Blue-Green Cities aim to reintroduce the natural water cycle into urban environments and provide effective measures to manage fluvial (river), coastal, and pluvial (urban runoff or surface water) flooding while championing the concept of multi-functional green space and land use to generate multiple benefits for the environment, society, and the economy.

Visible water in cities has massively declined in the last century and many areas are facing future water scarcity in response to changes in climate, land use and population.
The concept of Blue-Green Cities involves working with green and blue infrastructure components to secure a sustainable future and generate multiple benefits for the environmental, ecological, social and cultural spheres.
This requires a coordinated approach to water resource and green space management from institutional organisations, industry, academia and local communities and neighbourhoods.
		

The natural water cycle is characterised by high evaporation, a high rate of infiltration, and low surface runoff.
This typically occurs in rural areas with abundant permeable surfaces (soils, green space), trees and vegetation, and natural meandering water courses.
In contrast, in most urban environments there is more surface runoff, less infiltration and less evaporation.
Green and blue spaces are often disconnected.
Meaning for a city to be Blue-Green, it requires a further step beyond the implementation of blue and green infrastructure.
The lack of infiltration in urban environments may reduce the amount of groundwater, which can have significant implications in some cities that experience drought.
In urban environments water is quickly transported over the impermeable concrete, spending little time on the surface before being redirected underground into a network of pipes and sewers.
However, these conventional systems (‘grey’ infrastructure) may not be sustainable, particularly in light of potential future climate change.
They may be highly expensive and lack many of the multiple benefits associated with Blue-Green infrastructure.

Land planning and engineering design approaches in Blue-Green Cities aim to be cost effective, resilient, adaptable, and help mitigate against future climate change, while minimising environmental degradation and improving aesthetic and recreational appeal.
Key functions in Blue-Green Cities include protecting natural systems and restoring natural drainage channels, mimicking pre-development hydrology, reducing imperviousness, and increasing infiltration, surface storage and the use of water retentive plants.
A key factor is interlinking the blue and green assets to create Blue-Green corridors through the urban environment.

Blue-Green Cities favour the holistic approach and aim for interdisciplinary cooperation in water management, urban design, and landscape planning.
Community understanding, interaction and involvement in the evolution of Blue- Green design are actively promoted(e.g.
Newcastle's LAA).
Blue-Green Cities typically incorporate sustainable urban drainage systems (SUDS), a term used in the United Kingdom, known as water-sensitive urban design (WSUD) in Australia, and low impact development or best management practice (BMP) in the United States.
Green infrastructure is also a term that is used to define many of the infrastructure components for flood risk management in Blue-Green Cities.

Water management components in Blue-Green Cities are part of a wider complex “system of systems” providing vital services for urban communities.
The urban water system interacts with other essential infrastructure such as information and telecommunications, energy, transport, health and emergency services.
Blue-Green Cities aim to minimise the negative impacts on these systems during times of extreme flood while maximising the positive interactions when the system is in the non-flood state.
Key barriers to effective implementation of Blue-Green infrastructure can arise if planning processes and wider urban system design and urban renewal programmes are not fully integrated.
Blue-Green Cities aim to reintroduce the natural water cycle into urban environments and provide effective measures to manage fluvial (river), coastal, and pluvial (urban runoff or surface water) flooding while championing the concept of multi-functional green space and land use to generate multiple benefits for the environment, society, and the economy.
Visible water in cities has massively declined in the last century and many areas are facing future water scarcity in response to changes in climate, land use and population. The concept of Blue-Green Cities involves working with green and blue infrastructure components to secure a sustainable future and generate multiple benefits for the environmental, ecological, social and cultural spheres. This requires a coordinated approach to water resource and green space management from institutional organisations, industry, academia and local communities and neighbourhoods. 		

The natural water cycle is characterised by high evaporation, a high rate of infiltration, and low surface runoff. This typically occurs in rural areas with abundant permeable surfaces (soils, green space), trees and vegetation, and natural meandering water courses. In contrast, in most urban environments there is more surface runoff, less infiltration and less evaporation. Green and blue spaces are often disconnected. Meaning for a city to be Blue-Green, it requires a further step beyond the implementation of blue and green infrastructure. The lack of infiltration in urban environments may reduce the amount of groundwater, which can have significant implications in some cities that experience drought. In urban environments water is quickly transported over the impermeable concrete, spending little time on the surface before being redirected underground into a network of pipes and sewers. However, these conventional systems (‘grey’ infrastructure) may not be sustainable, particularly in light of potential future climate change. They may be highly expensive and lack many of the multiple benefits associated with Blue-Green infrastructure. 
Land planning and engineering design approaches in Blue-Green Cities aim to be cost effective, resilient, adaptable, and help mitigate against future climate change, while minimising environmental degradation and improving aesthetic and recreational appeal. Key functions in Blue-Green Cities include protecting natural systems and restoring natural drainage channels, mimicking pre-development hydrology, reducing imperviousness, and increasing infiltration, surface storage and the use of water retentive plants. A key factor is interlinking the blue and green assets to create Blue-Green corridors through the urban environment.
Blue-Green Cities favour the holistic approach and aim for interdisciplinary cooperation in water management, urban design, and landscape planning. Community understanding, interaction and involvement in the evolution of Blue- Green design are actively promoted(e.g. Newcastle's LAA). Blue-Green Cities typically incorporate sustainable urban drainage systems (SUDS), a term used in the United Kingdom, known as water-sensitive urban design (WSUD) in Australia, and low impact development or best management practice (BMP) in the United States. Green infrastructure is also a term that is used to define many of the infrastructure components for flood risk management in Blue-Green Cities.
Water management components in Blue-Green Cities are part of a wider complex “system of systems” providing vital services for urban communities. The urban water system interacts with other essential infrastructure such as information and telecommunications, energy, transport, health and emergency services. Blue-Green Cities aim to minimise the negative impacts on these systems during times of extreme flood while maximising the positive interactions when the system is in the non-flood state. Key barriers to effective implementation of Blue-Green infrastructure can arise if planning processes and wider urban system design and urban renewal programmes are not fully integrated.
Colin Thorne