Unveiling the Tails of Atmospheric Moisture Extremes in the Eastern Mediterranean: Non-Stationary GNSS-Based Evidence for High-Impact Hydroclimatic Conditions

The Eastern Mediterranean is a well-established climate change hotspot, where intensifying hydrological extremes increasingly translate into high-impact weather conditions with cascading societal consequences. While long-term changes in mean atmospheric moisture are relatively well documented, much less is known about the evolution of extreme moisture states that act as precursors to severe precipitation, flooding, and compound hydroclimatic hazards.

In this study, we investigate the extreme behaviour of precipitable water vapour (PWV) using homogenised, high-frequency GNSS-derived observations from a dense network located in the Eastern Mediterranean transition zone. To ensure climate-quality consistency, the dataset was processed following internationally recognised standards, including IGS Repro3 strategies, covering the period 2010–2024. Moving beyond conventional trend-based analyses, we employ a non-stationary Extreme Value Theory (EVT) framework, combining Generalised Extreme Value (GEV) and Peak-Over-Threshold (POT) approaches to characterise the tails of the PWV distribution. This enables an assessment of changes in the magnitude, frequency, and persistence of rare moisture extremes under ongoing warming, independent of mean climatological shifts.

Return levels corresponding to different recurrence intervals are estimated to provide observational constraints on extreme atmospheric moisture scaling and its consistency with theoretical Clausius–Clapeyron expectations. The statistical results are further interpreted in the context of large-scale atmospheric drivers using ERA5 reanalysis data, shifting the focus from describing atmospheric states to identifying weather conditions conducive to high-impact hydroclimatic outcomes.

This contribution directly aligns with the objectives of the FutureMed COST Action (CA22162) by bridging physical climate processes, advanced statistical characterisation of extremes, and impact-relevant indicators of risk. By focusing on extreme moisture states rather than mean conditions, the study supports a shift from describing what the atmosphere is to assessing what weather conditions are likely to do in terms of hydroclimatic impacts, thereby improving the understanding and predictability of high-impact weather in the Eastern Mediterranean region.