<p>Floods are one of the most devastating natural events that threaten social and economic conditions more than any other natural disaster. Therefore, the aim of this study was to map the Iso-severity flood patterns and determining the seasonality of flood events over different return periods in Ardabil province, Iran with diverse relief and climatic regions. Iso-severity refers to the spatial mapping of areas experiencing similar flood intensities, which is a central concept in our study. Thus, the data of 32 Rivers were used in the spatiotemporal analysis in a 40-year recorded period. EasyFit software was used to determine the most appropriate statistical distribution for the discharge data at different return periods. Then, the frequency of monthly and seasonal flood events was quantified and the significant trend of flood frequency in each river gauge station was tested, and the seasonality of flood events was explored. According to the results, about 63.63% of the floods occurred in April. The seasonality of flood events showed that the maximum frequency and percentage of flood events are mostly occurred during the spring season over different return periods. As in some stations, almost 100% of the floods occurred in spring and this shows that the floods in Ardabil province are spring floods. Iso-severity flood mapping in different return periods showed that the frequency of floods was higher in central and northern regions and highlands of the study area. It is necessary that in the southern and severe flooding area, proper planning with a focus on integrated watershed management should be implemented to reduce the flood occurrence in the future and minimize its human and economic losses.</p>