The study concluded: "In essence, there was a detectable effect of anthropogenic global warming in the teleconnection and moisture transport leading to Mays 2015's high precipitation."
Climate change and poor construction of dams and levees have combined to increase global flooding. This video looks at how researchers are investigating new ways to fix these issues.
In March this year, the World Resources Institute (WRI) published the first public analysis of all world data on current and future river-flood risks.
It found the number of people affected by river flooding worldwide could nearly triple in the next 15 years. It said 50 million people would be affected with an annual potential cost to the world economy of around £340bn.
Climate change, population growth and socio-economic development are driving the increase, it said.
By 2030, it found, if there isn't any increased investment in flood prevention, the UK could be facing a yearly bill of more than £2bn, and almost 80,000 people will be affected by rising tides.
A recent study which looked at global warming and flooding found human influence could have caused the wettest month on record in Texas and Oklahoma during May 2015.
Of the findings, The Guardian said: "The detection of human influence on extreme weather is a rapidly maturing field and each year we are finding more and more evidence of the connections. The corollary is that without efforts to reduce greenhouse gases, we can expect more frequent and intense extreme weather in the future."