Wind speed reconstruction from a tree-ring difference index in northeastern Inner Mongolia

Abstract

The lack of instrumental wind speed data beyond the industrial era limits our ability to evaluate the contributions of natural versus anthropogenic processes on long-term changes in wind speed. It is thus desirable to find proxies for historical changes in wind speed. Persistent and strong winds can cause compression wood composed of wider and denser rings in conifer trees at leeward sides. This work hypothesizes that the asymmetric wind impact on tree radial growth provides information about wind speed changes. To test the hypothesis, we developed a Tree-Ring Difference Index (TRDI) representing the differences between tree ring widths at the windward and leeward sides. Thirty-four trees subjected to strong and persistent winds in a Picea mongolica forest in northeastern Inner Mongolia were analyzed. The TRDI based on 124 cores correlates significantly with the maximum wind speeds recorded from May to August, indicating that this proxy can be used for wind speed reconstruction. Our reconstruction reveals long-term changes in wind speed including an upward trend from 1940 to 1954, followed by continually decreasing wind speeds from 1955 to 1990 and increasing values from 1991 to 2010. The reconstructed wind speeds include strong multi-decadal variability and significant correlations with the Pacific Decadal Oscillation (PDO).