Effects of subgrid heterogeneities in soil infiltration capacity and precipitation on regional climate: a sensitivity study

One of the most pronounced features of the land surface is its heterogeneity. In order to further understand land-atmosphere interactions and improve climate modeling it is very important to investigate effects of subgrid scale heterogeneities, especially hydrological-process heterogeneities. In this paper, after the construction and sensitivity tests of a hydrological model (VXM), which accounts for precipitation heterogeneity (PH) and infiltration heterogeneity (IH), we incorporated VXM into the NCAR (National Center for Atmospheric Research) regional climate model RegCM2 and thus obtained the augmented regional climate model (hereafter, ARCM). By using 3-month (May-July) observational data of 1991 Meiyu season, we conducted numerical experiments with ARCM, analyzed the sensitivities, and found that: (1) The regional climate and surface hydrology are very sensitive to IH as well as PH, i.e., the simulations for the surface fluxes, soil temperature, soil moisture, precipitation and surface runoff can be greatly affected by those heterogeneities. (2) ARCM can effectively improve the simulation of hydrological processes, i.e., it can greatly enhance the surface runoff ratio (i.e., the ratio of surface runoff to precipitation), which is consistent with observations over humid areas in China. (3) It seems that the IH influence on the surface climate is larger than the PH influence. (4) The modeled climate is sensitive to the VXM parameters. For example, it is significantly modified after the surface impermeable fraction has been accounted for, suggesting some features of aridification.