Griffin Daniel

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Griffin
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  • Article
    How unusual is the 2012–2014 California drought?
    (John Wiley & Sons, 2014-12-30) Griffin, Daniel ; Anchukaitis, Kevin J.
    For the past three years (2012–2014), California has experienced the most severe drought conditions in its last century. But how unusual is this event? Here we use two paleoclimate reconstructions of drought and precipitation for Central and Southern California to place this current event in the context of the last millennium. We demonstrate that while 3 year periods of persistent below-average soil moisture are not uncommon, the current event is the most severe drought in the last 1200 years, with single year (2014) and accumulated moisture deficits worse than any previous continuous span of dry years. Tree ring chronologies extended through the 2014 growing season reveal that precipitation during the drought has been anomalously low but not outside the range of natural variability. The current California drought is exceptionally severe in the context of at least the last millennium and is driven by reduced though not unprecedented precipitation and record high temperatures.
  • Article
    Winter-to-summer precipitation phasing in southwestern North America : a multicentury perspective from paleoclimatic model-data comparisons
    (John Wiley & Sons, 2015-08-19) Coats, Sloan ; Smerdon, Jason E. ; Seager, Richard ; Griffin, Daniel ; Cook, Benjamin I.
    The phasing of winter-to-summer precipitation anomalies in the North American monsoon (NAM) region 2 (113.25°W–107.75°W, 30°N–35.25°N—NAM2) of southwestern North America is analyzed in fully coupled simulations of the Last Millennium and compared to tree ring reconstructed winter and summer precipitation variability. The models simulate periods with in-phase seasonal precipitation anomalies, but the strength of this relationship is variable on multidecadal time scales, behavior that is also exhibited by the reconstructions. The models, however, are unable to simulate periods with consistently out-of-phase winter-to-summer precipitation anomalies as observed in the latter part of the instrumental interval. The periods with predominantly in-phase winter-to-summer precipitation anomalies in the models are significant against randomness, and while this result is suggestive of a potential for dual-season drought on interannual and longer time scales, models do not consistently exhibit the persistent dual-season drought seen in the dendroclimatic reconstructions. These collective findings indicate that model-derived drought risk assessments may underestimate the potential for dual-season drought in 21st century projections of hydroclimate in the American Southwest and parts of Mexico.