GIS as a tool for planning new road stretches in respect of climatological factors

When planning a new road stretch there is a need for an evaluation of the local climate to estimate the winter road maintenance costs and what problems that could be expected along the road, e.g. areas subjected to frequent road slipperiness. At present these evaluations are performed manually and by field studies. In this paper a new perspective at solving the problem is presented, by means of using Geographical Information Systems (GIS). The basic approach uses three distinct weather types, each being characterised by local climate features. The weather types, which have been mapped separately, are clear days, clear/calm nights and cloudy/windy conditions. The main parameters used are solar irradiance, cold air drainage and pending and height above sea level. To be able to get an overview of surface temperature variations in the landscape and their frequency of occurrence, the climatological features were classified according to the extent of temperature decrease (or in some cases increase). Three risk-classes were used for low temperatures (2, 1 and 0), with lowest temperatures being assigned the value 2, 1 is an intermediate class and the average of the whole area is represented by 0, e.g. horizontal ground in the case of incoming solar radiation. When a higher than average temperature is expected, for instance in many urban areas or sunny slopes, risk classes -1 and -2 are used. Frequencies of the studied situations were obtained from weather statistics and multiplied by the risk classes. Finally maps for each weather situation were combined into one map showing the expected relative risks and frequencies of low temperatures as climatological risk points. These climatological points, of for example two alternative road stretches, can be compared in order to evaluate the differences in local climate. The software IDRISI, PC Arc/Info and a digital elevation model were used for the calculation and mapping.