Abstract
We used a hydro-ecologic model (RHESSys) constrained by measurements of stream discharge, and spatially distributed snow and soil moisture, to simulate the impacts of operational forest treatments, historical wildfire and climate warming on productive mixed-conifer forests. We compared the response of two headwater catchments at the rain-snow-transition elevation in the wetter central Sierra and more water-limited southern Sierra. The variability of precipitation exerted a greater influence on annual evapotranspiration and runoff than vegetation changes from operational fuels treatment or historical wildfire. The short-term impacts of vegetation changes associated with wildfire, however, did have a greater effect on evapotranspiration and runoff than temperature increases in a warming climate. The average central-Sierra headwater response of evapotranspiration and runoff to fuels treatments (-12%, +12%, respectively) and wildfire (-43%, +46%) were greater than the projected responses to a 4.5oC temperature increase (+2% and -7%). The response in the southern Sierra was limited by lower annual precipitation and showed no response to fuels treatments; but the catchment showed respective changes of -11% and +17% in evapotranspiration and runoff for wildfire, versus +9% and -3% to a 4.5oC temperature increase. These results suggest that in the central Sierra, reductions in vegetation from either fuels treatments or historical wildfire can, temporarily, offset reductions in streamflow from a warming climate. In the southern Sierra, impacts of fuels treatments were small, and only more-extensive vegetation removal as would occur with wildfire, results in significant changes in hydrologic fluxes. Further research is needed to investigate how initial hydrologic changes and climate effects evolve as vegetation adapts and regrows following disturbance.
Highlights
It has long been known that mountain watersheds such as those on the western slopes of the Sierra Nevada, and the critical water supplies originating in these areas, are sensitive to climate warming (Pupacko, 1993; Jeton et al, 1996)
Selective thinning implemented in Bear Trap reduced mean LAI (Canopy Cover) from 9.9 (0.51) to 9.1 (0.49), with reductions from modeled wildfire being 8.8 (0.37) with Strategically Placed Landscape Treatments (SPLATs) and 7.7 (0.29) without SPLATs
The difference can likely be attributed to a greater vegetation change from a reduction in forest cover in the Big Sandy headwater simulated wildfire, a single event that burned the entire catchment during 95th percentile weather conditions in which high-severity wildfires are more likely to occur
Summary
It has long been known that mountain watersheds such as those on the western slopes of the Sierra Nevada, and the critical water supplies originating in these areas, are sensitive to climate warming (Pupacko, 1993; Jeton et al, 1996). Climate projections for California point to a 3.1–5.0◦C increase in temperatures by the year 2100, with annual precipitation increasing or decreasing as much as 15% (Pierce et al, 2018). While confidence in precipitation projections is low to medium, taken together the projected temperature and precipitation reinforce the need to consider climate scenarios that are hotter and drier than even the most-severe droughts of the past 1100 years (Griffin and Anchukaitis, 2014)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
