Using Green and Blue Infrastructure for Urban Flood Mitigation

Technical approaches inspired by concepts such as green and blue infrastructure (GBI) may offer alternatives for urban adaptation to climate change with significant environmental and socioeconomic benefits. Nevertheless, adopting green and blue approaches to consolidated urban areas is a challenge due to the high costs involved, such as the costs for GBI adoption and land use opportunity costs. Households and firms may not have incentives to adopt GBI and then the expected change relies on urban renovation potential, when vacant lots or the older real estate stock are substituted by new buildings that adopt the GBI techniques. We study the municipality of Belo Horizonte, which has just approved a new Master Plan that includes instruments that give economic incentives to developers to use GBI. Developers may have the Charges for Additional Building Rights (CABR, Outorga Onerosa do Direito a Construir) partially waived if they adopt GBI.

Given the level of uncertainty of these processes, this research investigates the potential of these instruments to effectively produce change in terms of the adoption of GBI approaches in the face of different scenarios of climate change, GBI costs, and land value. We use a quantitative multidisciplinary approach to address these questions and simulate six scenarios combining different levels of GBI adoption, different GBI devices (rain barrels, rain gardens, and green roofs), and climate change implied by higher levels of extreme rain fall events. Results indicate 1) current land use and only detention basins as GBI are not sufficient to significantly reduce flood risk in the Belo Horizonte urban context; 2) maximum renovation with GBI adopted may reduce flow peaks ranging from 50% for RP-2 years rain (very often event) to 5% for RP-100 years rain (rare event); 3) real estate markets will probably include GBI only in highly valued areas, because of both the cost-benefit comparison between CABR and GBI costs, and the typical market renovation trends – single-family houses in lower valued areas will be hardly converted in new building with GBI in the foreseeable future. If the level of GBI adoption is low across the studied catchment areas, GBI devices have limited capacity to mitigate extreme rainfalls. Climate change will probably increase significantly the level of extreme rainfall events in Belo Horizonte. If GBI devices are broadly adopted, they may reduce peak flows and volumes, and they also offer other benefits beyond drainage. These findings prescribe civic and policy attention and call for more direct public intervention in the GBI adoption.