aeolian dynamics variability in central sahel between 1950...

Parallel session 2B - Monsoon syslem: Climate I

Pr.2B.3

Aeollan dynamics variability in central Sahel between 1950 and 2000:Are meteorological data about wind representative of the climate change

and its environmental impact? Examplo of the synoptic stationsMaYne-Soroa and Nguigmi (Niger.Lake Chad basin)

Boubu IlASS,\!'H: ":, ,\lain IWR,\'Il', ".ibu G..\IHIA " ,\roou I)l[UIIlOll ...R('njamin,;I;GOUi'iOU NGATCII,\ ', Jean-Louts I~,\JOT • Ilu"id l;t:IJAG 1.1, ,\hdoul "urhn TRJ\ORE'

I Universitc Abdou Moumoun], Fueulle .I"" S.:i~lICC'" Opl. de Geologic, BP. 10661. Ni:IlI1t:)'. ~iScrI Laboraioirc M:!C, l:nin~l:;ilf de ROUC11, ClIIRS, 76S21. Monl Saint Aignan, France

) LTIIE, Univcrslrede Grenoblc, HP 53, J~O-ll. Grenoblc. France• Univcrsitcde NgJJoumlcrf. Dpr. Dc:;Sciences de la Terre, BP 454. Ng:lOlmdtrC:. Carneruun

! l..ulm!'D!(l;rC B101':,\KO, UMR IKD 211.94010"',.SA, lIMR CI>:RS 75SJ, Universite de Puns 1'..51 Creleil.Crerci], France

': Labcmtoirc IISM, Uni\'ersilc de Montpellier 2, IKO. JolOQ5, Mompellier, Fr.IIlC<'• Di'l'CI;on de la MCtNrolC'[.;1c :-:Jli(1n~1e du Nigl:r(DMl'Ij. BP 21ii. :-.'i.:IIll~)'. :-Jlg~r

Climaric crises that occurred in Snhel since 1970 were described mainly with l':III1f;,1I

variations. Ncvenhctcss, prccipuations arc observed only some lens d:,),:, lJ )'eIII. conccntrurcdin a few months. while (b)'s without wind an: rare. The aim of this study ;5 It, dc.·;clilmclimatic vuriability with original meteorological darn of wind chnmcrcrivtics 111111 h\),iull":~'

visibility from synoptic 5t:l1i'1II5 in Nigcr: Maine-Sowa (I ).2J~N·II.'ll:I°E. J3R III [1,1) [111(1

Nguigmi (14.25"N-IJ.12°E, 287 m asl). These stations are located in the wcstcm pan nf Ih\~

Lake Chad basin. This very fbl ami is covered by unI'ollsolidaa'd line .':1I1d dcp,)sll, :11111 :h~

scuree vegetation is not IJ real obstacle for the wind, These stations urc under the IrlI,kchll)' ... fNE·SW winds originated in the Boucle depression (Northern Chad) whcr..· (ltrSI ij c;lrr;cuaway. We used three daily (6:00. 12:00 and 18:00) measures of wind (direction nnd speed i1t

10 meters above the ground), horizontal visibilit), and COrrcSI)onllin~ types of weather.Sienificant winds (> 0.5 m.s-t i are more common in Muine-Scroa (~3.71,:~ tlf tile allm;llsurcs) than in N£uigmi {71.4'iQ. and wind speeds are faster :11 I:!;O(l am in the bothstations. In Mninc-Soroa, the main wind direction axis is ;>.lE·SW (.1 1.5%) while in \"guigrnithe main axis is E·\\' (21.5%). Major variations described with the rainfall fit with major windspeed varintions. Thus, IWO periods arc noticed: "950-1969 [wet) with higher wind speedvariability and 19iO·19S6 (dry) characterised by increased wind speed, paniculurty ill

Nguigml. Major changing periods (1967.1971 and 19S4-198(,) arc marked by declines ofmean speed 01' winds. mainly from NL SW. \V and S directions. On the contrary, NW and Nwind speeds arc strengthened, t\long the whole.data series, speeds present an upward trend inNguigmi arul a sliglll decline in Maine-Sowa, In both starions, horizonml visibility decreasesufter 1969 from nn average of 26 kmto 16,2 km in Matnc-Soroa (from 24.510 I(i.) km inNguigrni), Bill, dust haze decreased suhstantially since the 70's and, on the contrary. sandyhaze ~Il(J blowing sand increased substanrinlly. This increase of sandy hUle and blowing sandihm 1Il0\'e coarser panicles than dust haze testify occurrences of local or regional winderosion. perhaps. as :. ccnscqucncc of less natural \'t"gl."lalion covering the soils near thesuuions.

Aeolian dynamics variability in central Sahel: Are meteorological wind representa2ve of climate change and its environmental impact in the Sahel?

Example of synop2c sta2ons in Maïne-‐Soroa and Nguigmi (Niger, Lake Chad basin) between 1950 and 2000.

4th Interna7onal Conference-‐ AMMA

Hassane B., Durand A., Garba Z., Diedhiou A., Ngounou Ngatcha B., Rajot J-‐L., Sebag D., Traore A.

Hassane B. et al.-‐4th Interna0onale Conference AMMA Presenta7on

Global scale: rising trend of temperature averages (IPCC, 2007)

In Niger: 150 km southward shiJ of isohyets (Ozer et Erpicum, 1995)

Large varia)ons in climate parameters


Dry season : 8-‐9 months -‐  Dry winds (harma3an) -‐  mobiliza7on and emission of dust into

the atmosphere

Rainy season: 3-‐4 months -‐  Moist winds (monsoon) -‐  rainfalls

Seasonal cycle

July –August January –February


Rainfall is concentrated in three months during some tens days only.

But, windless days are rare and these stations are near one of the most

important source of aeolian dust in the world: the Bodélé depression.

Seasonal cycle


In arid areas, is it possible to describe the climate change

by wind parameters (wind direction and speed, horizontal visibility)?

Hassane B. et al.-‐4th Interna0onale Conference AMMA Datas

Data from two synoptic stations in Niger,

Mainé-Soroa (1936) and Nguigmi (1921).

Data are collected from original manuscripts archived in DMN.

wind (10 m above the ground) and horizontal visibility

at 6:00, 12:00 and 18:00 TU since 1950.

Hassane B. et al.-‐4th Interna0onale Conference AMMA Results

May to october

November to april

Wind direc)ons: 1950-‐1992

NE (20.9%), N (12.1%), E (8.5%) SW (10.3%), W (8.5%), S (6.9%)

NE (14.8%), N (6.6%), E (13%) SW (4.6%), W (8.7%), S (5.7%)

(82.7%) (74%)


Wind speed: intra-‐annual variability (1950-‐1992)

During the rainy season, wind speed maxima occur at the begening of July in Maïné-Soroa and two weeks later in Nguigmi.


Wind speed: interannual variability (1950-‐1992)

On both stations wind speed increase between the 1970s and the middle 1980s


Wind speed: daily variability m.s-‐1

m.s-‐1


Horizontal visibility: intra-‐annual variability (1950-‐2000)

High visibilities occur during the rainy season, Low visibilities occur during the dry season


Horizontal visibility: interannual variability

Horizontal visibility shows a significant decrease since 1969.


Types of dust haze

Light Dust Haze 5 km <D< 10 km

Thick Dust Haze D ≤ 1km

Dust haze frequency increase strongly, particularly at Maïné-Soroa since late 1960.

◊: 6h +: 12h


Types of weather

BS= BRUME SECHE (DUST HAZE) S= BRUME DE SABLE/POUSSIERE (SANDY HAZE) CS= CHASSE SABLE (BLOWING SAND)

◊: 6h +: 12h

1987

1983

1984


Types of weather

1987 1983

Manga december 1977

Durand

Manga december 2002

Durand

Hassane B. et al.-‐4th Interna0onale Conference AMMA Conclusion

winds and horizontal visibility are relevant parameters of climate evolution analysis in arid environment

1950-‐1966 1967-‐1992 (2000) 1967-‐1972 changing

1973-‐1986 arid

Higger NE and E Winds speed

Dust haze increase

horizontal visibility decreases since 1969

Lower significant wind observa7ons

wet 1987-‐1992 (2000)

Semi-‐arid

Lower wind speed average

Sandy haze and sand blowing

increase

Predominant W and SW wind direc7on

Lack of vegeta7on

Aeolian dynamics variability in central Sahel: Are meteorological wind representa2ve of climate change and its environmental impact in the Sahel?

Example of synop2c sta2ons of Maïné-‐Soroa and Nguigmi (Niger, Lake Chad basin) between 1950 and 2000.

4th Interna7onal Conference-‐ AMMA

Hassane B., Durand A., Garba Z., Diedhiou A., Ngounou Ngatcha B., Rajot J-‐L., Sebag D., Traore A.

THANK YOU

Hassane B., Durand A., Garba Z., Diedhiou Arona, Ngounou

Ngatcha B., Rajot Jean-Louis, Sebag David, Traoré A.K. (2012)

Aeolian dynamics variability in central Sahel between 1950

and 2000 : are meteorogical data about wind representative

of the climate change and its environment impact ? :

example of the synoptic stations Maïné-Soroa and Nguigmi

(Niger, Lake Chad basin)

In : African monsoon multidisciplinary analyses : 4th AMMA

International Conference : program and book of abstracts =

Analyses multidisciplinaires de la mousson Africaine : 4e

conférence internationale AMMA : programme et livre des

résumés

Toulouse : AMMA, 1 p.

AMMA International Conference : Parallel Session 2B.

Monsoon System : Climate 1, 4., Toulouse (FRA),

2012/07/02-06

aeolian dynamics variability in central sahel between 1950...

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