Analysis of Trend and Periodicity in Long-Term Annual Rainfall Time Series of Nigeria - Hydrologic Time Series Analysis: Theory and Practice - page 266

Periodograms of the annual rainfall series over three zones of the study
area are presented in Figs 12.14(a-c ) . Three dominant peaks of rainfall cycles
are evident over the zones. The cycles have periods 14 and 33 years over
Sahel zone, 3 and 33 years over Savanna zone, and 3, 7 and 33 years over the
Guinea zone. The 3-year oscillation period may be linked to the stratospheric
Quasi-Biennial Oscillation (QBO) of equatorial zonal winds (Reed et al.,
1961), the 7-year to tropical sea-surface temperatures (including El Nino-
Southern Oscillation events, ENSO; Tosic and Unkasevic, 2005), the 14-year
to the sunspot cycle (Makarau and Jury, 1997; Currie and O'Brien, 1988), and
the 33-year to the Atlantic Multi-Decadal Oscillation (AMO) of sea surface
temperature (Zhang and Delworth, 2006; Chang-Seng, 2007).
Fig. 12.14. Periodogram of annual rainfall over (a) Sahel,
(b) Savannah and (c) Guinea zones.
12.5 Conclusions
Global climate change could have important effects on various environmental
variables including rainfall in many countries of the world. Changes in rainfall
regime directly affect agriculture, water resources management, hydrology
and ecosystems. Hence, the significance of investigating the changes in the
spatial and temporal rainfall patterns is imperative for suggesting suitable
strategies for sustainable management of water resources, agriculture,