The climate and the long-term water balance of Fluxnet Canada’s coastal Douglas-fir forest

The few years of continuous measurements of NEE of a coastal Douglas-fir forest need to be evaluated in terms of the past and future climates. Warm dry periods increase the loss of carbon through respiration. Inter-annual variation in summer available water has a large impact on forest productivity. A 100-yr weather record (solar, temperature and precipitation) was created for the east coast of Vancouver Island from a number of stations within the Georgia Basin. The daily water balance was simulated for a reference stand (55-year-old Douglas-fir). Daily net radiation and vapour pressure deficit were simulated from the weather data and canopy resistance characteristics were used in the Penman-Monteith equation to calculate daily transpiration. Daily interception and evaporation of precipitation and drainage from the root zone were also simulated. Measured data were used to evaluate the model. The continuous NEE measurements have taken place during a period of reduced variability and small increase in summer rainfall, and warmer minimum air temperatures throughout the year. In the past this productive site has had periods of significant summer water deficit and potential reduction in carbon sequestration.