Progress in hydrological research in the Mackenzie GEWEX study

Abstract

This paper reports some of the achievements in hydrological research associated with the Mackenzie GEWEX Study (MAGS). MAGS is a multifaceted study of the energy and water cycle in the Mackenzie River Basin, north-western Canada, and emphasizes cold-region processes and modelling. It pursues methodologies of scaling-up process studies to a large river basin that has few measurement sites. This methodology involves new developments, adapting mid-latitude algorithms to the high latitude setting and promoting the use of remote sensing tools for scaling-up. Intensive hydrological process studies have been concentrated at a number of sites. These have been chosen to represent different biophysical facets of the Mackenzie River Basin. They include northern basins in open tundra and at tree-line, a western basin representing the hilly and mountainous western side of the basin, central basin sites of wetlands, Precambrian Shield terrain and the Mackenzie Basin counterpart of the large Laurentian Great Lakes. The most southerly site represents a mixed-wood boreal forest site that is undergoing land-use change as a result of forest harvesting. Regional community model analysis indicates that processes of lee cyclogenesis result in differential input of precipitation across the basin. Significant results centre on models of snow accumulation featuring the role of blowing snow, intercepted snow and snowmelt. These models emphasize the importance of snow patchiness to speed of melt. Snowmelt infiltration into frozen soils is important in controlling runoff, and tundra microlandforms play a unique role in determining the surface runoff characteristics. On the western margins of the basin, there is a very significant difference in the hydrological behaviour of slopes of different aspects as a result of differences in permafrost and vegetation. In the central basin, a deeper understanding of components of the water budget is being gained through stable isotope analysis of wetland waters. The importance of wetland-controlled spring flow, and its impact on spring breakup characteristics on the Mackenzie River, is being explored. A quite unique influence of Precambrian Shield terrain on the water balance results from the large storage capacity of deep bedrock fissures. They can substantially delay streamflow response to snowmelt. The large lakes of the Mackenzie Basin echo, only in part, the behaviour of the Laurentian Great Lakes. A surprising and rapid response of evaporation to warming during the 1998 El Nin˜o warming episode occurred, which could serve as a surrogate for warming resulting from climate change. In the southern and central forested parts of the basin, vegetation types play a substantial role in the water balance, particularly in influencing interception and subsequent sublimation during winter. The latter is an important component of the water balance and a major cold-region process, the modelling of which is an important achievement of MAGS. Remote sensing provides passive microwave satellite data to help identify snow-water characteristics and calculate the break-up and freeze-up dates of the Mackenzie great lakes, and AVHRR data to help develop algorithms for evapotranspiration modelling, and to use in calculating the surface solar radiation budget on a basin scale. Ongoing research is successfully integrating a GCM model land-surface scheme, regional community climate model and hydrological model to simulate the water balance of sub-basins and of the total Mackenzie River Basin system. Expected achievements at the end of MAGS Phase I are outlined and some goals for future MAGS research are discussed. Copyright © 2000 John Wiley & Sons, Ltd.