Combining green and grey infrastructure can be a cost-effective way to address water supply challenges and enhance cities’ climate resilience, while also delivering environmental and social co-benefits. However, to ensure proposed projects deliver outcomes that are equitable and sustainable, planners and policymakers must proceed with care. From UCCRTF’s experience, it is essential to:

• Conduct robust public engagement, especially with historically marginalized communities. People living on cities’ margins may depend on non-traditional water sources – e.g., canals, reservoirs or outdoor drinking fountains – for bathing, drinking and washing. Especially for any infrastructure project that may change the availability of these kinds of water sources, planners must speak with all stakeholder groups to ensure their concerns are heard and integrated into project plans.

• Respect land rights and land use. Green infrastructure tends to require more land than traditional grey infrastructure, so planners should take care to understand and respect jurisdictional boundaries, as well as the ways in which communities use land – even if the use is not officially sanctioned. For instance, if skateboarders skate in an empty reservoir, or if community members have planted a garden in an unoccupied green space, planners should include these groups in public engagement efforts.

• Use multicriteria analysis (MCA) to assess value. Because green-grey projects deliver co-benefits beyond monetary cost savings, planners should look beyond traditional economic cost-benefit analysis to weigh the pros and cons of a proposed green-grey project. Multi-criteria analysis is a way of systematically assessing projects, by analysing proposals against several different criteria (both quantitative and qualitative) weighted against their relative importance.

• Consistently monitor green-grey infrastructure performance. Cities that consistently gather data and report on infrastructure performance make it easier for planners to demonstrate benefits and identify areas for improvement. Over time, robust data collection leads to better projects; it can also empower cities to engage in public-private partnerships with financiers and funders who want to see evidence of efficacy.

• Engage with policymakers. Policymakers who understand the benefits of green-grey infrastructure promote it through policies, laws and regulations; depending on the jurisdiction, they may also allocate funding for green-grey infrastructure projects, or advocate for it in city budget decision-making.

• Seek out partnerships for sustainable finance. Infrastructure upgrades are costly. Green-grey infrastructure has not only been shown to be less costly than grey-only infrastructure; it also has become a space for public-private partnerships and finance innovation, as demonstrated by UCCRTF’s work in New Clark City. Cities including Quito, Ecuador and Washington D.C. have developed water funds[7] and piloted environmental bonds[8] to pay for green-grey water management projects, delivering environmental, economic and social benefits in a way that’s sustainable for cities’ budgets.
   

Urbanization, population growth and climate change are driving flood risks and water supply challenges in many Asian cities. Green-grey infrastructure – when undertaken with care – can be a cost-effective way of responding, while also delivering multiple environmental, social, and economic co-benefits.