B. M. Wotton

Climate Change and Forest Fire Potential in Russian and Canadian Boreal Forests

In this study outputs from four current General Circulation Models (GCMs) were used to project forest fire danger levels in Canada and Russia under a warmer climate. Temperature and precipitation anomalies between 1 × CO2 and 2 × CO2 runs were combined with baseline observed weather data for both countries for the 1980–1989 period. Forecast seasonal fire weather severity was similar for the four GCMs, indicating large increases in the areal extent of extreme fire danger in both countries under a 2 × CO2 climate scenario. A monthly analysis, using the Canadian GCM, showed an earlier start to the fire season, and significant increases in the area experiencing high to extreme fire danger in both Canada and Russia, particularly during June and July. Climate change as forecast has serious implications for forest fire management in both countries. More severe fire weather, coupled with continued economic constraints and downsizing, mean more fire activity in the future is a virtual certainty. The likely response will be a restructuring of protection priorities to support more intensive protection of smaller, high-value areas, and a return to natural fire regimes over larger areas of both Canada and Russia, with resultant significant impacts on the carbon budget.

Climate change and forest fires

This paper addresses the impacts of climate change on forest fires and describes how this, in turn, will impact on the forests of the United States. In addition to reviewing existing studies on climate change and forest fires we have used two transient general circulation models (GCMs), namely the Hadley Centre and the Canadian GCMs, to estimate fire season severity in the middle of the next century. Ratios of 2 x CO2 seasonal severity rating (SSR) over present day SSR were calculated for the means and maximums for North America. The results suggest that the SSR will increase by 10-50% over most of North America; although, there are regions of little change or where the SSR may decrease by the middle of the next century. Increased SSRs should translate into increased forest fire activity. Thus, forest fires could be viewed as an agent of change for US forests as the fire regime will respond rapidly to climate warming. This change in the fire regime has the potential to overshadow the direct effects of climate change on species distribution and migration.

Future wildfire in circumboreal forests in relation to global warming

Despite increasing temperatures since the end of the Little Ice Age (ca. 1850), wildfire frequency has decreased as shown in many field studies from North America and Europe. We believe that global warming since 1850 may have trig- gered decreases in fire frequency in some regions and future warming may even lead to further decreases in fire frequency. Simulations of present and future fire regimes, using daily outputs from the General Circulation Model (GCM), were in good agreement with recent trends observed in fire history studies. Daily data, rather than monthly data, were used be- cause the weather and, consequently, fire behavior can change dramatically over time periods much shorter than a month. The simulation and fire history results suggest that the impact of global warming on northern forests through forest fires may not be disastrous and that, contrary to the expectation of an overall increase in forest fires, there may be large regions of the Northern Hemisphere with a reduced fire frequency.

Forest fire occurrence and climate change in Canada.

The structure and function of the boreal forest are significantly influenced by forest fires. The ignition and growth of fires depend quite strongly on weather; thus, climate change can be expected to have a considerable impact on forest fire activity and hence the structure of the boreal forest. Forest fire occurrence is an extremely important element of fire activity as it defines the load on suppression resources a fire management agency will face. We used two general circulation models (GCMs) to develop projections of future fire occurrence across Canada. While fire numbers are projected to increase across all forested regions studied, the relative increase in number of fires varies regionally. Overall across Canada, our results from the Canadian Climate Centre GCM scenarios suggest an increase in fire occurrence of 25% by 2030 and 75% by the end of the 21st century. Results projected from fire climate scenarios derived from the Hadley Centre GCM suggest fire occurrence will increase by 140% by the end of this century. These general increases in fire occurrence across Canada agree with other regional and national studies of the impacts of climate change on fire activity. Thus, in the absence of large changes to current climatic trends, significant fire regime induced changes in the boreal forest ecosystem are likely.

CLIMATE CHANGE AND PEOPLE-CAUSED FOREST FIRE OCCURRENCE IN ONTARIO

Climate change that results from increasing levels of greenhouse gases in the atmosphere has the potential to increase temperature and alter rainfall patterns across the boreal forest region of Canada. Daily output from the Canadian Climate Centre coupled general circulation model (GCM) and the Hadley Centres HadCM3 GCM provided simulated historic climate data and future climate scenarios for the forested area of the province of Ontario, Canada. These models project that in climates of increased greenhouse gases and aerosols, surface air temperatures will increase while seasonal precipitation amounts will remain relatively constant or increase slightly during the forest fire season. These projected changes in weather conditions are used to predict changes in the moisture content of forest fuel, which influences the incidence of people-caused forest fires. Poisson regression analysis methods are used to develop predictive models for the daily number of fires occurring in each of the ecoregions across the forest fire management region of Ontario. This people-caused fire prediction model, combined with GCM data, predicts the total number of people-caused fires in Ontario could increase by approximately 18% by 2020–2040 and50% by the end of the 21st century.

Fire, climate change, carbon and fuel management in the Canadian boreal forest

This paper was presented at the conference ‘Integrating spatial technologies and ecological principles for a new age in fire management’, Boise, Idaho, USA, June 1999 Fire is the dominant stand-renewing disturbance through much of the Canadian boreal forest, with large high-intensity crown fires being common. From 1 to 3 million ha have burned on average during the past 80 years, with 6 years in the past two decades experiencing more than 4 million ha burned. A large-fire database that maps forest fires greater than 200 ha in area in Canada is being developed to catalogue historical fires. However, analyses using a regional climate model suggest that a changing climate caused by increasing greenhouse gases may alter fire weather, contributing to an increased area burned in the future. Direct carbon emissions from fire (combustion) are estimated to average 27 Tg carbon year–1 for 1959–1999 in Canada. Post-fire decomposition may be of a similar magnitude, and the regenerating forest has a different carbon sink strength. Measurements indicate that there is a net carbon release (source) by the forest immediately after the fire before vegetation is re-established. Daytime downward carbon fluxes over a burned forest take 1–3 decades to recover to those of a mature forest, but the annual carbon balance has not yet been measured. There is a potential positive feedback to global climate change, with anthropogenic greenhouse gases stimulating fire activity through weather changes, with fire releasing more carbon while the regenerating forest is a smaller carbon sink. However, changes in fuel type need to be considered in this scenario since fire spreads more slowly through younger deciduous forests. Proactive fuel management is evaluated as a potential mechanism to reduce area burned. However, it is difficult to envisage that such treatments could be employed successfully at the national scale, at least over the next few decades, because of the large scale of treatments required and ecological issues related to forest fragmentation and biodiversity.

Climate, Weather, and Area Burned

Publisher Summary This chapter defines weather as short-term processes that result in variations in the atmospheric conditions ranging from minutes to a fire season. Processes that influence the atmosphere over time periods longer than a fire season are defined as climate. There are several factors that control the climate and weather at any one location. These factors include variations in solar radiation due to latitude, distribution of continents and oceans, atmospheric pressure and wind systems, ocean currents, major terrain features, proximity to water bodies, and local features—including topography. As climate varies, the corresponding weather variables can vary in magnitude and direction. Forest fires are strongly linked to weather and climate. Fire has been an integral ecological process since the arrival of vegetation on the landscape. The objective of this chapter is to highlight the connection between climate/weather and the area burned by forest fires. This chapter is divided into sections that describe the relationships between surface weather and area burned, upper air features and area burned, and teleconnections and area burned. It closes with a short discussion on how global changes might influence forest fire activity and area burned in the 21st century.

Interactive effects of vegetation, soil moisture and bulk density on depth of burning of thick organic soils

Theborealbiomeischaracterisedbyextensivewildfiresthatfrequentlyburnintothethickorganicsoilsfound in many forests and wetlands. Previous studies investigating surface fuel consumption generally have not accounted for variation in the properties of organic soils or how this affects the severity of fuel consumption. We experimentally altered soil moisture profiles of peat monoliths collected from several vegetation types common in boreal bogs and used laboratory burn tests to examine the effects of depth-dependent variation in bulk density and moisture on depth of fuel consumption. Depth of burning ranged from 1 to 17cm, comparable with observations following natural wildfires. Individually, fuel bulk density and moisture were unreliable predictors of depth of burning. However, they demonstrated a cumulative influence on the thermodynamics of downward combustion propagation. By modifying Van Wagners surface fuel consumption model to account for stratigraphic changes in fuel conditions, we were able to accurately predict the maximum depth of fuel consumption for most of the laboratory burn tests. This modified model for predicting the depth of surface fuel consumption in boreal ecosystems may provide a useful framework for informing wildland fire management activities and guiding future development of operational fire behaviour and carbon emission models. Additionalkeywords: bog, boreal,carbon,fire,ground-layerfuels,peat,peatland, smouldering,Sphagnum,surfacefuel combustion.

Fire weather index system components for large fires in the Canadian boreal forest

Canadian Fire Weather Index (FWI) System components and head fire intensities were calculated for fires greater than 2 km 2 in size for the boreal and taiga ecozones of Canada from 1959 to 1999. The highest noon- hour values were analysed that occurred during the first 21 days of each of 9333 fires. Depending on ecozone, the means of the FWI System parameters ranged from: fine fuel moisture code (FFMC), 90 to 92 (82 to 96 for individual fires); duff moisture code (DMC), 38 to 78 (10 to 140 for individual fires); drought code (DC), 210 to 372 (50 to 600 for individual fires); and fire weather index, 20 to 33 (5 to 60 for individual fires). Fine fuel moisture code decreased, DMC had a mid-season peak, and DC increased through the fire season. Mean head fire intensities ranged from 10 to 28 MW m −1 in the boreal spruce fuel type, showing that most large fires exhibit crown fire behaviour. Intensities of individual fires can exceed 60 MW m −1 . Most FWI System parameters did not show trends over the 41-year period because of large inter-annual variability. A changing climate is expected to create future weather conditions more conducive to fire throughout much of Canada but clear changes have not yet occurred.

Moderate drop in water table increases peatland vulnerability to post-fire regime shift

Northern and tropical peatlands represent a globally significant carbon reserve accumulated over thousands of years of waterlogged conditions. It is unclear whether moderate drying predicted for northern peatlands will stimulate burning and carbon losses as has occurred in their smaller tropical counterparts where the carbon legacy has been destabilized due to severe drainage and deep peat fires. Capitalizing on a unique long-term experiment, we quantify the post-wildfire recovery of a northern peatland subjected to decadal drainage. We show that the moderate drop in water table position predicted for most northern regions triggers a shift in vegetation composition previously observed within only severely disturbed tropical peatlands. The combined impact of moderate drainage followed by wildfire converted the low productivity, moss-dominated peatland to a non-carbon accumulating shrub-grass ecosystem. This new ecosystem is likely to experience a low intensity, high frequency wildfire regime, which will further deplete the legacy of stored peat carbon.