Improving boundary layer flow simulations over complex terrain by applying a forest parameterization in WRF

Abstract. The impact of a forest parameterization on the simulation of boundary layer flows over complex terrain is investigated. Short- and long-term simulations are run for 12 hours and 1.5 months, respectively, with and without forest parameterization and the results are compared to lidar and meteorological tower observations. The test cases are based on the Perdigao 2017 campaign. Short-term simulations focus on low-level jet events over the double-ridge, while long-term simulations cover the whole intensive observation period of the campaign. Simulations without forest parameterization do not reproduce the interaction of the boundary layer flow with the double ridge satisfactorily. Surface winds are overestimated and flow separation and recirculation zones are not or only partly simulated. The additional drag of the forest parameterization considerably improves the agreement of simulated and observed wind speed and potential temperature by reducing the positive wind speed bias and increasing the correlation. The positive effect of the forest parameterization on the boundary layer flow is visible both in the short- and long-term simulations.