Ricardo Sanchez-Murillo, Luis González-Hita, Miguel Mejía-González, Blanca Carteño-Martinez, Juan Carlos Aparicio-González, Dustin Mañón-Flores, Lucía Ortega, Milica Stojanovic, Raquel Nieto, Luis Gimeno

Mexico encompasses a large spectrum of landscapes with topographic, geographic, and climatic factors interacting in a complex ecohydrological setting. For decades, isotope hydrogeological tools have been applied in Mexico using short-term or seasonal local meteoric water lines as valid input functions. Yet, a systematic evaluation of meteoric isotope characteristics is still lacking. Here we report on the spatial and temporal isotope variations of 21 precipitation monitoring stations across Mexico. Our database includes 608 monthly samples collected from 2018 to 2021 over four regions (between 5 and 2,365 m asl): the Pacific coast, the Gulf of Mexico/Caribbean Sea region, and the Central and Northern Plateaus. Precipitation δ18O seasonality from the dry (winter) to the wet season (summer) was characterized by a notable W-shaped variability. Monthly precipitation amounts and δ18O compositions exhibited poor to strong linear regressions (Adj. r20.01 to 0.75), with inverse (positive) relationships over the northern monsoon-affected region. Low d-excess (5.1 to 9.7‰) corresponded with greater terrestrial moisture contributions (20.5%) over the arid northern regions. Moisture inputs from the Gulf of Mexico/Caribbean Sea and the Pacific Ocean were associated with near-equilibrium or greater d-excess values (8.8 to 14.3‰), respectively. The best-fit linear models for δ18O (Adj. r2=0.85) and δ2H (Adj. r2=0.88) were determined on topographic and geographical predictors, resulting in an updated high-resolution precipitation isoscape (100 m2 grid) for Mexico. Orographic barriers (-2.10‰ in δ18O/km) coupled with the interaction of tropical cyclones and cold fronts, the evolution of the North American Monsoon system, and the passage of easterly trade winds play a remarkable role in controlling the spatial isotope rainfall variability. Our findings provide a robust baseline for ecohydrological, climatic, forensic, archeological, and paleoclimate studies in North America.