Quantification of Hydrologic Response to Forest Disturbance in Western U.S. Watersheds
Location
Logan, UT
Start Date
3-29-2022 4:15 PM
End Date
3-29-2022 7:00 PM
Description
Forests influence the partitioning of precipitation into evapotranspiration versus streamflow. In coniferous western forests, recent widespread tree mortality has provided opportunities to improve understanding of the relationship between forest cover change and water yield and inform management of forested watersheds in the context of climate change, increased demands on water, and drought. This work investigated hydrologic response to forest disturbance in the western United States. First, I synthesized findings from 78 published studies of streamflow or snowpack response to forest disturbances. Results indicated that streamflow and snowpack may increase, not change, or even decrease with reduced forest cover due to disturbance. Decreased streamflow occurred due to net increases in evapotranspiration, particularly following non-stand replacing disturbance. Higher post-disturbance subcanopy radiation caused increased evaporation from soil or snowpack, and rapid post-disturbance vegetative recovery resulted in increased transpiration. Next, I investigated streamflow response to forest disturbance in 159 watersheds using hydrologic, climatic, and forest data from an existing curated hydro-climatological watershed dataset and the US Forest Service's Forest Inventory and Analysis (FIA) dataset. Streamflow change due to tree mortality was found to depend on aridity. In wetter watersheds, disturbances tended to increase streamflow, while post-disturbance streamflow more often decreased in arid watersheds with high potential evapotranspiration to precipitation ratio. The work presented here found that disturbances that do not remove the entire canopy (e.g., due to insects, drought, disease, thinning, low-severity wildfire) may lead to different water yield and snowpack responses than disturbances that remove the entire canopy (e.g., clearcut harvesting, severe wildfire).
Quantification of Hydrologic Response to Forest Disturbance in Western U.S. Watersheds
Logan, UT
Forests influence the partitioning of precipitation into evapotranspiration versus streamflow. In coniferous western forests, recent widespread tree mortality has provided opportunities to improve understanding of the relationship between forest cover change and water yield and inform management of forested watersheds in the context of climate change, increased demands on water, and drought. This work investigated hydrologic response to forest disturbance in the western United States. First, I synthesized findings from 78 published studies of streamflow or snowpack response to forest disturbances. Results indicated that streamflow and snowpack may increase, not change, or even decrease with reduced forest cover due to disturbance. Decreased streamflow occurred due to net increases in evapotranspiration, particularly following non-stand replacing disturbance. Higher post-disturbance subcanopy radiation caused increased evaporation from soil or snowpack, and rapid post-disturbance vegetative recovery resulted in increased transpiration. Next, I investigated streamflow response to forest disturbance in 159 watersheds using hydrologic, climatic, and forest data from an existing curated hydro-climatological watershed dataset and the US Forest Service's Forest Inventory and Analysis (FIA) dataset. Streamflow change due to tree mortality was found to depend on aridity. In wetter watersheds, disturbances tended to increase streamflow, while post-disturbance streamflow more often decreased in arid watersheds with high potential evapotranspiration to precipitation ratio. The work presented here found that disturbances that do not remove the entire canopy (e.g., due to insects, drought, disease, thinning, low-severity wildfire) may lead to different water yield and snowpack responses than disturbances that remove the entire canopy (e.g., clearcut harvesting, severe wildfire).