The 'cold drop' phenomenon caused flash flood disaster 28 years ago

The flash floods that killed at least 95 people in the Valencia region in 1996 were the result of climate change, post-summer dry soil and cold drops.

The deadliest flash floods in Spain since 1996 have raised questions about the level of flood defences needed to cope with the annual heavy autumn rains in the Valencia region, according to the Telegraph .

Rescuers search for people trapped in the rubble after floods in Letur, Albacete province. (Photo: Manu/PA-EFE).

Heavy autumn downpours along Spain's Mediterranean coast are caused by a phenomenon called "cold drop ." This occurs when warm, moist Mediterranean air meets a sudden cold front from the north, causing localized heavy rain.

Valencia is on the coast and is particularly vulnerable to high-altitude depressions in the fall because the Mediterranean Sea remains warm. Such phenomena are not new, but they are becoming more extreme due to human-caused climate change. Global warming caused by heat-trapping greenhouse gases helps fuel storms. That means when storms do form, they can unleash greater force.

Rainfall intensity has quadrupled in Spain over the past 50 years, according to a recent study by the Polytechnic University of Catalonia, which found that heavy and heavy rains have increased. The threshold for heavy rain is 60mm of rain. During this cold front, rainfall has been around 200mm and up to 400mm in some areas such as the town of Utiel in the Valencia region.

Cold drops are extremely unpredictable. Heavy rains do not always cause flash floods, but Valencia is particularly susceptible. Flash floods are more likely because after the summer, the soil in Spain can become hard and impermeable. When heavy rains occur suddenly, water remains on the ground, making the risk of flash floods worse. At the same time, rivers in Spain, especially in the Mediterranean basin, are short and steep with narrow floodplains. River and stream beds fill up quickly, posing a threat to nearby communities. Urbanization of floodplains also reduces natural absorption capacity as soil is replaced with concrete. Valencia's sewer system is not designed to handle intense rainfall. Despite efforts to modernize infrastructure, the area remains susceptible to flash floods. Research data suggests that similar disasters will occur more frequently and with greater force in the future.