Statistical analysis of record-breaking events

[wibble]

Disclaimer: I'm not a statistician, I'm a phlyarologist.

I'm currently reading 'Rivers' by Griff Rhys Jones. It was a Christmas gift. On page 131 it says:

In the Plynlimon area [Wales] the average annual rainfall is 85.06 inches [...] the wettest year on record was 2000 when 124 inches fell and the driest was 1976 with just 57.9 inches.

This nugget of information set me wondering.

Now, this book isn't about climate change, it's about England's rivers. (Its style is a bit odd, it meanders in no specific direction, but then I suppose that fits its theme). 'Rivers' was published in 2009. It mentions, in passing, that the wettest year on record for a small part of the globe occurred just nine years ago (without commenting on that aspect of it).

As another example, there's the 'warmest year on record' situation. This was in either 1998 or 2005 depending on who you listen to. But whichever one of those it is, this event happened within the last decade (ok, -ish).

The Tunguska event happened a century ago -- and as I understand it, events of that scale are one-a-century (so we're overdue for another). The Californian faultline has long been reported as 'overdue for The Big One.' Numbers like those have been crunched.

What I'd like to know is what is the probability of extreme weather events breaking records. Have there been any studies examining the statistical likelihood of such events?

It seems pretty clear to me that the longer you measure things, and the more things you measure, the more records you'll eventually break. But is it valid to simply dismiss recent extreme events on this basis?

What about 'clustering' (is that the right term?) of extreme events? If more records are being broken in the recent past, is that statistically significant... or not?

Could the apparent frequency of extreme weather be a fabrication caused by the fact that information about global events is more readily available to us now (as opposed to, say, thirty years ago)?

The fact that long-term weather records (appear to be) being broken at the present time may, to some, be interpreted as 'just natural weather variation.' Maybe that's correct -- I don't know. My own gut feeling is that these are clear indications that climate is being disrupted.

Might information of this kind help to clarify some of the confusion in relation to climate change?

Apologies if this is already covered on Manpollo somewhere...

[776281]

Extreme weather 2011
Flood
Missippi
Manitoba
Queensland
Victoria
Tasmania

Drought
UK
http://www.guardian.co.uk/environmen...march-60-years
Texas
http://www.lakewyliepilot.com/2011/0...rrounding.html
Kansas
http://www.hdnews.net/Story/Wheatcrop051211
Kenya
http://www.youtube.com/watch?v=EPiFNS8dIVo
Western Australia
http://www.bom.gov.au/climate/drought/drought.shtml
Afganistan
http://www.irinnews.org/Report.aspx?ReportId=91736

Tornados
Had a few of those too

A sad list that is far from complete. So many places are facing very poor crops.

[776281]

More extreme weather
Drought
France
http://www.bloomberg.com/news/2011-0...e-says-1-.html

The crop has entered a “critical stage,” and weather in the next two weeks will be decisive for yields, Christian Vanier, FranceAgriMer’s industry coordinator for cereals, said in a presentation in Montreuil-sous-Bois, near Paris.

China

With one of the driest springs on record, farmers in most areas of central and south China are desperate for rain. However, rainfall has been substantially below normal since the beginning of the year.

Russia
Not this year
http://online.wsj.com/article/SB1000...071498786.html

"I have heard that there are concerns about a potential repeat drought," said Cropcast senior agricultural meteorologist Donald Keeney. "However, all of our long-term forecast data suggest that there won't be a repeat drought in Russia this summer."

But they also say

"The spring plantings continue to be behind normal pace and rains are needed in coming weeks or the situation will certainly deteriorate," said Rabobank analyst Erin FitzPatrick.

Effect on food prices
http://www.bloomberg.com/news/2011-0...nada-rain.html

Less than a year after the worst drought in a generation destroyed one-third of Russia’s wheat crop and sent global food prices surging, more bad weather is damaging fields from North America to Europe to Asia.

New South Wales
Not drought but too dry (What?)

The climatic drought maybe over, but Bungendore farmer John Reardon says dry times continue.

"It is starting to get fairly critical because we need rain to give us some winter growth," he said.

Out of season rain
India

http://www.sundaytimes.lk/110515/Plus/plus_12.html

Too much water in the dry zone tanks could spell disaster to elephants unless steps are taken, warn conservationists.
Kumudini Hettiarachchi reports
Forewarned is forearmed and as the country faces unusual weather patterns and rains when there should be none, resulting in reservoirs and tanks in the dry zone filling to the brim, conservationists have sent out an alert that elephants may be in trouble.

[gazelle]

I find this a little misleading. With the media bias toward any negative or eye-catching, the reports on droughts/floods/storms will exceed the number of reports that "all is well, no problems here".
Also, if we are nudging the boundaries, then we're bound to get a cluster of "record-breaking" events (e.g. if temperature is trending upwards, then we're going to keep getting "hottest on record" reports... but this would occur even if the trend had levelled out, or was even decreasing slightly).

I think that rather than listing weather events or bad seasons, the important thing is to identify the long-term trend, in either number or severity.

I'm sure it's out there, but I haven't been able to find any study into this, apart from long-term temperature trends.

[776281]

Not too many hits for good rain
http://www.industrysearch.com.au/New...ok-ABARE-18005
Nup that was 2005
http://www.weeklytimesnow.com.au/art...ticulture.html

While other tree crops, especially nuts, and grape vines have been hammered by disease outbreaks during the wet spring and summer, the rain was welcomed in Victoria's olive groves.

Lots of sports teams have had a good start to the season, not so many crops. Individually these droughts may not be all that exceptional, but the total picture must be. Regular rain is not so common.

Lets see what the price of wheat and flour do this year.

[sinimod]

Originally Posted by gazelle

I find this a little misleading. With the media bias toward any negative or eye-catching, the reports on droughts/floods/storms will exceed the number of reports that "all is well, no problems here".
Also, if we are nudging the boundaries, then we're bound to get a cluster of "record-breaking" events (e.g. if temperature is trending upwards, then we're going to keep getting "hottest on record" reports... but this would occur even if the trend had levelled out, or was even decreasing slightly).

I think that rather than listing weather events or bad seasons, the important thing is to identify the long-term trend, in either number or severity.

I'm sure it's out there, but I haven't been able to find any study into this, apart from long-term temperature trends.

I haven't done a whole lot of checking around on this topic, but Section 3.8 of Chapter 3, Working Group I of the 2007 IPCC report is a very good source of information concerning extreme weather events. They summarize the understanding of climate scientists concerning extreme weather events up to 2007 in FAQ 3.3. The first paragraph of FAQ 3.3 reads:

Since 1950, the number of heat waves has increased and widespread increases have occurred in the numbers of warm nights. The extent of regions affected by droughts has also increased as precipitation over land has marginally decreased while evaporation has increased due to warmer conditions. Generally, numbers of heavy daily precipitation events that lead to flooding have increased, but not everywhere. Tropical storm and hurricane frequencies vary considerably from year to year, but evidence suggests substantial increases in intensity and duration since the 1970s. In the extratropics, variations in tracks and intensity of storms reflect variations in major features of the atmospheric circulation, such as the North Atlantic Oscillation.

I agree with gazelle that the media can easily bias our thinking about extreme weather events as they are so newsworthy. It seems the last few years have had a plethora of extreme weather events, but viewed within a historical context, it may not seem quite so bad. Having said that, it appears some regions might be changing more rapidly than others, for reasons that may not yet be clear.

[776281]

OK just the record breaking
Record low for Lake Constanace/Bodensee
http://www.hvz.baden-wuerttemberg.de...0007&btn=1&m=W
07.07.1817 6:36 [M]
18.08.1821 5.91 [M]
24.05.1999/11.06.1999 5.65 [M]
And now 4.80 [M]
Perhaps Baerbel would like to comment on this one.

http://climateprogress.org/2011/05/1...ng-gulf-coast/

Scientists expect the historic flooding could lead to the largest dead zone on record, which could stretch the massive area all the way to the Texas coast. An expanded dead zone will be a major stress on fish, shrimp, and other species struggling to rebound from last year’s oil spill because marine life will suffocate and die if it can’t swim away from or otherwise flee these hypoxic conditions. Thus, as the Thibodaux Daily Comet notes, it will be “another setback for fishermen trawling the Gulf in hopes of making up for last year’s spring fishing season, which was shut down in much of the state by the BP oil spill.”

But also near records
eg http://www.chinadaily.com.cn/china/2...t_12511857.htm

What also has stuck is the spacial proximity of severe drought and severe flooding, but I do not know if there is any data on this from an historical perspective.

[776281]

http://scienceblogs.com/deltoid/

On the front page of The Australian today we find the headline Summer of disaster 'not climate change': Rajendra Pachauri. If you read the actual quotes from Pachauri in the article and not the fabricated one in the headline, you'll find that Pachauri said something rather different:

"What we can say very clearly is the aggregate impact of climate change on all these events, which are taking place at much higher frequency and intensity all over the world.

"On that there is very little doubt; the scientific evidence is very, very strong. But what happens in Queensland or what happens in Russia or for that matter the floods in the Mississippi River right now, whether there is a link between those and climate change is very difficult to establish. So I don't think anyone can make a categorical statement on that."

[776281]

http://www.climatewatch.noaa.gov/art...rnado-outbreak

The tornado outbreak across the southern United States in late April 2011 was deadly, devastating, and record breaking.

These days, when the weather breaks records, it’s natural to wonder if global warming is to blame. So it’s not surprising that in recent weeks, climate scientists have been fielding lots of questions about the possible connection between global warming and tornadoes.

Even before the April 2011 outbreak, scientists have been looking for long-term changes in U.S. tornado activity. The research that’s already been done paints an inconclusive picture. The number of smaller tornadoes seems to have increased; the number of large tornadoes has not. Between better technology—radars, satellites, the internet—and greater public awareness, it’s likely that the increase is due to more reports, not more tornadoes.

If we can’t detect a change in tornadoes themselves, says Hoerling, we might be able to detect a long-term change in the weather conditions that contribute to tornadoes. Key among those factors are the instability of the atmosphere, the amount of water vapor in the part of the atmosphere known as the planetary boundary layer, and vertical wind shear.

An unstable atmosphere is a significant predictor of whether thunderstorms that could lead to tornadoes will happen on a given day. If the atmosphere has become more unstable in recent decades, it could affect tornado outbreaks. The CSI team compiled a record of atmospheric instability over the Gulf of Mexico and the southern United States from 1979-2010 and saw no sign of a long-term change.

Other weather conditions being equal, increased water vapor means more potential heat to be released through condensation and stronger updrafts, fueling potentially stronger storms. Hoerling and the CSI team have analyzed observations of water vapor over recent decades, and they don’t see any long-term change in humidity over the Gulf of Mexico or the southern United States in April. The only signal they see is year-to-year variability.

So can't get a signal in the data, any possible signal is well lost in the noise.

[wibble]

Originally Posted by 776281

So can't get a signal in the data, any possible signal is well lost in the noise.

Lies, damn lies and sadistics... a Google for "record-breaking weather and climate change" leads me to a Fox News item http://www.foxnews.com/us/2011/05/09...#ixzz1Lxx64Z6B which lists several recent US events and then attempts a conclusion "scientists say there's no link" ...

[...]

U.S. scientists also looked for the fingerprints of global warming and La Nina on last month's deadly tornadoes, but couldn't find evidence to blame those oft-cited weather phenomena.

NOAA research meteorologist Martin Hoerling tracked three major factors that go into tornadoes — air instability, wind shear and water vapor — and found no long-term trends that point to either climate change or La Nina. That doesn't mean those factors aren't to blame, but Hoerling couldn't show it, he said.

Climate models say that because of changes in instability and water vapor, severe thunderstorms and maybe tornadoes should increase in the future. But it may take another 30 years for the predicted slow increase to be statistically noticeable, said NOAA research meteorologist and tornado expert Harold Brooks.

... However, the piece concludes with:

But Kevin Trenberth, climate analysis chief at the National Center for Atmospheric Research in Boulder, said the preliminary study that Hoerling conducted was flawed and too simplified. He said there is evidence of an increase in instability in the atmosphere happening now.

(So, Fox News, do 'scientists' say there is a link or not?)

[sinimod]

The Year of Living Dangerously 2010 Extreme Weather Cost Lives, Health, Economy

The extreme weather of 2010 exacted a huge human and economic toll here as well. More than 380 people died and 1,700 were injured due to weather events throughout the year. And the magnitude of these events forced the Federal Emergency Management Agency, or FEMA, to declare 81 disasters last year For nearly 60 years, the annual average has been 33.

And 2011 has been worse in the US and across the globe up to this point. Are the last two years just statistical outliers? The upward trend of extreme weather events over the last 30 years would argue otherwise.

A February 2011 special report from Reuters noted that it’s been rough going for the $500 billion U.S. property insurance business, explaining that “storms are happening in places they never happened before, at intensities they have never reached before and at times of year when they didn’t used to happen.”

Dr. Evan Mills, a scientist in the Environmental Energy Technologies Division at the Lawrence Berkeley National Laboratory confirms that in the United States, “insured weather-related losses in recent years have been trending upward much faster than population, inflation, or insurance penetration, and far outpace losses for non-weather-related events.”

…a report by the National Center for Atmospheric Research, Climate Central, The Weather Channel, and the National Oceanic and Atmospheric Administration shows that “if temperatures were not warming, the number of record daily highs and lows being set each year would be approximately even. Instead … record high temperatures far outpace record lows across the U.S.”

Almost every region of the United States experienced unusually heavy precipitation last year that many flood occurrences were exceeded. This prompted FEMA Administrator Craig Fugate to say, “the term ‘100-year event’ really lost its meaning this year.”

Taking these record flooding levels into account, the U.S. Army Corps of Engineers raised its 100-year-flood estimates nearly a foot in May 2010, effectively increasing the amount of water necessary to qualify for a very rare flood event. In other words, flood levels that were once rare are now classified as common.

Rising temperatures over the ocean cause more water vapor to condense, contributing to increased rainfall. The intensity of individual rain events has increased dramatically over the past 50 years, concurrent with greenhouse gas levels

And according to Kevin Trenberth, the head of climate analysis for of the National Centre for Atmospheric Research

There is a systematic influence on all of these weather events nowadays because there is more water vapour lurking around in the atmosphere than there used to be, say, 30 years ago. It’s about a four per cent extra amount, provides plenty of moisture for these storms and it’s unfortunate that the public is not associating this with the fact that this is one manifestation of climate change. And the prospects are that these kinds of things will only get worse in the future.

2011 has already been a very bad year, and Trenberth doesn't think things will get any better in 2012.

[776281]

http://tamino.wordpress.com/2011/05/...f-the-twister/

Shortly after it became clear that April 2011 broke the U.S. record for the most April tornados, the Washington Post reported that it was not a “legitimate” record … yet. That’s because earlier years’ counts are adjusted upward in an attempt to compensate for our increasing ability to detect tornados in the U.S. However, it didn’t take long for April to shatter, not only the actual record of observed number of tornados, but the adjusted record as well.

2011 is already the “year of the twister,” and it isn’t over yet. It also follows hard upon an onslaught of extreme weather events over the last year. Heat waves, floods, droughts, storms, wildfires, have inflicted heavy casualties around the globe, and the U.S. has not been immune to the plague. It’s long past time that we should take global warming seriously, not just as a scientific fact but as a genuine threat to health and safety. Forewarned is forearmed — unless the warning is ignored.

[sinimod]

U.S. had most extreme spring on record for precipitation

Nature's fury reached new extremes in the U.S. during the spring of 2011, as a punishing series of billion-dollar disasters brought the greatest flood in recorded history to the Lower Mississippi River, an astonishingly deadly tornado season, the worst drought in Texas history, and the worst fire season in recorded history. There's never been a spring this extreme for combined wet and dry extremes in the U.S. since record keeping began over a century ago, statistics released last week by the National Climatic Data Center (NCDC) reveal.

The percent area of the Contiguous U.S. experiencing much above average heavy 1-day precipitation events in spring 2011 hit a record high, nearly 16%. The 102-year average is 9%. The previous record of 15.5% was set in 1964. Heavy springtime 1-day precipitation events in the U.S. have been increasing since 1960, in line with measured increases in water vapor over the U.S. due to a warming climate.

Percent increase in the amount falling in heavy precipitation events (defined as the heaviest 1% of all daily events) from 1958 to 2007, for each region of the U.S. There are clear trends toward more very heavy precipitation events for the nation as a whole, and particularly in the Northeast and Midwest. Climate models predict that precipitation will increasingly fall in very heavy events, similar to the trend that has been observed over the past 50 years in the U.S.

This drying of the Southern U.S. and increased precipitation in the Northern U.S. is expected to occur because of a fundamental shift in the large scale circulation of the atmosphere. The jet stream will retreat poleward, and rain-bearing storms that travel along the jet will have more moisture to precipitate out, since more water vapor can evaporate into a warmer atmosphere. The desert regions will expand towards the poles, and the Southern U.S. will experience a climate more like the desert regions of Mexico have now, with sinking air that discourages precipitation. A hotter climate will dry out the soil more, making record intensity droughts like this year's in Texas more probable. So, is it possible that the record extremes of drought and wetness this spring in the U.S. were due to a combination of La Niña and climate change. It is difficult to disentangle the two effects without doing detailed modelling studies, which typically take years complete and publish. One weakness in the climate change influence argument is that climate models predict the jet stream should retreat northwards and weaken due to climate change. Indeed, globally the jet stream retreated 270 miles poleward and weakened during the period 1970 - 2001, in line with climate model expectations. Thus, a stronger and more southerly jet stream over the U.S. during the spring is something we should expect to see less and less of during coming decades.

The future: simulated change in precipitation during winter and spring for the years 2089 - 2099 as predicted by fifteen climate models, assuming we continue high emissions of heat-trapping carbon dioxide.

[wibble]

Originally Posted by sinimod

U.S. had most extreme spring on record for precipitation

Meanwhile, back on Planet Eaarth...

The UK in April 2011 - "a very remarkable month in hydrometeorological terms"

April was a very remarkable month in hydrometeorological terms: provisionally it was the warmest April in the 352-year Central England Temperature series, estimated (river) outflows from Britain were the lowest on record for the last week of April, and the end-of-month soil moisture deficits were the highest (for England & Wales) in a 50-year series.

The exceptional aridity of the early spring, following a relatively dry 2010, has resulted in agricultural and hydrological drought conditions affecting large parts of southern Britain. Currently, the primary impacts are on farmers and growers, an increased risk of forest and heath fires and, importantly, on river flows. Correspondingly, replenishment to most gravity-fed reservoirs was very meagre and overall stocks for England & Wales registered their second largest March/April decline since 1997.

Looks like GaiasDaughter is right, we need to work together. As in: "excuse me, you guys across the Pond - can you spare some of your water, please?"

Grist pointed me to another sterling effort from Stephen Thomson of Plomomedia entitled: A link between climate change and Joplin tornadoes? Never.

[776281]

http://thinkprogress.org/romm/2011/0...ly-since-1816/

2010 – 2011: Earth’s most extreme weather since 1816?
Dr. Jeff Masters

Every year extraordinary weather events rock the Earth. Records that have stood centuries are broken. Great floods, droughts, and storms affect millions of people, and truly exceptional weather events unprecedented in human history may occur. But the wild roller-coaster ride of incredible weather events during 2010, in my mind, makes that year the planet’s most extraordinary year for extreme weather since reliable global upper-air data began in the late 1940s. Never in my 30 years as a meteorologist have I witnessed a year like 2010–the astonishing number of weather disasters and unprecedented wild swings in Earth’s atmospheric circulation were like nothing I’ve seen. The pace of incredible extreme weather events in the U.S. over the past few months have kept me so busy that I’ve been unable to write-up a retrospective look at the weather events of 2010. But I’ve finally managed to finish, so fasten your seat belts for a tour though the top twenty most remarkable weather events of 2010. At the end, I’ll reflect on what the wild weather events of 2010 and 2011 imply for our future.

[wibble]

http://www.wunderground.com/blog/Jef...?entrynum=1831

Where will Earth's climate go from here?
The pace of extreme weather events has remained remarkably high during 2011, giving rise to the question--is the "Global Weirding" of 2010 and 2011 the new normal? Has human-caused climate change destabilized the climate, bringing these extreme, unprecedented weather events? Any one of the extreme weather events of 2010 or 2011 could have occurred naturally sometime during the past 1,000 years. But it is highly improbable that the remarkable extreme weather events of 2010 and 2011 could have all happened in such a short period of time without some powerful climate-altering force at work. The best science we have right now maintains that human-caused emissions of heat-trapping gases like CO2 are the most likely cause of such a climate-altering force.

(Author's emphasis.)

Thanks, Tony. That's the kind of thing I've been hunting for (while, naturally, being conscious of the possibility of confirmation bias/ cognitive dissonance).

Is it simply too early days to expect any peer-reviewed content on this topic? -- Not that I'd necessarily recognise a peer-reviewed article if it jumped up and down on my chest bearing a harpsichord and singing ~peer-reviewed content is here again~

[wibble]

Desmogblog: Forget Tornadoes. Lets Talk--Unendingly--About Heat Waves and Global Warming

NASA climatologist Gavin Schmidt, who told Media Matters that it's

...very probable that any particular heat wave happening now will be shown to have become more likely because of global warming…Of all the different extreme events that can happen, the partial attribution of heat waves to ongoing climate change is one of the easier connections.

Interesting comment by 'solitha':

Try this link instead:
http://www.ncdc.noaa.gov/extremes/re...2011/07/17?sts[]=US#records_look_up

July 17 - 18 records broken, 28 tied for high max.
July 18 - 30 broken, 41 tied.
July 19 - 36 broken, 33 tied.
July 20 - 75 broken, 65 tied.
July 21 - 133 broken, 73 tied.
July 22 - 191 broken, 72 tied.
July 23 - 183 broken, 64 tied.

The fact that there are still ALL-TIME records being broken is even more alarming. It's still early in the summer.

[sinimod]

Here is a nice little piece in USAToday with a baseball analogy on climate extremes entitled Our view: What's going down? Not temperatures, or AC bills:

What's happening is extraordinarily hot weather, centered in the Southern Plains. Oklahoma's average temperature in July (88.9 degrees) was the hottest for any state for any month on record. Dallas is closing in on its record of 42 consecutive days of 100-plus degree weather. Newark set an all-time high of 108 on July 22. Washington, D.C., has had 24 days at 95 degrees or above, approaching the record of 28. Nationally, last month was the fourth hottest July on record, with communities in all 50 states setting high temperature records.

While scientists caution that no individual extreme weather event can be conclusively linked to global warming, this summer is consistent with computer-model predictions of hotter days, warmer nights and more severe droughts.
Here's one way to think of it: The atmosphere is juiced like athletes on performance-enhancing drugs. During baseball's steroid era, steroids didn't turn singles into home runs. But what used to be fly balls to the warning track ended up over the fence.
Similarly, climate change and urbanization don't cause heat waves and droughts so much as intensify them. So what used to be a 95-degree day can become a 100-degree day. Or what once was a 75-degree nighttime low can turn into an 80-degree night.

Opponents of efforts to combat global warming talk about the price of putting a tax on carbon or creating a market-based system to reduce greenhouse gas emissions. The leading "cap and trade" bill in the Senate, for example, would cost an estimated $350 in 2025 per four-person household.
But the climate change skeptics and deniers — many of whom hail from Texas and Oklahoma, the epicenter of this summer's misery — rarely discuss the price of inaction. If you accept that climate change is occurring, such costs are reflected in higher air conditioning bills and wilted crops.
According to a study by Tufts University researchers for the Natural Resources Defense Council, climate change will cost the average four-person household an additional $340 in energy costs in 2025, plus $2,950 for hurricane damages, real estate losses and water-supply costs.

[sinimod]

U.S. Heat Records Continue Crushing Cold: Incredible 22 to 1 Ratio in August

When new daily high temperature records overwhelmed low temperature records by well over 20 to 1 in the first 9 days of August, it was impressive enough, but the amazing excess has continued right through the end of the month. The over 3000 daily heat records swamped the 142 cold records by 22.2 to 1.

For meteorological summer (June-August) as a whole, the ratio increased to 11.4 to 1 from 8.4 to 1 through July, and the year to date is now at 3.4 to 1, more than 50% above the average for the previous decade.

[sinimod]

Human contribution to more-intense precipitation extremes

Given that atmospheric water-holding capacity is expected to increase roughly exponentially with temperature—and that atmospheric water content is increasing in accord with this theoretical expectation—it has been suggested that human-influenced global warming may be partly responsible for increases in heavy precipitation. Because of the limited availability of daily observations, however, most previous studies have examined only the potential detectability of changes in extreme precipitation through model–model comparisons. Here we show that human-induced increases in greenhouse gases have contributed to the observed intensification of heavy precipitation events found over approximately two-thirds of data-covered parts of Northern Hemisphere land areas. These results are based on a comparison of observed and multi-model simulated changes in extreme precipitation over the latter half of the twentieth century analysed with an optimal fingerprinting technique. Changes in extreme precipitation projected by models, and thus the impacts of future changes in extreme precipitation, may be underestimated because models seem to underestimate the observed increase in heavy precipitation with warming.

The researchers compared observed and simulated precipitation events in the second half of the twentieth century and found that simulations may have underestimated the trend in extreme precipitation events.

Our results also show that the global climate models we used may have underestimated the observed trend, which implies that extreme precipitation events may strengthen more quickly in the future than projected and that they may have more severe impacts than estimated.