Numerical simulations of fractional vegetation coverage influences on the convective environment over the source region of the Yellow River

The spatial distribution of fractional vegetation coverage (FVC) over the source region of the Yellow River (SRYR) shows heterogeneity and has changed much for vegetation degradation during the past 30 years. In this paper, three numerical tests were conducted using the Weather Research and Forecasting (WRF) model for a fair weather case and a rainy case over the SRYR. The first test used FVC derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) data, the second test took a spatial constant FVC (=50 %), and the last one deployed the model default FVC. The results showed that simulated 2-m height potential temperature decreased and specific humidity increased as FVC increased for both cases. The magnitudes of the sensible and latent heat fluxes were different over the wetland at the fair day and the rainy day. There was a divergence center near the Zoige wetland in the fair weather case but a convergent center in the rainy case. As a conclusion, when the default FVC in the WRF model were replaced by the new MODIS-derived FVC data, the root-mean-square errors (RMSEs) between measurements and the simulated 2-m height air temperature and relative humidity decreased for both cases, the mean RMSEs between measurements and the simulated 2-m height air temperature and relative humidity declined by 0.3 K and 3.0 % in the fair day, 0.4 K and 3.4 % in the rainy case. The mean differences of simulated precipitation for seven ground stations were 1.1 mm for the fair day and 4.2 mm for the rainy case. Therefore, the updated MODIS FVC has influences on the convective environment over the SRYR.