A dendroclimatic reconstruction of annual precipitation amounts in Iowa since 1680

Tree ring widths from white oak (Quercus alba) in central Iowa were found to be accurate indicators of total precipitation for a period beginning near the end of the prior growing season and extending until the end of the growing season in the year of ring formation. Regression‐based estimates of annual (August–July) precipitation for Iowa were obtained for the 300‐year period of tree ring record (1680–1979). The correlation coefficient between actual and estimated precipitation values was +0.74 for the 60‐year period of data used to calculate the regression coefficients and +0.72 for the preceding 46 years of independent data. These results show that tree rings are reliable indicators of wet and dry periods in Iowa, thereby providing a 300‐year record of precipitation variations for use by scientists and planners.