Revisiting interannual to decadal teleconnections influencing seasonal rainfall in the Greater Horn of Africa during the 20th century

摘要

This paper revisits teleconnections for three major rainy seasons at the Greater Horn of Africa for the period 1901-2013. Sea surface temperature-based climate indices known to influence Short, Kiremt, and Long Rains are used in a comprehensive statistical analysis to detect non-stationary behaviour in teleconnections and to split them into interannual and decadal time scales. Physical mechanisms are proposed for identified significant non-stationary teleconnections. Interannual variability in the October-December Short Rains is predominantly influenced by the Indian Ocean Dipole (IOD) with a percent variance explained (PVE) of up to 80% in recent years. However, abrupt shifts in this teleconnection occurred around 1918, 1951, 1987, and recently. The Short Rains also correlate strongly with El Nino-Southern Oscillation (ENSO). However, ENSO influence on Short Rains is mediated by in-phase occurrence of IOD. Decadal variations in Short Rains are more directly explained by low-frequency variability in the Pacific Ocean (PO). A hitherto undocumented non-stationary relation was found between Atlantic Nino 3 and June-September Kiremt Rains. The non-stationarity seems to be related to a decadal regime shift in the West African monsoon system in the late 1960s. The variability of Kiremt Rains is also strongly associated with ENSO, although the recent increased correlation is not non-stationary. Consistent with recent studies, the post-1998 March-May Long Rains decline is strongly associated with decadal variability in the PO. The PVEs in the stable correlations using Pacific Decadal Oscillation and Interdecadal Pacific Oscillation indices range from 25 to 64%, mostly due to low-frequency variability (>8 years). The results have ramifications for seasonal-to-decadal forecasting and can be taken to design modelling studies to gain insights into the physical mechanisms.