Palaeoflood records for the Red River, Manitoba, Canada, derived from anatomical tree-ring signatures

Palaeoflood records for the Red River in southern Manitoba, Canada, were derived from anatomical tree-ring signatures in Quercus macrocarpa (Michx) collected at 16 living-tree sites, several historical buildings and archaeological sites, and subfossil logs buried in river alluvium. Prolonged inundation of trees during spring and early summer induces the development of anatomical anomalies (flood rings) that provide a proxy record of extreme floods. Flood-signature records for the Lower Red River basin (LRB) extend from ad 1999 to 1648 and suggest that the Red River flood of 1826 was the largest during the last 352 years. The tree-ring record identifies five of the largest seven floods in the LRB during the last 200 years and documents extreme floods in 1747, 1762, 1826, 1852, 1950, 1979 and 1997. The Upper Red River basin tree-ring flood record extends from ad 1997 to 1448 and contains flood rings for 1510, 1538, 1658, 1682, 1726, 1727, 1741, 1747 and 1762. Factors influencing the formation of flood rings, and hence efficacy of flood-ring records, include flood timing, age and availability of trees, and variations in response along the stem. Evidence from the LRB indicates intervals of increased flood frequency during the mid-1700s, the mid-1800s, and the second half of the twentieth century, and intervals without extreme flooding in 1648-1746, 1763-1825 and 1862-1949. The tree-ring evidence supports the premise that high Red River flows are non-stationary and that past climatic and landscape changes may have influenced local flood risks.