REPRESENT HILL-VALLEY MOISTURE CONTRAST BY LAND SURFACE MODEL WITH LATERAL SUBSURFACE FLOW

Abstract

 Recently, it has been suggested that saturated lateral flow on a local scale, such as hillslope hydrodynamics, affect the terrestrial water heat balance such as evapotranspiration and soil moisture, and that these areas are not uncommon globally. However, no study expresses the contrast of hydrological quantities on the hillslope at a fine resolution on the global scale with reasonable computational cost. Here, we implemented a subgrid saturated lateral flow scheme in the integrated land simulator (ILS), and carried out a global simulation for 163 years. Then we expressed the hill-valley moisture contrast by diagnostically downscaling the simulation results using subgrid topography information. The results suggested that by considering the saturated lateral flow, the soil moisture and the evaporation tend to decrease in a wide range of the global average, and the runoff amount increases in the area where the evaporation decreases, especially in the alpine area. We re-evaluated the land surface water balance from the viewpoint of water redistribution by the hillslope dynamics, and experimentally explained the possibility of the existence of vegetation in the valley in the arid area. In addition, we compared the downscaled result with high-resolution soil moisture satellite observation data (SMAP) and expand the possibility of verification of a global land model by high-resolution satellite data. Although it is necessary to improve the method of applying land cover in the subgrid and climate forcing dataset, it was suggested that the hill-valley moisture contrast can be represented in the global land model with the saturated lateral flow.