India has 4,407 large dams of which more than 1,000 would be 50 years or older by 2025, a new study has shown. Older dams pose greater safety risks, cost higher in terms of maintenance and have declining functionality due to sedimentation, stated a study by the Canada-based United Nations University Institute for Water, Environment and Health, released in January. Climate change is also likely to accelerate the ageing of dams, it said. India must conduct a cost-benefit analysis of its ageing dams, and conduct timely safety reviews in order to ensure their operational and ecological safety, as well as the safety of those who inhabit the areas downstream, experts told IndiaSpend.