Illuminating piece in The Guardian

Amsterdam is home to 45,000 sq metres of ‘blue-green’ roofs, which absorb rainwater and allow it to be used by building residents to water plants and flush toilets

You might visit Amsterdam for its canals, and who could blame you, really. But the truly interesting waterways aren’t under your feet – they’re above your head.

Beautiful green roofs have popped up all over the world: specially selected plants growing on structures designed to manage the extra weight of biomass. Amsterdam has taken that one step further with blue-green roofs, specially designed to capture rainwater. One project, the resilience network of smart, innovative, climate-adaptive rooftops (Resilio), has covered more than 9,000 sq metres (100,000 sq ft) of Amsterdam’s roofs, including 8,000 sq metres on social housing complexes. Citywide, the blue-green roof coverage is even bigger, estimated at more than 45,000 sq metres.

The “sponge city” concept is becoming increasingly popular. Planners deploy more green spaces that soak up downpours that are getting heavier as the world warms. That simultaneously reduces flooding and recharges the underlying layer of absorbent rock, which can then be tapped into in times of need. Whereas cities used to be designed to divert rainwater away as quickly as possible, increasingly, they are exploiting that resource.

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