UNDERSTANDING IMPACTS OF SUBSURFACE AND SURFACE HETEROGENEITY ON EVAPOTRANSPIRATION IN MOUNTAIN PINE BEETLE INFESTED WATERSHEDS

Drastic changes of the landscape in the Rocky Mountain West due to the Mountain Pine Beetle (MPB) infestation are impacting the distribution of water throughout the hydrologic cycle. Vast areas of once green and thriving Lodgepole pine trees are now seen as dead and gray–resulting in significant changes in evaporation and transpiration. In this work, the relationship between subsurface characteristics and surface heterogeneity, and evapotranspiration (ET) are investigated using ParFlow, an integrated hydrologic model. An increase in groundwater recharge in Rocky Mountain watersheds affected by the MPB is just one anticipated hydrologic change attributed to a reduction in ET. In an effort to establish a more formal relationship between distributions of subsurface characteristics and ET, ParFlow was used to compute and compare ET for a homogeneous forest covered land surface using a heterogeneous subsurface representation of a Rocky Mountain watershed. The ET distribution was also used to obtain volume-averaged estimates as a preliminary step to understand how ET changes between the tree and hillslope scales. Furthermore, MPB affected areas can exhibit a wide range of surface variability from completely live or dead (green or gray) forest to a heterogeneous mix of green and gray. Investigation over several degrees of heterogeneity was completed to determine how surface conditions based on the phase of MPB attack influences ET. Being able to understand the fundamental relationships and factors influencing ET in a mountain setting not only works to gain a better understanding of how water is distributed and potentially redistributed throughout the hydrologic cycle during MPB presence, but serves as an important step in future MPB research.