An agent based model for analyzing land use dynamics in response to farmer behaviour and environmental change in the Pampanga delta (Philippines)
Abstract Agent based models (ABMs) are increasingly employed to understand land use change in agro ecosystems. Here we use an ABM named CHANOS to capture how a range of variables influences decision making processes among farmers with respect to their choice of cropping system, and to analyze the resulting changes in land use patterns. The model is experimental but is empirically based and nourished by field data acquired in the Pampanga delta, Philippines, where rice cropping and aquaculture have been competing over the last 40 years at the expense of natural habitats. Among the variables we include agent behavioural profiles but also forcing factors relevant to the natural, economic and political settings of the system: e.g. continuous (deltaic land subsidence) and discrete (typhoon events) environmental processes, external market forces, and changes in government driven agricultural policies. Assessing the relative weights of these factors was performed through a detailed analysis of decisional outcomes. The farmers fall into three behavioural categories: rational, collective minded and boundedly rational. Likewise, four different environmental dynamics are driven respectively by no deltaic subsidence, steady subsidence, accelerating subsidence, and subsidence punctuated by additional external variables such as listed above. Twelve scenarios were elaborated by combining the agent behaviour algorithms with the environmental dynamics. Results reveal three categories of land use change: an extension of paddy over natural habitat, of aquaculture over natural habitat and paddy, and a succession of periods alternating between paddy and aquaculture. Several indicators show that the rational agents are the most reactive and adaptive to environmental changes. Collective minded agents act independently from environmental changes. Their ability to cope with change is limited and adaptations take longer to propagate. Boundedly rational agents reveal adaptive capacities but are less reactive than rational agent. CHANOS thus provides a dynamic tool for understanding the social fabric and behavioural processes behind land use change.