Preprints
https://doi.org/10.5194/hess-2020-679
https://doi.org/10.5194/hess-2020-679

  21 Jan 2021

21 Jan 2021

Review status: this preprint is currently under review for the journal HESS.

How does water yield respond to mountain pine beetle infestation in a semiarid forest?

Jianning Ren1,3, Jennifer Adam1, Jeffrey A. Hicke2, Erin Hanan3, Naomi Tague4, Mingliang Liu1, Crystal Kolden5, and John T. Abatzoglou5 Jianning Ren et al.
  • 1Department of Civil & Environmental Engineering, Washington State University, 99163, Pullman, USA
  • 2Department of Geography, University of Idaho, 83844, Moscow, USA
  • 3Department of Natural Resources and Environmental Sciences, University of Nevada, 89501, Reno, USA
  • 4Bren School of Environmental Science & Management, University of California, 93106, Santa Barbara, USA
  • 5Management of Complex Systems, University of California, 95344, Merced, USA

Abstract. Mountain pine beetle (MPB) outbreaks in western United States result in widespread tree mortality, transforming forest structure within watersheds. While there is evidence that these changes can alter the timing and quantity of streamflow, there is substantial variation in both the magnitude and direction of responses and the climatic and environmental mechanisms driving this variation are not well understood. Herein, we coupled an eco-hydrologic model (RHESSys) with a beetle effects model and applied it to a semiarid watershed, Trail Creek, in the Bigwood River basin in central Idaho to evaluate how varying degrees of beetle-caused tree mortality influence water yield. Simulation results show that water yield during the first 15 years after beetle outbreak is controlled by interactions among interannual climate variability, the extent of vegetation mortality, and long-term aridity. During wet years, water yield after beetle outbreak increases with greater tree mortality. During dry years, water yield decreases at low to medium mortality but increases at high mortality. The mortality threshold for the direction of change is location-specific. The change in water yield also varies spatially along aridity gradients during dry years. In relatively wetter areas of the Trail Creek basin, water yield switches from a decrease to an increase when vegetation mortality is greater than 40 percent. In more water-limited areas on the other hand, water yield typically decreases after beetle outbreaks, regardless of mortality level. Results suggest that long-term aridity can be a useful indicator for the direction of water yield changes after disturbance.

Jianning Ren et al.

Status: open (until 02 Apr 2021)

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Jianning Ren et al.

Jianning Ren et al.

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Short summary
Mountain pine beetle outbreaks have caused widespread tree mortality. While some research shows that water yield increases after trees are killed, many others document no change or decreases. The climatic and environmental mechanisms driving hydrologic response to tree mortality are not well understood. We demonstrated that the direction of hydrologic response is a function of multiple factors and previous studies do not necessarily conflict with each other but represent different conditions.