Impact of Irrigation in the Oasis in Northwestern China on Vertical Turbulent Heat Flux Using Large-Eddy Simulation

This study aims to investigate the response of turbulent eddies to mesoscale, heterogeneous, land use change in the oasis in Northwestern China. For this purpose, two experiments were carried out using the WRF-LES model for the experiments before irrigation (BI) and after irrigation (AI), capturing the change of the heterogeneity strength due to irrigation in the oasis. The area-averaged method was used to calculate the area-averaged flux while the wavelet analysis was used to decompose the pattern of surface turbulent heat fluxes into multiscale patterns.The results show that irrigation has an important impact on vertical heat flux, soil moisture, and soil temperature. Irrigation increases the heterogeneity strength, which greatly impacts the dispersion of flux pattern. The dispersion height of sensible heat flux decreases with the decrease in sensible heat flux AI experiment. The shape of turbulent eddies in the AI experiment is reticular, which is similar to that in the BI case, but energy spectra of the sensible heat flux pattern decrease after irrigation. In addition, the dispersion height of latent heat flux depends on sensible heat flux, and energy spectra of latent heat flux pattern decrease in AI experiment. Regarding the results related to the spatial lag correlation coefficient, the height of the response of the vertical heat flux to the surface flux in BI is higher than the one in AI. The shift distance in AI is shorter than that in BI. Strong surface heating leads to large correlation coefficients and strong entrainment at the top of convective boundary layer.