Resource Category: Journal Papers and Book Chapters

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.

The sensitivity of soil landscapes to climatic variability and hydroclimatic events can
be expressed as a landscape change safety factor, the ratio of potential disturbance to resistance to
change. The use of a geographic information system (GIS) enables the spatially-explicit modeling
of landscape sensitivity, but also raises the risk of violating the characteristic scales of disturbance
and resistance, because the GIS technically simplifies the extrapolation of models, and associated
concepts, to landscapes and scales not represented by the digital data base. Embedding landscape
sensitivity into hierarchy theory, the formal analysis of the hierarchical structure of complex systems,
provides a conceptual framework for the transfer of models and variables among landscape scales.

This paper examines 20th-century environmental change in the subhumid southwestern Canadian Plains, specifically in relation to the dominant agricultural landscape and to the climate of the past millennium as reconstructed from proxy data. Anthropogenic landscape change in the last century has been dominated by the conversion of grasslands to ranchland and cropland. This has heightened landscape vulnerability to climatic fluctuations, especially drought. Instrumental climate
records, extending back to the 7 880s, highlight the variability of precipitation in this region. Proxy environmental records, derived from lake cores and tree-ring analysis, extend this picture into the last millennium and show that drought has been a recurring theme of the Prairie
climate. Tree-ring records suggest that some droughts in the last millennium may have exceeded in severity any in the instrumental record. The sustainability of Prairie agriculture depends on adaptation to the amplitudes of climatic change and variability evident in these proxy records.