Water balance study of a groundwater-dependent oak forest

Abstract

The objectives of this study were (1) to estimate the water balance components of an oak stand by calibrating a Hydrus 1-D model, (2) to determine the groundwater consumption by the water table fluctuation method and (3) to compare the results of the modelling with a remote-sensing based estimation. Model simulation described the observed soil moisture and groundwater level relatively well, the root mean square errors varied between 12.0 and 14.9% for the soil moisture measurements and 5.0% for the groundwater level. Groundwater consumption was estimated also by the water table fluctuation method, which provided slightly different groundwater consumption rates than estimated by the Hydrus model simulation. The simulated evapotranspiration was compared with results of a remote-sensing based estimation using the surface temperature database of MODIS. According to the Hydrus model, the estimated evapotranspiration resulted from transpiration (73%), interception loss (23%) and soil surface evaporation (4%) in the two-year study period. The proportion of groundwater consumption was 58% of the total transpiration. During the dry growing season of 2007 the groundwater consumption was significant with 66% of the total transpiration. Water supply from groundwater was found to be less important in the wet growing season of 2008 with 50%. The remote-sensing based estimation of evapotranspiration was about 4% lower than the model based results of nearby comparable sites.