Abstract. Multi-year, multi-technique studies often yield key insights into methodological limitations but also process-level interactions that would otherwise go un-noticed if analysed at one point in time or in isolation. We examined the components of forest water balance for an 80-year-old Scots pine (Pinus sylvestris L.) stand in the Campine region of Belgium over a ten year period using five very different approaches; our methods ranged from data intensive measurements to process model simulations. Specifically, we used the conservative ion method (CI), the Eddy Covariance technique (EC), an empirical model (WATBAL), and two process models that vary greatly in their temporal and spatial scaling, the ORCHIDEE global land-surface model and SECRETS a stand- to ecosystem-scale biogeochemical process model. Herein we used the EC technique as a standard for the evapotranspiration (ET) estimates. We also examined ET and drainage in ORCHIDEE as influenced by climate change scenarios from the Hadley model. Results demonstrated that the two process models corresponded well to the seasonal patterns and yearly totals of ET from the EC approach. However, both WATBAL and CI approaches overestimated ET when compared to the EC estimates. Overestimation of ET by WATBAL increased as ET increased. We found positive relationships between ET and the process drivers to ET (i.e., vapour pressure deficit [VPD], mean air temperature [Tair], and global radiation [Rg]) for SECRETS, ORCHIDEE, and the EC estimates, though few were significant. Estimates of ET from WATBAL and the CI approach were uncoupled from VPD, Tair, and Rg. Independent of the method examined, ET exhibited low interannual variability. Consequently, drainage fluxes were highly correlated with annual precipitation for all five approaches examined. Estimates of ET increased in climate change scenarios for ORCHIDEE while drainage decreased.
Effects of intensified silviculture on timber production and its economic profitability in boreal Norway spruce and Scots pine stands under changing climatic conditions
