Climate change increases demands on construction planning

Today's planning norms are based on historical information. However, the weather is likely to subject our buildings and factories to far tougher tests. Although there is great uncertainty surrounding the climate in the future, the risk assessments must be considerably sharpened up as we build for the future.

Sweden has unique series of measurements for weather and water on which to look back - among the biggest archive data in the world in fact. The first regular temperature measurements began a full 145 years ago, and systematic wind observations over 60 years ago.

Using automatic weather stations, temporary variations and extreme conditions, such as squalls, could start being gauged regularly during the 1990s. The weather statistics provide a reliable source of data for indicating what kinds of effects the weather has on different industries, and they govern many of society's planning norms.

SMHI is involved in generating climate data in various kinds of construction project, including roads, bridges, seaports, wind farms and real estate. A risk assessment is usually also required into the possible frequency of extreme weather conditions, for which SMHI provides what are known as 'statistical return times'. Bridges, for example, are often built based on a return time of 50-100 years.

The return times mostly refer to water levels or water flows and form the basis for how robust a construction should be, or where it can best be located.

The size of a 100-year flow depends on the watercourse and the exact position within the watercourse. A 100-year flow is the water flow that statistically occurs once in 100 years. However, the probability that the 100-year flow actually happens during a 100-year period is as much as 63 per cent.

"Mother Nature has recently been ringing bells to tell us we need to expand our risk assessments, especially following the catastrophic storms in southern Sweden back in January. We're receiving more and more enquiries for climate information for vulnerability analyses," says Jan Andersson, head of marketing at SMHI.

The City of Göteborg is one customer for whom SMHI has generated a climate base to be used in assessing the effects of extreme weather in the short and long term.

Another is the Swedish Road Administration, which is reviewing vulnerability and risk analyses for the road transport network in eastern central Sweden. SMHI is projecting what consequences extreme torrential rain would have in the form of floods.

A recent study of government authorities, companies and industry organisations, etc., provides a summary of the work in progress in Sweden to prepare for a change in climate. The study shows that quite a lot is in fact being done to protect against extreme weather events with the climate as it is now. However, the conclusion indicates that far too little is being done with the future climate in mind.

Projections of weather in 100 years' time show an average rise of four degrees Celsius in the average annual temperature in Sweden, compared to the global standard period (1961-1990). Developments from the end of the 1980s until today follow the same trend as the future scenarios, and the average temperature has been above normal for 15 of the last 16 years.

There are still great uncertainties in the future scenarios, particularly dependent on the quantities of climate-affecting carbon dioxide that will be released into the atmosphere. However, all indicators suggest that we are heading towards an increasingly warm climate with more precipitation, which will give rise to a higher number of extreme and more intensive situations. There is a risk of more heat waves, more powerful storms and torrential rain.

"We are facing increased risks in connection with construction. However, the future holds a wide range of different scenarios and the local variations could also be massive. Using historical data and future scenarios it's possible to analyse likely events and effects based on parameters such as geographical location, existing buildings and so on. The important thing is to chart the risks and thus enable ourselves to prepare for different eventualities," says Jan Andersson.