The flash flood that killed at least 95 people in the Valencia region in 1996 was the result of climate change, dry soil after summer and the cold drop phenomenon.
The flash floods, the deadliest in Spain since 1996, raise questions about the level of flood protection needed to cope with the heavy annual autumn rains in the Valencia region, according to Telegraph.
Heavy fall rains along Spain’s Mediterranean coast are caused by the “cold drop” phenomenon. This phenomenon occurs when warm, humid air in the Mediterranean meets a sudden cold airflow from the north, causing localized heavy rain.
Valencia is located on the coast and is particularly at risk of low pressure at high altitudes in autumn because the Mediterranean Sea is still warm. Such phenomena are not new but are becoming increasingly extreme due to human-caused climate change. Global warming caused by heat-trapping greenhouse gases helps provide more energy for storms. That means when a storm appears, it will release greater power.
Rainfall intensity has quadrupled in the past 50 years in Spain, according to recent research by the Polytechnic University of Catalonia, which shows an increase in heavy and heavy rains. The threshold for heavy rain is 60 mm of rain. During this cold front, rainfall was about 200 mm and up to 400 mm in some areas such as the town of Utilel in the Valencia region.
Cold drop is extremely difficult to predict. Heavy rain does not always cause flash floods, but Valencia is susceptible. Flash floods are more likely to occur because after summer the soil in Spain can be dry and impermeable to water. When sudden heavy rain occurs, water stagnates on the ground, making the risk of flash floods worse. At the same time, the rivers in Spain, especially the Mediterranean basin, are quite short and steep with narrow mudflats. River and stream beds fill up quickly, creating a threat to nearby communities. The process of urbanization in flood areas also reduces natural absorption capacity because soil is replaced by concrete. The sewer system in Valencia is not designed to handle intense heavy rain. Despite efforts to modernize infrastructure, the area is still prone to flash floods. Research data indicates that similar disasters will occur more frequently and with greater force in the future.