|WEI, LIANG - University Of Idaho|
|LINK, TIMOTHY - University Of Idaho|
|HUDAK, ANDREW - Us Forest Service (FS)|
|MARSHALL, JOHN - University Of Idaho|
|KAVANAGH, KATHLEEN - University Of Idaho|
|ABATZOGLOU, JOHN - University Of Idaho|
|ZHOU, HANG - University Of Idaho|
|PANGLE, ROBERT - University Of New Mexico|
Submitted to: Hydrological Processes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/3/2015
Publication Date: 1/28/2016
Citation: Wei, L., Link, T., Hudak, A., Marshall, J., Kavanagh, K., Abatzoglou, J., Zhou, H., Pangle, R., Flerchinger, G.N. 2016. Simulated water budget of a small forested watershed in the continental/maritime hydroclimatic region of the United States. Hydrological Processes. 30(13):2000-2013.
Interpretive Summary: Despite a general decrease in annual streamflow attributed to climate change observed across the Pacific Northwest, a 33% increase in streamflow has been documented from 1939-2012 in the Benton Basin within the Priest River Experimental Forest (PREF) in Northern Idaho. In order to address this paradox, the physically-based Simultaneous Heat and Water (SHAW) model was applied to the basin to gain a better understanding of the water cycle dynamics within the PREF. Simulations for water years 2004 through 2009 indicated that vegetation growth reduced streamflow by 50mm during this six year period. This approach appears promising to help elucidate the mechanisms responsible for hydrological trends and variations resulting from climate and vegetation changes on small watersheds in the region.
Technical Abstract: Widespread decreases in annualized streamflow have been observed across mountain watersheds in the Pacific Northwest of the United States over the last ~70 years, however in some watersheds, observed streamflow has increased. To deconvolve the combined effects of climate and vegetation on long-term water balance trends, it is necessary first to develop and evaluate the performance of a relatively simple modeling framework, to simulate both the internal watershed dynamics and streamflow. We used the physically-based Simultaneous Heat and Water (SHAW) model to simulate a 4 km2 watershed in northern Idaho. The model simulates seasonal patterns and annual water balance components including evaporation, transpiration, storage changes, deep drainage, and trends in streamflow. Independent measurements were used to parameterize the model, including forest transpiration, stomatal feedback to vapor pressure, forest properties (height, leaf area index, and biomass), soil properties, soil moisture, snow depth, and snow water equivalent. No calibrations were applied to fit the simulated streamflow to observations. The model reasonably simulated the streamflow dynamics during the evaluation period from water year 2004 to 2009, which verified the ability of SHAW to simulate the water budget in this small watershed. The simulations indicated that annual variation in streamflow was driven by the variation in precipitation and soil water storage. Moreover, vegetation growth reduced the streamflow by 50mm during the six year period. One key parameterization issue was leaf area index, which strongly influenced interception across the catchment. Although the model was not designed to estimate streamflow, the short flowpaths in this watershed allowed it to predict annual trends well. This approach appears promising to help elucidate the mechanisms responsible for hydrological trends and variations resulting from climate and vegetation changes on small watersheds in the region.