Sensitivity of numerical simulations in an idealized valley to surface parameters

Land surface models (LSMs), i.e. parameterization schemes for evaluating surface-atmosphere exchange implemented in meteorological models, usually prove inadequate over complex terrain,where orography strongly influences atmospheric processes and their interaction with the surface. In particular, LSMs use several parameters to suitably describe the surface and its interaction with the atmosphere, whose determination is often affected by many uncertainties. To this date, the sensitivity of meteorological model results to these parameters has not yet been studied systematically in complex terrain.The purpose of this work, which lies in the context of the TEAMx-related project ASTER, funded by the EGTC European Region Tyrol-South Tyrol-Trentino, is to evaluate the sensitivity of simulations with the Weather Research and Forecasting (WRF) meteorological model to variation of parameters describing land cover. Specifically, an idealized three-dimensional topography consisting of a valley-plain system is adopted and the analysis of the results focuses on the development of thermally-driven circulations. The analysis considers both the sensitivity to the type of vegetation cover and to the systematic variation of surface parameters based on typical values found in the literature. In particular, this analysis is carried out using the Global Sensitivity Analysis (GSA) methodology in order to quantify the uncertainty associated with the variation of each parameter evaluated and to estimate the optimal computational effort required for this type of study. The outcome of this analysis allows to evaluate which are the parameters that most influence model results and therefore should be estimated with particular attention in order to obtain reliable simulations over complex terrain.