Hydrological resilience to forest fire in the subarctic Canadian shield

Abstract

Understanding the role of forest fires on water budgets of subarctic Precambrian Shield catchments is important because of growing evidence that fire activity is increasing. Most research has focused on assessing impacts on individual landscape units, so it is unclear how changes manifest at the catchment scale enough to alter water budgets. The objective of this study was to determine the water budget impact of a forest fire that partially burned a $450 km 2 subarctic Precambrian Shield basin. Water budget components were measured in a pair of catchments: one burnt and another unburnt. Burnt and unburnt areas had comparable net radiation, but thaw was deeper in burned areas. There were deeper snow packs in burns. Differences in streamflow between the catchments were within measurement uncertainty. Enhanced winter streamflow from the burned watershed was evident by icing growth at the streamflow gauge location, which was not observed in the unburned catchment. Wintertime water chemistry was also clearly elevated in dissolved organics, and organic-associated nutrients. Application of a framework to assess hydrological resilience of watersheds to wildfire reveal that watersheds with both high bedrock and open water fractions are more resilient to hydrological change after fire in the subarctic shield, and resilience decreases with increasingly climatically wet conditions. This suggests significant changes in runoff magnitude, timing and water chemistry of many Shield catchments following wildfire depend on pre-fire land cover distribution, the extent of the wildfire and climatic conditions that follow the fire.

JAMES BUTTLE REVIEW: A resilience framework for physical hydrology

“…While this is said to provide a buffer to climate extremes and variability (Staudinger et al, 2017), precipitation is often substantially higher than dynamic storage capacity (Hayashi, 2020;Hood & Hayashi, 2015) so resistance may be actually relatively low. Spence et al (2020) (Hopp & McDonnell, 2009) but wetter conditions can diminish resistance (Carey et al, 2010).…”

“…While this is said to provide a buffer to climate extremes and variability (Staudinger et al, 2017), precipitation is often substantially higher than dynamic storage capacity (Hayashi, 2020; Hood & Hayashi, 2015) so resistance may be actually relatively low. Spence et al (2020) identified that antecedent land cover distribution dictated how resistant, and subsequently resilient, permafrost catchments in northern Canada were to forest fire by controlling the amount of area needed to burn to generate a change in hydrological function. This highlights how resistance is a function of the catchment physiography.…”

“…A challenging example may be hydrological resilience to forest fire. While Spence et al (2020) identified the distribution of non-resilient catchments to forest fire in Canada's north they only identified where function was likely to change and under what precipitation conditions immediately after the fire. They recognized, but neglected to fully address that many of these boreal catchments burn semi-regularly ($75-150 years), and a baseline hydrological regime is arguably comprised of several burn cycles (Beyene et al, 2021).…”

Soil moisture and temperature dynamics in juvenile and mature forest as a result of tree growth, hydrometeorological forcings, and drought

“…Consequently, afforestation influences runoff generation processes (Levia et al, 2020) and regulates soil moisture that provides the catchment template for flooding and hydrological drought (Brodribb et al, 2020) that are expected to be exacerbated under climate change. In addition, afforestation impacts (micro)meteorological conditions and boundary layer energy balances (Hannah et al, 2008), biogeochemical cycling in soils (Levia et al, 2020) and the landscape resilience to fire (Spence et al, 2020) as well as affecting soil habitat conditions, including the spread of soil and plant pathogens (Krause et al, 2013).…”

Assessing the broadscale effects of wildfire under extreme drought conditions to boreal peatlands

“…All of these changes have consequences for water table depths and fuel moisture patterns across the landscape, but when and where drought will occur and how the frequency may change is more difficult to predict. Understanding how these changes affect boreal systems, their ecological function, carbon cycling, wildlife habitat, fire regimes, and successional trajectories have all been topics of recent research (Rogers et al, 2015(Rogers et al, , 2020Veraverbeke et al, 2017;Sulla-Menashe et al, 2018;Whitman et al, 2018;Boelman et al, 2019;Marchand et al, 2019;Thompson et al, 2019;Spence et al, 2020;Walker et al, 2020a,b;Baltzer et al, 2021). The effects of a changing climate, in particular drought on peatland wildfire (Thompson et al, 2019), as well as an understanding of peatland-fire interactions (Nelson et al, 2021), have been topics of little research until recently.…”