IMPACTS OF CHANGES IN WINTER PERIOD TEMPERATURE ON SNOWPACK WATER AVAILABILITY: A CASE STUDY FROM SOUTHERN FINLAND

Masoud Irannezhad, Anna-Kaisa Ronkanen, Bjørn Kløve, University of Oulu, Finland

Abstract

Variations in temperature of winter period directly affect water content of snowpack due to shifting of precipitation falling form from snow to rain or vice versa. Using temperature and precipitation data with combination of the temperature-index model of snowmelt, we evaluated changes in snowpack water availability in southern Finland. The model was calibrated and validated according to observed precipitation, temperature and snow water equivalent data from 1946 to 2011. Trend analyses at the 5% significance level by Mann-Kendall non-parametric test determined that the mean temperature increased (by 0.01 °C/year), and the precipitation decreased (by 1.00 mm/year) during the winter periods from 1858 to 2011 based on the data from Kaisaniemi meteorological station. Decreasing trends in number of days with negative temperature (by 0.24 day/year), and in average value of all these negative mean temperatures (by 0.006 °C/year) during the winter periods of whole period of study were found. These decreasing trends resulted in less frequent snowy days (by 0.12 day/year) and reduction of snowfall amounts (by -1.08 mm/year). The number of rainy days increased (by 0.055 day/year), while there were no clear trends in rainfall, number of days with positive mean temperature and average value of all positive temperatures in the all winter periods. The snowpack water availability during the winter time showed a decreasing trend by 1.26 mm per year. It can be concluded that the decreases in the water content of snowpack in Southern Finland caused by increases in the temperature of winter period that decreased the snowfall and increased frequency of rainfall events.