Quantifying Atmospheric Humidity in the Western Mediterranean During the Iron Age and the Roman Era Gázquez, Fernando Voigt, Claudia Castillo-Baquera, Aurora García-Alix Daroca, Antonio Jiménez Moreno, Gonzalo Jiménez-Espejo, Francisco Martegani, Lucía Rodrigo Gámiz, Marta Jiménez Bonilla, Alejandro Rodríguez-Rodríguez, Miguel Atmospheric Humidity Western Mediterranean Iron age The projects PID2021‐123980OA‐I00 (GYPCLIMATE), PID2021‐125619OB‐ C21, and PID2021‐125619OB‐C22 of the AEI of Ministerio de Economía y Competitividad of Spain and UE FEDER funds supported this study. F. G acknowledges the RyC fellowship of the Spanish AEI, RYC2020‐029811‐I and the Grant PPIT‐UAL, JdA‐FEDER 2022‐2026 (RyC‐PPI2021‐01). L. M. was funded by the FPU21/06924 Grant of the Ministerio de Educación y Formación Profesional of Spain and C.V. by the MSCA post‐ doctoral fellowship of the European Commission (101063961). Atmospheric moisture is a key hydroclimatic parameter that influenced ancient societies, agriculture, and ecosystems. However, quantitative constraints on pre‐industrial atmospheric humidity values are rarely available. Here, the triple oxygen ( 17O/16O and 18O/16O) and hydrogen ( 2 H/1 H) isotope compositions of lacustrine gypsum are used to quantify changes in summer atmospheric relative humidity (RHs) in the southern Iberian Peninsula from 650 BCE to 500 CE. RHs was 59 ± 4‰ from 450 to 350 BCE, approximately 10% higher than at present, and decreased to 50% ± 2% before the Roman conquest of the Iberian Peninsula in 218 BCE. Drier conditions (49% ± 3%) prevailed from 300 to 500 CE, coinciding with the decline and fall of the western Roman Empire in 476 CE. Long‐term RHs values correlated inversely with the strength of the North Atlantic Oscillation, suggesting that hemispheric climate patterns influenced atmospheric moisture in the western Mediterranean during the Iron Age and Roman times. 2025-12-18T08:48:16Z 2025-12-18T08:48:16Z 2025-12-28 journal article Gázquez, F., Voigt, C., Castillo‐Baquera, A., García‐Alix, A., Jiménez‐Moreno, G., Jíménez‐Espejo, F., . . . Rodríguez‐Rodríguez, M. (2025). Quantifying atmospheric humidity in the western mediterranean during the iron age and the roman era. Geophysical Research Letters, 52(24), 11. doi:https://doi.org/10.1029/2025GL120424 0094-8276 1944-8007 https://hdl.handle.net/10481/108936 10.1029/2025GL120424 eng http://creativecommons.org/licenses/by-nc-nd/4.0/ open access Attribution-NonCommercial-NoDerivatives 4.0 Internacional Wiley