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.