Tropical monsoon countries like Bangladesh have experienced erratic spatiotemporal rainfall distribution, heavy rainfall, and extensive erosion in recent decades. The erosive nature of the soil in the country poses a serious ecological problem. However, there is a lack of studies on the spatiotemporal distribution of rainfall erosivity and precipitation concentration trends in Bangladesh. This study intends to investigate the Rainfall erosivity over the past three decades in Bangladesh. Using the Precipitation Concentration Index (PCI) and the Modified Fournier Index (MFI), this study attempted to demonstrate precipitation concentration and erosivity distribution during 1991–2020. The PCI and MFI indices were calculated using monthly precipitation records from 30 observatories nationwide. PCI values ranged between 15.43% and 21.04%, indicating substantial irregularity in rainfall across Bangladesh, while the MFI value higher than 98 shows a very high erosion capacity of rainfall in a shorter period. The mean annual rainfall erosivity factor (R-factor) found 865 MJ mm ha− 1 hr− 1 y− 1 with a range of 711.89–1019.97 MJ mm ha− 1 hr− 1 y− 1, suggesting moderate to higher erosivity potential in annual rainfall. All the stations exhibited higher erosivity values in monsoon (597.673–902.893 MJ mm ha− 1 hr− 1 y− 1), followed by pre-monsoon (325.779–436.599 MJ mm ha− 1 hr− 1 y− 1) and post-monsoon (166.67–241.52 MJ mm ha− 1 hr− 1 y− 1). Higher rainfall erosivity is concentrated in Bangladesh’s mid-central to northeastern region, while the southwest, northeast, and southeastern areas are at higher risk of monsoon rainfall erosivity. Though decreasing trends in annual rainfall erosivity were observed in 26 stations, monsoon and post-monsoon rainfall erosivity showed an increasing trend in 19 and 8 stations, respectively. The outcome of the current study is expected to help address the challenges of climate change and sustainable development issues in Bangladesh and similar climate-vulnerable countries around the world.