Socioeconomic development, subsidence, and climate change have led to high flood risks in coastal cities, making the vulnerable, especially elderly people, more prone to floods. However, we mostly do not know how the accessibility of life-saving public resources for the elderly population will change under future scenarios. Using Shanghai as a case, this study introduced a new analytical framework to fill this gap. We integrated for the first time models of coastal flooding, local population growth, and medical resource supply-demand estimation. The results show that under an extreme scenario of coastal flooding in the year 2050, in the absence of adaptation, half of the elderly population may be exposed to floods, the supply of medical resources will be seriously insufficient compared to the demand, and the accessibility of emergency medical services will be impaired by flooding. Our methodology can be applied to gain insights for other vulnerable coastal cities, to assist robust decision making about emergency responses to flood risks for elderly populations in an uncertain future.