Background
The authors write that the upper Blue Nile basin is one of the most important river basins in Africa, because "it contributes about 60% of the Nile's flow at Aswan, Egypt (Yates and Strzepek, 1998; Sutcliffe and Parks, 1999; Conway, 2005) ... and its availability is a matter of survival for Egypt and Sudan." In addition, they say it is the largest and most economically imperative water resource for Ethiopia, which "is planning irrigation and hydropower projects using the Blue Nile River (Tesemma et al., 2010), while all the other riparian countries are working on increasing their share of the water to boost their economic developments."

What was done
In studying this important river and the region that feeds it, in the words of Taye and Willems, "the temporal variability of basin-wide rainfall extremes and river flow extremes from four gauging stations was investigated," and "on the basis of a quantile anomaly analysis method, decadal variations in extreme daily, monthly, and annual quantiles were studied, and the periods of statistical significance were identified."

What was learned
The two Belgian scientists found that, in regard to river flows and rainfall depths, "the 1980s had statistically significant negative anomalies in extremes in comparison with the long-term reference period of 1964-2009, while the 1960s-1970s and the 1990s-2000s had positive anomalies, although less significant." Most important of all, however, they report that "there is neither consistent increasing nor decreasing trend in rainfall and flow extremes of recent years." And, therefore, they say that "anticipated trends due to global warming could not be identified."

What it means
Once again, for another part of the world, and in spite of the oft-repeated "doom-and-gloom" prognostications of climate alarmists, the global warming experienced over the past half-century or so has not led to either extreme increases or decreases in rainfall and subsequent river flow in Africa's upper Blue Nile Basin.

References
Conway, D. 2005. From headwater tributaries to international river: Observing and adapting to climate variability and change in the Nile basin. Global Environmental Change 15: 99-114.

Sutcliffe, J.V. and Parks, Y.P. 1999. The Hydrology of the Nile. IAHS Special Publication 5.

Tesemma, Z.K., Mohamed, Y.A. and Steenhuis, T.S. 2010. Trends in rainfall and runoff in the Blue Nile Basin: 1964-2003. Hydrological Processes 24: 3747-3758.

Yates, D.N. and Strzepek, K.M. 1998. Modeling the Nile basin under climatic change. Journal of Hydrologic Engineering 3: 98-108.