865. Impact of Climate Change on Heavy Rainfall in the Mediterranean Region in September

In Japan, the hot days continue into September, and although fall seems to have arrived, the heat is expected to return toward the end of the month. Abnormal weather patterns have been observed around the world this year. In particular, the Mediterranean region, which normally experiences minimal rainfall during the summer, experienced unusually heavy rains in early September, resulting in significant human and material losses.

On September 19, World Weather Attribution, an organization that analyzes the link between extreme events and climate change, highlighted the role of climate change in the heavy rains that hit the Mediterranean region in the first half of September, affecting countries such as Spain, Greece, Bulgaria and Libya.

On September 3, a storm named "Daniel" dumped heavy rain in a matter of hours in Spain, causing severe flooding. Greece and Bulgaria experienced torrential rains and flooding from September 4 to 7, and Libya was hit by catastrophic rainfall on September 10 that caused two dams to burst in Derna, resulting in numerous fatalities.

Acknowledging the inherent uncertainty, the researchers mentioned that the probability of such a heavy rainfall event was estimated to be once every 10 to 40 years in Spain, once every 80 to 250 years in Greece, and once every 300 to 600 years in Libya. Anthropogenic climate change is likely to have increased the probability and intensity of such extreme rainfall events by 10-40% over a large region including Greece, Bulgaria, and Turkey. In cases like the one observed in Libya, the probability of occurrence was potentially 50 times higher and the intensity about 50% greater.

This summer, Greece faced a historic heat wave and wildfires, exacerbated by Daniel. In Libya, the damage was compounded by the breakdown of the country's infrastructure management and maintenance systems, including dams, due to the ongoing conflict. In addition, the dams, built in the 1970s, were not designed to withstand rainfall that occurs every 300 to 600 years, and the lack of an early warning system made it difficult to assess the risks posed by "Daniel" in advance.

The researchers emphasized the importance of designing and maintaining infrastructure in the future with an eye not only to current or past climate, but also to future climate. While this is a challenge for conflict-affected countries such as Libya, it underscores the need to consider both long-term average rainfall decline and short-term instances of extreme heavy rainfall.

Contributor: IIYAMA Miyuki (Information Program)