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A 500-Year Precipitation History From the Bavarian Forest
Wilson, R. J., Luckman, B. H. and Esper, J.  2005.  A 500 year dendroclimatic reconstruction of spring-summer precipitation from the lower Bavarian Forest region, Germany.  International Journal of Climatology 25: 611-630.

What was done
Two versions of a March-August precipitation chronology were developed from living and historical tree-ring widths for the Bavarian Forest region of southeast Germany for the period 1456-2001.  The first version, standardized with a fixed 80-year spline function (SPL), was designed to retain decadal and higher frequency variations, while the second version used regional curve standardization (RCS) to retain lower frequency variations.

What was learned
Significant year-to-year and decadal variability was seen in the SPL chronology, where March-August precipitation varied on these shorter time scales.  However, there did not appear to be any trend toward wetter or drier conditions over the 500-year period.  The RCS reconstruction, on the other hand, better captured lower frequency variation, suggesting that March-August precipitation was substantially greater than the long-term average during the periods 1730-1810 and 1870-2000 and drier than the long-term average during the periods 1500-1560, 1610-1730 and 1810-1870.

What it means
According to the authors, their RCS reconstruction is the "first dendroclimatic reconstruction in Europe to capture such low-frequency information and indicates that traditionally derived [tree ring] reconstructions in the region are missing important low-frequency signals."  In light of these findings, we expect more studies will utilize the RCS method to further unlock the secrets of precipitation trends and variability over the past millennium and beyond by better capturing lower frequency variations on multi-decadal, centennial and millennial time scales.  Only then will we have a valid benchmark to compare the instrumental record against; and only then will we be able to determine if recent precipitation trends are anthropogenically-forced or merely natural fluctuations induced by non-anthropogenic phenomena.

Reviewed 29 June 2005