Contemporary fire regimes of Canadian forests have been well documented based on forest fire records between the late 1950s to 1990s. Due to known limitations of fire datasets, an analysis of changes in fire-regime characteristics could not be easily undertaken. This paper presents fire-regime trends nationally and within two zonation systems, the homogeneous fire-regime zones and ecozones, for two time periods, 1959–2015 and 1980–2015. Nationally, trends in both area burned and number of large fires (≥200 ha) have increased significantly since 1959, which might be due to increases in lightning-caused fires. Human-caused fires, in contrast, have shown a decline. Results suggest that large fires have been getting larger over the last 57 years and that the fire season has been starting approximately one week earlier and ending one week later. At the regional level, trends in fire regimes are variable across the country, with fewer significant trends. Area burned, number of large fires, and lightning-caused fires are increasing in most of western Canada, whereas human-caused fires are either stable or declining throughout the country. Overall, Canadian forests appear to have been engaged in a trajectory towards more active fire regimes over the last half century.

Abstract. We present a global high-resolution calculation of the Canadian Fire Weather Index (FWI) System indices using surface meteorology from the ERA5 HRES reanalysis for 1979–2018. ERA5 HRES represents an improved dataset compared to several other reanalyses in terms of accuracy, as well as spatial and temporal coverage. The FWI calculation is performed using two different procedures for setting the start-up value of the Drought Code (DC) at the beginning of the fire season. The first procedure, which accounts for the effects of inter-seasonal drought, overwinters the DC by adjusting the fall DC value with a fraction of accumulated overwinter precipitation. The second procedure sets the DC to its default start-up value (i.e. 15) at the start of each fire season. We validate the FWI values over Canada using station observations from Environment and Climate Change Canada and find generally good agreement (mean Spearman correlation of 0.77). We also show that significant differences in early season DC and FWI values can occur when the FWI System calculation is started using the overwintered versus default DC values, as is highlighted by an example from 2016 over North America. The FWI System moisture codes and fire behaviour indices are made available for both versions of the calculation at https://doi.org/10.5281/zenodo.3626193 (McElhinny et al., 2020), although we recommend using codes and indices calculated with the overwintered DC, unless specific research requirements dictate otherwise.

The Fire Weather Index (FWI) System is the basic method of fire danger rating for fire management agencies in Canada. The spatial interpolation of this weather-based system can be difficult in areas where weather stations are sparse. Previous studies have shown that interpolation of precipitation is especially problematic owing to the isolated nature of convective summer storms. Environment and Climate Change Canada (ECCC) has recently developed the Canadian Precipitation Analysis (CaPA), a gridded precipitation product that integrates forecast data, station observations and Doppler radar, to improve precipitation estimates. The objective of the present study was to evaluate whether CaPA is indeed superior to the currently used interpolation method (thin-plate spline), and to assess the impact of the two precipitation estimates on the FWI System for the province of Ontario. Overall, the results showed the CaPA had increased skill in areas of radar coverage. In non-radar areas, where the ECCC station network was much sparser, there were less significant differences between the methods. Precipitation estimates from the CaPA also significantly improved the estimation of the Fine Fuel Moisture Code, Initial Spread Index and FWI in areas of radar coverage, improving estimates of potential fire danger.