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Abstract:
Earth System Models (ESMs) are currently the most advanced tools with which to study the interactions between humans, ecosystem productivity and the climate. The inclusion of storm damage in ESMs has long been hampered by their big-leaf approach which ignores the canopy structure information that is required for process-based wind throw modelling. Recently the big-leaf assumptions in the large scale land surface model ORCHIDEE-CAN were replaced by a three dimensional description of the canopy structure. This opened the way to the integration of the processes from the small-scale wind damage risk model ForestGALES into ORCHIDEE-CAN. The resulting enhanced model was completed by an empirical function to convert the difference between actual and critical wind speeds into forest damage. This new version of ORCHIDEE-CAN was parametrized over Sweden. Subsequently, the performance of the model was tested against data for historical storms in Southern Sweden between 1951 and 2010, and South-western France in 2009. In years without big storms, here defined as a storm damaging less than 15 × 106 m3 of wood in Sweden, the model error is 1.62 × 106 m3 which is about 100 % of the observed damage. For years with big storms, such as Gudrun in 2005, the model error increased to 5.05 × 106 m3 which is between 10 % and 50 % of the observed damage. When the same model parameters were used over France, the model reproduced a decrease in leaf area index and an increase in albedo, in accordance with SPOT-VGT and MODIS records following the passing of Cyclone Klaus in 2009. The current version of ORCHIDEE-CAN (revision 4262) is therefore expected to have the capability to capture the dynamics of forest structure due to storm disturbance both at regional and global scales, although the empirical parameters calculating gustiness from the gridded wind fields and storm damage from critical wind speeds may benefit from regional fitting.
