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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 12 | Copyright

Special issue: Drought forecasting and warning

Hydrol. Earth Syst. Sci., 18, 4965-4978, 2014
https://doi.org/10.5194/hess-18-4965-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 10 Dec 2014

Research article | 10 Dec 2014

Predicting East African spring droughts using Pacific and Indian Ocean sea surface temperature indices

C. Funk1, A. Hoell2, S. Shukla2, I. Bladé3, B. Liebmann4, J. B. Roberts5, F. R. Robertson5, and G. Husak2 C. Funk et al.
  • 1US~Geological Survey and University of California Santa Barbara Geography, Santa Barbara, USA
  • 2University of California Santa Barbara Geography, Santa Barbara, USA
  • 3Universitat de Barcelona and Institut Català de Ciències del Clima, Barcelona, Spain
  • 4University of Colorado and NOAA Earth Systems Research Laboratory, Boulder, USA
  • 5NASA Marshall Space Flight Center, Huntsville, USA

Abstract. In eastern East Africa (the southern Ethiopia, eastern Kenya and southern Somalia region), poor boreal spring (long wet season) rains in 1999, 2000, 2004, 2007, 2008, 2009, and 2011 contributed to severe food insecurity and high levels of malnutrition. Predicting rainfall deficits in this region on seasonal and decadal time frames can help decision makers implement disaster risk reduction measures while guiding climate-smart adaptation and agricultural development. Building on recent research that links more frequent East African droughts to a stronger Walker circulation, resulting from warming in the Indo–Pacific warm pool and an increased east-to-west sea surface temperature (SST) gradient in the western Pacific, we show that the two dominant modes of East African boreal spring rainfall variability are tied to SST fluctuations in the western central Pacific and central Indian Ocean, respectively. Variations in these two rainfall modes can thus be predicted using two SST indices – the western Pacific gradient (WPG) and central Indian Ocean index (CIO), with our statistical forecasts exhibiting reasonable cross-validated skill (rcv ≈ 0.6). In contrast, the current generation of coupled forecast models show no skill during the long rains. Our SST indices also appear to capture most of the major recent drought events such as 2000, 2009 and 2011. Predictions based on these simple indices can be used to support regional forecasting efforts and land surface data assimilations to help inform early warning and guide climate outlooks.

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Western Pacific SST gradients influence eastern East African precipitation in predictable ways. At seasonal and decadal timescales, warm equatorial western Pacific SSTs and cool eastern Pacific SSTs reduce precipitation in East Africa. The gradient between these regions can be used to make reasonably accurate forecasts in one of the world's most food-insecure regions. Recent warming in the western Pacific and stationary eastern Pacific conditions have produced large precipitation declines.
Western Pacific SST gradients influence eastern East African precipitation in predictable ways....
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