P45  Modeling the Effects of Forest Disturbances with the Noah-MP Land Surface Model

Chen, Fei, Guo Zhang, Michael Barlage, Ying Zhang, Christine Wiedinmyer, National Center for Atmospheric Research, Boulder, CO., Jeffery A. Hicke, and Arjan Meddens University of Idaho, Moscow, ID

Over the past decade, warmer climate and frequent drought have resulted in unprecedented levels of bark beetle-caused tree mortality and forest fire across the western mountain regions of North America. These disturbances modify forest structures and radiative properties. This study presents results of modeled impacts of forest disturbances on forest-atmospheric exchange of heat and moisture, and surface hydrological cycles with the Noah-Multi-Physics (Noah-MP) land surface model. The Noah-MP model, containing an explicit, separate vegetation canopy that uses a two-stream radiation transfer approach along with three options for shading effects, and represents radiation and turbulence processes necessary to simulate these effects in forest canopy.

For beetle-kill trees, the model is able to reproduce the observed large reduction in summer daytime evaporation, accompanied by large increase in sensible heat fluxes. Simulations also show that more spring snowmelt and less spring-summer transpiration produce wetter soils and more runoff. This modeled trend is similar to runoff change in harvested forests where reduced forest density and cover results in more spring snowmelt and annual water yields. For sites burnt by wildfire, the model captures the observed large reduction in summer latent and sensible heat fluxes and the  increase in soil heat storage. The forest fire effect is strongest in winter daytime net radiation and sensible heat flux. This study highlights the need for taking into account the transient effects of forest disturbances in modeling land-atmospheric interactions and their potential impacts on regional weather and climate.