A 360 YEAR TEMPERATURE AND PRECIPITATION RECORD FOR THE PASCO BASIN DERIVED FROM TREE-RING DATA

Dendroclimatology, the study of past climatic variations by means of tree-ring analysis, is used to produce estimates of seasonal and annual temperature and precipitation from the 17th through 20th centuries. In this study these estimates, reconstructions, are derived in five different ways for regions that each include the Pasco Basin of south central Washington. The best of five sets of results were selected, based on the verification of the reconstructions with independent instrumental data. The reconstructed annual temperature of the Pasco Basin for the last three centuries was on the average 0.17 degrees Fahrenheit higher and had a standard deviation which was 4% larger than for the 20th century. The greatest reconstructed difference in the average temperature was in winter and the greatest reconstructed difference in the variance (standard deviation) was reconstructed in autumn. The average annual precipitation reconstructed for 1602 to 1900 was 0.32 inches higher than it has been in the 20th century. The change in average and standard deviation of reconstructed precipitation was greatest in autumn. Both the seasonal and annual reconstructions for temperature and precipitation exhibit large and persistent variations from the mean which are often most pronounced in the 17th century. Droughts were more commonmore » starting with the last half of the 17th century, with values that sometimes exceeded the 20th-century maximum amounts and duration. While there are some similarities among the four seasons and two variables, many differences between the seasonal reconstructions exist. 28 refs., 6 figs., 6 tabs.« less