Maximizing urban services provided by green and gray infrastructure to increase future urban sustainability

Background/Question/Methods

Urban social-ecological systems are increasingly threatened by changing climate and extreme events. Many of the fastest-growing urban regions are situated along rivers and coasts or in arid and semi-arid regions and experience increased flooding and prolonged drought and heat events, respectively. Cities in developing countries, such as in Latin America, tend to be most vulnerable to extreme events, particularly as a result of dense populations and legacy infrastructure with increasing upkeep costs and decreasing efficiency. Green infrastructure (e.g., wetlands) can be an economically feasible alternative to built gray infrastructure (e.g., drainage pipes) and may provide a multi-functional set of ecosystem services, such as flood and temperature mitigation, that contribute to the future resilience of cities. We examined how existing green and built gray infrastructure regulate flooding and temperature by modeling spatially explicit indicators of these services (e.g., runoff, land surface thermal emissions, and evapotranspiration) in the cities of Valdivia, Chile and Phoenix, Arizona, USA. We also explored future sustainability goals of each city from municipal policies and local stakeholder input to compare with the services provided by existing green and gray infrastructure.  

Results/Conclusions

We expand the existing framework of ecosystem services in cities by incorporating services provided by natural or green infrastructure, as well as built gray infrastructure and combinations (‘hybrids’) of green and gray infrastructure. For example, as proxies for climate regulation and air temperature, we modeled indicators of thermal emissivity and evapotranspiration for the study area in Valdivia, Chile based on spatially explicit green (56% of land area) and built (44% of land area) environment.  Emissivity increased (indicating warmer temperatures) with building density, as expected, and was strongly correlated (r² = 0.96) with runoff estimates modeled for a 12mm rain event.  Overall, however, indicators for temperature regulation were best predicted by a combination of the natural and built environment within the region. Until now, green and gray infrastructure have been seen primarily as conflicting features of a city, rather than for their potential complementary solutions. Future work will co-develop scenarios to explore diverse strategies for green and gray infrastructure to meet future sustainability goals of each city.