At least nine people have died, and several more are missing, after Storm Daniel swept across Greece, Turkey, & Bulgaria on Monday 4 and Tuesday 5 April 2023. In Greece a man died when a wall collapsed onto him in Volos on the Pagasetic Gulf, on Monday 4 September, and another man was killed in a vehicle-related incident, while on Wednesday 6 September the body of an elderly woman who was missing was found close to the city, having apparently drowned in the storm. Another four people are still missing in Greece. Considerable damage to infrastructure has occurred, and about a hundred people were evacuated from affected areas.
In Turkey at least two people have died in flooding in Istanbul and dozens have had to be rescued as floodwaters covered two neighbourhoods of the city, while in Kirklareli Province, close to the border with Bulgaria, five tourists are known to have died when a flash flood hit a campsite at which they were staying, and another one is still missing. Across the border in Bulgaria, four people are known to have died and three more are still missing after flooding hit the Black Sea coastal region.
Most storms form due to heating of air over the sea. As the air is heated the the air pressure drops and the air rises, causing new air to rush in from outside the forming storm zone. If this zone is sufficiently large, then it will be influenced by the Coriolis Effect, which loosely speaking means the winds closer to the equator will be faster than those further away, causing the storm to rotate, clockwise in the northern hemisphere and anticlockwise in the southern hemisphere.
Whilst the high winds associated these storms is extremely dangerous, the real danger from such storms is often the flooding. Each millibar drop in air pressure can lead to a 1 cm rise in sea level, and large storms can be accompanied by storm surges several meters high. This tends to be accompanied by high levels of rainfall, caused by water picked up by the storm while still at sea, which can lead to flooding, swollen rivers and landslides; which occur when waterlogged soils on hill slopes lose their cohesion and slump downwards, over whatever happens to be in their path.
Such storms are common in tropical regions, but less so on the more temperate Mediterranean. However, this summer much of the eastern Mediterranean has suffered a prolonged heat wave, with temperatures regularly exceeding 40°C, and heat related deaths recorded across much of southern Europe, as well as a series of wildfires which have swept across Greece and other countries as vegetation has dried out. These events have been caused by a combination of an anticyclone (high pressure system) which formed over the Sahara then migrated northwards, intensified by an El Niño system over the southern Pacific, which tends to drive temperatures upwards in the Northern Hemisphere, both of which are considered to have been intensified by global warming.
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