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Fire is the major stand-renewing disturbance in the circumboreal forest. Weather and climate are the most important factors influencing fire activity and these factors are changing due to human-caused climate change. Under a future warmer climate, we expect more severe fire weather, more area burned, more ignitions and a longer fire season, although there will be large spatial and temporal variation in the fire activity response to climate change. Results indicate increases of 25 to 300% in area burned and a lengthening of the fire season by 30 to 50 days over a large portion of the Northwest Territories, Canada. This field of research allows better understanding of the interactions and feedbacks between fire, climate, vegetation and humans, and identification of vulnerable regions. Projections of fire activity for this century can be used to explore options for mitigation and adaptation. [ABSTRACT FROM AUTHOR]

Thunderstorms and associated lightning play an important role in the cycling of water and energy during the warm season, over the boreal and subarctic ecosystems of northern Canada, including the Mackenzie Basin. A variety of observational data sets and model-derived products have been used to characterize these storms, to examine their impacts on the forests of the Basin and on polar bear habitat in western Hudson Bay, and to assess predictive applications of lightning information. The convective storm season and resultant lightning activity are characterized as short but intense with a strong peak in cloud-to-ground (C-G) flashes during June and July. The maximum area of lightning activity varies in space and in time, and there is evidence that smoke from fires enhances the probability of positive CG flashes. Although fire occurrence in the Basin peaks in July, much of the burned area occurs in June. Fires have also significantly changed vegetation and permafrost conditions, resulting in a decrease in the stability of polar bear maternity den sites, the collapse of dens and deterioration of the surrounding habitat in western Hudson Bay. A tree-structured regression method for constructing statistical probability forecast models successfully predicts the probability of lightning in 3-h projection intervals out to 45-48 h. [ABSTRACT FROM AUTHOR]

Cloud systems and their associated precipitation are fundamental aspects of the Mackenzie Basin climate system. Special measurements of these systems, including cloud radar sampling, were carried out in three intense observing periods between autumn 1998 and spring 1999 at Fort Simpson near the center of the basin. Cloud and precipitation features were closely linked to synoptic forcing conditions. Multi-layering of clouds was common and precipitation was typically reduced through sublimation beneath or between cloud layers. Proposed satellite missions such as CloudSat will detect many of the clouds but will lead to biases in inferred cloud thickness and multi-layering. State-of-the-art operational models tend to produce too much high cloud but too little surface precipitation due to sublimation and evaporation rates being too high. [ABSTRACT FROM AUTHOR]