Why Athens flooded with just 40 mm of rain

Meteorologist Thodoris Kolydas explains why Athens flooded with just 40 mm of rain during storm Adel.

According to Kolydas, 40 mm of rainfall in a dense urban environment — with heavy construction, small streams, and very low soil absorbency — is already enough to create significant disruption. Data from the EAA/meteo station network recorded rainfall amounts in central Athens reaching 40 mm, while areas such as Zografou and Goudi exceeded 38–39 mm. “These figures alone were sufficient to cause local water accumulation, traffic delays and minor flooding on streets with poor drainage,” he notes.

To illustrate the impact, Kolydas adds that 100–200 mm of rain in a single area can have far more severe consequences. “In Epirus, within a similar timeframe, we saw rainfall reach those levels, burdening rivers, aquifers and mountainous drainage basins — systems far more vulnerable to sudden flood reactions than Athens. If Attica struggles with 40 mm, imagine regions where the volumes triple or quintuple.”

Kolydas also highlights the operational challenges in forecasting. Large parts of Attica — and Greece in general — still have insufficient radar coverage, which hinders real-time assessment of rainfall intensity. However, he stresses that modern tools can offer 1–2 hours of early warning, including satellite products and high-resolution forecasting models capable of detecting storm tops and the strengthening of convective cores.

“Today’s storm showed again that even 35–40 mm can cause substantial impacts in Attica,” he says. “It also reminded us how crucial it is to make full use of every available early-warning tool, especially in a country where radar networks have gaps, extreme phenomena are becoming more frequent and intense, and the operational reaction window is extremely valuable. With better use of satellite data and models, warning one or two hours earlier is absolutely realistic — and often decisive.”