East African 675 Year MCEOF Hydroclimatic Lake Proxy Data Synthesis Tierney, J.E.; Smerdon, J.E.; Anchukaitis, K.J.; Seager, R. Tierney, J.E. Smerdon, J.E. Anchukaitis, K.J. Seager, R. hydrology earth science/paleoclimate/paleolimnology (empirical orthogonal function,null,68% confidence interval lower bound,dimensionless,null,paleolimnology,null,null,N,null) earth science/paleoclimate/paleolimnology (age,null,null,year Common Era,null,paleolimnology,null,null,N,null) earth science/paleoclimate/paleolimnology (empirical orthogonal function,null,null,dimensionless,null,paleolimnology,null,null,N,median) earth science/paleoclimate/paleolimnology (empirical orthogonal function,null,68% confidence interval upper bound,dimensionless,null,paleolimnology,null,null,N,null) earth science/paleoclimate/paleolimnology (empirical orthogonal function,null,95% confidence interval lower bound,dimensionless,null,paleolimnology,null,null,N,null) earth science/paleoclimate/paleolimnology (East Africa>LATITUDE >LONGITUDE ) The recent decades-long decline in East African rainfall suggests that multidecadal variability is an important component of the climate of this vulnerable region. Prior work based on analysing the instrumental record implicates both Indian and Pacific ocean sea surface temperatures (SSTs) as possible drivers of East African multidecadal climate variability, but the short length of the instrumental record precludes a full elucidation of the underlying physical mechanisms. Here we show that on timescales beyond the decadal, the Indian Ocean drives East African rainfall variability by altering the local Walker circulation, whereas the influence of the Pacific Ocean is minimal. Our results, based on proxy indicators of relative moisture balance for the past millennium paired with long control simulations from coupled climate models, reveal that moist conditions in coastal East Africa are associated with cool SSTs (and related descending circulation) in the eastern Indian Ocean and ascending circulation over East Africa. The most prominent event identified in the proxy record - a coastal pluvial from 1680 to 1765 - occurred when Indo-Pacific warm pool SSTs reached their minimum values of the past millennium. Taken together, the proxy and model evidence suggests that Indian Ocean SSTs are the primary influence on East African rainfall over multidecadal and perhaps longer timescales. STUDY NOTES: Synthesis of lacustrine hydroclimatic proxy records from East Africa using a Monte Carlo empirical orthogonal function (MCEOF) approach. MCEOF1 timeseries and spatial loadings plus 68% and 95% uncertainty bounds are reported. Site information for Lake proxy records utilized Lake Latitude Longitude Proxy Average DT References Challa -3.32 37.70 "BIT, dDwax, varve thickness" 33 "Verschuren et al. (2009), Nature; Tierney et al., (2011) QSR; Wolff et al. (2011) Science" Naivasha -0.77 36.35 Lake level reconstruction 3 "Verschuren et al. (2000), Nature" Victoria -1.00 33.00 % shallow water diatoms 5 "Stager et al. (2005), J. Paleolimnol." Edward -0.25 29.50 % Mg in authigenic calcite 4 "Russell and Johnson (2007), Geology" Tanganyika -6.70 30.00 Charcoal 10 "Tierney et al. (2010), Nature Geosci." Masoko -9.33 33.76 Magnetic susceptibility 10 "Garcin et al. (2006), Palaeo3; Garcin et al. (2007), J. Paleolimnol." Malawi -10.00 34.22 Terrigenous mass accumulation rate 6 "Brown and Johnson (2005), G3; Johnson and McCave (2008), Limnol. Oceanogr." NCDC-Paleoclimatology https://www.ncdc.noaa.gov/data-access/paleoclimatology-data - Bauer Bruce Investigator : Tierney, J.E. Investigator : Smerdon, J.E. Investigator : Anchukaitis, K.J. Investigator : Seager, R. 2013-01-28 ONLINE Files online, ASCII https://www.ncdc.noaa.gov/paleo/study/13686 https://www1.ncdc.noaa.gov/pub/data/paleo/paleolimnology/eastafrica/tierney2013nature11785-s2.xls https://www1.ncdc.noaa.gov/pub/data/paleo/paleolimnology/eastafrica/tierney2013mceof.txt https://www1.ncdc.noaa.gov/pub/data/paleo/paleolimnology/eastafrica/tierney2013nature11785-s2.xls https://www1.ncdc.noaa.gov/pub/data/paleo/paleolimnology/eastafrica/tierney2013mceof.txt English https://www.ncdc.noaa.gov/paleo/study/13686 https://www1.ncdc.noaa.gov/pub/data/paleo/paleolimnology/eastafrica/tierney2013nature11785-s2.xls https://www1.ncdc.noaa.gov/pub/data/paleo/paleolimnology/eastafrica/tierney2013mceof.txt Jessica E. Tierney, Jason E. Smerdon, Kevin J. Anchukaitis, and Richard Seager. 2013. Multidecadal variability in East African hydroclimate controlled by the Indian Ocean. Nature, Vol. 493, No. 7432, pp. 389-392. DOI: 10.1038/nature11785 Kevin J. Anchukaitis and Jessica E. Tierney. 2012. Identifying coherent spatiotemporal modes in time-uncertain proxy paleoclimate records. Climate Dynamics, DOI: 10.1007/s00382-012-1483-0 START YEAR: 1275 AD * END YEAR: 1950 AD 29.5 -10 37.7 -.25