72
P. Sagna et al.
In Senegal, the impact of the rainfall deficit on groundwater resources has been
greatest on the northern coast (the Niayes) where almost all of the country’s truck
farms are located. In this location, decreases in groundwater levels occurred mainly
in the 1970s and 1980s (Aguiar et al. 2010; Sambou 2015): the droughts of the 1970s
and 1980s caused the groundwater level to decrease from 50 to 22 m between 1958
and 1984 (Aguiar et al. 2010). Malou (2004) noted that this was the most severe
documented drying trend of groundwater reserve. During the droughts, groundwater
recharge was very low (Dasylva and Cosandey 2005). Moreover, the drop was exacerbated by losses through evapotranspiration. On the horst of Ndiass (far south of the
northern coast), the fall in groundwater levels, over the last 25 years, caused mainly
by human activity, varied from 20 to 25 m (MEPN 2005).
The combination of declining rainfall, increased temperature (evaporation and
evapotranspiration), the intensity of showers (which favors runoff to infiltration),
and the multiple human uses of water result in scarce resources and low groundwater levels globally. The drying up of wells in many villages is evidence of this
phenomenon.
3.3 Impacts of Rainfall Variation on Socioeconomic Activities
Rainfall variability has repercussions for farming, grazing, and fishing in West Africa.
Impacts vary from one crop to another and by region.
3.3.1 Impacts of Rainfall Variations on Farming
In Ivory Coast, farmers mainly plant two types of crops: cocoa, a perennial crop
grown in the southern forest area, and yams, a food crop grown in the central and
northern savannah. Dependence on rainwater for these crops correlates to coefficients
of 0.88 for cocoa production and 0.75 for yams. In general, the long rainy season is
decreasing, with recorded drops from six to four months. During half of the years
in deficit, the water requirement of cocoa trees was not met during the long rainy
season. This prolonged water stress resulted in the death of both young and adult
plants, which in turn led to a decline in the production of butter from cocoa beans.
In recent decades, yam production was also negatively affected by irregular rainfall.
Among the farmers surveyed, about 55% marketed part of their production. However,
they unanimously acknowledged that their incomes from yam production had not
met their needs for years because few farmers earned more than Euros 152.
In Benin, corn is the main food crop in the South. In Couffo, the rainwater excess,
especially in 2007–2008, caused loss of part of the corn harvest. In low-lying areas,
some farmers lost all of their crops (Houssou-Goé 2008). In the Ouémé basin, cotton,
groundnut, and sorghum are predicted to grow better with the reduction in the length
of the cropping season forecast for the 2030 horizon. On the other hand, crops
vulnerable to drought, like cassava, yam, corn, and rice, will be negatively impacted.
P. Sagna et al.
In Senegal, the impact of the rainfall deficit on groundwater resources has been
greatest on the northern coast (the Niayes) where almost all of the country’s truck
farms are located. In this location, decreases in groundwater levels occurred mainly
in the 1970s and 1980s (Aguiar et al. 2010; Sambou 2015): the droughts of the 1970s
and 1980s caused the groundwater level to decrease from 50 to 22 m between 1958
and 1984 (Aguiar et al. 2010). Malou (2004) noted that this was the most severe
documented drying trend of groundwater reserve. During the droughts, groundwater
recharge was very low (Dasylva and Cosandey 2005). Moreover, the drop was exacerbated by losses through evapotranspiration. On the horst of Ndiass (far south of the
northern coast), the fall in groundwater levels, over the last 25 years, caused mainly
by human activity, varied from 20 to 25 m (MEPN 2005).
The combination of declining rainfall, increased temperature (evaporation and
evapotranspiration), the intensity of showers (which favors runoff to infiltration),
and the multiple human uses of water result in scarce resources and low groundwater levels globally. The drying up of wells in many villages is evidence of this
phenomenon.
3.3 Impacts of Rainfall Variation on Socioeconomic Activities
Rainfall variability has repercussions for farming, grazing, and fishing in West Africa.
Impacts vary from one crop to another and by region.
3.3.1 Impacts of Rainfall Variations on Farming
In Ivory Coast, farmers mainly plant two types of crops: cocoa, a perennial crop
grown in the southern forest area, and yams, a food crop grown in the central and
northern savannah. Dependence on rainwater for these crops correlates to coefficients
of 0.88 for cocoa production and 0.75 for yams. In general, the long rainy season is
decreasing, with recorded drops from six to four months. During half of the years
in deficit, the water requirement of cocoa trees was not met during the long rainy
season. This prolonged water stress resulted in the death of both young and adult
plants, which in turn led to a decline in the production of butter from cocoa beans.
In recent decades, yam production was also negatively affected by irregular rainfall.
Among the farmers surveyed, about 55% marketed part of their production. However,
they unanimously acknowledged that their incomes from yam production had not
met their needs for years because few farmers earned more than Euros 152.
In Benin, corn is the main food crop in the South. In Couffo, the rainwater excess,
especially in 2007–2008, caused loss of part of the corn harvest. In low-lying areas,
some farmers lost all of their crops (Houssou-Goé 2008). In the Ouémé basin, cotton,
groundnut, and sorghum are predicted to grow better with the reduction in the length
of the cropping season forecast for the 2030 horizon. On the other hand, crops
vulnerable to drought, like cassava, yam, corn, and rice, will be negatively impacted.