Extreme rainfall events like the DANA storm in Valencia could happen every 47 years (and not every 500 as previously thought).

BarcelonaThe torrential and extreme rains that devastated the Valencian Community a year ago could be repeated much more often than previously thought: every 47 years, not every 500 as previously believed. This is the conclusion of a study by the Center for Land Policy and Valuation (CPSV) at the Polytechnic University of Catalonia (UPC), which was published to coincide with the first anniversary of the tragic storm. Led by professors Blanca Arellano and Josep Roca, the study is based on an analysis of data from 350 stations of the State Meteorological Agency (AEMET) from 1950 to 2024. It has determined that the more than 700 liters per square meter accumulated in the Valencian Community "were not a unique, exceptional phenomenon," but rather an event with a "significant probability" of recurring. "The return period for the rainfall of October 29, 2024, falls far short of Aemet's initial forecasts, instead being reduced to 47 years," the study states. The figures indicate that even more extreme episodes, accumulating more than 1,600 l/m² in just 24 hours, could occur every 500 years. "Flood studies should be adjusted to this prediction," the report concludes. The data also indicate that torrential rains could occur every two to three years, and that rainfall exceeding 400 l/m² in a single day could happen every ten years. To prepare the study, the CPSV team mapped the extent of the rainfall and modeled the flood of October 29 of last year. They also analyzed the causes of the extreme rainfall in the Valencian Community.

Review urban planning

The study states that one of the key factors in understanding the scale of last year's tragedy was the "inappropriate" land use and "high urban density" in flood-prone areas, a result of urban planning that "has ignored" flood risk maps and official hazard studies. In this regard, the researchers call for an "urgent update" of rainfall risk studies and urban development plans. They also propose revising flood hazard maps, incorporating new data series and climate change scenarios, as well as "prohibiting" new urban development in flood-prone areas. Furthermore, they emphasize that existing residential areas in flood-prone zones must be adapted. The report also highlights several other factors that explain the extent of the catastrophe caused by that storm. One is the "exceedance" of the flood zone projections established in official maps: they state that the flooding in Valencia "exceeded the projected flood footprint." They also note that the rains impacted an area where "precipitation of this magnitude" had "never been recorded." The study also points to the climate crisis, reminding us that the warming of sea water and the increase in water vapor accumulated in the atmosphere raise the risk of extreme rainfall in autumn.