There is just a week left to see the exhibition at the Danish Architecture Centre about climate change that shows how urban planning and the design of buildings and hard landscaping have to adapt now for changes in weather patterns in the future.

Looking up from my desk, as I’m writing this morning, it is raining but it’s really the sort of shower that anyone would expect at this time of year … late March so Spring in north-west Europe. This is not the sort of weather the exhibition is talking about but then back last summer, just a couple of weeks after I moved into this apartment, Copenhagen had one of the flash rain storms that are becoming more frequent here. There was torrential rain for several hours and the street drains could no longer cope and pools of water started to form across the road and pavements. Like many apartment buildings in the city, we have a basement where residents store boxes and bikes and so on. I had a phone call to say the basement was flooding, because the pump had failed, and was told that if I wanted to save or salvage my things down there I should do it right away. It was hardly a disaster for me - I lost a couple of cardboard boxes - but further along the street several businesses in semi basements, four or five steps down from the pavement, had much more serious problems. Industrial pumps were called in but most of those businesses had to shut for several months as floors and electrical systems were dried out or replaced. Six months on and at least one business has still not reopened.

For a city like Copenhagen, new developments with ever denser building with more and more ground covered with tarmac or hard surfaces, designed to drain quickly, it actually means there could be dramatic consequences if these sudden rain storms become more frequent as predicted.

And these storms are dramatic. On the 2nd July 2011 there was a rain storm in Copenhagen where a fifth of the normal annual rainfall fell in just three hours. Neighbours have told me that whereas this time I had to move my things out of less than 10cm of water, on that day the basement rooms filled right up to the ceiling. In the city underpasses and road tunnels were flooded and closed, utility services were lost and the extent of property damage was phenomenal.

Having said all that, the exhibition is not all about doom and gloom. In fact far from it as the real message is that we have to accept that these changes are coming and therefore we should start to adapt our construction methods and planning to make appropriate changes now. Simply planning for an emergency response, for if and when, is not a sensible approach. By starting now we can be in control and there will be gains because making changes in advance “presents us with a unique opportunity to improve our cities and create greener cities with more open spaces where rainwater can be handled and urban life can thrive.”

The first part of the exhibition shows with excellent graphics how much more of the city is now built over so the natural process of water soaking into the soil or running away along natural drainage channels is no longer possible. In the past rain water and dirty waste water … so everything from water on the roads contaminated with oil from traffic to sewage has been dealt with through the same system of drains or, where there are separate storm drains and household drains, these often back up and contaminate each other when the system is under pressure when there is a sudden storm.

There is also a stark lesson to be learnt from the past about what happens when you prevaricate. By the 19th century Copenhagen was densely built up with houses and businesses tightly packed around narrow streets and courtyards. Then the problem was not surface drainage but dealing with human waste. There was no sewage system in the city and in 1835 a cholera outbreak killed thousands of people and started a discussion about the need for drains. Political differences, problems with financing such extensive work and potential disputes dealing with individual land ownership stymied any progress until the 1850s when a second major outbreak of cholera killed 5,000 people in the city. Even though work then started on clearing slums and improving the drains it was not until the 1880s that Charles Ambt, the city engineer, began to draw up detailed plans for the necessary engineering works including a scheme to take sewage out through a tunnel under the harbour and out into the sound. The Nordic Exhibition in Copenhagen of 1888 showed the citizens all the wonders that were then available for modern plumbing and sanitation but even then the first street to have water closets was Stokholmsgade in 1893, nearly 60 years after that first cholera outbreak, and it was not until 1901 that Copenhagen completed a full sewage system and paved the streets in the city. To be blunt, the point here is that this time, facing climate change, we cannot afford to take sixty years to decide what to do and start the work.

The second part of the exhibition shows a number of completed or ongoing or planned projects that are designed to cope with the anticipated increase in the number of rain storms. These are presented as opportunities rather than enforced and expensive solutions that will be necessary if we wait until we have to do the work.

With adventurous and imaginative schemes the people who live in the cities and in the suburbs are getting new facilities and renewed urban areas at little or certainly reduced direct cost; the city councils are getting a renewed infrastructure at markedly less cost than by waiting until works are absolutely needed after a major and destructive storm and the utility companies, who have to provide solutions and have to deal with any failures in the system, can actually often introduce smaller local schemes on private or city land as long as the owners see a gain which is much much cheaper than the company having to buy land for the construction of mega solutions.

Simple schemes shown include designs for permeable pavements and surfacing to deal quickly with surface water but without overwhelming the drains. On a larger scale there are several proposals shown to build underground tanks to hold water from flash floods so it can be dealt with slowly over the following days and weeks. More natural-looking options - rather than hard engineering solutions - include schemes with planting or new ponds and drainage channels or well-planted temporary flood plains. New artificial surfaces can be installed for sports facilities that keep the surface dry but take rain water down to permeable sub structures.

So, at Gladsaxe new sports facilities for the Gymnasium have been built around and over ponds and canals for a new drainage system that holds back flood water so it can be dealt with locally by the system over a more reasonable period. For this project costings have been given to show how the different parties have benefitted financially. A traditional project with an underground storm basin would have cost 102 million DKK. The completed project with surface solutions cost 72 million DKK. The municipality has influenced the project and gained financially by providing advice and expertise that was financed from the project costs. The citizens of Gladsaxe saved 30 million DKK on supply expenses and they gained sports facilities, playgrounds, nature trails and new urban spaces.

At the headquarters of Nordisk a nature park of 31,000 square metres has been built with half laid out across the roof of car parks. Covered with grass and meadow plants, it absorbs rain water rather than having it run off the alternative of hard roofing into drains and provides a pleasant new facility for staff and visitors to the company.

In Middlefart management of water is seen as an opportunity to create a Climate City to turn 450,000 square metres into a greener and healthier neighbourhood.

In Køge there is scheme to establish new green spaces and rain water from roofs will be cleaned and returned for washing clothes and flushing toilets.

In Viborg a large new park is being laid out with lakes that retain water that can be cleaned and returned to the water system. Again there is considerable gain from such careful management of storm water … the utility company gains access to a large space where it can manage and clean the water, the municipality can influence the design from the start and gets a new park and the citizens are protected from flooding caused by a sudden cloud burst and gain a new recreational space.

Not all the schemes are on such a large scale. Helenevej in Frederiksberg is the first climate street in Denmark with a permeable surface that absorbs large amounts of water when there is a cloudburst and at Vilhem Thomsens Allé in Valby, rainwater is handled within the courtyard of the housing scheme creating a recreational space and reducing water bills as retained water is now used rather than metered water for watering the planting. The utility company gains financially because it does not have to construct new pipes to take rainwater away from the area.

If people still need to be convinced about the need for such schemes, the exhibition has stark figures for the financial cost of wasting water. An average Danish family uses 40 litres of water per person each day for flushing toilets and for washing which is roughly the amount of rainwater that could be collected from a roof surface of 40 square metres so if water could be stored until it is needed then the roof on a house, on average 200 square metres, could provide all the water needed for washing clothes and flushing toilets rather than the family using drinking water … with a potential saving for a family of 5,000 DKK a year in water charges.

The Rain is Coming - how climate adaptation can create better cities

Danish Architecture Centre until 6th April 2015