Impacts of soil moisture and atmospheric moisture transport on the precipitation in two typical regions of China

The effects of soil moisture and atmospheric moisture flux convergence (MFC) on the precipitation are studied in two typical regions in China, one contains both arid and semi-arid regions and the other encloses humid and semi-humid regions. Eight simulations using the weather research and forecasting (WRF) model are conducted by varying the soil moisture and MFC. It is found that in both regions, MFC has stronger effects on precipitation than soil moisture. By decomposing the precipitation change into sub contributing factors, it is found that the contribution of MFC to precipitation differ greatly between different regions. MFC affects precipitation indirectly through changing the precipitation efficiency and directly by changing the moisture influx in the arid and humid regions, whereas, in the semi-arid regions it affects the precipitation mainly by changing the precipitation efficiency and in the semi-humid regions, mainly through changing the moisture influx. Soil moisture affects the precipitation mainly through modifying the precipitation efficiency. Wet soil conditions can increase the surface pressure and reduce the moisture flux in humid regions. The mechanisms of MFC change are explored by decomposing delta MFC into thermodynamic (delta TH), mean circulation dynamic (delta MCD), and transient eddy (delta TE) components. MFC increases mainly through the positive contribution of delta MCD, while the delta TH and delta TE mostly contribute negatively. Both delta MCD and delta TH contribute to the changes in MFC through the convergence/divergence term, rather than through the advection term. delta TE is negative over the relatively flat regions and positive over the complex terrain with sharp terrain height gradients.