On the Nature of the Recent Southwestern Drought Philip Pegion1, Siegfried Schubert, Randy Koster, Max Suarez. NASA-GSFC Global Modeling and Assimilation Office

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On the Nature of the Recent Southwestern
DroughtPhilip Pegion1, Siegfried Schubert,
Randy Koster, Max Suarez.NASA-GSFC Global
Modeling and Assimilation Office
1. SAIC
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Motivation We want to understand the cause of the
recent drought, and can we determine if it has
ended?
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Desert SW. region
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Observed Precipitation Desert SW region.
25-month running mean anomaly (mm/day)
Anomaly mm/month
YEAR
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Observed Precipitation Desert SW region.
25-month running mean anomaly (mm/day)
Anomaly mm/month
YEAR
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Observed Precipitation of normal
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HADISST Sea Surface Temperature anomaly (K)
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Observed Precipitation Desert SW region.
25-month running mean anomaly (mm/day)
Anomaly mm/month
ENSO
2nd EOF HADISST
YEAR
Correlation 0.51
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Model Description

• NASA Seasonal-to-Interannual Prediction Project
  (NSIPP-1) AGCM
• 4th Order finite difference dynamical core
  (Suarez and Takacs, 1995).
• Simple K-scheme boundary layer (Louis et al.,
  1982).
• Relaxed Arakawa-Schubert (RAS) convection
  (Moorthi and Suarez, 1992).
• Chou and Suarez (1994, 2000) radiation.
• Mosaic land model (Koster and Suarez, 1996).
• AMIP
• 3.75o longitude, 3o latitude, 34 levels
• 14 member ensemble (1902-present)
• Additional AMIP runs at 2o and 1o degree.
• DSP
• 0.625o longitude, 0.5o latitude, 34 levels
• Initialized December 1, 2001 with the NCEP
  Reanalysis.

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Precipitation Desert SW region.
25-month running mean anomaly (mm/day)
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Precipitation Desert SW region (1998-2004)
7-month running mean anomaly ( of normal)
CMAP Model ensemble mean
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October 2001 -March 2002
Precipitation ( from normal)
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October 2001 -March 2002
Surface Air Temperature Anomaly (K)
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October 2001 -March 2002
200 mb Height Anomaly (m)
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October 2001 -March 2002
200 mb Height Anomaly (m)
Model La NINA Composite
NCEP La NINA Composite
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October 2001 -March 2002
850 mb vq Anomaly (m s-1 g Kg-1)
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• High Resolution GCM runs
• Initialized 00z1DEC2001 with the NCEP/NCAR
  reanalysis.
• Run through end of March.
• 10 ensemble member run over Reynolds SST
• 10 additional ensemble members with MODIS SST.

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DJFM 2002 SST anomaly (K)
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DJFM 2002 Precipitation Anomaly (mm/day)
0.5deg DSP w/ MODIS SST
0.5deg DSP w/ Reynolds SST
CMAP
MODIS - Reynolds
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DJFM 2002 Precipitation ( of normal)
0.5deg DSP w/ Reynolds SST
0.5deg DSP w/ MODIS SST
CMAP
MODIS - Reynolds
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DJFM 2002 200 mb Height Anomaly (m)
0.5deg DSP w/ MODIS SST
0.5deg DSP w/ Reynolds SST
NCEP/NCAR Reanalysis
MODIS - Reynolds
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DJFM 2002 Precipitation ( of normal)
Ensemble 1 MODIS SST
Ensemble 2 MODIS SST
0.5deg DSP w/ Reynolds SST
Ensemble 2 Reynolds SST
NCEP/NCAR Reanalysis
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Has the long term drought ended, or is last
winter just a bump in the time series?
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Annual Mean SST Anomaly (K)
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Annual Mean SST Anomaly (K)
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12 month coupled model forecast
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• Conclusions
• Recent drought was of the most severe and longest
  lasting in recent times.
• Start of drought is linked with changes in
  Pacific Ocean SSTs
• Most severe part of drought, 2002, lies outside
  of the envelope of response in the model.
• Some hi-resolution runs do get the correct
  magnitude of the winter drought.
• Last winter rains provided big relief to the
  drought, but the southwest hasnt recovered yet.

Surface Elevation
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JFM 2002 200 mb Height Anomaly (m)
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DJFM 2002 200 mb Height Anomaly (m)
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DJFM 2002 200 mb Height Anomaly (m)
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Precipitation Desert SW region (1998-2004)
7-month running mean anomaly (mm/day)
CMAP Model ensemble mean
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Precipitation Desert SW region (1998-2004)
7-month running mean anomaly (normalized)
CMAP Model ensemble mean