A Future Without Control Basins: Compound Forest Disturbance and the Disappearance of Undisturbed Forested Catchments in the Western United States

Abstract

In recent decades, forest disturbances caused by wildfire, insect and disease-induced forest mortality and drought have increased in frequency and magnitude, especially in the Western United States. Forest disturbances have been shown to alter water budget partitioning. However, the water budget response to disturbance is inconsistent and is still being characterized within forest disturbance hydrology (FDH) literature. In this review and synthesis, we evaluate how FDH literature has grown in recent decades (2000–2021), and we extract papers discussing compound (or overlapping) forest disturbances in the Western United States. We then compare literature findings with the actual prevalence of forest disturbance (caused by wildfire, insects and disease) in forested catchments in the Western United States, at HUC-8, −10 and −12 scales. We find that 94% of HUC-8 basins, 85% of HUC-10 basins, and 60% of HUC-12 basins have experienced compound wildfire and insect/disease disturbance over the period 2000–2022, and virtually, no basins remain undisturbed. These figures contrast with recent FDH literature, where relatively few studies evaluate the hydrologic implications of compound disturbances. These findings suggest that FDH literature is not ‘meeting the moment’ and perhaps, more critically, that true control (or ‘static’) basins are nearly nonexistent in the Western United States. We highlight that as a community of ecohydrologists, we must rethink how we assess post-disturbance water budget partitioning. This will require better tools (e.g., models) to assess post-disturbance hydrology, more observations and especially cross-disciplinary collaborations between hydrology and forestry communities.