poster at CFCC2015

1.  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