Hydrological response to compounding impacts of climate change and forest management in the upper Kings River basin, CA, USA

In the western United States, the Sierra Nevada region experienced decades
of fire suppression-driven changes in forest structure and composition,
resulting in increased vulnerability to drought, water stress, tree
mortality, and exposure to severe wildfires. Sierra Nevada’s watersheds
and forests are predicted to undergo warmer and drier conditions due to
climate change, making them even more vulnerable to disturbances.
Restoring forests by reducing forest density and fuel accumulation has the
potential to improve forest resilience to droughts and climate change,
increase water availability, and provide other ecosystem benefits. In this
study, we investigated the individual and compounding effects of forest
treatments on evapotranspiration and streamflow in the upper Kings River
basin under different warming scenarios using the SWAT+ model. We
simulated large-scale forest treatments throughout the landscape to
evaluate the hydrological response to warming across a water-energy
gradient and the extent to which forest treatments can offset the
warming-driven response. Warming increased evapotranspiration in
energy-limited forests, while in water-limited forests, evapotranspiration
declined due to increased water stress. The water made available through
biomass reduction due to forest treatments was directed towards increasing
potential runoff or sustaining the remaining trees by providing additional
water for evapotranspiration, controlled by water/energy availability. We
found that large-scale forest restoration in the upper Kings River basin
has the potential to partially mitigate warming impacts on streamflow by a
maximum of 48% and 36% under +1.5°C and +3.0°C warming, respectively, thus
reducing the severity of warming impacts on streamflow and vegetation
water stress. These benefits are most prominent in the first year
following forest treatment and gradually decline over time, persisting up
to 10 years.