Desertification in the Sahel: climatic or human driven causes?

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Desertification in the Sahel:

climatic or human driven

causes?

Pierre OZER1 _{and André OZER}2

1 _{Environment Science & Management Dpt.,}_{pozer@ulg.ac.be} 2 _{Dpt. of Geography,}_{aozer@ulg.ac.be}

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Archeological sites and lake deposits (8000 B.P.)

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Introduction

Desertification is land degradation in arid, semi-arid

and dry sub-humid areas resulting from various

factors, including climatic variations and human

activities. (UNCCD)

Desertification is taking place due to population

pressure, socioeconomic and policy factors which

lead to overgrazing, deforestation and poor

agricultural practices. In addition, rainfall shortages

enhance degradation in the fragile drylands

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Focus on the Sahel

150 mm

700 mm

Hyper-arid climate Arid &

semi-arid climate Dry subhumid

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OZER et al., in press 250 350 450 550 650 750 1921 1931 1941 1951 1961 1971 1981 1991 2001 P lu v io m ét ri e a n n u el le ( m m ) . Pluviométrie annuelle Moyenne centrée [9 ans] Moyenne 1921-1967 Moyenne 1968-2004 Moyenne 1968-1987 Moyenne 1994-2004 Sahelian rainfall (1921 – 2004) Rainfall abrupt change in 1968 108 mm 1921-1968 1969-1987 1988-2004

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Drought…

In 1963, the size of Lake Chad was about 23500 km

2

_.

After over 30 years of rainfall shortages (2000), its

area was reduced to 1355 km

2

.

2000 1963

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Drought… How large is the problem?

NIGER

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Drought… How large is the problem?

300 mm

limit for agriculture (millet)

NIGER

Isohyets moved southwards by up to 200 km !

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Drought…

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Held et al., 2005

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Held et al., 2005

Will it rain tomorrow ?

« Short-term » dramatic drought (early 1980s)

« Long-term » structural rainfall shortages (from ~~ 2050s ?)

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Human activities

Who’s with me ???

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Human population in the Sahel (1950 – 2005) and projections 0 60 120 180 240 1950 1960 1970 1980 1990 2000 2010 2020 2030 2040 2050 P o p u la ti o n ( m il li o n s) . _1950-2005 Low variant Medium variant High variant After UNPP, 2007 16 193 35 64

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… agricultural overexploitation Maradi, Niger, ~500 mm

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… overgrazing

Zinder area, Niger, ~400 mm

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… overgrazing

Zinder area, Niger, ~400 mm

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…forest resources reduction for … local use Zinder area, Niger, ~400 mm

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Increasing population leads to…

…forest resources reduction to feed enlarging cities in fuelwood Zinder area, Niger, ~400 mm

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0 50 100 150 200 250 300 350 400 450 500 1961 1966 1971 1976 1981 1986 1991 1996 2001 2006 YEARS T R E N D S ( 1 9 6 1 = 1 0 0 ) . POPULATION

CULTIVATED AREAS (MILLET) YIELDS (MILLET)

LIVESTOCK ROUNDWOOD

Human pressure trends in the Sahel (1961 – 2007) (1961 = 100)

DEFORESTATION

OVERGRAZING AGRICULTURAL

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0 50 100 150 200 250 300 350 400 450 500 1961 1966 1971 1976 1981 1986 1991 1996 2001 2006 YEARS T R E N D S ( 1 9 6 1 = 1 0 0 ) . POPULATION

CULTIVATED AREAS (MILLET) YIELDS (MILLET)

LIVESTOCK ROUNDWOOD

Human pressure trends in the Sahel (1961 – 2007) (1961 = 100)

DEFORESTATION

OVERGRAZING AGRICULTURAL

PRESSURE

INCREASING GAP BETWEEN POPULATION INCREASE AND FOOD PRODUCTION !!!

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Urban population trends in the Sahel (1961 – 2005) (1961 = 100) 0 500 1000 1500 2000 2500 3000 3500 1961 1966 1971 1976 1981 1986 1991 1996 2001 YEARS T R E N D S ( 1 9 6 1 = 1 0 0 ) . Mauritania Senegal SAHEL

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Geomorphological

consequences

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…sand movement threatening infrastructures… Gouré area, Niger, ~300 mm

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…soil erosion witnessed by tree roots… Gouré area, Niger, ~300 mm

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…sand movement threatening roads… Gouré area, Niger, ~300 mm

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…sand movement impacting roads… Gouré area, Niger, ~300 mm

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…totally degraded soils (sand sea)… Maine-Soroa area, Niger, ~400 mm

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…sand dunes movement threatening oasis… Maine-Soroa area, Niger, ~400 mm

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…sand dunes movement threatening oasis… Maine-Soroa area, Niger, ~400 mm

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Dust storm distribution during the dry

season in the Sahel

« Humid » period 1951-1968

« Recent » period 1987-1997

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Evolution of the number of days affected

by dust storms during the dry season

(Tombouctou, Mali, 1930-1997)

-10 10 30 50 70 90 110 1 9 3 0 1 9 3 3 1 9 3 6 1 9 3 9 1 9 4 2 1 9 4 5 1 9 4 8 1 9 5 1 1 9 5 4 1 9 5 7 1 9 6 0 1 9 6 3 1 9 6 6 1 9 6 9 1 9 7 2 1 9 7 5 1 9 7 8 1 9 8 1 1 9 8 4 1 9 8 7 1 9 9 0 1 9 9 3 1 9 9 6 J o u rs d e v is ib il it é < 5 0 0 d a m

Jours visi <500 dam

Moyenne lissée 5 ans

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ERS 1/2 SAR (07/08.12.1995) – Interférométrie – Image de cohérence (Aleg – Mauritanie)

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Evolution of the landscape in the

Makaortchi-Gayi region (S-E Niger)

Stable soils Moving dunes Vegetation Quartzite soils Delta Delta 0.2% 0.24% 0.56% 23% 14% 6% Moving dunes 8% 14% 36% Vegetation 1987 1975 1957-1958

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So…

Desertification

in the Sahel in

the near future ?

Current rainfall Expected rainfall 0 60 120 180 240 P o p u la ti o n ( m il li o n s) . _1950-2005 Low variant Medium variant High variant Expected population Current population

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