We live in the Age of Cities, witnessing the most rapid urban migration in history. Today, already half of the world’s population lives in urban areas. Continuing population growth and urbanization are projected to add another 2.5 billion people to cities around the world by 2050.

Looking at the Asia Pacific region, the numbers are staggering: in 2015, 2.38 billion people lived in urban areas, representing 60% of the world’s urban population. The urban population of the region more than doubled between 1975 and 2011 and is projected to almost double again between 2000 and 2025 (an increase of 1.1 billion people).

The impact of urbanisation is huge. On the one hand, it creates extraordinary opportunities for people to improve their lives, find jobs, earn money, get education, trade goods, have access to water, get health care, communicate with people, etc. On the other hand, it causes overwhelming problems and challenges to provide all these people with transport, housing, food, energy, water, sanitation, education, etc.

Urban Environment and Climate Change
Adding to the significant challenges of urbanisation described above, cities also face serious environmental and climate challenges. Cities produce great amounts of pollution and waste which cause a multitude of environmental problems, such as disease, damage of the natural environment, climate change, deterioration of water resources, etc. (see table).  Adding to this, cities are increasingly vulnerable and exposed to natural disasters, such as earthquakes, flooding, droughts and volcanic eruptions. The impact of such disasters in densely populated urban areas are often severe and far-reaching.

Specifically in the Asia Pacific region, high urbanisation levels and urban poverty make many cities highly vulnerable to natural disaster. Considering just the threat of flooding: out of 305 urban agglomerations across the region, no less than 119 are in flood-risk coastal zones and are susceptible to sea-level rise. In 2011, the Asia Pacific region recorded 212 million victims of various natural disasters and physical damage of almost USD 300 billion (compared to USD 366 billion worldwide).

crowd people city

Water and the City

It is clear that urbanization is presenting us some of the most important challenges of our time. However, is also represents one of the greatest opportunities and responsibilities to shape the sustainable and resilient cities of the future.

When we specifically consider the urban challenges related to water, we see a multitude of issues that threaten the sustainable development of cities, such as pollution of groundwater and surface water, lack of clean drinking water, poor drainage infrastructure, groundwater extraction and flooding.

Many of these water issues are interrelated and are part of the same urban water cycle: poor drainage systems may result in pollution of surface water, pollution of surface water may result in a lack of clean drinking water, a lack of clean drinking water may result in groundwater extraction, groundwater extraction may result in subsidence which increases the risk of flooding, etc.

It is important to consider these issues in the context of the urban water cycle, which is critically different from the natural water cycle.


Looking at these differences, it becomes immediately apparent that the way we design and build cities, with all its different pieces of infrastructure: houses, roads, parks, ports, roads, etc., has a huge impact on the water flow in and around the city.

As we start looking at the concept of Blue-Green Cities, it is useful to distinguish between grey infrastructure and green infrastructure. Grey infrastructure being more conventional, engineered infrastructure and green infrastructure being inspired by and drawing on nature.

gray green

Blue-Green Cities

The concept of Blue-Green Cities is a powerful and innovative approach to address urban water challenges, aiming to recreate a more nature-oriented water cycle in the urban environment by bringing together water management and green infrastructure. Examples of blue-green infrastructure are permeable paving, rain gardens, constructed wetlands, parks and gardens, planted drainage assets (green roofs, green walls), bioretention systems, controlled water storage areas (e.g. car parks, recreational areas), etc.

The key functions of Blue-Green infrastructure components include water use/reuse, water treatment, detention and infiltration, transport, evapotranspiration, local amenity provision and generation of viable habitats for local ecosystems. In many cases, the components serve several functions.

The resulting benefits are many, such as better management of storm water, conservation of water resources (increasing the resilience to drought), water pollution control, public well-being (recreational water use, parks and recreation grounds), support climate change adaptation and mitigation, healthier soils and reduction in soil erosion, avoided impacts of flood events, etc.

Necessarily, planning for and designing Blue-Green Cities requires a holistic view of the urban water cycle and interdisciplinary cooperation in water management, urban design and landscape planning. Moreover, Blue-Green Cities is not just a responsibility of policy makers, engineers or architects: it also calls on citizens and communities to be actively involved as solutions and interventions may be closely tied to the way they live and work.

There are many blue-green city programs and projects worldwide, such as Water Sensitive Cities in Australia, Blue Green Dream (partnership between Berlin, London, Rotterdam and Paris), BlueGreenCities (UK) and Amsterdam Rainproof.


The Challenge: Blue-Green Cities in Indonesia

Indonesia is no exception to the global urbanisation trend: the percentage of people living in urban areas has increased from just 31% in 1990 to 53% in 2014 and projected to increase to 71% by 2050. In absolute terms that’s almost 135 million people living in cities in 2014 and 228 million in 2015. There are 11 cities with more than 1 million people, 27 cities with more than 500,000 people and 83 cities with more than 100,000 people.

Indonesian cities face many of the same challenges of other growing cities around the world as they struggle to absorb the large inflow of people, provide the necessary infrastructure and services and divide benefits equally among citizens.

At the same time, shaped by its people, history and culture, urbanisation in Indonesia has its unique characteristics. This means that approaches and solutions for cities elsewhere around the world may not automatically be fitting in the context of Indonesian cities, which brings us to the challenge we put-out in this water challenge program:

The Indonesia-Netherlands Water Challenge 2016 invites Indonesian students and young professionals to develop their own Blue-Green ideas and solutions for Indonesian cities.