Environmental Impact of Dams on the Nile (Part 2)

 Following on from the background information detailed in the previous post, the details associated with the combination of climate variability and the implementation of the GERD project on the Nile can be explored. These details are primarily sourced from the investigative report by Eldardiry and Hossain, where different climate and dam scenarios were computed against a 'baseline' or 'status quo' in order to determine the changes the flow regime and hydrological impacts along the Nile (Eldardiry & Hossain, 2020). 

Figure 1: Plot 'a' shows the monthly evapotranspiration (ET) along the upper Nile, 'b' shows the monthly release volume of the HAD system and 'c' shows the monthly water stress along the upper Nile.

The plots in figure 1 clearly show that during the summer months, the HAD release volume increases alongside the ET rates thereby decreasing the water stress in the region and irrigating the Nile Delta. During this period of the year it is crucial to maintain flow volumes otherwise large scale drought is likely to occur. Since the GERD controls 53% of the water that feeds the HAD, if the GERD is filled in too short of a time period, this is likely to create serious environmental and subsequent economic issues downstream. This is shown in figures 2 and 3.

Figure 2: Comparison of the HAD water level under the 3 and 7 year filling scenarios for the GERD. The water stress level used is slightly higher, indicating a more variable climate along the Upper Nile. The blue lines indicate the average level, and red lines indicate linear regression. The thick lines are levels computer for high initial water level and the thin lines are levels computed for low initial water level.

Figure 3: Comparison of HAD release volumes during the course of the hydrological year. The different lines represent different filling scenarios alongside different climactic scenarios.

Figures 2 and 3 clearly show that if the GERD filling is mis-managed, there will be a serious deficit of water inflow into the HAD system, thereby decreasing the water availability along the lower Nile. If the GERD is filled in an abrupt 3-year period, the volume of flow from the Blue Nile into the HAD will decrease by 30%, creating a 16% deficit in total flow into the HAD and lower Nile (Wheeler et al, 2016).

This will cause significant water stresses in the Nile Delta, and is highly likely to create wide-scale environmental change such as salinisation, desertification and possible crop yield reductions. Worst case scenarios could see crop failures although it is important to note the probability of this outcome is very low even if the GERD filling is not managed adequately (Wheeler et al, 2018).

Figure 2 shows that under both climactic scenarios, if the GERD is filled in a 7 year period, the likelihood of significant change in the HAD water level beyond the seasonal variation will be minimal, in contrast to a 3 year filling period. Similar effects are seen in figure 3 which also details the decrease in seasonal variation in the HAD release volume under improper filling scenarios for the GERD. If the GERD is filled in 7 years, the HAD release volume will decrease slightly but recover to normal levels within 2 years of the GERD being operational, whereas if the GERD is filled in 3 years the HAD release volume will experience drastic decreases and only recover to normal levels after 7 years (Eldardiry & Hossain, 2020).

The interactions between the HAD and GERD systems highlights the trade-off and cost-benefit analysis that is required to produce effective and properly managed hydrological projects that appropriately accounts for the economic, social and environmental variables involved.