Environmental Drivers of Subterranean Radon Dynamics in Volcanic Systems: Modeling, Prediction, and Forecasting in a Warming World

Abstract This study investigates the seasonal dynamics and environmental controls on radon ( 222 Rn) concentrations in Los Verdes Cave, a volcanic lava tube in Lanzarote, Spain. Continuous monitoring of radon levels, together with external and internal climatic parameters (temperature, humidity, atmospheric pressure, wind speed), over an annual cycle, revealed distinct ventilation regimes characterized by pronounced seasonal variability. Radon concentrations exhibited peak values during the summer–autumn period (up to 882 Bq/m³), with minima observed in winter–spring (as low as 17 Bq/m³), indicating thermally driven ventilation inversions. A time-series ARIMA model identified external air temperature as the principal driver, wherein elevated temperatures led to reduced convective exchange and enhanced radon accumulation within the cave. Relative humidity and atmospheric pressure were also significant contributors, with underground air humidity exceeding 70% promoting radon retention. The validated model was used to forecast future radon scenarios under IPCC RCP4.5 and RCP8.5 climate trajectories, forecasting radon concentration increases of 5–60% by the year 2100 as a function of projected surface warming. These projections underscore implications for occupational exposure in confined volcanic environments, contribute to the broader understanding of subterranean greenhouse gas behaviour, and offer analog insights for astrobiological exploration in extraterrestrial lava tubes. The modeling framework enhances the ability to decouple radon variability associated with climatic forcing from geogenic anomalies potentially indicative of volcanic unrest. Overall, this study demonstrates the utility of statistical time-series approaches for forecasting radon behaviour under evolving climatic conditions and highlights the necessity of long-term environmental monitoring in geologically active subsurface ecosystems. Graphical Abstract The graphical abstract aims to highlight the most important aspects of the research presented. The lava tube under study, Cueva de Los Verdes, is located on the island of Lanzarote, one of the Canary Islands (Spain). To the right, the green box shows the annual concentration of 222 Rn in Cueva de los Verdes (hourly records and daily mean). The average annual concentration was 169 Bq/m³, with recorded values ranging from a minimum of 17 Bq/m³ to a maximum of 882 Bq/m³. In addition, measurements were obtained for internal temperature and relative humidity (Tint and RH), external temperature (Text), atmospheric pressure, and average wind speed, which allowed the assessment of the environmental parameters influencing 222 Rn concentrations in the cave. The grey box presents part of the conceptual model: the winter–spring phase of maximum ventilation, characterized by the lowest 222 Rn concentrations. During this phase, a thermal inversion occurs, whereby colder, denser external air displaces the warmer, lighter cave air, enhancing ventilation and promoting air renewal. Understanding the influence of environmental parameters on 222 Rn concentrations has enabled the prediction of its behavior and the forecasting of radon levels under climate change scenarios. The yellow box represents the worst-case scenario for 2100, in which 222 Rn concentrations could increase by up to 60% compared to current levels.