What's that blue in the green?

by Natalie Páez – July 16th, 2023



Water is a cornerstone for urban development. We have known it for centuries, with many cities emerging around water: from ancient Egyptian settlements along the Nile to most of the contemporary metropolises we see today. Indeed, water is not only fundamental for human health and for maintaining lively ecosystems, but it is crucial for our food provision and energy generation systems. Access to water in sufficient quantity and quality is essential for people and ecosystems to thrive, and those civilizations who have mastered water have mastered their survival.

However, urbanization has impacted the water cycle significantly, leading to several challenges. A prime example is the extensive impermeabilization of surfaces that rapidly drains urban runoff to prevent flooding and property damage. While effective for managing heavy rainfall events, this practice has interfered with natural infiltration processes, potentially threatening local groundwater reserves. Additionally, the changes in land use resulting from impermeabilization often result in a decrease in green areas, which in turn affects evapotranspiration rates and contributes to elevated urban temperatures. These effects will become even more evident with the anticipated impacts of climate change, which include more frequent and extreme weather events, as reported in the latest IPCC report.

Moreover, heavy metals and trace organic compounds quickly find their way into natural water bodies as runoff flows over roadways, parking lots, and building facades. This type of pollution is difficult to control in most cities that lack decentralized stormwater treatment facilities and robust pollution control measures in place.

But wait, there’s more! As cities concentrate people, assets, and economic activities, urban water consumption has skyrocketed. In the current urban water management paradigm, many cities gather water from several kilometers away, which is economically and energetically expensive. This water then undergoes multiple treatment processes, reaching the standards for drinking water quality, only to be used once and discharged downstream. This is rather wasteful, considering that only 3% of the freshwater extracted is actually consumed by people. A higher water demand also means a higher wastewater production, which contains several pollutants that are harmful to people and ecosystems downstream when left untreated. This is the case in several cities in the developing world. Even in cities with wastewater treatment in place, certain pollutants remain stubbornly difficult to remove using conventional methods, and they can persistently move and accumulate in the environment.

Collect, use and dispose: can we really not do it better?

 Yes, we can! – or better: we must. As we continue to expand urban spaces in the face of a changing climate, it is increasingly crucial to rethink our water management strategies. Cities are key areas for transforming our relationship with water and building climate change resilience. This can be achieved by enabling ecological processes of infiltration, retention and evapotranspiration that better resemble the natural water cycle. This implies shifting the narrative of a linear urban water use towards a cyclic approach where the interconnection between water supply, drainage, and water ecosystems is better acknowledged and managed.

Implementing Urban Green Infrastructure (UGI) is a powerful alternative for facing this endeavor, as it introduces systems that resemble naturally occurring processes of water infiltration and purification while having additional benefits for urban landscapes. These include cooling down the city, creating habitats for plants, animals, and insects, lowering the city’s freshwater consumption, and increasing the livability of cities. Indeed, you have already walked along a river and noticed how fresh and relaxing it was, right? That’s what we need more of! Let’s look at one city that has implemented UGI for better water management.

Learning from green Singapore

Singapore is a remarkable example of how UGI can be used to shift our relationship with water in cities. With the majority of its water imported from neighboring Malaysia, Singapore strives to achieve self-sufficiency and water security by diversifying its water supply portfolio. On top of this, this densely-populated city grew acutely aware of the threats posed by climate change, including potential droughts and increased flooding.

Embracing a city-wide UGI-based approach, Singapore is effectively reducing its growing water demand while bolstering its water supply. This strategy involves promoting rainwater harvesting, exploring water reclamation techniques, and investing in cutting-edge desalination technologies, all aimed at reducing reliance on imported water. Impressive as it may sound, the city currently covers 30% of its water demand from reclaimed water,  20% from rainwater and an additional 10% from desalinated water.

Key to their success is the implementation of multifunctional parks, reservoirs, bioretention ponds, swales, wetlands, rain gardens, and green roofs, all designed to harness and treat stormwater and reused water. This not only enhances the city’s water supply but also greatly improves stormwater drainage, thus mitigating flooding risks. An unexpected bonus of this UGI-driven initiative is the transformation of urban spaces into vibrant recreational areas, fostering a strong sense of identity among citizens and enhancing the overall livability of the city.


Left: A bioretention swale near the Kallang river. Right: A sedimentation basin. Both stormwater management facilities consist of plants and soils that require minimal maintenance and help to remove pollutants from Singapore’s runoff. Source: Liao, KH. Socio Ecol Pract Res 1, 67–81 (2019)

Another interesting example is the redesign and naturalization process of sections of the Kallang river, which transformed the formerly channelized river into a meandering river integrated with the city. Through changing channel widths, vegetated banks, and riverbed modifications, the Kallang River now has different flow patterns that house several plants and animals. Indeed, an ecological survey from 2012 found that biodiversity in the park increased by 30% after these interventions. The multifunctional use of the floodplain and riparian zone of the river allows for different interactions with the citizens, who can enter the park and enjoy the water when the river level is low.

Left: A cleansing biotope for water treatment by the Kallang river. Right: The naturalized Kallang river flowing through the Bishan-Ang Mo Kio Park. Source: Liao, KH. Socio Ecol Pract Res 1, 67–81 (2019)

Cool! But how can we make this happen everywhere?

As Singapur, many other cities have successfully implemented UGI for managing their water challenges. What do these cities have in common?

  • a city-wide vision and willingness to use public land for piloting projects,
  • a strong intersectoral collaboration in city administrations – among water, green space, and planning sectors-,
  • an institutional framework (programs, regulations, guidelines),
  • and engagement of private sectors and citizens in project development and responsibilities.

Certainly not an easy task, but one that is worth uptaking.

To sum up

Water is vital for sustainable urban living, and better water management becomes even more critical as we face the impacts of climate change. Implementing green infrastructure is a powerful strategy with multiple benefits for the water cycle and our communities and ecosystems. Urban Green infrastructure supports sustainable urban development, mitigates flooding, improves water quality, and fosters biodiversity in urban areas, making cities more resilient and adaptive to future challenges.

Do you want to know more?