How are decisions really made to manage flooding, water scarcity or water contamination in the world’s megacities? We might assume that most decisions would be made on a cool, rational weighing of the technical options that are most likely to result in a reduction of risk. We know, however, that few decisions are made on technical criteria alone. In some cities, authorities may not be able to consider some water management options, such as using recycled waste water for drinking, because of the potential for political opposition. In other cities, elected officials are susceptible to pressures to appease particular voting constituencies in their allocation of water resources. Over time, what options are considered and what decisions are taken give concrete shape to the built environment. These decisions affect how the city grows, what physical infrastructure is put in place, where and for what purposes. The intangible but potent social and political influences on decision-making can be called “social-political infrastructure”: the norms, values, rules and relationships that influence and reinforce persistent patterns of decision-making in cities – and shape urban development – in ways similar to the “hard” infrastructure of the built environment. In a recent editorial, a research team from ASU and the Laboratory for Sustainability Sciences at the National Autonomous University of Mexico (UNAM) argue for the need to take these social and political processes seriously in attempts to address urban resilience. Quantitative modeling of urban dynamics is important as a tool for learning, for system management and for thinking about the future. It can be very difficult to represent these social and political processes in modeling system dynamics. It is much easier, for example, to model the way that topography and rainfall influence the risk of flooding than it is to quantitatively model how electoral politics or public perception of technology affect that risk. Yet if we are not able to incorporate key social and political factors into our modeling efforts, we may be missing key drivers of system dynamics – and thus failing to capture the essence of what shapes the systems we depend on. The interdisciplinary and international ASU-UNAM research team, led by School of Sustainability Professor Hallie Eakin, proposes an innovative toolkit to tackle the challenge. Using participatory methods, they are working with residents, water managers, urban planners and health officials in Mexico City to understand how they understand water issues, what different actors perceive as the primary causes of urban vulnerability, how those perceptions relate to the type of information prioritized by each actor and how this affects the decisions that they make in the city. The perspectives of actors are represented in quantitative models of urban flooding and water scarcity through a technique called Agent Based Modeling supported by decision analysis approaches. Essentially, key actors in the city are characterized as “agents” with different preferences and options for action. As these actors interact across the landscape and respond to rainfall extremes, infrastructure failures and other urban challenges, they make decisions. Collectively, these decisions affect who and what is vulnerable to flooding and scarcity, and where problems manifest in the city. This approach allows decision-makers and residents in the city to not only explore what might happen if, for example, rainfall increases under climate change, but also – and perhaps more important—how shifts in the influence of political processes or social pressures can change urban priorities over water investments, and thus affect who and what is vulnerable to such climatic changes.