Results & Discussion
Results
To make it easier to observe trends, I designed bar charts in Fig 8 and Fig 9, and converting to the same unit makes it easier to observe changes in response variables since different provinces have different forest areas. For the number of fires (Fig 15), Newfoundland and Labrador, Ontario, Quebec, and Nunavut have had relatively few fires during 36 years, and fires have occurred more frequently in Alberta, British Columbia, Northwest Territories, Saskatchewan and Yukon Territory. After about 2013, fires began to occur frequently in Nova Scotia. In New Brunswick, there were two peaks in the number of fires around 2005 and 2015. For burned area of the fire (Fig 16), the frequency of large fires is relatively high in Manitoba, Yukon, Northwest Territories, and Saskatchewan.
Large-scale fires are concentrated in Taiga Plain, Taiga Shield, Boreal Shield, Boreal Plain, Taiga Cordillera, Boreal Cordillera, and Montane Cordillera. In other words, large-scale fires are concentrated in boreal forest ecosystems. The tree species in the Boreal region are mainly coniferous forests, and some characteristics of coniferous forests are responsible for the occurrence of forest fires. For example, black spruce forests are highly flammable, and plants such as heather feather moss, lichens, and shrubs burn easily (National Park Service 2021). The low-hanging branches of black spruce dangle from the flammable moss layer and ground vegetation, and the lower branches provide a ladder for the fire to climb to the upper part of the tree, which creates a crown fire and the upper part of the tree burns where the seed cones appear (National Park Service 2021). Boreal has dry and cold winters, the summer is humid and warm. Lightning strikes occur frequently in summer. Lightning is also an important cause of fires. Manitoba has the highest number of fires, and large-scale fires are also more frequent. Since about 1995, the number of fires in Manitoba has gradually increased. This may be due to Manitoba's geographic location, with its ecoregions containing prairie, southern arctic, boreal shield, Hudson plain, boreal plain, and taiga shield. This makes Manitoba cold, dry, windy, and especially vulnerable to climate change. Other ecozones do not have large fires because of the topography, climate and structure of the ecosystem. For example, the Pacific Maritime ecozone has a cool and humid climate. The climates of the polar ecoregions are cold, and the tundra biome is the predominant ecotype, so such conditions are difficult to cause a fire. In addition, by combining the above three graphs, we can get the relationship between the number of fires and the burning area and the ecological area. During the 36 years, there were more fires, and the provinces with larger burning areas were usually located in the boreal area.
Discussion
Fig 18. Anomalies of average temperature varies with year and month.
Fig 19. Anomalies of Hargreaves climate moisture deficit varies with year and month.
Fig 20.Anomalies of Hogg’s climate moisture index varies with year and month.
Fig 21. Anomalies of maximum temperature varies with year and month.
Fig 22. Anomalies of precipitation varies with year and month.
In Fig. 18 to Fig. 22, the x - axis represents the time, and the y - axis represents the difference between the fire occurrence month and the normal data. Each square represents the month in which the fire occurred, and the red area represents the number of fires that occurred in this month. It represents how the number of climate anomalies varies by year and month.
For the anomalous amount of mean temperature, in most months, from 1990 to 2021, the mean temperature at the time of the fire was higher than the 1961-1990 normal mean temperature. The deviation of the maximum temperature is similar to the deviation of the mean temperature, and their distribution is more skewed towards positive values. This means that the occurrence of fires is strongly related to both the average temperature and the maximum temperature rise.
For the Hargreaves climate moisture deficit anomalies in January, February and December, the climate humidity index deviation is approximately 0. This means that during the 3 months of the 36-year period, the climate humidity index has barely deviated from the normal data. But from August to November, their distribution is more skewed towards positive values, which means that the deviation of climate moisture deficit increases, compared with normal data. The climate moisture deficit is the difference between measured evapotranspiration and effective precipitation. Autumn lasts from August to November, and most forests in Canada receive little rain during this time. As a result, it is very likely that the increase in climate moisture deficit has a significant impact on the occurrence of fire.
In most months, the distribution of deviations from Hogg's climate moisture index is skewed toward negative values, and extreme variations are common. This could also imply that the decrease in humidity index has a high probability of influencing the occurrence of fire.
The distribution of precipitation deviations is more skewed toward negative values in January, February, November, and December. These distributions have a lot of peaks, which means they have a lot of extreme deviations. This demonstrates a strong link between decreased precipitation and the occurrence of wildfires.
In general, fires were associated with less precipitation, higher mean and maximum temperatures, a greater Hargreaves climate moisture deficit, and a lower Hogg's climate moisture index. Climate change mainly contributes to the changes in these factors, so we can say that there is a strong relationship between climate change and the occurrence of fires.
Correlation Analysis
Figure 23. Correlation between the month of fire and the prior months of the fire month. (We can click through the previous 6 months with the left and right arrows.) the average temperature, CMD is Hargreaves climate moisture deficit, CMI is Hogg's climate moisture index, maximum average temperature, and precipitation.
In Figure 23, the plots show the correlation between the deviations of the individual climate parameters in the month of the fire and the mean values of the five months before the fire. The average value of the deviation of the average temperature of the first five months has the greatest correlation with the fire occurrence month, followed by the maximum temperature, Hargreaves climate moisture deficit, Hogg's climate moisture index, and precipitation. This means that changes in the average temperature are most likely to affect the occurrence of fires.
Climate change, as we all know, may cause an increase in greenhouse gas emissions, resulting in an increase in global temperature. Therefore, we can speculate that climate change will increase the likelihood of fires. Combining all of the above findings, it is possible to conclude that the boreal forest ecosystem is the most vulnerable to climate change and increased fire frequency. However, the study also has some flaws. For example, in the fire data, we obtained from the official website of the Canadian government, the records of the months when the fires occurred are not comprehensive. In addition, the results presented by the study do not allow good extrapolation of the correlation between fire area and climate change. However, with limited resources, the study demonstrates that climate change is likely to increase the number of fires.