The impact of climate change on precipitation and water availability is of
major concern for policy makers in the Mono Basin of West Africa, whose
economy mainly depends on rainfed agriculture and hydropower generation. The
objective of this study is to project rainfall, flows and evapotranspiration
(ET) in the future period and understand their changes across Mono River
Basin. Observed data were considered for the historical period 1980–2010,
and a Multi-model ensemble for future projections data of eight selected
Regional Climate Models under RCP 4.5 and RCP 8.5 over the periods 2011–2100
was used. The GR4J model was used to simulate daily flows of the Mono
watershed. The ensemble mean shows a decrease and increase streamflows
between
The future projection of climate change reported by the 5th
Intergovernmental Panel on Climate Change (IPCC) assessment indicated that
the global mean temperature will continue to rise for the rest of 21th
century, and the amplitude for 2081–2100, relative to 1986–2005 ranges
from 0.3 to 4.8
The impact of climate change on precipitation and water availability is of major concern for policy makers in the Mono Basin of West Africa. In order to proffer solutions to the problems associated with water resources management within the Mono, there is a need to understand the relationship between these variables at the basin's scale.
The aim of this work is to project the rainfall, flows and ET in the future period and understand their changes.
This study area has already been described by certain authors
(Batablinlè et al., 2018; Ernest et al., 2014). The Mono river basin is
in West Africa and extends over 560 km from the north to the south. This
transboundary watershed covers 15 680 km
Within the West African context, rainfall in the study area is characterized
by two types of Rainfall regimes In southern basin, (from 6
Study area location and considered stations (sources Batablinlè et al., 2018).
Two sources of data have been used in this paper. The first one is CORDEX
program. Models
GR is a family of lumped hydrological models designed for flow simulation at various time steps. The models are now available in a flexible two main R-packages called airGR. The GR4J model has been extensively tested in a large number of watersheds in France, Australia, Brazil (Perrin et al., 2001). It has been used in a context of climatic variability in the Upper Ouémé basin (Ague et al., 2014). The GR4J model was used to simulate daily flow of the Mono watershed. The model parameters were calibrated and validated on a daily scale with respect to the hydro-meteorological inputs observed from 1971 to 1987 and from 1988 to 2010, respectively. These sub-periods are homogeneous and belong to the dry or wet sequence obtained after the analysis of the stationarity break in the rainfall and flow chronicles. Statistical analyses produced Nash-Sutcliffe efficiencies (NSEs) of 0.76 and 0.61 for model calibration and validation, respectively, which were considered acceptable.
The changes from the reference period are assessed as shown by Eq. (1)
for ET, rainfall or flow :
Sensitivity analysis is used to determine the influence of two main climatic variables on future flows. The daily average variables used in this study are: Future precipitation and evapotranspiration (ET). Flows sensitivity to climate variables was estimated by varying each variable individually, leaving the other variables constant.
A sensitivity coefficient (Eq. 2) was calculated to determine the degree of
influence of each climate variable on the flow:
The free software R was used to compute all the statistical parameters such as the seasonal averages as well as the annual averages and all plots presented.
The changes relating to the evapotranspiration (ET) and rainfall between
the future and the historical period are shown in Fig. 2. Under the RCP4.5
scenario, an increase in ET is projected by the mean-models that can
fluctuate from 20 % to 45 % on average in some areas in the south. This
projection varies from 5 % to 38 % northward and from 5 % to 10 % in the
basin center. On this same projection period and under the scenario RCP8.5,
the mean-model also predicts also a strong increase in ET the southward of
the basin ranging from 10 % to 45 % against 3 % to 40 % and 5 % to 15 % the
northward and the center, respectively (Fig. 2 to the left). If we
consider the seasonal change (over the same projection period), under the
RCP8.5 scenario, the mean-models predicts a decrease in rainfall from
Spatial projected changes in ET (to the left, panel
The changes relating to the streamflows between the future and the
historical period are calculated. Regarding the results of relative changes
for monthly streamflows (figure is not represented), the lowest decrease is
Figure 3 depicts relative changes of Annual and seasonal streamflows (the near future and the far future were considered). Regarding these results, the streamflows (MAM and JJA) for the time period 2011–2040 (the near future) will increase between 2 % and 50.3 % under the RCP4.5 scenario and 12 % and 55 % under the RCP8.5 scenario while the streamflows (DJF, SON and An) will decrease between 10 % and 49 % under the RCP4.5 scenario and between 4 % and 56 % under the RCP8.5 scenario, respectively. In summary, mean models used have announced in general, a decrease of the streamflows over Mono basin (Fig. 3) for the time period 2071–2100 (the far future) for the both scenarios. Monthly streamflows characteristics reflect the monthly changes in rainfall characteristics: A shift towards the rainy season (particularly, Murch to July) and a decrease in the dry months (particularly, November to April) are observed for all climate scenarios in Mono basin.
Annual and seasonal changes in streamflows between the futures (2011–2040 in top and 2071–2100 in below) and the historical period (1981–2010) for the average multi-models forced by RCP4.5 and RCP8.5 greenhouse gas scenarios in Mono Basin.
Figure 4 (to the right) presents the low (Q95) and high (Q05) flows
magnitudes for the baseline period and the percent change in the future. The
Q95 and Q05 here were computed based on the streamflows mean for the multi
model ensemble. The relative mean changes of high flow (Q5), low flows (Q95)
under two RCPs in the future are presented in Fig. 4. Simulations using the
RCP4.5 scenario indicate more moderate changes to streamflows (Q5 and Q95),
whereas the RCP8.5 climate scenarios project larger changes. Under both
RCPs, decreases in general of Q5, and Q95, are projected in all three future
sub periods (A
The relative mean changes of Q5 and Q95 under two RCPs (RCP4.5 and
RCP8.5) in the future (A
Figure 4 (to the left) shows the relationship between future flows and two
main climatic variables. The results show that future rainfall will have a
positive influence on future flows. Indeed, the increase of this variable
leads to an increase in futures flows. On the other hand, an increase in
future evapotranspiration leads to a decrease in future flows. For
example, at annual scale, an increase of 0 % to 30 % of the rainfall
leads to an increase in flows from 1 to 5 m
The ET and rainfall are an important climate variables that directs the change in flows. Evapotranspiration is the highest outgoing water flux in the hydrological cycle and is of vital importance in assessing the effects of climate change in water availability. Allen et al. (1998) show, Evapotranspiration changes, on their own or in combination with rainfall changes, can contribute to changes in hydrological indices such as mean monthly river flows. Our study predicts an increase of ET while the rainfall will decrease over Mono basin. Simulations of future streamflows in the Mono River project lowest increases and highest decreases of streamflows.
This can have a negative effect on future water availability in the area. the energy use is also dependent on water resources, and the availability and reliability of renewable sources are function of climate conditions, which can vary according to global climate changes. A possible and expressive loss in electricity production capacity could bring serious social and economic risks to the country. It was also observed that the impact of rainfall reduction in flow production in the Mono Basin will be accentuated. Similar to previous studies in other region, results showed that the evapotranspiration is in?uenced, to a large extent, by precipitation (Liu et al., 2008). Morocco and Algeria appear to show an increase in ETref and a decrease in precipitation for future periods, meaning that water stress will become an even more severe problem in these countries in the future (TERINK et al., 2013). Jung et al. (2010) also found that the deficit of available water resources would lead to a negative global land surface evapotranspiration trend. Furthermore, a significant decrease in water availability (surface water and groundwater) due to a decrease in rainfall showed by Giertz and Diekkrüger (2003) will exacerbate following the scenario RCP8.5. Our work shows that such a change diagnosed on the present climate is likely to persist of more and more in the future. The decrease of the rainfall in the Mono basin appears to be consistent with the evolution of the ETP because a sharp increase in ETP could favor a decrease in the rainfall.
This study evaluated changes in climatic variables including precipitation,
flows and evaporation due to climate change over the Mono basin in west
Africa in the future periods (2011–2100) using regional climate models under
middle and highest emission scenarios (i.e., RCP4.5 and RCP8.5). The
rainfall, flows and evaporation over the historical period 1980–2010 have
been analyzed at seasonal scales and interannual scales. The key findings of
this study are summarized below:
Compared to the base period, Simulations of future streamflows in the Mono
River project lowest increases and highest decreases of streamflows. It
predict an increase of ET while the rainfall will decrease. The results of the Sensitivity of flows to climatic variables shows that
there will be impacts on water availability from climate change, reducing
the streamflows in the studied area. These results can serve as a basis for the implementation of prevention and
water resource management strategies in the Mono catchment.
The software R is freely available (
All data can be accessed via the references: Models data have been used in this study. It is a set of eight climatic models outputs with daily time step and spatial resolution of
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All authors developed the main research idea. LB, LEA and KDJ performed the analyses and evaluated the stress tests. LB wrote the manuscript with contributions and revisions from all authors.
The contact author has declared that neither they nor their co-authors have any competing interests.
Publisher’s note: Copernicus Publications remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
This article is part of the special issue “Hydrology of Large River Basins of Africa”. It is a result of the 4th International Conference on the ”Hydrology of the Great Rivers of Africa”, Cotonou, Benin, 13–20 November 2021.
All my gratitude to the International Association of Hydrological Sciences and local organizers who gave me financial support and took charge of my participation in 4th International Conference on the “Hydrology of the Great Rivers of Africa”, Cotonou, Benin. We are also grateful to the anonymous reviewers whose thoughtful and constructive comments have improved the quality of the article.
This research has been supported by the International Association of Hydrological Sciences (grant no. 13 SYSTA).