Climate Change and its Impact on Road Conditions in Winter.

In France, the observed temperature has increased by almost 1degreesC during the last century and this rise has mainly occurred since the 1970s. The IPCC projects that the increase in temperatures will continue during thenext decades. For most greenhouse gas emission scenarios, climate models calculate a global warming of about 0.2degreesC per decade at the beginning of the twenty-first Century. It is very likely that warming will accelerate after 2050 at a rate depending on the emission scenarios taken for hypothesis. Increase in temperature will be stronger over continental regionsat mid-latitudes which concentrate a major part of the roads and of the traffic in the world. There is no doubt that climate change will have in these regions an important impact on the maintenance activities of the roadsin winter. In a nutshell, the number of frost days, of cold waves and snowfalls will significantly decrease. This will probably limit the damage byfrost of the road structures and the number of days when the traffic willbe disturbed by snow. However, less favourable factors have to be taken into account, such as the rise of the summer temperatures or the increase in the intensity of winter precipitations in certain regions. A sound assessment of the impact of climate change on the roads and their winter maintenance needs a solid understanding of the processes intervening between thepavement and the meteorological conditions. The use of physically-based simulation models is necessary to quantify the respective role of various factors like the air temperature and humidity, the cloudiness, the precipitation or the physical properties of the road structure. It also needs realistic climate scenarios on a regional scale which are now available. Because snow and frost conditions are common but not very frequent, France is aparticularly interesting case to assess the impact of climate change on road maintenance activities in winter. Recent results will be presented to illustrate the possible impact of various climate scenarios to be expectedon the number frost and snow days. Particular attention will be devoted to the number of days when snow is likely to stay on the roads. For the covering abstract see ITRD E139491.