Rains in Valencia, Spain last week were catastrophic for a number of reasons.
More moisture in the air, a hotter Mediterranean, greater development in the affected areas with more impermeable concrete roads, parking lots and structures shedding water.
The pictures are similar to what we saw in Asheville, NC area after Hurricane Helene, looking like some giant with a hydraulic machine simply ran roughshod over whole areas. Cars, buildings, concrete – it doesn’t matter, human constructions simply cannot stand up to the force of massive, moving water.
The tragedy has raised questions about whether earlier warningscould have prevented so many deaths, while the widespread damage shows how many cities aren’t adapted to withstand rainfall amplified by climate change.
An extremely hot Mediterranean and warmer air temperatures exacerbated a type of storm system that is becoming more common in the Iberian peninsula due to global warming. Experts who spoke with Bloomberg Green said that a building boom in the region in recent decades may have put people in harm’s way and reduced stormwater drainage.
“It may happen that the paths we have left for water aren’t large enough, and in recent decades that’s happened too many times,” said Ernest Blade, professor of river and hydrologic engineering at the Universitat Politècnica de Catalunya.
The storm which hit southeastern Spain earlier this week was a particularly intense example of a “dana” storm, a common phenomenon in the area at this time of year. Danas (short for “depresión aislada en niveles altos”) develop when cold autumn air moving south meets warm, moist air typically flowing from the Mediterranean, creating high-altitude storm clouds. These can dump very large amounts of rainfall in a short space of time. This year, the Mediterranean reached a mean temperature of 28.5C (83.3F) in mid-August. It’s remained anomalously warm, making this type of intense storm more likely to develop. Climate change is driving up air temperatures, which allows storms to hold more water — a 7% increase for every 1C of temperature rise.
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A rapid analysis by the World Weather Attribution initiative found the recent extreme rainfall in Spain was around 12% heavier and twice as likely as it would have been in a pre-industrial climate. One-day bursts of rain in the region are increasing as fossil fuel emissions warm up the planet, the group said.
The flooding was also more likely due to the hot, dry year the region had. That’s left soil hard-baked, reducing how much water could soak into the ground.
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Adapting for heavier rainfall will be essential for lowering the risk of future disasters. “Reducing the volume and speed of run-off can be done by replanting upland areas and improving soil health, as well as increasing the capacity of urban areas to absorb, hold or disperse water,” said Kevin Collins, a senior lecturer in environment and systems at the Open University in the UK. He suggested strengthening dams and bridges, which have proven to be vulnerable, too.
Climate change is going to be expensive. You won’t save money by not allocating for strengthening infrastructure, and you won’t avoid expense by skirting new regulations on building in vulnerable areas. The change is here.
I hope this won’t be “a crisis wasted” on their part, and they won’t spend resources to rebuild the city the way it was.
The Guardian‘s imagery suggests that much of the city were infilled lowlands. Rebuilding codes should take into account the urban terrain associated with flash flooding.
They should also prepare for increasing heat by reducing their “urban heat island effect” aggravated by the paved treeless urban canyons shown in the “before” pictures, perhaps converting more streets to ped and bike only.