Seasonal Variability of Early and Late Onset Monsoon Seasons in the Sahel

Variability in Sahel rainfall has large implications for the local population, many of whom are engaged in subsistence farming activities. Two examples of rainfall variability that can impact crop viability are the date of onset and seasonal total rainfall. In this work, we study several recent “early” and “late” monsoon onset seasons using observational data. We seek an answer to the question of whether an “early” onset tends to translate to a wetter than normal June-September (JJAS) season and if a “late” onset season tends to translate to a drier than normal season. We find that there is little consistency in terms of the start of season dictating the overall seasonal nature of precipitation in the Sahel. We posit that this is due to different mechanisms controlling each of the processes. These findings have important implications for crop planting and management, notably, by showing that “early” or “late” onset seasons have little predictive capability for total seasonal rainfall. In terms of understanding and predicting for crop yields in early warning contexts, knowing the season has begun early or late may not be the most useful tool for extrapolating food security outcomes.