Climate

"There was one winter I remember when the ground just froze. It snowed, then it rained and

froze and the caribou couldn't get at their food. That affected the health of the herd in a serious way." (Gladys Netro in Sherry and Vuntut Gwitchin First Nation 1999:186).

Introduction

The climate of Vuntut National Park and the Old Crow Flats Special Management Area is continental. It is the climate of an extensive inland area effectively protected from oceanic influences by the surrounding mountain ranges ( Figure 7.1a). Winters, dominated by a vast high pressure system, are generally long, dry and very cold except when interrupted by the intrusion of the relatively warm moist air associated with a low pressure system. Summers are short and variable; relatively warm, dry conditions giving way to cool blustery weather depending on the position and strength of the dominant low pressure system.

Regional climatic conditions are the result of the modification of the large scale pressure patterns and the solar (sun) energy regime by topography (the shape of the land). Three main climatic regions are found within Vuntut National Park and the Old Crow Flats Special Management Area ( Figure 7.1b): the Old Crow Flats which dominate the region, the surrounding pediment slopes which drain into the Flats, and the mountains from which these pediments extend. The winter cold is most intense in the Old Crow Flats which has the coldest mean January temperatures of any region in the Yukon (-30 EC to -35 EC). July mean temperatures (12 EC to 15 EC) are, however, higher than many areas of the southern Yukon. On the pediment slopes some relief can be expected from the very deep cold of winter and the heat of summer. In the mountains of northern Vuntut National Park, summers are generally cooler, due to higher elevations and increased influence of the cold Beaufort Sea to the north, while winters are variable but not as cold. Annual precipitation is in the 200 mm to 300 mm range on the Flats and pediments, and probably increases locally, at least in the mountain regions. Wind conditions are strongly influenced by local topography. For example, in winter, topography produces both very long periods of low wind speeds over the Flats, and gale force winds in the mountain valleys. At Old Crow, the only long term weather station in the area, prevailing winds are from the northeast in all months due to northeast-southwest tending valley.

Climate plays a vital role in the life of the Vuntut Gwitchin who look to the land and wildlife as their traditional source of physical nourishment and inspiration. The way of life of the Vuntut Gwitchin respects the power of weather and their seasonal round is in balance with the often severe climatic conditions which dominate their land.

The ecosystem in northern regions such as Vuntut National Park is particularly sensitive to changes in climate. These changes can take the form of long term trends, such as a trend towards warmer summers which the General Circulation Models (GCMs) suggest will result from a doubling of atmospheric carbon dioxide (CO₂₎. These changes can also be seen in an increase or decrease in the year to year variability of climate, or in the frequency of occurrence of extreme events. Either of these types of climate change would have an effect on biotic resources within the Park and Special Management Area.

The treeline is the large-scale, climatological position of the boundary or ecotone between the boreal forest and the tundra. Trees occur north of the climatological treeline in favourable locations such as protected valleys with year-round moisture sources. The treeline boundary is used by climatologists to integrate the effects of climate and surface conditions in defining the extent of the Arctic (Alt 1987). Koeppen (1923) approximated the treeline by the 10 degree C July isotherm (line of constant temperature), while others define tundra as the region with less than three months with average monthly temperatures in excess of 6 degrees C. Bryson (1966) showed the link between the mean summer position of the arctic front (see below) and the climatological treeline. Nichols (1976) in his discussion of the historical aspects of the northern Canadian treeline (forest-tundra ecotone) suggests that parts of the present forest-tundra boundary and spruce outliers may be relics from times of prior warmth. He shows the northern edge of subarctic forest and the northern limit of tree species ( Figure 7.1c). Numerous other maps of the circumpolar Arctic (e.g., Hare 1970) and northwestern Canada (e.g., Cohen 1997) show the position of the treeline as passing through the study area. Wiken et al. (1981) show the northern limit of trees as passing through the pediment area of the northern Vuntut National Park (Plate VI and Figure 7.1c).

The spring and early summer range of the caribou lies just north of the treeline while the traditional activities of the Vuntut Gwitchin make use of both the forest and tundra in their seasonal round. The position of the treeline has been used extensively in monitoring past climate change and predicting the impacts of possible future climatic conditions. Extensive palaeontological work in the Park and Old Crow Flats Special Management Area has shown that this area has been particularly sensitive to changing climate in the past.

There is presently much concern regarding the apparent decrease in the water levels in the Old Crow Flats (see also Ecology and Hydrology). Any change in the water levels of the lakes in the Old Crow Flats would have a profound impact on the ecosystem and thus the livelihood of the Vuntut Gwitchin. The possibility that global scale climate change is a factor in this change has been raised.

This chapter describes what is known about the climate of Vuntut National Park and the Old Crow Flats Special Management Area based on the instrumental record from Old Crow and short term field stations observations discussed in the literature. Whenever possible, the climate is linked to the traditional seasonal round of the Vuntut Gwitchin and to traditional knowledge of weather events and their relationship to the ecosystem.

In the course of this synthesis, Vuntut National Park climate is compared to conditions in Ivvavik National Park to the north, and, where applicable, to other areas of the Yukon and Alaska. The relationship of the study area to the warming trend currently affecting much of northwestern Canada is also examined. Gaps in the climate knowledge base are identified and recommendations for future efforts are made. It is beyond the scope of this report, which is a synthesis of existing results, to create a climatology of the Old Crow Basin. Future efforts to create a regional climatology of the Old Crow Basin will be severely hampered by the lack of data from the Flats and pediment slopes and the lack of synoptic observations from Old Crow weather station.