Analysis of rainfall variability for the October to December over Tanzania on different timescales during 1951–2015

Abstract

AbstractThis study has utilized spectral analysis to ascertain the nature of decadal rainfall variability, while correlation, singular value decomposition (SVD), and composite analyses were employed to explore and understand the possible associated mechanisms. Inferences were drawn to the interannual timescales. The spectrum analysis of October to December (OND) rainfall revealed dominant signals at 2.4, 2.9, and 5.0, and a band near 16–25 years. These cyclicities suggest that dominant drivers of Tanzania rainfall anomalies evolve on interannual and decadal timescales. Interannual variations in Tanzania rainfall are mostly linked to the Indian and Pacific oceans. Significant sea surface temperature (SST) anomalies in the Indian and Pacific oceans included those associated with Indian Ocean Dipole (IOD) and El Niño‐Southern Oscillations (ENSO), respectively and are linked to changes in the atmospheric circulation anomalies over the western Indian Ocean. The observed circulation variations are most likely to influence Tanzania rainfall. In contrast, wet and dry decades are mostly linked to the Indian and Atlantic oceans. The Indian ocean provides stronger teleconnections with Tanzania rainfall at decadal timescales, consistent with interannual timescales teleconnections. Notably, the ‘dipole’ like forcing observed at interannual timescales is less coherent at decadal timescales over the Indian Ocean. As such, the Indian Ocean displayed a coherent monopole pattern in decadal SST. As a result of these differences, the location of the western Indian ocean centre of convection activities observed at interannual timescales has shifted to around the central Indian Ocean at decadal timescales. Wet decades in Tanzania rainfall are associated with the condition of enhanced convection and increase moisture content centred over the central Indian Ocean. This convective condition was observed to spread to a large area of the Indian Ocean and the African continent, including the study area.