Extreme rainfall, floods due to warming: study

Using more than 8000 weather stations around the world and data going back to 1900, researchers have found a link between global warming and an increase in extreme rainfall. By Aileen Macalintal.
Lead author Dr Seth Westra said rainfall extremes were increasing over the period studied, 1900 to 2009, and this was linked to a one-degree rise in atmospheric temperature during this period. Westra is a senior lecturer at the University of Adelaide school of civil, environmental, and mining engineering.
Researchers found that the greatest increases are in the equatorial regions. “Although this is also the region with greatest uncertainty,” Westra said the upsurges are “statistically significant, and therefore are cause for concern,” since heavy and frequent rainfalls cause serious floods around the world.
He said rainfall intensity increased by 7 per cent for every degree increase in global atmospheric temperature. “While a 7 per cent increase in precipitation extremes per degree might not seem like much, I would imagine that the implications on increasing global flood risk would also be substantial.”
The study, Global increasing trends in annual maximum daily precipitation, says: “Annual maximum daily precipitation data represents one of the most important and readily available measures of extreme rainfall, and is used frequently as an input to assessments of flood risk.”
To examine rainfall data from 1900 to 2009, the research team used daily rain gauges over 24 hours, as well as digitised data from the early 20th century.
“This technology was available from 1900 onwards, and older hand-written charts have been digitised as part of the dataset compilation. Nevertheless, prior to 1950 the precipitation data is mostly confined to Eurasia, North America, Southern South America, Australasia and India,” explained Westra.
The study also involved researchers from the University of NSW and the University of Victoria, Canada.
The tropical countries exhibited the strongest increases but the researchers noted that some level of increase seems to be taking place at the majority of weather gauging stations.
“We found that the ‘association’ between extreme rainfall and global near-surface atmospheric temperature was constant through time,” said Westra. “However, the global near-surface atmospheric temperature series has been increasing more strongly since the early 1970s. Connecting these two statements would imply that rainfall extremes should have been increasing more quickly from the 1970s onwards, although we did not explicitly test for this.”
Westra also commented on the uneven geographic coverage: “Note that we did take the uneven global distribution of precipitation into account in our analysis, by giving the more densely gauged areas less weight than the less densely gauged areas.”

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