A frost assessment method for mountainous areas

Abstract

The present paper describes a model for frost assessment in mountainous areas in relation to forest management. Data were collected at 38 locations within a 625 km 2 region, which is characterised by a diverse topography and vegetation cover. Air temperature measurements were performed during the peak of the growing season. (July–August 1996) in the southern Swedish mountains at elevations between 500 and 1200 m a.s.l. The variation in nighttime minimum temperatures was analysed in relation to the prevailing weather and terrain type of the measuring sites. From the analysis of the temperature and weather conditions, i.e., wind and radiation, it was concluded that more than 90% of the frost situations, occurring during the study period, were of the radiation type. It was further concluded that the variation among the studied stations was closely related to the terrain type during these situations. Frost occurred most frequently in narrow valleys, then in concave and flat locations. Elevated and convex areas were found to have very few situations of radiation frost. Local terrain information was used together with a calculated frost index for assessment of the spatial variation in frost risk. Furthermore, a grid net was applied to the study area and the pixels were given a terrain form of the type convex, slope, flat, wide concave or narrow concave according to the dominating terrain curvature. For each pixel a frost index value was estimated from the recorded temperatures at the field stations. A cluster analysis was used to group the terrain types according to the index, whereby six obvious clusters were obtained each with clearly differentiated frost intensity. The analysis showed that this kind of treatment is a suitable method for assessing the spatial variation in frost risk.