The Lamb Index from the Early Years Onward

In the wake of very dry conditions in the West African Sahel from 1968 to 1974 and the accompanying famine, a number of researchers began investigating the causes of this drought and the mechanisms that control the climate of the region and its variability more generally.  These efforts required finding ways of characterizing seasonal and annual precipitation in the region based upon the limited precipitation datasets that were generally available to the research community at the time.  An index of standardized seasonal precipitation departures based upon data from about twenty rainfall stations scattered throughout West Africa, with long and largely complete monthly records from the 1940s onward, was maintained and updated by Peter Lamb and his associates and came to be commonly known as the Lamb Index.  This index became a widely-recognized means of characterizing the precipitation variability of the region and documented the dramatic decline in precipitation that began during the 1960s and culminated in the extreme drought years of the early to mid-1980s.  Here we discuss aspects of the efforts and challenges involved in maintaining and updating the Lamb Index in its early years.  In the succeeding years great progress was made by a multitude of researchers to establish the teleconnections that linked ocean variability with seasonal precipitation variability in the Sahel.  Dr. Lamb sought also to extend the teleconnection chain and to document how variations in daily precipitation characteristics contributed to the variability seen in the Lamb Index.  Here we also discuss the development of indices based upon daily precipitation data from the Sahel that were used to characterize the extent and intensity of the daily disturbance lines that, in aggregate, produced the seasonal results seen in the Lamb Index.