388
A. Amani et al.
with higher resolution to provide near-real-time water levels, as well as short-term
forecast of flood risks, as well as medium-term forecasts of drought hazards and longterm projections of climate change impacts. Preliminary results are very encouraging;
the system will continue to be updated, tested and validated to enable its operational
use by decision-makers at all levels.
Keywords Flood · Drought risk management · Early warning · Medium-term
forecasts · Long-term projections · Lake chad · Climate variability
1 Introduction
Lake Chad and its basin are located in the eastern Sahel Region on the southern edge
of the Sahara Desert. It is a vast resource of freshwater shared by Cameroon, The
Central African Republic, Chad, Niger, Nigeria and Libya. The average depth is only
1.5 m, making it a shallow lake with a relatively low volume of water and therefore
extremely sensitive to any variation of its inflows. The hydrological regime of the
lake and related basin, which constitutes the largest surface water input, is influenced
by rainfall patterns in the wet tropics and equatorial southern regions of the basin
(Leblanc et al. 2011). Ninety-five percent of the lake’s water supply depends mainly
on the Chari-Logone River System flowing from the Adamawa Plateau and draining
from the Central African Republic, Cameroon and Chad, while the Komadugu-Yobe
River and its tributaries draining from Nigeria and Niger provide less than 2.5% of
the lake’s water. The remaining water comes from direct precipitation falling on the
lake (LCBC 1998). Therefore, any variation of the discharge of the Chari-Logone
and other tributaries has a direct impact on the volume and area of the lake. The most
distinctive feature of Lake Chad is its water volume variability.
The lake has experienced a long history of wet and dry periods over geological, annual and seasonal time scales. Observed droughts in the Sahel Region and
within the basin after the 1970s had great impact on lake discharges of the different
tributaries, particularly the Chari-Logone ensemble. These droughts led to a drastic
decrease in the amount of freshwater available in the lake basin; as a consequence, the
hydrology of the lake has experienced progressive and extensive change over the last
50 years (Lemoalle et al. 2012; L’Hôte et al. 2002). The lake area has varied between
2,500 km
2 and 25,000 km
2 during this period, with significant consequences for the
livelihoods of the millions of people dependent on the resources of the lake and its
basin. Policelli et al. (2018) observed that despite various evidence of changing lake
size, an updated time series of the lake’s total surface water area does not exist except
for 1986–2001, which was derived from thermal remote sensing (Leblanc et al. 2011).
However, the EU Joint Research Center Global Surface Water Dataset (Pekel et al.
2016) provides data for the 32 years from March 1984 to October 2015 based on
the Landsat archive that could provide a new understanding of the spatio-temporal
variability of inundation in Lake Chad.
A. Amani et al.
with higher resolution to provide near-real-time water levels, as well as short-term
forecast of flood risks, as well as medium-term forecasts of drought hazards and longterm projections of climate change impacts. Preliminary results are very encouraging;
the system will continue to be updated, tested and validated to enable its operational
use by decision-makers at all levels.
Keywords Flood · Drought risk management · Early warning · Medium-term
forecasts · Long-term projections · Lake chad · Climate variability
1 Introduction
Lake Chad and its basin are located in the eastern Sahel Region on the southern edge
of the Sahara Desert. It is a vast resource of freshwater shared by Cameroon, The
Central African Republic, Chad, Niger, Nigeria and Libya. The average depth is only
1.5 m, making it a shallow lake with a relatively low volume of water and therefore
extremely sensitive to any variation of its inflows. The hydrological regime of the
lake and related basin, which constitutes the largest surface water input, is influenced
by rainfall patterns in the wet tropics and equatorial southern regions of the basin
(Leblanc et al. 2011). Ninety-five percent of the lake’s water supply depends mainly
on the Chari-Logone River System flowing from the Adamawa Plateau and draining
from the Central African Republic, Cameroon and Chad, while the Komadugu-Yobe
River and its tributaries draining from Nigeria and Niger provide less than 2.5% of
the lake’s water. The remaining water comes from direct precipitation falling on the
lake (LCBC 1998). Therefore, any variation of the discharge of the Chari-Logone
and other tributaries has a direct impact on the volume and area of the lake. The most
distinctive feature of Lake Chad is its water volume variability.
The lake has experienced a long history of wet and dry periods over geological, annual and seasonal time scales. Observed droughts in the Sahel Region and
within the basin after the 1970s had great impact on lake discharges of the different
tributaries, particularly the Chari-Logone ensemble. These droughts led to a drastic
decrease in the amount of freshwater available in the lake basin; as a consequence, the
hydrology of the lake has experienced progressive and extensive change over the last
50 years (Lemoalle et al. 2012; L’Hôte et al. 2002). The lake area has varied between
2,500 km
2 and 25,000 km
2 during this period, with significant consequences for the
livelihoods of the millions of people dependent on the resources of the lake and its
basin. Policelli et al. (2018) observed that despite various evidence of changing lake
size, an updated time series of the lake’s total surface water area does not exist except
for 1986–2001, which was derived from thermal remote sensing (Leblanc et al. 2011).
However, the EU Joint Research Center Global Surface Water Dataset (Pekel et al.
2016) provides data for the 32 years from March 1984 to October 2015 based on
the Landsat archive that could provide a new understanding of the spatio-temporal
variability of inundation in Lake Chad.