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By Kimberly Rogers

Just as dryland pastoralists are coping with climate risk arising from drought cycles, farmers in coastal regions are facing hazards such as flooding and erosion that accompany sea level rise. Static dikes or sea walls are often used to protect coastal cropland from encroaching seas, but can be difficult to maintain on energetic coasts. Sometimes, poorly maintained infrastructure may in fact amplify the very dynamics that they are put into place to dampen.

In coastal Bangladesh where I have worked for the past decade, rural farming communities are dealing with environmental stress resulting from interactions between a large infrastructure system and vigorous coastal processes. The expansive system of ring dikes, called by the Dutch term polders, was emplaced in the 1970’s and 80’s for protecting rice paddy fields from salinization by tides and storm surges. Out of the 2.8 million hectares in Bangladesh’s coastal zone, almost half are poldered, providing more than 8 million people with food security.

Although the polder system in Bangladesh was initially successful, years of poor oversight have resulted in unintended feedbacks between the polders and natural river and tidal flows. Sediment now clogs channels, restricting water drainage and elevating flood risk. Smallholder farmers whose livelihoods are at stake when flood control infrastructure fails are particularly vulnerable. Across the coastal region, farmers attempt to locally mitigate the effects of the failing infrastructure system when response of the state water board is outpaced by the rate of collapse. Decisions by farmers to informally participate in polder repair reflect their level of trust in the government, as well as historical cooperation between neighbors, but are spatially heterogenous.

I met Drs. Gunnar Dreßler and Birgit Müller of the POLISES group last year at the Arizona State University Winter Modeling school, and described the problem of the failing infrastructure system in Bangladesh. They suggested that I come to UFZ and work with them to build an agent based model for examining how the system may respond to future climate and policy scenarios.

This fall, I took advantage of their kind invitation and spent 6 weeks as a Visiting Researcher in the POLISES group developing a model concept for better understanding how heterogeneous polder governance contributes to coastal flood vulnerability. Using quantitative survey data collected from 200 households in flood-vulnerable communities of southwest Bangladesh, we began developing rules for simulating the collective impact of spatially variable infrastructure governance and how it impacts overall socioecological system fitness. The empirical dataset also includes rates of local sea level rise, land surface elevation, and probabilities of storm surge events along the Bengal coast.

Gunnar, Birgit, and I are continuing to develop the model, and once fully operational, we will use it to test the effectiveness of various formal and informal policies on infrastructure sustainability under changing physical conditions. The goals of the model are both practical and educational: we plan to use the model outcomes to develop policy briefs for assisting local and national governments in determining the best strategies for polder rehabilitation. Likewise, it will help us to better understand how coupled human-natural and technical systems may respond to shifting climatic conditions.