Drought in the African Sahel:

scientific research and societal implications

Alessandra GianniniInternational Research Institute for Climate and Society

The Earth Institute at Columbia University

IRI Asia-Pacific Regional Program project on:“Climate forecast applications for disaster mitigation in Indonesia, Philippines and Vietnam”

NASA/GPCP 1979-2004warm ENSO – neutral anomalies

BUT ...- seasonality (e.g. Haylock and McBride 2001; Naylor et al. 2001)- spatial scales

DJF

(1)

SO

N(0

)

RegCM3 25km resolutioncourtesy of J. Qian, H. Li (IRI) NOAA/GHCN station prcp

http://www.pbs.org/wnet/africa/explore/sahel/sahel_overview.html

Photos courtesy of USGS, UNESCO/D. Roger, UN

r = 0.60A. Giannini, R. Saravanan and P. Chang, 2003. Science, 302, 1027-1030Also see e.g. Bader and Latif, 2003 (GRL); Lu and Delworth, 2005 (GRL)

Outline

1. Simulations of Sahel drought with climate modelsa. atmospheric models forced with historical sea surface temperature

Giannini, Saravanan and Chang 2003, 2005b. coupled ocean-atmosphere models (IPCC 4AR)

Biasutti and Giannini 2006

2. Mechanisms of Sahel drought/African climate variability and change(Giannini, Biasutti, Held and Sobel, in preparation)a. stabilization – top-down

e.g. Chiang and Sobel 2002b. monsoon/moisture supply – bottom-up

e.g. Lindzen and Nigam 1987

3. Climate and society interactionsreflections on the role of science and scientists

Outline

1. Simulations of Sahel droughta. atmospheric models forced with historical sea surface temperature

Giannini, Saravanan and Chang 2003, 2005b. coupled ocean-atmosphere models (IPCC 4AR)

Biasutti and Giannini 2006

2. Mechanisms of Sahel drought/African climate variability and change(Giannini, Biasutti, Held and Sobel, in preparation)a. stabilization – top-down

e.g. Chiang and Sobel 2002b. monsoon/moisture supply – bottom-up

e.g. Lindzen and Nigam 1987

3. Climate and society interactionsreflections on the role of science and scientists

spatial signature of July-September African rainfall variabilityG

ulf

of G

uine

a pa

tter

nS

ahel

pat

tern

Giannini et al., 2005 (Clim. Dyn.)

temporal signature and relation to surface temperature

Giannini et al., 2005 (Clim. Dyn.)

decadal interannual

Giannini et al., 2003, 2005

Giannini et al., 2003, 2005

decadal interannual

NASA/GISS analysis of surface temp – linear trend 1950-2000Hansen et al. 1999 (J. Geophys. Res.)

regression of NASA/NSIPP1 Sahel PC and sfc tempGiannini et al. 2003, 2005

IPCC 4AR Multi-model averageBiasutti and Giannini 2006

IPCC 4AR Multi-model average

Biasutti and Giannini, 2006 (GRL, in press)

Biasutti and Giannini, 2006 (GRL, in press)

Outline

1. Simulations of Sahel droughta. atmospheric models forced with historical sea surface temperature

Giannini, Saravanan and Chang 2003, 2005b. coupled ocean-atmosphere models (IPCC 4AR)

Biasutti and Giannini 2006

2. Mechanisms of Sahel drought/African climate variability and change(Giannini, Biasutti, Held and Sobel, in preparation)a. stabilization – top-down

e.g. Chiang and Sobel 2002b. monsoon/moisture supply – bottom-up

e.g. Lindzen and Nigam 1987

3. Climate and society interactionsreflections on the role of science and scientists

Top-down: stabilization

Chiang and Sobel, J Climate 2002(Yulaeva and Wallace , J Climate 1994)

El Nino – central equatorial Pacificglobal warming – global tropical oceans(e.g. Neelin et al., GRL 2003)

atmosphericadjustment:net surfaceheat fluxes

What role for theland surface??

(e.g. Chiang and Lintner, J. Climate 2005)

Bottom-up: monsoon/moisture supply

Rotstayn and Lohmann, J Climate 2002

surface air temperature

(minus global mean)

precipitation

Haarsma et al., GRL 2005 2050-2080 minus 1950-1980

Michela Biasutti, personal communication

Outline

1. Simulations of Sahel droughta. atmospheric models forced with historical sea surface temperature

Giannini, Saravanan and Chang 2003, 2005b. coupled ocean-atmosphere models (IPCC 4AR)

Biasutti and Giannini 2006

2. Mechanisms of Sahel drought/African climate variability and change(Giannini, Biasutti, Held and Sobel, in preparation)a. stabilization – top-down

e.g. Chiang and Sobel 2002b. monsoon/moisture supply – bottom-up

e.g. Lindzen and Nigam 1987

3. Climate and society interactionsreflections on the role of science and scientists

Reflections on:

desertification- “Farmers freed of blame in Sahel drought” (SciDev.net)- multidisciplinary studies,

linking climate and environmental/ecological sciences

global warming - social/environmental equity

precipitation surface temperature

moisture convergence evaporation

Sahel surface temperature variability (1930-2000)

CMAP precipitation(66%)

NCEP/NCAR sfc temp(91%)

what constitutes a monsoon?

Seasonal cycle of surface temperature/precipitation

Lu and Delworth 2005 (Geophys. Res. Lett.)

The relative roles of Atlantic, Indian and Pacific SSTs