To state how many days have freezing or thawing we use the measure ‘zero-crossings’. The more days the temperature crosses through zero, the greater the risk of skidding on the roads.
Brand new statistics from SMHI show that zero-crossings are most common in the southern parts of Sweden during the winter, with an average of up to 40 days. The number of days with this type of temperature change has increased during winters, particularly along the coast of Norrland and in central Norrland in northern Sweden.
“These changes are due to the weather becoming warmer,” says climate expert Lennart Wern. “Many areas which have previously had stable, cold winter weather now have a milder climate, where the temperature creeps up around zero degrees Celsius more often.”
Greater risk of skidding in the north in the future
Future scenarios with continued warming indicate that the number of zero-crossings will decrease overall. Up until the next turn of the century, the temperature will often be far enough above zero degrees.
In spring and autumn in particular there will be fewer changes around zero. This is also a prominent feature in winter in southern Sweden.
The number of zero-crossings for northern Sweden, however, is expected to increase in the winter.
“The number of days with zero-crossings in central and northern Sweden seems to continue to increase considerably during the winter. Some scenarios state increases of more than 30%. Road maintenance problems in the winter could also grow worse in combination with increased precipitation,” says climate scientist Erik Kjellström.
More salt with more zero-crossings
More instances of skidding also increases the risk of larger quantities of salt being spread on the roads.
“Road maintenance personnel constantly monitor the development of the road surface temperature and air humidity in order to use salt as a preventive measure. More instances with a risk of skidding means, of course, that more salt is used,” says Anita Ihs, Research Director at VTI, the Swedish National Road and Transport Research Institute .
Centre for climate change adaptation
Zero-crossings also have a significant impact on road networks and bridges. The change in temperature also influences vegetation, particularly in the spring.
The new analysis of zero-crossings over the past 50 years has been carried out through the Swedish National Knowledge Centre for Climate Change Adaptation, which is establishing at SMHI.
The analysis will soon be available in Swedish.