This study provides a comprehensive assessment of the effects of severe flood stress on the phytochemical composition and multifunctional characteristics of Glycyrrhiza uralensis (Ural licorice). Aqueous extracts from different plant parts collected before (2023) and after flooding (2024) were analyzed using spectrophotometric, photometric, and gravimetric methods to evaluate antioxidant capacity, sun protection potential, and corrosion inhibition efficiency. Flooding induced a pronounced metabolic reorganization, marked by a significant increase in total phenolic content (TPC) and a decrease in total flavonoid content (TFC), resulting in an elevated TPC/TFC ratio. These changes reflected the accumulation of more conjugated, redox-active phenolic structures with extended π-systems, enhancing both electron-donating ability and metal adsorption efficiency. Functionally, post-flood extracts exhibited higher antioxidant activity, greater photostability, and improved corrosion inhibition in both neutral and acidic media. Pearson correlation analysis confirmed that TPC and TFC were the primary determinants of multifunctional performance, though partial correlation reversals indicated a redistribution of biochemical roles under stress. Research findings highlight flooding as a powerful biochemical modulator that increases G. uralensis protection potential and provide valuable insights into how environmental extremes change plant metabolism for adaptive multifunctionality.