8 mega-floods in 11 days: what are the reasons behind heavy rainfall around the world?

On Friday, a man walked through the flooded yard of his home in Paramas, Greece.

Catastrophic flooding in Libya, which could kill up to 10,000 people, is just the latest in a series of heavy rainfall events that have hit the globe over the past two weeks.

The first 11 days of September saw eight devastating flooding events across four continents. Before Storm Daniel in the Mediterranean, flooding was raging eastern Libya, with heavy rains inundating parts of central Greece, northwestern Turkey, southern Brazil, central and coastal Spain, southern China, Hong Kong and the southwestern United States.

Andrew Hall, a research meteorologist at the National Oceanic and Atmospheric Administration's Physical Sciences Laboratory, said it's unusual to see so many unrelated extreme weather events around the world in such a short period of time.

In Drna, Libya, on Monday, people walk past the bodies of flood victims.

"Sometimes these events come together, whether it's in a country, a hemisphere or a global scale," he said. "At the moment, it seems that globally, this is the prime time for a series of flood events."

As with many other forms of extreme weather, scientists say climate change is likely to have an impact on rainfall and flooding, but understanding the relationship accurately can be tricky.

Overall, studies show that global warming is exacerbating the Earth's water cycle. Warmer temperatures increase evaporation, which means a warmer atmosphere can hold more moisture. As a result, storms may bring more intense precipitation, which can lead to severe flooding.

People mourn on Saturday in Mucum, Rio Grande do Sul, Brazil.

People mourn in Mucum, Rio Grande do Sul, Brazil. Claudia Martini/Xinhua/Getty Images

As the world warmed, researchers observed these changes. According to the Environmental Protection Agency, global precipitation has increased by an average of 0.04 inches per decade since 1901.

However, many factors affect flood events and their severity, and teasing out traces of climate change when they interact can be challenging, Hall said.

"From an altitude of 1,000 feet, if it's hotter, there's more water vapor, so there's more precipitation in the sky," he said. "But when you look at a particular event and a specific set of physical processes associated with that event, it's hard to attribute to each process in that causal chain."

On the one hand, the types of extreme weather that caused the eight catastrophic flood events this month all have different root causes.

A neighborhood in Larissa, Greece, was flooded on Sunday.

A Mediterranean storm named Daniel brought heavy rain to central Greece and Libya. Typhoon Anemone and its aftermath hit Hong Kong and southern China, bringing record rainfall, flooding in urban and rural areas, destroying roads and triggering more than 100 landslides.

The downpour caused flash floods in central and coastal Spain, northwestern Turkey, and thousands of miles away in the Brazilian state of Rio Grande do Sul. This month's fast-moving thunderstorm in southern Nevada triggered flash floods across the region, flooding the Las Vegas Strip and stranding more than 70,000 people at Black Rock Desert Burning Man.

On September 5, a man was rescued and evacuated during floods in Istanbul.

For certain types of extreme flood events, such as those associated with Mediterranean cyclones such as Daniel, there simply isn't enough data to look at changes over time.

"We really don't have samples or records long enough to detect changes because their occurrence is not that common," Hall said.

In other cases, local factors, such as how wet and dry the ground is or the basic topography of an area, can have a huge impact on the development of flooding and its consequences.

On Monday, Shahat, Libya, was hit by a heavy storm and heavy rainfall, damaging roads.

In addition to loss of life and property, flooding increases people's risk of exposure to waterborne pathogens, which have a significant impact on outbreaks of deadly diseases.

Hall said the number of devastating floods this month was painful, but said he was particularly concerned about the situation unfolding in Libya.

"If you look at the damage and the number of deaths caused," he said, "you'll be blown away." ”

A woman holds her son after heavy rains in Vilamanta, Spain, September 4, as they clean the dirt from her house.