Critical Ecosystems and Disturbance Science: Capturing the Feedbacks between Climate, Drought Mortality, Wildfire, and Hydrology

Abstract:

West watersheds in the United States are increasingly affected by a combination of novel climate conditions (such as snow-to-rain regime shifts), extreme events (droughts and floods), wildfire behavior, and forest mortality. We term the interaction and feedback between these processes “disturbance science.” Existing ecohydrologic models are often ill-suited for understanding the independencies and feedbacks within disturbance science, particularly coupled process-level interactions between multiple climate, ecosystem, and hydrologic drivers.

We have developed a unique multi-physics ecohydrologic framework—the Advanced Terrestrial Simulator (ATS)—to better understand basin-scale disturbance science. We demonstrate the framework using a well-instrumented small watershed in northern New Mexico, a watershed that has been exposed to moderate wildfire, drought-induced forest mortality, and frequent flooding events in the last 5-10 years. We modeled wildfire behavior is modeled using the FIRETEC platform as well as direct observations from the 2013 fire season, including litter bulk load and canopy destruction. Ecologic changes were simulated using a novel 2D spatial dynamic vegetation model that captures spatiotemporal vegetation response to climate change.

We examined three representative disturbance-driven scenarios: (1) pristine pre-fire vegetation, (2) observed moderate fire behavior, and (3) modeled intense fire conditions, focusing on short- and long-term hydrology to illustrate impacts over a range of temporal scales. Results show dramatic post-disturbance impacts on hydrologic regimes with significant changes to baseflow (in response to reduced basin-wide transpiration) and streamflow in response to convective precipitation events (linked to removal of groundcover). These flashy, or rapid, runoff events are a key driver of catastrophic erosion, with deleterious impacts to the catchments and downstream channel morphology often exhibited in Mountain West. Results also highlight opposing responses to long-term reductions in baseflow and increased propensity of flashy storm events, both of which significantly alter water resource availability, altering the ability of these systems to support ecological and social functions such as the energy-water nexus.