A Recent Abrupt Decline in the East African A Recent Abrupt Decline in the East African Long RainsLong Rains

Bradfield Lyon and David G. DeWittBradfield Lyon and David G. DeWitt

Presented by: Tufa DinkuPresented by: Tufa Dinkutufa@iri.columbia.edutufa@iri.columbia.edu

International Research Institute for Climate and SocietyInternational Research Institute for Climate and SocietyThe Earth Institute at Columbia UniversityThe Earth Institute at Columbia University

    

OutlineOutline

• The DeclineThe Decline

• The Driver(?)The Driver(?)

• Modeling experimentModeling experiment

Rainfall Decline: RegionalRainfall Decline: Regional

CAMS_OPI (mm/day) anomaly for Mar-May 2011

CMAP Mar-May(1999-2010 average) anomaly (from 1979-2010 mean)

Mar-May total RR , averaged over (10S-12N, 30-53E) Box..

Apr-May PRCP (1998-2008) – (1979-1996)Apr-May PRCP (1998-2008) – (1979-1996)

CMAP

GPCP

Rainfall Decline: EthiopiaRainfall Decline: Ethiopia

Rainfall Decline: EthiopiaRainfall Decline: EthiopiaAnnual Rainfall, country average from different number of stations

Spatial Rainfall patternSpatial Rainfall pattern

Weights for leading mode(16.3% of VAR) of March-May precipitation obtained from EOF analysis of CAMS_OPI data for 1979-2011

Principal component time series for March-May leading mode

What is the driver?What is the driver?

March-May SST anomaly averaged from 1999-2011, expressed as a standardized departure from the 1971-2000 mean

Loadings for the 2nd mode of March-May SST based on an EOF analysis for the period 1950-2011.

Principal component time series (1950-2011)

The Driver: The Driver: East Africa April-May Rainfall Index and Tropical SST Correlation (1979-2010)

ModelingModeling

Modeling ExperimentModeling Experimenta. Multi-model ensemble mean (72

members) MAM RR anomaly (mm/day) from simulations using observed SSTs, averaged over1999-2009.

a. Ensemble mean (24 members) ECHAM5 precipitation anomaly (mm/day) from idealized runs forced with observed March-May SST anomalies averaged over 1999-2010 for the tropical Indian Ocean only.

b. As in b, but for model runs forced with SSTs only for the tropical Pacific. Top legend only for a); bottom legend for b and c.