Tree-ring based reconstructions of precipitation for the southern Canadian Cordillera

This paper reconstructs precipitation variability in the southern Canadian Cordillera over the past 3-400 years using dendroclimatological techniques. Fifty-three total ring-width (RW) chronologies, 28 earlywood (EW) and 28 latewood ( LW) chronologies were developed from open-grown, low-elevation stands of Pseudotsuga menziesii (Douglas-fir) and Pinus ponderosa ( ponderosa pine) across the southern Canadian Cordillera. RW, EW and LW chronologies from both species were used to develop 13 annual ( prior July to current June) precipitation reconstructions across the region. The reconstructions range in length from 165 to 688 years, pass verification tests and capture 39-64% of the variance in the instrumental record. Coincident, prolonged intervals of dry conditions are estimated for the years: 1717-1732, 1839-1859, 1917-1941 and 1968-1979. Shorter dry intervals are identified between 1581-1586, 1626-1630, 1641-1653 1701-1708, 1756-1761, 1768-1772, 1793-1800, 1868-1875, 1889-1897 and 1985-1989. The historic drought of the 1920-1930s was the longest but not the most intense across this area in the last 300 years. Wet conditions occur in the majority of reconstructions for the years: 1689-1700, 1750-55, 1778-1789, 1800-1830, 1880-1890, 1898-1916 and 1942-1960. These data, in conjunction with data from adjacent areas, are used to provide the first maps of decadal precipitation anomalies for the region between 1700 and 1990.