The present study was carried out to identify temporal changes in rainfall patterns in the Sevanagala sugarcane project area in Sri Lanka. Rainfall data collected from the agrometeorological station of the Sevanagala sugarcane project from 1984 to 2018 were taken for analysis. Dates of rainfall onset and date of terminations, and length of rainfall seasons were assessed. The single mass curve method was used to confirm the consistency of the data set. The Mann-Kandal test was conducted to identify of statistical significance of changes in rainfall onset date, date of termination, and length of rainfall season. The time series trend of the rainfall onset date, date of termination, and length of rainfall season were quantified using Sen’s slope estimation method. The results revealed that bi-modal rainfall distribution is prominent in the Sevanagala sugarcane project area. On average, the first rainfall season is distributed from March to July, and the second rainfall season is from October to February. Analogically, the rainfall season onset date for the first and second rainfall seasons was the twenty-eighth of March and the fourteenth of October, respectively. Termination dates of the first and second rainfall seasons were the twenty-ninth of May and the twenty-ninth of December, respectively. Based on the Mann-Kandal test, it was revealed that the rainfall season onset date in the first rainfall season was significantly delayed at a rate of 2.6 days per decade during the 1984 to 2018 period. The termination date of the first rainfall season did not exhibit any significant change over time during the study period. The rainfall onset date of the second rainfall season was also shown a significant delaying trend by 2.7 days per decade during the respective 35-year period. The length of the first rainfall season has not shown a significant change over time. The length of the second rainfall season has shown a significant change by shortening its length at a rate of 7.6 days per decade. Hydro-climatological challenges incurred due to these changes in rainfall season onset date and season length can have a negative effect on the soil water balance of the sugarcane plantations. Thus, precautions must be taken to mitigate this issue at the farmer’s field scale as well as the waterbasing scale. Most adverse hydro-climatological conditions can often be eliminated by completing land preparation activities in advance and planting operations immediately after starting of rainfall.