Partitioning the forest water balance within a boreal catchment using sapflux, eddy covariance and process-based model.

In the hydrological cycle, water is lost from terrestrial ecosystems either laterally through stream runoff or vertically as evapotranspiration (ET) back to the atmosphere. Although it is well known that ET losses represents an important water loss pathway at local to global scales, the magnitude and relative importance of ET and its individual flux components varies considerable among different ecosystems. In this study, we combined empirical sapflux and eddy covariance measurements with estimates from a process-based model to partition the water balance in a boreal forested catchment. This study was conducted within the Krycklan Catchment, which has state-of-the-art infrastructure for hydrological measurements, thereby providing us the unique opportunity to compare the absolute and relative magnitude of ET and its flux components to other water loss pathways (i.e., stream runoff). During the growing season, ET was the major water loss pathway, representing ca. 85% of the incoming precipitation and being roughly 7 times greater than stream runoff. Both the empirical results and model estimates suggested that tree transpiration (T) and canopy interception (IL) represented 45% and 35% of total ET loss; respectively, and thus together were responsible for 70% of the water loss during the growing season. Understory evapotranspiration (ETu) was less important than T and IL during most of the study period, except for late autumn when ETu was the largest ET flux component. Overall, our study highlights the importance of trees in regulating the water cycle of boreal catchments, implying that forest management impacts on stand structure as well as climate change effects on tree growth are likely to have large cascading effects on the way water moves through these forested landscapes. [ABSTRACT FROM AUTHOR]