Background
"Since the major droughts in the West African Sahel during the 1970s," according to the authors, "it has been widely asserted that mean annual summer rainfall has declined since the late 1960s."

What was done
In exploring the basis for this widespread assertion, Chappell and Agnew analyzed mean annual summer rainfall data for the Sahel between 1931 and 1990.

What was learned
It was determined, in the words of the authors, that previously published work "failed to consider the location of the rainfall station network each year in relation to the spatial and temporal heterogeneity of West African Sahel rainfall."  In rectifying this situation, they determined that prior analyses "incorrectly identified a decline in rainfall," which they were able to demonstrate was "an artifact of the changing location and number of rainfall stations."

What it means
Chappell and Agnew say their findings "call for a re-evaluation of previously published work on West African Sahel rainfall, particularly global climate model scenario outputs that were compared against 'observations' of mean annual rainfall."  In addition, they suggest that "other global climate data with known spatial and temporal heterogeneity and those based on station networks that have changed during the 20th century should also be re-evaluated in order to avoid similarly incorrect interpretations," which makes us wonder what else the scientific community (including ourselves!) may have believed about earth's climate over the past century or so that may also have been erroneous.