Climate change impacts and adaptation in Bangladesh: an agent-based approach

Bangladesh exemplifies the complex challenges facing densely populated coastal regions. The pressures on the country are immense: around 145 million people live within an area of just 145,000 sq-km at the confluence of three major river systems: the Ganges, the Brahmaputra and the Meghna. While progress has been made, poverty remains widespread, with around 39% of children under five malnourished. Most of its land-mass lies below 10m above sea level with considerable areas at sea level, leading to frequent and prolonged flooding during the monsoons. Sea level rise is leading to more flooding as storm surges rise off higher sea levels, pushing further inland. Higher sea levels also result in salt-water intrusion into freshwater coastal aquifers and estuaries, contaminating drinking water and farmland. Warmer ocean waters are also expected to lead to an increase in the intensity of tropical storms. Bangladesh depends on the South Asian summer monsoon for most of its rainfall which is expected to increase, leading to more flooding. Climate scientists are also concerned about the stability of monsoon and the potential for it to undergo a nonlinear phase shift to a drier regime. Bangladesh faces an additional hydrological challenge in that the Ganges and Brahmaputra rivers both rise in the Himalaya-Tibetan Plateau region, where glaciers are melting rapidly. The Intergovernmental Panel on Climate Change (IPCC) concluded that rapid melting is expected to increase river flows until around the late-2030s, by which time the glaciers are expected to have shrunk from their 1995 extent of 500,000 sq-km to an expected 100,000 sq-km. After the 2030s, river flows could drop dramatically, turning the great glacier-fed rivers of Asia into seasonal monsoon-fed rivers. The IPCC concluded that as a result, water shortages in Asia could affect more than a billion people by the 2050s. Over the same period, crop yields are expected to decline by up to 30% in South Asia due to a combination of drought and crop heat stress. Bangladesh is therefore likely to face substantial challenges in the coming decades. In order to adequately understand the complex, dynamic, spatial and nonlinear challenges facing Bangladesh, an integrated model of the system is required. An agent-based model (ABM) permits the dynamic interactions of the economic, social, political, geographic, environmental and epidemiological dimensions of climate change impacts and adaptation policies to be integrated via a modular approach. Integrating these dimensions, including nonlinear threshold events such as mass migrations, or the outbreak of conflicts or epidemics, is possible to a far greater degree with an ABM than with most other approaches. We are developing a prototype ABM, implemented in Netlogo, to examine the dynamic impacts on poverty, migration, mortality and conflict from climate change in Bangladesh from 2001 to 2100. The model employs GIS and sub-district level census and economic data and a coarse-graining methodology to allow model statistics to be generated on a national scale from local dynamic interactions. This approach allows a more realistic treatment of distributed spatial events and heterogeneity across the country. The aim is not to generate precise predictions of Bangladesh's evolution, but to develop a framework that can be used for integrated scenario exploration. This paper represents an initial report on progress on this project. So far the prototype model has demonstrated the desirability and feasibility of integrating the different dimensions of the complex adaptive system and, once completed, is intended to be used as the basis for a more detailed policy-oriented model.