Study　region:　The　Minjiang　River,　located　on　the　western　side　of　the　Taiwan　Strait　of　East　Asia,　serves　as　a　typical　mountain　river　estuary　system.　Study　focus:　This　research　investigates　the　impact　of　reduced　sediment　discharge　on　the　geomorphological　changes　in　the　Minjiang　River　estuary　delta　and　its　adjacent　coasts.　By　integrating　45　years　of　shoreline　data　and　nautical　chart　bathymetry,　the　study　quantitatively　delineates　tempo-spatial　change　patterns　and　reveals　the　rapid　response　mechanisms　to　sediment　discharge　decrease.　New　hydrological　insights　for　the　region:　The　study　demonstrates　that　the　sandy　shoreline　near　the　Minjiang　River　estuary　exhibits　distinct　tempo-spatial　evolution　patterns　primarily　due　to　decreased　sediment　discharge.　The　estuarine　transition　zone　shows　greater　coastal　resilience,　with　shoals　providing　essential　sediment　sources　for　development,　while　the　shoreline　south　of　the　transition　zone　experiences　progressively　delayed　erosion.　The　Minjiang　River　delta　reacts　swiftly　to　decreased　sediment　discharge,　with　a　response　time　of　significantly　under　ten　years.　Despite　the　temporary　influence　of　extreme　weather　events　such　as　typhoons　on　erosion　states,　continuous　sediment　discharge　decrease　remains　the　dominant　factor.　These　insights　highlight　the　heightened　sensitivity　and　rapid　adaptability　of　mountain　rivers　to　environmental　shifts,　providing　significant　implications　for　understanding　the　repercussions　of　human　activities　on　estuarine　geomorphological　alterations.　©　2024　The　Authors