Drought in the African Sahel: scientific research and societal implications Alessandra Giannini International 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 warm ENSO – neutral anomalies BUT... - seasonality (e.g. Haylock and McBride 2001; Naylor et al. 2001) - spatial scales

DJF(1)SON(0) RegCM3 25km resolution courtesy of J. Qian, H. Li (IRI) NOAA/GHCN station prcp

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

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

Outline 1. Simulations of Sahel drought with climate models a. atmospheric models forced with historical sea surface temperature Giannini, Saravanan and Chang 2003, 2005 b. coupled ocean-atmosphere models (IPCC 4AR) Biasutti and Giannini 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 2002 b. monsoon/moisture supply – bottom-up e.g. Lindzen and Nigam Climate and society interactions reflections on the role of science and scientists

Outline 1. Simulations of Sahel drought a. atmospheric models forced with historical sea surface temperature Giannini, Saravanan and Chang 2003, 2005 b. coupled ocean-atmosphere models (IPCC 4AR) Biasutti and Giannini 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 2002 b. monsoon/moisture supply – bottom-up e.g. Lindzen and Nigam Climate and society interactions reflections on the role of science and scientists

spatial signature of July-September African rainfall variability Gulf of Guinea patternSahel pattern Giannini et al., 2005 (Clim. Dyn.)

temporal signature and relation to surface temperature Giannini et al., 2005 (Clim. Dyn.)

decadalinterannual Giannini et al., 2003, 2005

decadalinterannual

NASA/GISS analysis of surface temp – linear trend Hansen et al (J. Geophys. Res.) regression of NASA/NSIPP1 Sahel PC and sfc temp Giannini et al. 2003, 2005 IPCC 4AR Multi-model average Biasutti and Giannini 2006

IPCC 4AR Multi-model average Biasutti and Giannini, 2006 (GRL, in press)

Outline 1. Simulations of Sahel drought a. atmospheric models forced with historical sea surface temperature Giannini, Saravanan and Chang 2003, 2005 b. coupled ocean-atmosphere models (IPCC 4AR) Biasutti and Giannini 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 2002 b. monsoon/moisture supply – bottom-up e.g. Lindzen and Nigam Climate and society interactions reflections 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 Pacific global warming – global tropical oceans (e.g. Neelin et al., GRL 2003) atmospheric adjustment: net surface heat fluxes What role for the land 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 minus

Michela Biasutti, personal communication

Outline 1. Simulations of Sahel drought a. atmospheric models forced with historical sea surface temperature Giannini, Saravanan and Chang 2003, 2005 b. coupled ocean-atmosphere models (IPCC 4AR) Biasutti and Giannini 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 2002 b. monsoon/moisture supply – bottom-up e.g. Lindzen and Nigam Climate and society interactions reflections 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

precipitationsurface temperature moisture convergenceevaporation

Sahel surface temperature variability ( )

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