Seasonal and interannual variation in evapotranspiration, energy balance and surface conductance in a northern temperate grassland

The eddy covariance technique was used to measure evapotranspiration and sensible heat flux continuously for 2.5 years (three growing seasons) in a northern grassland near Lethbridge, Alta., Canada. The 1999 growing season had precipitation (226.9 mm) near the 30-year average value (1971–2000; 206.4±77.5; mean±S.D.). In contrast, the 1998 growing season precipitation (295.3 mm) was significantly above average and almost four times greater than the 2000 growing season precipitation (75.1 mm), which was significantly below average. The 1998 growing season had higher peak evapotranspiration (4.5 mm per day) than values observed in 1999 and 2000, when the highest evapotranspiration was approximately 3 mm per day. Evapotranspiration during the winter periods was normally