# Water vapor transport observed at a coastal Mediterranean site during the summer of 2021 and compared with ERA5

## TL;DR

This study analyzes water vapor transport in the Mediterranean during summer 2021 and compares it with ERA5 reanalysis data to improve extreme weather forecasting.

## Contribution

The study provides new insights into water vapor transport patterns and identifies a dry bias in ERA5 reanalysis data.

## Key findings

- ERA5 showed a dry bias of up to 3 g kg-1 compared to microwave radiometer data in the 450–650 hPa layer.
- Water vapor transport is crucial for understanding extreme weather events and improving rainfall and flood forecasts.
- North African inflows and remote Atlantic pathways significantly contribute to Mediterranean moisture transport.

## Abstract

Extreme events in the Mediterranean have increased in frequency and intensity over the past decade, and this trend is expected to continue. Characterizing these events using reliable observational datasets is essential for understanding the processes driving their development. This study uses observational data collected during the Mediterranean Experiment for Sea Salt And Dust Ice Nuclei (MESSA-DIN) from July to September 2021, at the coastal site of Soverato, on the Ionian coast of Southern Italy, to characterize the intense water vapor transport over the Mediterranean basin during the severe summer of 2021. Furthermore, we compare the observations to the atmospheric reanalysis ERA5 and describe the synoptic environment over the study period. The results highlight the role of water vapor transport in weather systems and local atmospheric processes, underscoring the importance of high-resolution water vapor atmospheric profiling to enhance the accuracy of extreme rainfall and flood forecasting. While ERA5 performed well in capturing synoptic-scale patterns, it exhibited a dry bias of up to 3 g kg-1 compared to microwave radiometer retrievals in the 450–650 hPa vertical layer. This bias likely reflects limitations in the reanalysis representation of tropospheric moisture transport, particularly from dominant North African inflows, in addition to contributions from remote Atlantic pathways and local sources.

The online version contains supplementary material available at 10.1038/s41598-026-36040-0.