Analysis of rainfall onset, cessation and length of growing season for western Kenya

Onset, cessation and length of growing season statistics are generated for both long and short rainy seasons in western Kenya. Onset identification is based on a daily analysis of the soil water balance over the initial growth stage (30 days) by identifying and quantifying the risk of failure of crop development. Cessation is based on a daily analysis of the soil water balance by identifying and quantifying the water stress in the root zone for maize. The length of growing season for a particular year is obtained from the difference between cessation and onset of that year. Historical daily climatic data of a 15–34-year period and soil data from 26 stations, spatially distributed in the study area, were considered. Results indicate that there exist organized progression of rainfall onset within the western Kenya region with the long rains showing a southerly progression while the short rains show a south-westerly progression. Cessation of rainfall for both seasons show strong localized influences, mainly surrounding Lake Victoria and forested areas, including orographic features. For stations with long length of growing season, the length varies more than the onset date.