Canada's Saskatchewan River system, whichrecently experienced its worse drought in 134 years, may be prone to moreprolonged and severe droughts than previously thought, suggests a new UCLAstudy based on tree rings that are more than 1,000 years old.
If global warming ends up decreasing precipitationand historical precedents repeat themselves, the region could be in far worseshape than policy-makers currently anticipate, warn the authors of the study,which appears in the current issue of the Journal of the American WaterResources Association.
"Past droughts and corresponding declines in river flow havebeen worse than anything we've seen for the past 100 years, including therecent drought, and this was before man began modifying the climate," said leadauthor Roslyn A. Case, who conducted the research as a UCLA graduate studentbut who now works for the Venice, Calif.-based environmental consulting firm ofMcDaniel Lambert Inc. "Human-induced climate change could make the situationeven worse."
The UCLAfindings, which represent the first large-scale reconstruction of the riversystem's flow rates, call into question the wisdom of current approaches toriver water management in the basin, which encompasses Alberta, Saskatchewanand Manitoba and covers 168,000 square miles, including some of Canada'slongest rivers.
"If future water policy and infrastructure development inthe Canada prairies continue to take only 20th-century water resources intoaccount, then the region is in for real trouble," said Glen M. MacDonald,co-author and chair of UCLA's geography department. "One reason the currentdrought seems so severe is the 20th century was one of the wettest periods theregion has experienced."
With core samples from old-growth trees in Alberta and Saskatchewan,the researchers pieced together annual water flow over varying periods for theregion's three main rivers: 1,113 years for the North Saskatchewan River, 522years for the South Saskatchewan River and 325 years for the SaskatchewanRiver.
Among their findings:
Between 900 and 1300, the North Saskatchewan Riverexperienced 10 decades of the lowest flow in its history; over those 400 years,the average flow of the river was 15 percent lower than the 20th-centuryaverage.
Between 1702 and 1725, river flows on the SouthSaskatchewan River were almost 20 percent below the 20th-century average.
Between 1841 and 1859, river flows on the SaskatchewanRiver were at least 22 percent below the 20th-century average.
Along the South Saskatchewan River, the early 20thcentury saw the highest river flows of the segment's 522-year reconstruction.
Tree rings from sites adjacent to Canada's prairies arereliable records of past precipitation and river flows in the area becausetrees form larger rings during years of high precipitation and form thin ringsduring years of little precipitation. The patterning persists for the life ofthe wood.
Case and MacDonald examined samples from 178 trees, themajority of which were living and none of which were damaged by their work.
To ensure the accuracy of their findings, the researchersinitially checked their river flow predictions against historical records forriver flows in the area.
In addition to recording the amount of precipitation in anygiven year, tree rings reflect the volume of river water flowing in any givenperiod since rivers serve as the principle destinations for the region'swatershed.
About 75 percent of water from the Saskatchewan Riversystem is used for domestic and agricultural purposes, including wheatproduction. The Saskatchewan River Basin is one of the world's leadingproducers of wheat.
Debate surrounding future allocations of these waters hasbeen hampered by the fact that government officials did not begin keepingconsistent, systematic records of the river system's flow rates until 1912.
"In order to understand what nature can throw our way interms of drought, we have to look deeper into the past than historical recordscurrently go," MacDonald said. "That view suggests the possibility of someunpleasant surprises."