Anthropogenic Climate Change Attribution to the Valencia’s deadly floods

Cut-off lows are, and will be in the future, one of the main threats related to severe weather in the Iberian Peninsula, especially in the Mediterranean arc. Cut-off lows are often accompanied by heavy precipitations in a short time promoting flash-floods, as well as hail, strong convectively wind gusts and/or tornadoes.   

On the week of October 27^th – November 4^th, 2024, a cut-off low affected the Iberian Peninsula with extreme socio-economic impacts in several Spanish regions and, especially, in the Valencia area. The severe weather phenomena on the surface have differed depending on the region: large hail (5-7 cm), several tornadoes, strong wind gusts and, above all, extreme precipitations. The most severe day was October 29^th in the Valencia region, with rainfall accumulations higher than 300 mm in a notable area and locally registering 771 mm in 24 hours. In addition, the Turís official weather station recorded numerous national records for rainfall intensity. Moreover, the convective system developed 11 tornadoes (two of them with intensity IF2) and large hail (~ 5 cm). The social impact of the floods in Valencia was very high, with more than 16.5 billion euros of damage to infrastructure (roads, railways, etc.), housing and croplands, as well as 225 fatalities.

In this survey, we focus on Valencia’s floods on October 29^th. Here, by performing model simulations with the WRF-ARW model and using a storyline approach, we find an enhancement in intensity and a significant increase in extreme accumulated rainfall area (e.g., 100 mm, 180 mm, 200 mm, and 300 mm) caused by current anthropogenic climate change conditions compared to preindustrial ones. Moreover, the enhanced available water vapor content played a central role, while CAPE, diabatic heating, and stronger vertical velocities boosted convective processes. A deeper warm cloud layer and elevated graupel concentration reveal microphysical mechanisms that enhanced precipitation volumes in a warmer climate, exceeding Clausius-Clapeyron scaling.

This study highlights the growing risks in the Mediterranean area and the urgent need for effective adaptation in urban planning to reduce the hydrometeorological extremes in human-induced climate change.