Tree-ring reconstruction of maximum and minimum temperatures and the diurnal temperature range in British Columbia, Canada
This paper demonstrates the possibility of reconstructing May-August maximum (Tmax) and minimum (Tmin) temperatures plus the diurnal temperature range (DTR) using ring-width (RW) and maximum density (MXD) series from treeline sites across Interior British Columbia. Multiple linear regression of three orthogonal principal components (derived from 12 ring-width and 7 maximum density chronologies) were used to reconstruct each climate parameter separately over the 1820–1991 interval. Calibration explains 64% (Tmax), 39% (Tmin) and 40% (DTR) of the variance in the instrumental climate record (1895–1991). The Tmax reconstruction shows cool 19th century conditions with the warmest period in the 1940s. This trend agrees well with other summer temperature reconstructions in the southern Canadian Cordillera. The coolest reconstructed Tmin values are in the 1880s and increase steadily to the 1990s. Regional climate data show that the DTR has decreased in the late 20th century due to differences in the rate of change in Tmax and Tmin. These exploratory reconstructions suggest that recent trends in DTR are not unique in Interior British Columbia in context of the last 180 years. Our results also indicate that: (1) Tmean, Tmax and Tmin may not vary consistently; (2) tree growth at these temperature-limited sites may be more closely related to Tmax than Tmean or Tmin; (3) recently reported changes in the relationships between mean temperatures and tree-ring variables may in part reflect the changing relative influence of maximum and minimum temperatures on mean temperature values. It may therefore be prudent, where possible, to reconstruct all three parameters to evaluate past temperature variability.