Implementation of a Topographically Controlled Runoff Scheme for Land Surface Parameterizations in Regional Climate Models

Abstract

The Common Land Model (CLM), the land component of the Community Climate System Model (CCSM), for simulating water and energy exchanges between land and atmosphere has water and energy biases resulting from deficiencies in some parameterizations related to hydrological processes. This paper presents the implementation of modified parameterizations in the terrestrial hydrological scheme of the CLM and their effects on the runoff prediction. In particular, the new formulation for topographically controlled baseflow developed in this study can represent effects of the surface macropores and the vertical change of hydraulic conductivity on baseflow. To assess the performance of the new improved parameterizations, we compare runoff results from a set of offline simulations using the consistent North American Regional Reanalysis (NARR) meteorological forcing dataset and realistic Surface Boundary Conditions (SBCs) with observations from the U. S. Geological Survey (USGS) gauge station for a study catchment around the Ohio Valley region. The new modified scheme especially incorporating topographically controlled baseflow plays a significant role in generating and partitioning surface runoff and subsurface runoff. It is also observed that the new model-simulated subsurface runoff makes a significant contribution to improve the runoff predictability in simulating declining recession curves due to the role of baseflow.