Inte rnatio nal Jo urnal o f Sc ie ntific & Eng inee ring Re se arc h, Vo lume 3, Issue 2, February -2012 1
ISS N 2229-5518
Analyze of climate variability and change impacts on hydro-climate parameters: case study of Côte d’Ivoire
KOUAKOU Koffi Eugène, GOULA Bi Tié Albert, KOUASSI Amani Michel
Abs tract- The w ater resources of Côte d’Ivoire are very much used f or w ater drinking supply of populations, breeding and also f or the agriculture. But the abundance of this resource knew disturbances as from the years 1968 to 1970. These upheavals resulted in a f all of precipitat ions of 12.4% to 31.4% and f low s w hich varied from 31.40% to 55.4%.
The projections carried out on the hydro-climate para meters under scenario A1B w ith the climate model Reg CM3 give an increase in the annu al average
temperatures of 3°C to 4.2°C and a dow nw ard trend of annual precipitations f rom 4.9% f rom 2100.
Inde x Terms : Climate variability and change, impacts, hydro-climate parameters, Côte d’Ivoire
—————————— ——————————
The economy of Côte d'Ivoir e is based on agricultur e (1 st
pr oducer of cocoa and 3rd pr oducer of coffee on the w orld). It is known that r ainfall distr ibution, alternating r ainy or dry seasons and their duration , ar e important factors in agr icultural pr oduction. Any climate change has impor tant impacts on agr icultur al pr oduction. A r eduction in rainfall leads to a r eduction of the main export cr ops pr oduction (cocoa, coffee, palm oil, rubber cotton,...) and food cr ops (r ice, yams, cassava, ...). In Côte d'Ivoir e, several author s [1,
2] highlighted the impacts of climat e variability on water
and the envir onment. Indeed, th ese studies show ed that rainfall dr opped by 10 to 37% according to localities and the flow s of the lar ge r ivers decr eased fr om 30% to 60%. This
situation of dryness modified the behavior of the populations. One of the r emar kable illustrations of the dr ought in Côte d'Ivoir e since thir ty years has been the displacement of the loop of cocoa in the Center-east r egion (Dimbokr o) to South-w est (San Pedr o).
Mor eover , w e note that the temperatur es incr eased of 1°C
since 1960 [2] and an incr ease of the seas on the continents.
Ther efor e, study climate change in Cote d'Ivoir e is a maj or innovation because human must anticipate the climate change to adj ust to r educe harmful impacts to life.
Côte d'Ivoir e is located in W est Africa. It forms a squar e
with sides betw een 2°30 and 8° 30 w est longitudes and betw een 4°30 and 10°30 north latitudes. The terr itory has an ar ea of 322462 km 2 and is bounded to the north by Mali and Bur kina Faso, east by Ghana , w est by Liber ia and Guinea and the South by the Atlantic Ocean.
Ther e ar e four climat e zones (Fig. 1):
- tr ansitory tr opical climate (North) rainfall fluctuate
betw een 1000-1300 mm/year ;
- mitigation transitory equator ial climate (Center ) has an annual rainfall between 1300 and 1750 mm ;
- transitor y equator ial climate (South) has abundant rainfall ranging betw een 1500 and 2500 mm /year ;
- mountain climate (W est) which has an annual rainfall
betw een 1500 and 2000 mm / year .
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Inte rnatio nal Jo urnal o f Sc ie ntific & Eng inee ring Re se arc h, Vo lume 3, Issue 2, February -2012 2
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Pettitt's test is to cut the main series of N elements into two sets at each time t betw een 1 and N-1. The main ser ies has a br eak at a time (T) given if the two subsets have differ ent distr ibutions.
For par ameters alr eady measur ed (rainfall, flow ...), this
method determines the per centage changes in these
variables after the ruptur e with the per iod befor e the r uptur e climate [5]. This method was applied to hydr o- climatic stations whose time ser ies has a r uptur e. Var iations in r ainfall and flow ar e obtained thr ough the following formula:
Change (Δ) = (average after rupture - average before rupture) /
average before breaking
Climate data used to character ize the curr ent climate change
come fr om the National Meteorology of Côte d'Ivoir e. These
x j 1
xi
(1)
data concer n pr ecipitations (Table 1) and temperatur es.
Hydr ometric data wer e pr ovided by the Department of
Hydr ology of Côte d'Ivoir e. These data ar e annual average of over flow for ten gauging stations in thr ee main basin of Côte d’Ivoir e (Bandama, Comoé, Sassandra) and the coastal basin of Agnéby (Table 2).
The climate model RegCM3 (Regional Climate Model ver sion 3) was used to assess the evolution of futur e cli mate. It is a r egional climate model developed by International
Cent er for Theor etical Physics [3]. It is capable of multiple fitments and includes thr ee components that ar e pr epr ocessing, pr ocessing and post-pr ocessing.
The model uses the following data:
- Physiogr aphic data such as topogr aphic data (elevation,
slope) of the USGS (United State Geological Sur vey) and the land cover of the GLCC (Global Land Cover Character ization) for the study ar ea;
- W eather data consist of r eanalysis data to initialize the
calculations. These include meteor ological data r espectively thermodynamic and dynamic var iables (temperatur e,
pr essur e, humidity and wind field hor izontal and vertical)
X j : average of the parameter on the per iod after the
r uptur e;
X i average of the parameter on the per iod befor e the r uptur e.
If Δ ≥ 0 then ther e is excess rainfall or flow ;
If Δ <0 then w e speak of low rainfall or flow .
RegCM3 climate model was used to simulate the temperatur e and pr ecipitation over thr ee per iods: a r efer ence period (1991-2000) and two hor izons (2031-2040 and 2091-2100). The simulation was carr ied out under the A1B emission scenario w ith 60 Km x 60 Km. spatial r esolution.
The amplitudes and r ates of changes in each horizon ar e
determined to find out how often the parameters decr eased or incr eased over the per iod.
The temperatur e variations ar e expr essed in °C and those of pr ecipitations in mm of water fell
of the continent part and the data of Sea Sur face
hor i
hor
X i
réf
X i
(2)
Temperatur e (SST).
With X i = monthly /annual average calculated on the hor izon determined
réf
X i = monthly/annual aver age calculated on the r efer ence
period,
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Inte rnatio nal Jo urnal o f Sc ie ntific & Eng inee ring Re se arc h, Vo lume 3, Issue 2, February -2012 3
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hor
i = monthly /annual var iations aver age of a given
hor izon.
The r ate of change in climatic parameters estimated ar e expr essed as a per centage and expr essed as:
Xhor Xr éf
Since the accession of the Côte d'Ivoir e to independence, the
pr omotion of agricultur e was at the base of the economic
r evival. Thus, the populations ar e r ushes on the for ests for the cultur e of coffee and cocoa.
hor
i
100 i i
r éf
Xi
(3)
This agr icultural policy r educed consider ably the for ests of
16 million hectar e to 3 million hectar es today.This
W ith X i = monthly /annual average calculated on each
hor izon,
X i = monthly /annual aver age calculated on the r efer ence period,
i = Rate var iations of a given hor izon.
Climate var iability in Cote d'Ivoir e is manifested by the fall of pr ecipitations following the appearance of ruptur e in rainfall series (Table 1). These r uptur es wer e held betw een
1963 and 1982. The rainfall deficits that have r esulted vary of
12% to 31%.
Flow s in main r iver s of Côte d'Ivoir e have been influenced by fluctuations in rainfall. Indeed, as pr ecipitations, the r uptur es in the hydr ological ser ies wer e detected betw een
1968 to 1979 per iod. Deficits calculated after r uptur es in
hydr ological ser ies on some basin ar e included between 31%
and 55% (Table 2).
agr icultural policy r educed considerably the for ests by 16 million hectar e to 3 million hectar es today. This situation exploited the r eheating of the atmospher e since the for ests constitute a significant carbon w ell.The follow-up of the annual temper atur es observed between 1960 and 2000 in various ar eas of Côte d'Ivoir e shows a continuous incr ease in this one (Fig. 2). It appears clear ly that the air b ecomes incr easingly hot in Côte d'Ivoir e. Indeed, betw een 1960 and
2000, the graphs show a r ise in the temper atur es of
approximately 1°C. This situation could be caused at the
same time by the r eduction in the local vegetable cover and by the w orld gas emissions for purpose of gr eenhouse of anthr opic or igin.
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Table 3 shows, by r eport the r efer ence per iod 1991 - 2000,
the evolution of annual cycle of temper atur es in Cote d'Ivoir e at 2031-2040 and 2091-2100 hor izonsThus, on the
2031- 2040 per iod, incr eases in monthly temperatur es could r ise fr om 0.41°C in March to 1.19°C in June w ith an annual average equal to 0.72°C. These incr eases in temperatur es become mor e significant at 2091- 2100 hor izon Indeed, at this hor izon, the annual incr ease temperatur e r eaches 3.57
°C. Ther efor e, monthly average changes may range fr om
2.55°C in October to 4.6°C in Apr il and December .
T1 : difference of temperatures between the reference period (1991-2000) and 2031-2040 horizon
T 2 : difference of temperatures between the reference period (1991-2000) and 2091-2100
horizon
Maps of Fig. 4 & 5 w er e also per formed to show the spatial variations of temper atur es expected for both hor izons. The follow ing observations can be dr awn fr om these maps .
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Indeed the r egions of South-w est and W est for med by the towns of San Pedr o, Man, and Guiglo and the North-east (Bouna will become the zones w ith str ong r ise in temperatur e w ith var iations ranging betw een 0,72 °C and 0,8
°C. In Nor th-w est (Odienné), North (Kor hogo) and finally
the south-est r egions, incr eases could fluctuate betw een 0.58
°C and 0.68 °C.
At the 2091-2100 hor izon, temperatur es could annually vary
of 3 °C t o 4.2 °C by r eport 1991-2000 per iod. But this variation is a function of thermal gradient occurs in continental and it appear s in par allel band with the low est values ar e in the South Seas and the highest ar e in the North.
Simulations carr ied out on pr ecipitations using the RegCM model allowed to obtain the r esult s which ar e consigned in table 6
The rates of var iations awaited of annual pr ecipitations shows a decr ease of the r ain in Côte d'Ivoir e of 2.5% and
4.9% r espectively on 2031-2040 and 2091-2100 hor izons.
How ever , specificities exist in the annual cycle. Indeed, the months of Mar ch and October w ill become w etter in Côte d'Ivoir e on 2031-2040 and 2091-2100 hor izons with r espective incr ease rates of 52.74% (98.41 mm) and 7.8% (14 mm) 52.74% (98.41 mm) 7.8% (14 mm). At the 2091-2100 hor izon, the incr ease r ates in pr ecipitations of Octob er and Mar ch pass to 69.04% (44.5 mm) and 22.2% (40 mm). Regar ding the other months, the gener al tendency of the rains is w ith the fall on the two hor izons especially the months of the rain season fr om April at September .
The map of fig. 6 & 7 shows the space evolution of the variations of the rainfall on the 2034 - 2040 and 2091 - 2100 hor izons. Two situations arise in the observation of this figur e: a downwar d or r ise tr end accor ding to localities. Indeed, the hor izon 2031-2040, most of the terr itory of the Côte d'Ivoir e could be under an annual pluviometric deficit fr om appr oximately 10%.
In the horizon 2091-2100, the deficits could be accentuated compar ed to the hor izon 2031-2040 w ith fall going up to
40%.
By r eport the per iod 2091-2100, what ar e the mountainous ar eas of w ester n and Agnibilekr ou, Abengour ou and that could become wetter with a sur plus of 10% to 20%. On the r est of the country, r ainfall is decr easing with deficits of up to 10% to 20%.
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The statistical tests applied to annual r ains ser ies allow ed to obser ve ruptur es between 1963 and 1982.
These r esults ar e consistent w ith studies conducted in W est
Afr ica [6, 7, 8]. Var iability of r ainfall also r esulted in significant r ainfall deficits r anging betw een 12 % and 31%. The str ong r eductions of rainfall ar e located primar ily in the for est (south) and the savanna (north).This str ong r eduction in pluviometry is caused by the massive destruction of the vegetable cover [9, 10, 11].
On basins of Côte d'Ivoir e, rainfall var iability involved a variability of flows mar ked by r uptur es betw een 1968 and
1979.
Hydrological deficits after ruptur es ar e important than
those of rainfall and vary betw een 31.4% and 55.4%. Our r esults agr ee with those of [7, 11, 10, 12] r ealized at the time
of similar studies. This high incidence of rainfall var iability on hydrology variability could be explained by the fact that ther e is an amplifying effect in flows due to the char acteristics of the basin: r unoff, infiltr ation, vegetation type, pr esence of gr oundwater .
Climate pr oj ections made in Côte d'Ivoir e show ed some expected impacts of climate change on temperatur es and pr ecipitations. The r esults showed an incr ease of
temperatur e var iations.
Accor ding to localities, incr eases in annual temperatur es ar e included betw een 0,5°C and 0,8°C at 2031-2040 hor izon and betw een 3°C and 4,2°C at 2091-2100 hor izon. The pr oj ections made on the temperatur es in Côte d'Ivoir e ar e in conformity with those envisaged by the IPCC [13, 14] (2007) which envisage thr ough climate models some incr eases in temperatur e of planet betw een 1.4°C and 5.8°C at 2100 hor izon.
Pr oj ections of r ainfall give a r eduction in annual r ainfall of
2.50% at the 2031-2040 horizon and 4.9% at the 2091-2100
hor izon. At the monthly and space scale, it appears either an
incr ease or decr eases in rainfall.
The rainfall incr eases or decr eases discussed in this study ar e imposed by the ther mal var iations of the equatorial Atlantic Ocean even if other for cings also seem to exist [15]. Accor ding [16, 17] some dominant modes of interannual variability of ocean ther mal fields ar e str ongly linked to climate changes in Afr ica. Accor ding to the studies conducted in Cote d'Ivoir e [18], an abnormal warming of sur face temperatur es of the Atlantic Ocean in its southern w est part involves decr eases in r ainfalls and causes a cooling of sur face temper atur es of the tr opica l Atlantic in the north
of the equator . This phenomenon is also at the or igin of the incr ease in pr ecipitations in certain countr ies of W est Africa as Côte d'Ivoir e.
Ther e is also that the space-time variations of the terr estrial envir onmental context modulate the mosaic of the r egional climates, in particular thr ough cycle of water and exchanges with the vegetable cover [19, 20].It is mainly about the continental pr ocesses of sur face thr ough desertification and degradation of soil pr operties [21, 22, 23].
This study pr esents the curr ent and futur e climate situation
of the Côte d'Ivoir e. Indeed, at the end of the study, it ar ises that climate var iability generated a decr eased of 12 to 31% of the r ainfalls and elevation of the temperatur e s ince the independence of the Côte d’Ivoir e. The r ainfall var iability caused a decr ease in also the mode of the rivers fr om 31 to
55%.W ith r egar d to the hor izons, pr oj ections show ed an incr ease in temper atur e of 3 to 4.5 C at the end of this
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century. The study also showed a continuous incr ease in the temperatur es since independence.
On the level of pr ecipitations, cer tain the climat e change does not have the same influence on the whole of the terr itory. Certain zones will under go incr eases wher eas in other , the rains could dr op.
Us Côte d’Ivoir e has an agr icultural vocation , this study
makes it possible to draw the attention of the leaders in
or der to take appr opriate measur es of adaptation to the climat e change. Fr om now on, the use of r esour ces water must be made in a rational w ay.
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