Coastal flooding is already one of the most dangerous and costly natural hazards that humanity faces globally and yet it will become even more frequent and challenging to manage because of climate change and other factors. In densely populated estuarine settings, a storm surge barrier is often an attractive and economical solution for flood protection. There are currently many storm surge barriers in operation around the world protecting tens of millions of people and trillions of pounds of property and infrastructure. However, with accelerating rates of sea-level rise being observed, along with changes in storminess, tides and river discharge, surge barriers are closing increasingly often, and closures are now occurring in months when they typically have not occurred in the past. Increased use of surge barriers in the future has critical implications for barrier management, maintenance and operation. In this paper we develop, validate and apply a novel statistical approach to assess how the number of storm surge barrier closures will likely increase in the future and change in frequency throughout the year, that can be used for different climate change scenarios and accounting for forecast errors in water levels. As representative case study examples, we focus on the Eastern Scheldt storm surge Barrier in the Netherlands and the Thames Barrier in the UK. We validate the method, demonstrating it accurately predicts past closure statistics for the Eastern Scheldt and the Thames Barriers over the 38 and 42 years they have been operational, respectively. Then we apply the method to estimate the potential future numbers of barrier closures considering a range of different projections of sea-level rise, along with changes in storm surges, tides and river discharge. We show that there is very likely to be a rapid acceleration in the number of barrier closures in the future, dominated by sea-level rise, with strong influence of the 18.6-year lunar nodal cycle, at both case study barriers. Finally, we illustrate how the tool can be used to help guide future barrier management, maintenance, operation and upgrade/replacement planning and inform adaptative flood management approaches. The tool we have developed could easily be extended to other storm surge barriers around the world.