Number of winter precipitation days reconstructed from southwestern tree rings

The potential of reconstructing the number of winter precipitation days from tree-rings in the southwestern United States is explored in this study. This variable, an alternative to the measure of total precipitation, has not previously been used in dendroclimatic reconstructions. However, it may be a more meaningful measure of seasonal rainfall and indicator of anomalies in atmospheric circulation features than total precipitation in areas such as the arid Southwest, where the distribution of rainfall is spatially variable. The number of precipitation days in the region encompassing southwestern New Mexico and southeastern Arizona was reconstructed for the time period 1702-1983 from a collection of tree-ring chronologies in this area. Results from this study show that tree-ring chronologies explain 71% of the variance in the regional record of the number of precipitation days. The reconstruction is statistically verified and validated with independent data. Tree-ring chronologies in this region are better able to explain variations in precipitation-day numbers than total precipitation, suggesting that other dendroclimatic studies may benefit from the use of this variable as well.