Vietnam is one of the countries in the world that will be most negatively affected by the sea-level rise (SLR). The large agricultural population in the coastal areas of the country is already constrained by saltwater intrusion now, and will be more so by SLR in the future. In the coastal district of Nga Son, Thanh Hoa Province of Vietnam, the farmers had maintained their livelihood under the salinity constraint on salt-tolerant sedge (Cyperus spp.) plants sold for handicraft and mat-making. In recent years, however, their livelihood has been eroded by declines in productivity and quality of the sedge due to increased salinity intrusion and shortage of fresh water supply. The income from sedge was reduced to a greater extent in a group of communes that are closer to the Gulf of Tonkin than the other group of communes with less negative impacts. The farmers’ responses to these changes showed similarity and differences between the two groups of communes. The seasonal peak of rainfall has become later and the sedge harvest had to be delayed. The farmers’ capability to adapt to the hydrological and climatic changes thus depends on their local hydrological conditions mediated by their financial situation. These constraints could be ameliorated by financial and engineering supports at various institutional levels. Agronomic efforts could also ameliorate the problems via provision of better suited crops on an improved characterization of the local environmental conditions.
