Changes to flow regime on the Niger River at Koulikoro under a changing climate

Abstract

A significant decrease in mean river flow as well as shifts in flood regimes have been reported at several locations along the River Niger. These changes are the combined effect of persistent droughts, damming and increased consumption of water. Moreover, it is believed that climate change will impact on the hydrological regime of the river in the next decades and exacerbate existing problems. While decision makers and stakeholders are aware of these issues, it is hard for them to figure out what actions should be taken without a quantitative estimate of future changes. In this paper, a Soil and Water Assessment Tool (SWAT) model of the Niger River watershed at Koulikoro was successfully calibrated, then forced with the climate time series of variable length generated by nine regional climate models (RCMs) from the AMMA-ENSEMBLES experiment. The RCMs were run under the SRES A1B emissions scenario. A combination of quantile-quantile transformation and nearestneighbour search was used to correct biases in the distributions of RCM outputs. Streamflow time series were generated for the 2026-2050 period (all nine RCMs), and for the 2051-2075 and 2076-2100 periods (three out of nine RCMs) based on the availability of RCM simulations. It was found that the quantile-quantile transformation improved the simulation of both precipitation extremes and ratio of monthly dry days/wet days. All RCMs predicted an increase in temperature and solar radiation, and a decrease in average annual relative humidity in all three future periods relative to the 1981-1989 period, but there was no consensus among them about the direction of change of annual average wind speed, precipitation and streamflow. When all model projections were averaged, mean annual precipitation was projected to decrease, while the total precipitation in the flood season (August, September, October) increased, driving the mean annual flow up by 6.9% (2026-2050), 0.9% (2051-2075) and 5.6% (2076-2100). A t-test showed that changes in multi-model annual mean flow and annual maximum monthly flow between all four periods were not statistically significant at the 95% confidence level.

Future Climate Change Impacts on Streamflows of Two Main West Africa River Basins: Senegal and Gambia

“…These results confirm that streamflow is vastly sensitive to both temperature and rainfall [46]. However, these results are not in agreement with the finding of Angelina et al [20] who showed an increase of mean annual flow of the Niger river basin at Koulikoro by 6.9% (2026-2050), 0.9% (2051-2075), and 5.6% (2076-2100) by using a SWAT model under the SRES A1B emissions scenario. Additionally, Azari et al [12] showed an increase in stream-flow under RCP4.5 and RCP8.5 in the Gorganroud River basin in the North of Iran.…”

“…Yet, the use of the bias correction generally has the inconvenience of not taking into account the different physical laws that govern the atmosphere [53]. However, Angelina et al [20] showed that the quantile-quantile transformation can improve the simulation of extreme values. It is also necessary to take into account difficulties associated with the transfer of the parameters of the hydrological model on periods other than those where the model was calibrated.…”

“…In this research we have not applied a specific approach to select the climatic models. We just used the most familiar model utilized in West Africa [20]. This fact could be one of the limits of our methodology.…”

Spatial Extent of Future Changes in the Hydrologic Cycle Components in Ganga Basin using Ranked CORDEX RCMs

“…The study of potential impacts of future climate change on water resources, as a way to recognize suitable mitigation and adaptation strategies holds utmost importance. There are many observations supporting the evidence of climate change, such as frequent occurrences of climatic extremes, rising sea level and diminishing snow packs (Amadou et al, 2014;Githui et al, 2009;Shamir et al, 2015;Yu et al, 2002). Since the climate and hydrologic cycle is inter linked, variability in climate is 15 expected to alter both the timings and magnitudes of surface runoff.…”

“…In recent decades, an indubitable relation between the climate change and water resources together with the potential impacts of climatic change on water resources and hydrology has gained considerable attention in hydrologic research community (Abbaspour et al, 10 2009;Akhtar et al, 2008;Amadou et al, 2014;Gardner, 2009). The study of potential impacts of future climate change on water resources, as a way to recognize suitable mitigation and adaptation strategies holds utmost importance.…”