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Understanding Eastern Africa Rainfall Variability and Change
(Towards Improved Prediction of Seasonal Precipitation)
Brant LiebmannUniversity of Colorado, Boulder, Colorado, USA
Chris FunkU.S. Geological Survey, Sioux Falls, South Dakota, USA
Martin Hoerling, Randall DoleNOAA, Boulder, Colorado, USA
Ileana BladéUniversity of Barcelona, Barcelona, Spain
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Model:ECHAM5 Atmospheric Model (Roeckner et al. 2006)
~ 0.75-degree resolution (T159) 40-member ensemble
Run with Specified Sea Surface Temperatures
Precipitation “Data”
Observations: Global Precipitation Climatology Centre (GPCC)
From Station Data – 1-degree resolution(Recently as few as 5 monthly reports in region)
Also GPCP (Station data augmented with Satellite)
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Period of Study: 1979-2012
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“Change” = Trend (mm/yr) * length of record (34 years)
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Seasonal Horn Precipitation Change
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October - December
Trend removed
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Sign of Eastern Pacific SSTs correctly predicts Horn precipitation in 76.5% of years
Ensemble Average
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March - May
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March - May
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Gradient in SST producesLow-level convergenceover Indonesia
Enhanced convection over Indonesia
Upper-level outflow (westward shift of ‘Walker’ circulation)
Enhanced subsidence over East Africa
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Percent correct prediction of observed Horn precipitation based
on sign of model Indonesia precipitation
Ensemble Average Ensemble Average
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40-member ensemble of ECHAM 5 atmospheric Model run with specified SSTs
The interannual anomaly of October-December Horn precipitation is well-simulated by the model ensemble-average,
although knowing SSTs in the east Pacific gives almost as good a result
The ensemble-average correctly predicts the sign of precipitation anomaly in March-May in two-thirds of years
(mostly from precipitation over Indonesia)
Model simulates observed change of 1979-2012 Horn precipitation for both March-May (decrease) and October-December (increase)