Urban areas are often concentrated in exposed areas like coasts and drylands and thus vulnerable to extreme events, which are increasing in frequency and magnitude under changing climate. A conceptual framework of urban social-ecological-technological systems (SETS) integrates three domains and considers the services and outcomes delivered by each when confronted with extreme events. For example, outcomes of a storm surge may be failure of a sea wall (technological), inequity in exposure (social), or absorption of waves by coastal wetlands (ecological). To unpack the ecological-environmental component of SETS, we ask: how do ecosystem structure and dynamics contribute to flood vulnerability, and can nature-based strategies (NBS) improve resilience to extreme events currently and in the future, as reflected in scenarios co-produced with practitioners and community leaders? Examples are taken from work done in nine United States/Latin American cities that form the Urban Resilience to Extremes Sustainability Research Network. For vulnerability, we developed metrics reflecting exposure, sensitivity, and adaptive capacity of biophysical elements of urban floodplains in parallel with metrics for social and technological vulnerability. We reviewed the types and efficacy of NBS in reducing heat and flooding exposure, and asked to what extent NBS in future visions meet criteria for building resilience.
Results/Conclusions
A large number of candidate ecological metrics of vulnerability to flooding were considered; from these, a subset encompassed slope, contaminated sites, percentage park and wetland, and aspects of soils and impervious surfaces in 500- and 100-year floodplains of urban streams and rivers. Ecological vulnerability analyses generated very different spatial distributions than social or technological vulnerability, indicating the importance of considering all three dimensions in mapping vulnerability within cities. Nature-based solutions, often considered more flexible, safe-to-fail alternatives to hard infrastructure, have been adopted in most study cities but to varying extents. Use of tree cover to ameliorate extreme heat is prominent in both current practice and future visions for hot, arid cities of Phoenix (Arizona, USA) and Hermosillo (Sonora, Mexico); however, tree species vary in their effectiveness. Urban wetlands and green infrastructure are effective in reducing urban flooding, and when incorporated into future visions increase resilience based on qualitative assessment and stormwater modeling. In sum, the ecological component of SETS plays an important role in reducing vulnerability and increasing resilience of urban systems to current and future extreme events.