ARIDITY ON THE CANADIAN PLAINS: PAST RECORDS AND FUTURE FORECASTS

The Prairie Ecozone is the only major region of Canada where drought is a landscape hazard; aridity is closely linked to soil erosion and degradation. Future management of prairie ecosystems and soil landscapes will therefore require an improved understanding of past and future trends and variability in regional aridity. We used instrumental and paleoclimatic records to define a regional baseline for prairie aridity, to evaluate the utility of modern climate normals (i.e. 1961-1990) as a benchmark for future climatic change, and to provide a historical and paleoclimatic context for a range of GCM forecasts of regional aridity spanning the next 80 years. The Canadian GCM forecasts the least increase in precipitation and the largest increase in temperature and therefore an approximately 50% increase in the area of subhumid climate and a significant area of semiarid climate by the 2050s. Tree rings and diatom-inferred lake salinity record prolonged arid events and show that modern climate normals are not representative of the full range of potential climatic conditions, even in the absence of global warming. The climate of the 20th century was anomalous in terms of the absence of sustained drought and the climate normal period of 1961-1990 may have been among the most benign of the past 750 years. Because both lake and tree-ring analyses recorded an abrupt amelioration of climatic conditions near the start of the instrumental record, we suggest that the immediate impacts of future global warming may be to return the prairie environment to past conditions in which persistent aridity was recorded for intervals of decades or longer.