The non-parametric Mann–Kendall test and Theil-Sen

Trend Estimate are used for the trend analysis.

The Standardised Precipitation Index (SPI) is used to

examine the regional rainfall fluctuation.

Extreme precipitation indices of ETCCDI are analysed to

investigate the likely reasons for the observed rainfall

recovery in the region.

Our research is designed to better understand the recent trend

of tropical West African rainfall through direct observation

by studying various aspects of the rainfall recovery for a large

part of the region between 1980 and 2013. These aspects

include:

(1) discussing spatio-temporal characteristics of the recovery

in terms of linear trends,

(2) assessing changes in frequency and intensity of extreme

rainfall using indices of the Expert Team of Climate

Change Detection and Indices (ETCCDI; Zhang et al.,

2011) and

(3) examining the impacts of the rainfall recovery on the

rainy season onset and retreat.

Nicholson S. 2005. On the question of the “recovery” of

the rains in the West African Sahel. J. Arid Environ. 63:

615-641 DOI: 10.1016/j.jaridenv.2005.03.004

Sanogo S, Fink AH, Omotosho JA, Ba A, Redl R and

Ermert V. 2015. Spatio-temporal characteristics of the

recent rainfall recovery in West Africa. Int. J. Climatol.

DOI: 10.1002/joc.4309

Zhang X, Alexander LV, Hegerl GC, Jones P, Klein Tank

A, Peterson TC, Trewin B, Zwiers FW. 2011. Indices for

monitoring changes in extremes based on daily

temperature and precipitation data. WIREs Clim.

Change 2: 851- 870, doi: 10.1002/wcc.147.

The rainfall data used

comprise of 167 and 254

stations with daily and

monthly records,

respectively. All these

stations have at least 80% of

data availability between

1980 and 2010 (Sanogo et al.

2015). Also the second

version of the African

Rainfall Climatology (ARC2)

for the period 1983-2013 is

used.

We are grateful to the financial assistance of the

International Science Programme (ISP) at the Uppsala

University, which has covered all of our expenses to attend

to the conference.

Fig.2: Annual rainfall trend from (a) station data (1980-2010) and (b) ARC2 (1983-2013)

Fig.3: The Standardized Precipitation Index computed for the period 1921-2010.

Fig.3: The Standardized Precipitation Index (SPI-3, 6

and12) computed for the period 1921-2010

The major findings of this study are as follows:

The recovery is more significant in the Sahel and the

month of August-October show the largest recovery.

The observed recovery is associated with an increase in

extreme rainfall events across the region.

SPI analyses confirm that West Africa has recovered

from the agricultural and hydrological droughts

conditions.

This study highlights that despite the observed increasing

rainfall trend, the very wet conditions of the 1950s and

1960s have not been re-established (Corroborating

Nicholson , 2005).

The results further suggest a later cessation of rains

without significant early onset over the region.

Abstract

Results

Objectives

Data used

Methods

Acknowledgements

References

Fig.5: Linear trends of onset (a-b) and retreat dates (c-d) in Julian day, and the length of the rainy season

(e-f), based on criteria defined by Wang and LinHo (2002) (blue line) and AGHRYMET (1996) (red line).

1Faculté des Sciences et Techniques(FST), Université des Sciences des Techniques et des Technologies de Bamako (USTT-B), Mali 2Institute for Meteorology and Climate Research , Karlsruhe Institute of Technology (KIT), Germany 3WASCAL, GRP - West African Climate System, Federal University of Technology, Akure, (FUTA), Nigeria 4Institute of Geophysics and Meteorology, University of Cologne, Germany

SPATIO-TEMPORAL CHARACTERISTICS OF THE RECENT

RAINFALL RECOVERY IN WEST AFRICA S. Sanogo1*, A.H. Fink2 , J.A. Omotosho3,

A. Ba1, R. Redl4, V. Ermert4

International

Science

Programme

(a)

(b)

Using daily and monthly rainfall data and the gridded

African Rainfall Climatology-Version 2 (ARC2), linear

trends in yearly and monthly rainfall totals as well as the

trend in precipitation extreme and intensity were

investigated. The majority of stations in the Sahel between

the West Coast and 15°E shows a statistically significant

increasing rainfall trend for annual totals. The recovery is

more significant in the Sahel compared to the Guinea

Coast. The August–October period shows the largest

rainfall recovery in the Sahel. The date of the retreat of the

rainy season significantly moved later into the year by 2

days per decade but a significant tendency to earlier onset

has not been observed. In the Guinea Coast, a tendency

toward a more intense 2nd rainy season suggests also a later

retreat of the rains. The recovery is reflected by more rainy

extreme rainfall events. However, ARC2 trends are broadly

consistent where ground calibration could be undertaken,

but trends are dubious for highlands in Guinea, Jos and

Cameroon due to missing gauge data over there.

Fig.4: Trend in precipitation extreme and intensity

Conclusion

University of Cologne

Fig.1: Validation of ARC2 monthly rainfall

Presented at the International Scientific Conference “Our Common Future under Climate Change”, 7-10th July 2015, Paris, France

* soul@lossa-mali-edu.org