Projected changes in days with zero-crossings for Norway

Abstract

This paper describes annual and seasonal changes in the number of days with 0°C crossings, comparing projections (2071–2100) based upon regional climate model (RCM) results under the medium and high emission scenarios with the period 1971–2000. A trend analysis of historical observations of days with zero-crossings (DZCs) for the period 1971–2016 showed a general increase in DZCs in cold seasons and regions and a decrease in DZCs in mild seasons and regions. A cold bias in the unadjusted EURO-CORDEX model ensemble rendered bias-adjustment necessary before analyses. In regions and seasons that are mild, temperatures will exceed 0°C during a larger part of the year by the end of this century, and the number of DZCs is thus projected to decrease. This decrease was found for lowland regions in spring and coastal regions in winter. In regions and seasons that are cold, temperatures will rise up above 0°C for a larger part of the year, such that the number of DZCs is projected to give more frequent crossings of the 0°C threshold. This increase was found for inland regions in winter and Finnmark, the northernmost county, in spring. Thus, more frequent icing of the snowpack is expected in Finnmark. However, less frequent icing in coastal and lowland regions may indicate a lesser need for winter road maintenance.