Spain is still reeling from recent floods in the Valencia region. In some areas, a year’s worth of rain fell in a single day. Sudden torrents raced through towns and cities. Over 200 people are dead. Rapid analysis suggests daily rainfall extremes in this region and season have become twice as common over the last 75 years and become 12% more intense.
The World Meteorological Organisation has pointed out that climate change is steadily increasing the risk of extreme floods like these. Warmer air can hold more water vapour, about 7% more per degree Celsius of warming. More moisture generally leads to more intense rainfall, and therefore more extreme floods.
The physics of how temperature influences the atmosphere’s capacity to hold moisture has been known for close to 200 years. But we’ve learned something worrying more recently. When water vapour condenses to form rain droplets, it releases heat which can fuel stronger convection and boost updrafts of air currents in storms. This means the intensity of extreme rainfall could increase not just 7% per degree of warming, but over twice that rate.
