Impact of effective roughness length on mesoscale meteorological simulations over heterogeneous land surfaces in taiwan

The Weather Research and Forecasting (WRF) modeling system obtains the aerodynamic roughness length (20) from a land use (LU) lookup table. The effective aerodynamic roughness length (~0eff) was estimated for the island of Taiwan by considering the individual roughness lengths (20/) of the underlying LU types within a modeling grid box. Two 2 datasets were prepared: one using the Zqj from the default LU lookup table and the other using the observed Zqj for three LU types (urban, dry cropland and pasture, and irrigated cropland and pasture). The spatial variability of the z0eff distribution was higher than that of the LU table-based Zq distribution. Three WRF sensitivity experiments were performed: (1) dominant LU table-based Zq (namely, SI), (2) 2^ estimated from the default 2q/ (namely, S2), and (3) 2Qeff estimated from the observed Zqj (namely, S3). Comparisons of the thermal field, temperature, and surface sensible and latent heat fluxes revealed no significant differences among the three simulations. The wind field overestimation and surface momentum flux underestimation in SI were reduced in S2 and S3, and these improvements were more prominent over areas with highly heterogeneous land surface conditions.