| This paper focuses on the quantification of the green – vegetation related
– water flux of forest stands in the temperate lowland of Flanders. The
underlying reason of the research was to develop a methodology for assessing
the impact of forests on the hydrologic cycle in comparison to agriculture.
The tested approach for calculating the water use by forests was based on
the application of the soil water balance model WAVE. The study involved the
collection of data from 14 forest stands, the calibration and validation of
the WAVE model, and the comparison of the water use (WU) components –
transpiration, soil and interception evaporation – between forest and
cropland.
For model calibration purposes simulated and measured time series of soil
water content at different soil depths, period March 2000–August 2001,
were compared. A multiple-site validation was conducted as well. Actual tree
transpiration calculated with sap flow measurements in three forest stands
gave similar results for two of the three stands of pine (Pinus sylvestris L.), but WAVE
overestimated the actual measured transpiration for a stand of poplar
(Populus sp.).
A useful approach to compare the WU components of forest versus cropland is
scenario analysis based on the validated WAVE model. The statistical Profile
Analysis method was implemented to explore and analyse the simulated WU time
series. With an average annual rainfall of 819 mm, the results reveal that
forests in Flanders consume more water than agricultural crops. A 30 years
average of 491 mm for 10 forests stands versus 398 mm for 10 cropped
agricultural fields was derived. The WU components, on yearly basis, also
differ between the two land use types (transpiration: 315 mm for forest and
261 mm for agricultural land use; soil evaporation: 47 mm and 131 mm, for
forest and cropland, respectively). Forest canopy interception evaporation
was estimated at 126 mm, while it was negligible for cropland. |