This project aims to investigate the changing mechanism of group cohesion. Study one indicated that perceived group cohesion in the community varied subject to the flood severity. Group cohesion was predicted by the group affect, group cognition, and group behaviour, but not general demographical characteristics. Study two revealed that groups with strong cohesion were able to alleviate the influence of external forces on the group. Compared to their counterparts, groups with weaker cohesion were less likely to buffer the impact of external forces on group performance and dynamics. Both studies contribute to the theoretical framework of group cohesion by scrutinizing the process of cohesion variation. Implications of the findings and suggestions to managerial practitioners and group leaders are discussed.