Seasonal variability of thermal conditions of a river valley on the example of the Swider river valley

Air temperature variability on the local scale is one of the most important elements of topoclimatic differentiation. The aim of this paper is to determine the seasonal variability of the thermal conditions of the downstream Świder River valley. The analysis was conducted from October 2011 until December 2014 using air temperature data from a measurement station in Adamówka (representative location for downstream Świder River valley) and from the reference meteorological station in Otwock-Świder, operated by the Institute of Geophysics of Polish Academy of Sciences. Differences of the average, maximum and minimum daily air temperature between the station in Adamówka and corresponding values under reference conditions (dTavg, dTmax, dTmin) were calculated for each season of the study period (spring, summer, autumn, winter). Only days with radiative type of weather were chosen to further analysis due to the greatest spatial diversity of climate elements within such periods. The differences found between air temperature values in Adamówka and Otwock-Świder were small, but stable during the year. Within the river valley, due to high heat capacity of the substrate and presence of forest complex, a reduction of thermal contrasts during the day was observed. Consequently, downstream Świder River valley was characteriszed by lower air temperature, both in terms of daily average and maximum values, compared to standard conditions at the reference meteorological station in Otwock-Świder. Opposite results were obtained only for minimum daily air temperature, which was higher in the river valley in autumn. This can be explained by the fact that at the end of the vegetation period the substrate with the higher heat capacity slowly emits energy, which resulted in an increase in the minimum daily temperature in this season. The authors suggest that further investigations should concentrate on determining the changes in differences between air temperature in reference station and many different stations representing the same type of topoclimate, and thus on the stability of those differences during the year. For this purposes long-term measurements of meteorological elements are required