Forest Disturbance Feedbacks From Bedrock to Atmosphere Using Coupled Hydrometeorological Simulations Over the Rocky Mountain Headwaters

Abstract

The mountain pine beetle (MPB) has dramatically influenced high‐elevation pine forests of western North America, with recent infestations causing millions of acres of forest mortality and basal area loss. While ecohydrologic implications of infestation have been studied extensively in recent years, few have explored atmospheric feedbacks of widespread canopy transpiration loss or the potential role of groundwater to amplify or mitigate changes to land energy. This work presents bedrock‐to‐atmosphere simulations of coupled meteorological and hydrologic states over the Colorado headwaters. Analyses compare configurations with (1) default land surface parameters and (2) disturbance simulations with adjusted transpiration parameters in infested cells. An analysis of variance was conducted to identify regions of significant response to mountain pine beetle. Changes to increased soil moisture and Bowen ratios were found to be statistically significant in MPB‐infested areas and in nonlocal valleys, while planetary boundary layer (PBL) response was significant only in high elevations of the headwaters watershed. Temperature‐humidity covariance was evaluated using mixing diagrams; the results suggest that increased surface Bowen ratios from MPB could affect entrainment of dry air from the troposphere. The PBL is hotter, drier, and higher under infested forest conditions, which could have implications to atmosphere‐vegetation feedbacks and forest drought stress. Finally, land‐atmosphere coupling was sensitive to antecedent subsurface moisture. Regions with shallow water tables exhibit greater magnitude response to MPB at the surface and in the PBL, a finding that has repercussions for ecosystem resilience and hydrologic representation in meteorological modeling.

Impact of Lateral Groundwater Flow and Subsurface Lower Boundary Conditions on Atmospheric Boundary Layer Development over Complex Terrain

“…PFWRF 3D has previously been run over this model domain to diagnose hydrology-land-atmosphere coupling under land disturbance conditions (Forrester et al 2018), with results suggesting that the energy and moisture flux sensitivity to widespread forest mortality is highly dependent on antecedent moisture conditions. This study uses the same atmospheric initial and boundary conditions and static soil, geology, and land use variables detailed in Forrester et al (2018). While they provide a complete description of the model configuration and development, we provide a brief summary here.…”

“…domain; in order to keep the free-drainage experiment as close in initial condition to the control as possible, PFWRF FD was initialized with saturated soil moisture conditions and a surface-level groundwater table. However, PFWRF 3D and WRF PFIC were both initialized with a hydrologic spinup of the ParFlow model domain (Forrester et al 2018), which was conducted by running the hydrologic model with repeated annual forcing from the North American Land Data Assimilation System (NLDAS; Cosgrove 2003), until the change in subsurface storage was within one percent of the annual forcing from one year to the next. Such a spinup method avoids initial moisture condition bias, as it supplies an equilibrium hydrologic state and reduces the tendency for artificial drift (Ajami et al 2014).…”

Persistent Hydrological Consequences of Hurricane Maria in Puerto Rico

“…corresponding latent heat flux is reduced, heat absorbed by the landscape from incident solar radiation must be largely transferred to the atmosphere via sensible heat (i.e., increased temperature), increasing the Bowen ratio (Forrester et al, 2018). When ET and its ©2019.…”

“…This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. corresponding latent heat flux is reduced, heat absorbed by the landscape from incident solar radiation must be largely transferred to the atmosphere via sensible heat (i.e., increased temperature), increasing the Bowen ratio (Forrester et al, 2018). Simultaneously, satellite imagery following strong hurricanes depicts that a clear surface "browning" and modified surface reflectance in the shortwave spectrum may further alter the sensible heat flux.…”

HESS Opinions: Improving the evaluation of groundwater representation in continental to global scale models

“…Maxwell et al 2007;Rahman et al, 2015), under land cover disturbance (e.g. Forrester et al 2018), under extremes (e.g. Kuene et al 2016) and due to groundwater pumping (Gilbert et al 2017).…”