Seasonal dynamics of canopy interception loss within a deciduous and a coniferous forest

Canopy interception loss is a key process in forest hydrology and the role of interception loss in relation to the forest water budgets and future impact of afforestation on water resources is important to quantify. Based on high frequency in situ monitoring, the effect of species- and leaf-cover-specific canopy structure metrics for interception loss estimation is examined at the two most typical forest types in Denmark. First, interception loss is estimated from precipitation and throughfall data collected in two even-aged (40-60 years) temperate oak (deciduous) and Norway spruce (coniferous) forests over 13 and 11 months, respectively. Second, based on these observations we estimated canopy structure parameters relevant for interception loss; direct throughfall (rho), the precipitation necessary to saturate the canopy (P'), the canopy evaporation as a fraction of precipitation (EC/P) and canopy storage capacity (S). Third, we compare observation-based interception loss with predictions obtained by the analytical Gash interception model using the derived canopy structure parameters. Lastly, the effect of species- and leaf-cover on the interception loss is quantified by applying the canopy structure parameters of the deciduous and coniferous forest on the same daily precipitation data set of approximately 1 year in the Gash model. We found that the derived canopy structure parameters reflect the seasonal change in the leaf cover of the deciduous forest and different parameters are identified for the two forest types. In the deciduous forest, improved agreement between observation-based and predicted interception loss is obtained using canopy structure parameters for the leafless and full-foliage periods instead of annual average values. The share of throughfall and interception loss to precipitation (total sum of precipitation = 526 mm) is 65% (340 mm) and 35% (186 mm) for the deciduous forest, respectively, and 49% (260 mm) and 51% (266 mm) for the coniferous forest, respectively. A seasonal variation of interception loss is observed in the deciduous forest where the share of interception loss to precipitation is 40% during the period with leaves on the trees (June to November) and 22% for the leafless periods (December to May). Thus, species- and leaf-cover-specific canopy structure metrics enhance model performance of throughfall and interception loss dynamics in forests.