This study aimed to address the knowledge gaps on adaptive capacity of rural farming households to slow-onset hazards such as seawater intrusion. It defined household‐level variables that can potentially explain adaptive capacity by using a principal component analysis and a regression model. In addition, it aimed to develop a measure-based index (MAI) to account for adaptation processes. The developed measure-based adaptation index addressed a number of shortcomings in previous studies and captured the variation in adaptation measures that rice farmers implement. The results indicated that adaptation takes place at different levels based on the propensity to adapt, the variety and diversity of adoption of various measures, the feasibility of the various measures, and the varying conditions of seawater intrusion. The research established a model of adaptation for seawater intrusion largely influenced by the rice farmers' economic capacity, which is crucial in optimizing the adaptation measures employed.