A just map: community and fluvial science working together for flood hazard vulnerability mapping in Massachusetts

In the Northeastern U.S., the most costly damages from intense storm events were impacts to road-stream crossings.  In steep post-glacial terrain, erosion by floodwater and entrained sediment is the largest destructive force during intense storms, and the most likely driver of major morphological changes to riverbanks and channels.  Steam power analysis is a tool that can successfully quantify floodwater energy that caused damages, however, prediction of which reaches or watersheds may experience future impacts remains uncertain. Downstream, in urban areas, floodwaters increasingly occupy larger geographic extents that spill well beyond traditionally mapped flood and hazard zones. Limiting these maps are critical biases: Often more information is available for coastal and urban areas (missing steeper terrain geomorphic hazard zones), base functional assumptions (that flood risk is dominantly inundation risk from a specific depth of water, ignoring the force of moving water, sediment or erosion), their concentration around the highest-value infrastructure (lower-value and lower-density development or undeveloped areas have little or no map coverage) and how these maps are utilized for regulatory purposes (e.g. mortgage and insurance requirements). Compounding the physical destruction of flooding is the unequal distribution of these impacts on socially vulnerable populations that are least able to recover from them.  We strive to improve the co-generated mapping of social vulnerability and flood risk by (1) utilizing measures of social vulnerability with greater social and geographical insight and nuance, including self-organizing maps (SOM) that cluster overlapping metrics, (2) applying modified flood hazard maps that accurately represent fluvial geomorphic hazards, urban flooding hazards, and climate change considerations, and (3) overlapping these to understand what factors influence current maps and policy practice; what populations and places may be overlooked or under-resourced relative to vulnerability; and use this collective insight to help inform and develop improved map products and policy approaches.  Integration of this information directly with practitioners’ resources allows communities to prioritize and make land-use decisions and flood-response and preparedness decisions that are informed by the specific vulnerabilities of their populations as well as the fluvial geomorphic workings of the larger watershed, and that have powerful local implications.  Outreach and educational programs focused on social vulnerability and fluvial systems for river practitioners and politicians at all levels align communities’ attitudes about flooding and rivers can ultimately result in ecologically sound, socially just, and more flood resilient policies and practices.