Simultaneous Cool and Early Warm Season Drought Over the Colorado Plateau

Two 2139-year long reconstructions of cool (NDJFMAM) and early warm season (July) precipitation have been developed from ancient conifers and relict wood at El Malpais National Monument, New Mexico. Both reconstructions have been verified on independent precipitation data and reproduce the large-scale ocean-atmospheric forcing of seasonal precipitation evident in the instrumental data. Simultaneous inter-seasonal drought on the Colorado Plateau, when both winter-spring and early summer precipitation were below average, occurred during the severe sustained drought of the 1950s. These “perfect” inter-seasonal drought conditions are highly unfavorable for the germination, maturation, and yield of dry land crops such as maize. Severe warm season drought along with dry winter-spring conditions has been implicated in poor crop yields and Anasazi migrations during the mid-12th and late 13th centuries. The new seasonal reconstructions indicate that the worst episodes of perfect drought occurred during the 8th and 16th century megadroughts, but perfect drought conditions are also reconstructed during the mid-17th century famines among the Pueblo and Spanish societies in New Mexico and during the late-13th century Great Drought among the Anasazi. Inter-seasonal drought conditions of the late-13th century were not as severe as estimated for the mid-17th century, but the cool and warm season reconstructions were both below normal for several years during this episode, which may have been among the years of greatest environmental stress to the Anasazi subsistence system.