Characterizing the surface dynamics of Canadian Prairie droughts

Large-area, prolonged droughts are among Canada's costliest natural disasters having major economic and environmental impacts including decreased agricultural production and hydro-electric power generation, increased freshwater transportation costs, reduced water quality, wetland loss, soil erosion and degradation, and ecological habitat destruction. At present, however, there is little (if any) advanced warning for drought occurrence, thus making preparation and any efficient response difficult. Although most areas of Canada periodically experience drought, the Canadian Prairies are most susceptible mainly due to their location in the lee of the Rocky Mountains and subsequent high precipitation variability. A variety of drought indicators at various temporal scales have identified large-area, multi-year dry episodes over the Canadian Prairies during the 1890s, 1910s, 1930s, 1980s, and most recently from 1999 to 2005. Although these studies have identified and to some extent, assessed the impacts from these past drought occurrences, none have comprehensively characterized them in terms of initiation, migration, persistence, and termination. These factors are critical with respect to better understanding of drought dynamics and prediction, and for relating their characteristics to the various impacts associated with severe drought occurrence.

Using two common meteorological drought indices (namely the Standardized Precipitation Index (SPI) and the Palmer Drought Severity Index (PDSI)), this study firstly identifies, and then compares the spatial and temporal dynamics among several major Canadian Prairie droughts during the period 1901 to 2005. In particular, a concept of drought stages is devised to better categorize, compare, and understand their occurrence. Results show that the majority of severe droughts (including that of 1999 to 2005) can be characterized by six distinct stages including 1) onset, 2) growth/extension, 3) persistence, 4) maximum extent, 5) retreat, and 6) termination. Variations in these stages among the different droughts are analyzed and discussed with focus on the spatial and temporal aspects regarding their onset, migration, and termination. Results from this investigation provide a better understanding of hydrologic extremes such as droughts and helps improve both preparation and coping mechanisms for future extreme events.