Monsoon Onset and Retreat
The hydrological onset and withdrawal index for the West Africa monsoon in the Sahel region (10°W – 10°E, 13°N – 18°N).
In the Sahel region, the knowledge of the beginning and the cessation of the rainy season related to the West African Monsoon (WAM) it is of fundamental importance for successful management of the crops.
The hydrological onset and withdrawal index (HOWI) is a prognostic index for the onset and the withdrawal of the WAM, computed using the boundary layer moisture transport (VIMT) averaged over the region with the maximum variability during the rising and the retreat of the monsoon, respectively.
Daily charts of the HOWI and of the VIMT are available and daily updated. A table with onset and withdrawal dates since 1979 is provided.