SIMULATED WATER-BALANCE OF SCOTS PINE STANDS IN SWEDEN FOR DIFFERENT CLIMATE-CHANGE SCENARIOS

The effects of climate change on the water balance of Scots pine were studied with a coupled water and heat flow model called 'SOIL'. Two forest soil types (a silty-sand and a sand) at five locations in Sweden were chosen to represent sites with different air temperature, growing season length and precipitation excess. The simulated water balance for the period 1961-1987 was compared with those simulated with two climate change scenario schemes: one is based on increased temperature and the other on both increased temperature and increased precipitation. Different assumptions regarding the effects of changes in leaf area index and minimum canopy resistance on transpiration were studied. Water stress increased substantially in the scenarios based on increased temperature only, which prevented transpiration from increasing. But with scenarios based on simultaneous changes in temperature and precipitation, water stress increased mainly during spring and transpiration increased by 50 mm and 100 mm in northern and southern Sweden, respectively, i.e. by 30-50%. When simultaneous changes in climate and stand characteristics were assumed, transpiration increased by 30-70% with the relative change being greatest for northern Sweden. Differences in water balance the locations and soil types were less pronounced in the climate change scenarios than in the present climate scenario.