The roles of subgrid topography on land-atmosphere interactions

Land surface heterogeneity is a prominent characteristic over many regions of the world. By altering the partitions of surface fluxes and the amount as well as the phase of precipitation, variations in topography have pronounced and observable control over land-atmosphere interactions. A regional climate model has been developed at the Pacific Northwest National Laboratory based on the Penn State/NCAR Mesoscale Model (MM5). The model uses a physically-based representation of subgrid orographic precipitation to account of the influence of subgrid variations in surface topography on surface hydrological processes such as precipitation, runoff, and snow. A distributed hydrology model with a detailed treatment of land surface processes has been coupled one-way with the regional climate model for various applications. The coupled modeling system has been used to examine the sensitivity of water resources to climate change and variability. Although snow cover and streamflow can be simulated very well by this one-way coupling of regional climate and distributed hydrology models, this approach is computationally intensive. Furthermore, extension of this approach to two-way land-atmosphere coupling is not trivial. We will describe the use of this one-way coupled models to provide guidance for developing a fully coupled land-atmosphere model. We will also describe applications of these models over the Pacific Northwest and eastern Mississippi, focusing on the evaluation of the subgrid parameterization of orographic precipitation and its important roles in coupling land-atmosphere processes over complex terrain.