Rezaei Jajarm, Mohammad JavadMohammad JavadRezaei JajarmAkbarzadeh, PooriaPooriaAkbarzadehShahMardan, Mohammad MohsenMohammad MohsenShahMardanAminzadeh, MiladMiladAminzadehRezazadeh, AmirAmirRezazadeh2025-09-022025-09-022025-08-18Journal of Hydrology 662: 134095 (2025)https://hdl.handle.net/11420/57194Suppressing evaporative losses from water reservoirs has long been a challenge. While various methods have been developed to reduce evaporation, physical covers, such as floating elements, offer an efficient measure for reducing evaporative losses from open water storages. Although the impact of floating covers on evaporation reduction is well-studied, the influence of cover geometry and associated opening attributes at the surface remains underexplored. This study investigates the effect of different cover geometries with identical surface coverage fraction on the evaporation suppression efficiency of partially covered reservoirs. The results show that openings with larger perimeters lead to higher evaporation rates and lower suppression efficiency. Rectangular, diamond, triangular, and circular opening geometries resulted in 33–69 %, 36–71 %, 46–73 %, and 48–75 % reduction in evaporation, respectively, under various surface flow and air boundary conditions. We observed that water surface flow and wind speed initially promote thermal mixing and reduce evaporation, but beyond a threshold, the increased heat transfer dominates, causing the evaporation rate to rise. To bridge laboratory findings with real-world environmental conditions, a mathematical model is developed using dimensionless analysis and nonlinear regression. The model shows good agreements with field measurements obtained from small reservoirs.en1879-27072025ElsevierEvaporation suppressionFloating coversNon-linear regression analysisOpening geometryWater reservoirsNatural Sciences and Mathematics::551: Geology, Hydrology MeteorologyJournal Article10.1016/j.jhydrol.2025.134095Journal Article