Surface water input from snowmelt and rain throughfall in western juniper: potential impacts of climate change and shifts in semi-arid vegetation

Authors: NIEMEYER, RYAN - University Of Idaho; LINK, TIM - University Of Idaho; Seyfried, Mark; Flerchinger, Gerald

Submitted to: Hydrological Processes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/7/2016
Publication Date: 8/17/2016
Citation: Niemeyer, R., Link, T., Seyfried, M.S., Flerchinger, G.N. 2016. Surface water input from snowmelt and rain throughfall in western juniper: potential impacts of climate change and shifts in semi-arid vegetation. Hydrological Processes. 30(17):3046-3060.

Interpretive Summary: In much of the western USA juniper is expanding and there is an ongoing change in precipitation form from snow to rain. Both of these trends may affect the amount of water supplying springs, rivers and springs that supply the rangelands with water, but is not clear just what that effect will be. The effect of juniper may be to reduce water supply by intercepting incoming precipitation in the tree canopy. We measured snow depth and water through flow under juniper cover for two seasons to determine the effect of interception. We found that interception loss from snow events was about 20% than for rainfall events. We used model simulations to estimate the effects of a warmer climate and found that the primary effect would be to change the timing of water availability, but no the amount. This information will be useful for future planning in terms of juniper control and water use management.

Technical Abstract: Shifts in both climate and land cover can both potentially impact above ground hydrological processes. In the western U.S., both climatic shifts from snow to rain-dominated precipitation and land cover shifts of pinyon and juniper species in grass and shrub-dominated landscapes alter interception, throughfall and snowpack dynamics. To better understand how shifts in both vegetation cover and precipitation phase alter above-ground hydrological processes, we assessed differences in rain interception, and snow and rain throughfall in western juniper, how western juniper alters snowpack dynamics, and how these above-ground processes differ across western juniper, mountain big sagebrush, and low sagebrush plant communities. We collected continuous throughfall with four large lysimeters, continuous interspace and below-canopy snow depth data, and conducted periodic snow surveys for two consecutive water years (2013 and 2014). Throughfall, estimated with the lysimeter data, was greater for snow relative to rain events, averaging 74.9% and 54.8% respectively. We validated the Simultaneous Heat and Water (SHAW) model with 8 years of continuous snow depth data and then simulated above-ground energy and water fluxes for an 8-year period with more hydrometerological variability. We simulated western juniper, low sagebrush, and mountain big sagebrush snow cover under both the current and a mid-21st century ensemble projected climate. Comparison of the simulations revealed that changes in vegetation principally change the amount of hydrological fluxes such as surface water input, while the future (warmer) climate alters the timing of those fluxes. Information from this study can help managers understand how both shifts in climate and semi-arid vegetation will alter fundamental hydrological processes.