Agricultural drought (AGD) is among the most well-known and devastating natural disasters globally, wreaking havoc on rain-fed agricultural countries, including Bangladesh. However, the spatiotemporal characteristics and consequences of AGD disasters are rarely studied during Bangladesh’s post-monsoon Aman rice growth period. Thus, the Penman-Monteith (P-M) equation and a crop coefficient model were used to assess the spatial and temporal variability of the post-monsoon Aman rice season in western Bangladesh between 1980 and 2017. To reveal the spatiotemporal changes in drought during the Aman rice growing phases in the western part of Bangladesh, the crop water deficit index (CWDI) was developed for AGD evaluation. In addition, based on risk formation theory, this study intends to construct a drought disaster risk index (DDR) for post-monsoon Aman rice for various growth phases. The results revealed that the crop water deficit was the lowest in the vegetative stage and the highest in the ripening phase. Among all the areas, the CWDI was highest in the Rangpur and Rajshahi regions. Drought risk was relatively higher in the late crop-growing period due to high temperatures, inadequate rainfall, climatic characteristics, and geographical settings. Precipitation, evapotranspiration, and a rapidly changing climate all contributed to variations in crop water deficits in the study region. Crop yields were reduced in all sub-areas. Spatially, higher values of DDR were observed in the northern areas of western Bangladesh. New adaptive measures and policies are essential to improving the adaptability and mitigation capacity of AGD risk. Farm-level adaptation, cropping patterns, and drought-resistant crops should be introduced in the study region. The findings of this research have guiding relevance for AGD disaster prevention, mitigation, and irrigation, as well as being practical for AGD management and application decision-making in western Bangladesh.