Three centuries of change in the Peace-Athabasca Delta, Canada

The Peace-Athabasca Delta in northern Alberta, Canada, is a dynamic wetland ecosystem. Climatic, hydrologic, biological, and historical data are synthesized to elucidate how the ecosystem has changed over the past 300 years. Annual temperature is now higher than it has been in the past 300 years. For much of the 1700s, the Delta was colder in winter and had a lower flood frequency than that of the last 30 years. The 1800s were characterized by long and cold winters, 4-12 year-long episodes of high or low water, and repeated human epidemics. The early twentieth century was relatively moist and cool. Since mid-twentieth century the Delta has experienced periods of both intense warmth and cold, desiccation and recharge. Since the mid-1960s, local and regional mean annual temperatures have increased 0.30A degrees C to 0.48A degrees C per decade while winter temperatures have increased 0.68A degrees C to 0.92A degrees C per decade; annual snowfall has decreased 12 to 41 cm per decade while winter snowfall has decreased 12 to 34 cm per decade. Major events in the past 45 years include climatic changes favoring a warmer, drier ecosystem; cultural and socioeconomic changes; building of the Bennett Dam; prevention of the Athabasca River mainstem avulsion in 1972; the Cree Creek avulsion of 1982; large fluctuations in water, vegetation, and wildlife; and the development of the Alberta Tar Sands. Increased rates of basin desiccation and wildfire activity and upstream land disturbances may combine to alter the Delta's biotic composition. There appears to be no relevant historical analogue of the present Delta.