Climatic influences on forest fire and mountain pine beetle outbreaks and resulting runoff effects in large watersheds in British Columbia, Canada

Abstract

Many studies have defined the interrelationships between climate, forest disturbance, and runoff at small scales (<100 km2), but few have translated these relationships to large watersheds (>500 km2). In this study, we explore the relationship between climate, extreme forest fire seasons, mountain pine beetle (MPB) outbreaks, and runoff in eight large watersheds within the Fraser and Peace drainage basins in British Columbia (BC), Canada from 1981–2019. Using a climate index based on precipitation and air temperature anomalies, we find extreme forest fire seasons (those that burned >5% of a watershed's area) are most likely to occur when a warm/dry summer is preceded by multiple seasons of cool/wet conditions. Using the climate suitability class (CSC) model to explore the relationship between climate and MPB outbreaks, we validate previous findings that lower‐than‐average precipitation, warm growing season temperatures, and lack of extremely cold temperatures during winter are connected to MPB outbreaks within central BC. However, the CSC model needs improvements to accurately assess MPB suitability in northern watersheds that are located outside the model's calibration region, either through weighted variables or lower degree day thresholds. Minimal runoff response occurs from these forest disturbances, with the most prominent runoff change being related to the 2014 fire season in the Osilinka and Mesilinka watersheds. The limited effects of forest disturbance on annual runoff are likely related to large watershed sizes, low percentages of disturbed area in some study watersheds and post‐MPB forest dynamics. These results provide valuable insight into the interrelationships of climate, forest disturbance and runoff in large Canadian boreal forested watersheds.

Effects of Thinning on Dynamics and Drought Resistance of Aspen-White Spruce Mixtures: Results From Two Study Sites in Saskatchewan

“…In addition, damage by insects such as forest tent caterpillar (Malacosoma disstria Hbn.) (Chen et al, 2017b;Cortini and Comeau, 2020), mountain pine beetle (Dendrochtonus ponderosae Hopkins) (Vore et al, 2020) and spruce beetle (Dendroctonus rufipennis Kirby) (Campbell et al, 2019) are expected to increase as a consequence of increases in both temperature and drought stress. Frequency and magnitude of fire damage (Vore et al, 2020) is also expected to increase due to warming and drought.…”

Reexamining forest disturbance thresholds for managing cumulative hydrological impacts

“…A vegetation index is needed to represent forest disturbance level which can indicate various types of forest disturbances (e.g., logging, fire and insect infestation such as mountain pine beetle infestation) as well as forest recovery following disturbances cumulated over space and time. In BC, as well as some parts of western North America, equivalent clear‐cut area (ECA), a commonly used and comprehensive index for capturing vegetation dynamics caused by various types of forest disturbances and recovery, has been successfully used in a number of watersheds (Lewis & Huggard, 2010; Vore, Déry, Hou, & Wei, 2020).…”

Canadian Continental-Scale Hydrology under a Changing Climate: A Review

“…A regional study of the western Canadian basins suggests increasing water surplus (precipitation minus potential evapotranspiration) along the Pacific coastline in all seasons but summer, where conditions are projected to be hotter and drier [48]. The loss of vast tracts of montane forests from timber harvesting, wildfires and pest outbreaks in a warming climate may also be altering surface hydrological processes including increased winter snow accumulations and earlier, faster spring melts [49]. Hydrological extremes may also be exacerbated in Pacific coastal watersheds such as the Fraser owing to projected increases in the frequency and intensity of landfalling atmospheric rivers, or narrow bands of concentrated moisture transport in the upper atmosphere [50].…”