Climate change is a critical issue facing the countries of the Nile basin. While individual weather events are difficult to attribute to climate change, their sum is already having adverse effects on socioeconomic conditions across the region. While climate change was not an overt focus of the Nile basin initiative’s (NBI’s) mandate when it was launched in 1999, it has emerged as a key challenge for countries of the Nile to take seriously. Understanding variability in river flows is one of the first steps in understanding climate change impacts and planning how to respond to them. Developing this understanding and getting it into use has been at the heart of the NBI’s technical work.