Predicting drought on seasonal-to-decadal time scales, Schubert, S.; Koster, R.; Hoerling, M.; Seager, R.; Lettenmaier, D.; Kumar, A.; Gutzler, D. , Bulletin of the American Meteorological Society, Oct, Volume 88, Issue 10, p.1625-1630, (2007), Doi 10.1175/Bams-88-10-1625