Phenology During Recent Droughts in the Southwestern U.S.A.

Droughts in the southwestern U.S.A. receive considerable examination of both the inherent climatic anomalies and subsequent effects. Here, we integrate spatial climate data and bioclimatic indices to further investigate climatic differences during the 1950s and 2000s droughts, and to present the concurrent phenologic differences. Higher temperatures and lower atmospheric moisture during the 2000s drought primarily occur in spring and summer, whereas similar conditions occur during the 1950s drought in fall. Phenologically these conditions indicate in general that the 2000s drought is less limiting in minimum temperatures and more limiting in water stress. In the variable topography of the southwest, however, differential responses of phenology appear along elevation gradients and between seasons. Considering the 2000s drought as a global-change-type drought, dry conditions under warmer temperatures that the data of this study support when compared to 1971-2000 climatologies, results suggest that phenologic responses to current and future climate change in the southwest may display spatiotemporal variability of both improved and worsened growing constraints.