 51 4.14 Relative risk of mortality at fixed time lags . 52 4.15 Relative risk of mortality at fixed water levels . 53 5.1 A socio-hydrological framework for Bangladesh . 58 5.2 Interactions resulting from climate change . 60 5.3 Interactions resulting from dam construction . 63 5.4 Interactions impacting mortality . 66 A.1 Accretion and erosion in Bangladesh . 84 List of Tables 2.1 Statistics for the Ganges-Brahmaputra-Meghna basin . 17 3.1 Water level data in Dhaka . 23 4.1 Number of days above danger level in Dhaka . 41 5.1 A selection of indicators from a socio-hydrological framework developed for Bangladesh .