This paper examines the statistical relationships between Palmer Drought Severity
Index (PDSI) data from the southwestern Canadian plains and tree–ring index
chronologies from nearby sites. Standardized tree–ring widths from white spruce
(Picea glauca) from the Cypress Hills (Alberta and Saskatchewan) and from lodgepole
pine (Pinus contorta) from the Bears Paw Mountains (Montana) account for 47%
and 39% of the variance in regional July PDSI. The corresponding regressions are
the basis for the first reconstructions of PDSI for the Canadian plains. This proxy
PDSI record extends from 1597 and demonstrates that, although 1937 was the worst
single drought year, the 20th century lacked the prolonged droughts of the 18th and
19th centuries, when decades of July PDSI were consistently below zero.
