On the Differences in the Intraseasonal Rainfall Variability between Western and Eastern Central Africa: Case of 25 - 70-Day Oscillations

Alain Tchakoutio,Armand Nzeukou

doi:10.4236/gep.2016.47015

Abstract

The intraseasonal timescale is critical in Central Africa, because the resources of the region are highly rainfall dependent. In this paper, we use 1DD GPCP rainfall product to investigate the differences in the space-time structures of the 25 - 70-day intraseasonal variability of rainfall, over the Western Central Africa (WCA) and the Eastern Central Africa (ECA), with different climate features. The results of Empirical Orthogonal Functions (EOFs) analysis have shown that the amount of variance explained by the leading EOFs is greater in ECA (58.4%) than in WCA (49.8%). For both WCA and ECA, the power spectra of the Principal Components (PCs) peaked around 40 days, indicating a MJO signal. The seasonality of ISO is evident, but this seasonality is much noticeable in ECA where almost 80% of the total yearly ISO power occurs during November-April season, against only around 60% for WCA. Moreover, the lagged cross correlations computed between WCA and ECA PCs time series showed that most of the WCA PCs led ECA PCs time series with a timescale of 8 - 12 days, revealing that the eastward propagation could potentially be the relationship between WCA and ECA modes. The interannual variations in the ISO activity are weak in WCA, when compared with ECA where the signal exhibits larger interannual variations, quite linked with ENSO.

Highlights

It is well-known that climate variability and change are a crucial problem in many tropical regions
In this paper we have investigated the intraseasonal oscillations of rainfall over central Africa, using 1DD GPCP rainfall product, with an emphasis on the comparison between the western central Africa and the Eastern parts of the region
The classical spectral analysis showed the strong prominence of intraseasonal scale in central African climate, especially in Eastern Central Africa (ECA) where the peak of the power spectrum is much sharp than Western Central Africa (WCA)

Summary

Introduction

It is well-known that climate variability and change are a crucial problem in many tropical regions Amongst these regions, the Central Africa (CA) is attractive because of the variety of its topography and surface conditions (Table 1). The western part of the region (15 ̊S - 15 ̊N; 5 ̊E - 30 ̊E) receives intense precipitation throughout the year, especially over the Congo Basin (Figure 1(b)). This subregion is almost covered by the Congo forest (Figure 1(c)), which keeps it quite relatively wet throughout the year. The two subregions (ECA and WCA), separated from each other by the Rift Valley, are very different in terms of topography, surface conditions and precipitation (Table 1)

Methods

Results

Conclusion