Climate-relevant physics in the new Noah-MP Land Surface Model coupled with WRF

The new Noah-MP (Multiple-Physics) land surface model (LSM) was released in WRFv3.4. The Noah-MP model has multiple options for various land processes, including 1) a multi-layer snowpack with liquid water storage and melt/refreeze capability; 2) a separate vegetation canopy with two-stream radiation transfer treatment considering the effects of 3-D canopy structure; 3) a dynamic vegetation model using Ball-Berry photosynthesis-based stomatal resistance; and 4) a groundwater-aquifer model with a TOPMODEL-based runoff scheme Historically, LSMs coupled to regional scale forecast models such as WRF focused primarily on the accurate partitioning of energy and water at the surface. Since these models were primarily used for short-term weather forecasting, less focus was given to long timescale processes, including interaction with aquifer groundwater and vegetation-climate feedbacks. Noah-MP contains physics options for both of these crucial climate processes. The Noah-MP groundwater-aquifer component contains a prognostic water table depth to an aquifer that interacts with the model soil layers throughout the simulation. Therefore, unlike the Noah LSM, Noah-MP can access additional water storage during droughts and recharge the aquifer during wet periods. Additionally, the aquifer water can be used to irrigate agricultural lands while conserving total water in the modeling system. In the current WRF model, vegetation horizontal coverage, leaf area index and albedo are prescribed from climatological values. Therefore, there are no climate effects on vegetation condition. Noah-MP contains a carbon allocation-photosynthesis model that maintains pools of carbon in leaves, stems, roots, wood and two soil carbon pools. The amount of leaf and stem carbon determines the horizontal and vertical density of vegetation, which then directly affects radiation and turbulent fluxes with the atmosphere. Since photosynthesis is driven by climate conditions, the model contains a direct land surface-climate feedback. Some preliminary results from the coupled WRF/Noah-MP LSM model testing will be shown from four-month simulations at 30km horizontal resolution in regional climate mode. The simulations will show how the climate-relevant features of the Noah-MP model with its detailed parameterization of water-table depth and dynamic vegetation improve simulations of regional climate especially in extreme weather situations such as drought.