Drought is a disastrous-triggering agent that exacerbates environmental services and socio-economic conditions. Considering the impact of climate change and rainfall deficiency over the extended period, the need for a systematic way to understand drought is necessary. Therefore, this research proposed to perform an assessment of drought severity in the lower Nam Phong River Basin, Thailand using the Standardize Precipitation Index (SPI) and Water Evaluation and Planning (WEAP) model. The findings demonstrated consistent results between the SPI index and WEAP model in determining drought severity impacts. It was found that Kosum Phisai, Nam Phong, and Muang Khon Kaen Districts were the most drought affected areas. The drought risk areas were identified and classified into four zones based on the size of the affected area in %: less (25%); moderate (27%); high (22%); and extreme (26%). The outcome results can be useful for water resources planning and drought severity management in other parts of Thailand.