Decadal water balance of a temperate Scots pine forest (&amp;lt;i&amp;gt;Pinus sylvestris&amp;lt;/i&amp;gt; L.) based on measurements and modelling

B Gielen,J Neirynck,D A Sampson,F Vermeiren,H Verbeeck,I A Janssens

doi:10.5194/bg-7-1247-2010

Abstract

Abstract. We examined the water balance components of an 80-year-old Scots pine (Pinus sylvestris L.) forest 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. Using and evaluating process based models with data is extremely useful as models are the primary method for integration of small-scale, process level phenomena into comprehensive description of forest stand or ecosystem function. 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. We found significant relationships between several meteorological variables (i.e., vapour pressure deficit [VPD], mean air temperature [Tair], and global radiation [Rg]) and ET on monthly basis for all approaches. In contrast, few relationships were significant on annual basis. Independent of the method examined, ET exhibited low inter-annual variability. Consequently, drainage fluxes were highly correlated with annual precipitation for all approaches examined, except CI.

Highlights

Vegetation strongly interacts with the terrestrial water cycle to influence runoff processes within vegetated catchments (Sahin and Hall, 1996)
We examined the water balance components of an 80-year-old Scots pine (Pinus sylvestris L.) forest 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
The conservative ion method (CI) method is considered less useful for these studies as our results show that the ET is overestimated by 58% when compared to the Eddy Covariance technique (EC) method (Fig. 5a)

Summary

Introduction

Vegetation strongly interacts with the terrestrial water cycle to influence runoff processes within vegetated catchments (Sahin and Hall, 1996). Forests play an important role in the water and energy balance of the land surface. Complex diurnal cycles of water evaporation and energy fluxes are generated by the forest floor, and from beneath and within the forest canopy; vegetation structure and canopy height strongly influence these water cycling processes (Rutter, 1975). Long term forest monitoring sites can provide a wealth of knowledge on the drivers of the interannual and long term seasonal variation of the water balance components, such as evapotranspiration (ET) and drainage of forests. Many different approaches ranging from measurements and empirical models to generic and site parameterised process-based models have been used to estimate ecosystem water balances

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Conclusion