Assessment of rainfall variability and trends in Rajshahi city, Bangladesh using non-parametric statistical methods

Rajshahi City in northwestern Bangladesh is relatively dry and vulnerable to rainfall variability and water stress. This study examines long-term rainfall variability and trends using a 35-year dataset (1990–2024) obtained from the National Aeronautics and Space Administration (NASA) Prediction of Worldwide Energy Resources (POWER) database. Non-parametric statistical methods, including the Mann-Kendall test and Sen’s slope estimator, were applied to analyze rainfall changes at monthly, seasonal, and annual scales. The results indicate a significant increasing trend in annual rainfall with a Sen’s slope of 34.32 mm/year. Monthly analysis shows increasing trends mainly from March to October, while winter months exhibit weak or insignificant changes. The seasonal analysis reveals that the monsoon period largely dominates rainfall increases, indicating a growing seasonal concentration of precipitation. Although increased rainfall may enhance short-term water availability, greater seasonal concentration may also elevate risks of flooding, waterlogging, and urban drainage challenges. These findings provide localized evidence of evolving rainfall dynamics in Rajshahi City and highlight the need for adaptive water-resource management and climate-resilient urban planning in Bangladesh.