The announcement followed meetings held on the sidelines of the African Union summit in Addis Ababa earlier this year, which was attended by leaders from across the continent. Information leaked after that meeting, and not denied by any of the governments involved, suggested that the three countries had agreed some technical details on how the reservoir that sits alongside the dam would be filled.
They agreed to fill Renaissance Dam Lake with 45 billion cubic meters of water over three years, so at a rate of 15 billion cubic meters annually. This means that as the upstream country, Ethiopia will keep 15 billion cubic metres to fill the lake, and the same volume will then be deducted from the water quotas of Egypt and Sudan.
But there are still some unanswered questions. What follows the filling of the first 45 billion cubic meters? When will the reservoir be at its full capacity of 75 billion cubic meters? How much water overall will be deducted from each of Egypt and Sudan’s shares?
I predict that three years after keeping the water in the reservoir, Ethiopia will start pumping it into turbines to generate electricity, and so drain this reservoir within one year. This volume of water is almost the same amount that Egypt and Sudan used to receive each year from the Blue Nile before the dam was built — at most 48.75 billion cubic meters — but in that scenario, the two downstream countries will receive it every three years instead of annually.
In addition, Egypt and Sudan would receive only half of this amount during the first three years of filling the Renaissance Dam Lake — which will then become an endless cycle of three-year refills of 45 billion cubic meters, and a permanent deduction of 15 billion cubic meters on an annual basis from the two countries’ quota.
This is apart from water losses as a result of evaporation from the lake, deep runoff, and water lost while falling from height to run the turbines — all of which experts estimate amount to around 12 billion cubic meters annually.
Let's look more closely at what is likely to happen with water in the three countries, and how things might change after the Renaissance Dam starts to operate.
Agricultural impact in EgyptThe Blue Nile is the main tributary of the river Nile, and it’s where the Renaissance dam is built. The tributary’s flooding cycle is such that seven ‘lean’ years of drought, with light floods, are followed by ‘fat’ years of heavy flooding.
For years, Egypt held back water in the High Dam reservoir during the periods of heavy flooding in order to reuse it during the ‘lean’ years. But now, after construction of the Renaissance dam, Ethiopia needs to fill its reservoir during both high- and low-flood years in order to sustain the production of electricity from the dam.
This leaves Egypt at a disadvantage: it might no longer be able to save more water in the High dam reservoir, which means that during periods of low flooding it will suffer from not having this extra water to draw from, as well as from the agreed cuts in its share as Ethiopia keeps filling the Renaissance dam reservoir.
The Blue Nile accounts for about 60 per cent of the total water in the River Nile — in essence, it controls the Nile’s water flow. Another tributary, the Atbara River which also carries a substantial amount of flood waters, is where Ethiopia’s Tekezé Dam has been built.
Ethiopia will now have sole rights to the flood water from both tributaries in order to guarantee that the dam lake will be filled. And it has not responded yet to Egypt’s concerns about the fate of water flow during the years of low flooding.
Will the priority be to store the scarce water behind the Ethiopian dam to generate electricity, or to pump it towards thirsty people in Egypt and Sudan?
Water problems in the region are being passed along to the years and generations to come
The result will be that Egypt will be forced to change its agricultural policy to deal with the scarcity of its water resources by cutting off rice cultivation. It has already reduced it by about 35 per cent this year, and a law approved by the parliament last April spells imprisonment and big fines for farmers who breach the rules. Half of the country’s rice supply will need to be imported, which — at the current consumption rates of four million tonnes — will amount to spending one billion dollars annually.
Egypt will also move its sugar cane plantations from Upper Egypt to cultivate sugar beet in the north of the country, adding to the suffering of poor people in Upper Egypt whose children already migrate to the north due to lack of employment opportunities. Sugar cane plantations come with 27 complementary industries in Upper Egypt, such as the production of methanol, molasses, rock candy, white vinegar and others. Without these industries unemployment rates will increase, adding to the loss of 150 years of experience in sugarcane farming.
Water-depleting banana plantations will also need to be reduced at least by half. Perhaps the same fate awaits cultivation of broadleaf vegetables such as taro, cabbage, clover and fodder. Summertime plantations may also need to be halved because of their heavy water consumption in the intense heat. 
These policy changes will also lead to salinisation of large land areas in the northern delta, which are already suffering from the intrusion of salt water from the Mediterranean Sea. Reducing the area of rice cultivation also means reducing the area to be flooded with the freshwater needed during the process.
As the water gap in Egypt worsens, the food gap is also expected to increase due to the rise in Egyptian food imports which currently cost Egypt about $12 billion to $15-17 billion annually. 
To bridge the water gap, Egypt will need to start desalinating sea water, a costly technique which would add more financial pressures and raise the price of water. The UAE, with all its huge petroleum resources, can only produce five billion cubic meters of water from desalinisation each year; in Saudi Arabia it’s 6.5 billion. These amounts will do very little to bridge Egypt’s water gap, currently estimated at 42 billion cubic meters and expected to reach 54 billion annually after the Renaissance Dam becomes fully operational.
A move to irrigation in SudanAs the Renaissance Dam starts working, the Blue Nile and Kassala provinces in eastern Sudan will also suffer from the absence of waters that used to flood the region four months each year, leaving the land fertile for planting crops after the water recedes. Sudan will also have to change its agricultural strategy, moving to irrigated agriculture in this area.
The change will affect one million hectares, and will require the construction of costly canals and drainage networks that will cost billions of dollars, which Sudan's economy is unlikely to afford.
But if the country can get support to establish an irrigation and drainage network in the two provinces, it could grow summer crops — especially cotton, seed food, maize and vegetables — in addition to ending flood-related damages to land and housing.
Nevertheless, it is a change that will also bring a shift towards using harmful chemical fertilizers and pesticides.
Sudan may see a benefit as the Renaissance dam will prevent silt from accumulating in the reservoirs of Sudanese dams Sennar and Roseires, which will increase their water storage capacity of water. However, it did not ask how the reservoirs of these two dams will be filled with the 11 billion cubic meters of water they need each year. This will likely take a very long time.
Benefits in EthiopiaIn the absence of agreements on the future of Blue Nile flows in the region, Ethiopia will seize control of most of the Nile’s waters. It is expected that the lake of the Renaissance Dam will guarantee about one billion hectares of arable land, which Ethiopia will offer to investors.  This will take up about 10 billion cubic meters of lake water each year.
This is why Ethiopia has rejected any reference, in the text of the Khartoum Declaration of Principles signed by the three countries, to the dam being used only to generate electricity — adding the text “and for economic development” to indicate its intention to exploit the dam's water for agricultural, industrial and infrastructural uses within its territory. 
There are still many unresolved issues, and the delay in reaching clear agreements is not to the advantage of Egypt or Sudan. In general, it is clear that we are seeing only the tip of an iceberg in what is becoming an ongoing conflict. Water problems in the region are being passed along to the years and generations to come.
Nader Noureddine is a professor of water resources and land reclamation at Cairo University, Egypt.
This piece was produced by SciDev.Net’s Middle East & North Africa desk.