The effects of climate change on the temperature conditions of lakes

Climate change, as indicated by changes in air temperature, was simulated with the SILMU (the Finnish Research Programme on Climate Change) scenarios. The effects of air temperature change on the temperature regime of five lakes were studied with a temperature model using two approaches. The parameters describing the temperature regime were vertical temperature distribution, length of the stratification period, time of freezing and time of ice break-up. The surface areas of the lakes range from 0.25 km2 to 161 km2 and depths from 13 to 85 m. For one lake (Pääjärvi) the averages and the standard deviations of the temperature parameters in a changing climate were computed for the years 2036–2065. For the year 2050 (June-August) the surface temperature increases by 1.8deg.C, and the low and high estimates are 0.5deg.C and 2.6deg.C. For the other lakes a spatial approach was used. Representative values for air temperature in the years 2020, 2050 and 2090 were used to obtain a spatial description of the temperature regime of small lakes all over Finland. All the results showed significant changes in the temperature regime, e.g. changes of 30–60 days were predicted in the length of stratification and ice-covered period.