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Author Topic: Extreme weather event attribution  (Read 1775 times)


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Extreme weather event attribution
« on: December 29, 2016, 06:08:32 PM »
A couple of papers arising from / weather@home

Real-time extreme weather event attribution with forecast seasonal SSTs
K Haustein et al 2016

Here we present a new method which can assess the fraction of attributable risk of a severe weather event due to an external driver in real-time. The method builds on a large ensemble of atmosphere-only general circulation model simulations forced by seasonal forecast sea surface temperatures (SSTs). Taking the England 2013/14 winter floods as an example, we demonstrate that the change in risk for heavy rainfall during the England floods due to anthropogenic climate change, is of similar magnitude using either observed or seasonal forecast SSTs. Testing the dynamic response of the model to the anomalous ocean state for January 2014, we find that observed SSTs are required to establish a discernible link between a particular SST pattern and an atmospheric response such as a shift in the jetstream in the model. For extreme events occurring under strongly anomalous SST patterns associated with known low-frequency climate modes, however, forecast SSTs can provide sufficient guidance to determine the dynamic contribution to the event.

Assessing mid‑latitude dynamics in extreme event attribution systems
Daniel Mitchell et al 2016
Atmospheric modes of variability relevant for
extreme temperature and precipitation events are evaluated
in models currently being used for extreme event attribution.
A 100 member initial condition ensemble of the global circulation
model HadAM3P is compared with both the multimodel
ensemble from the Coupled Model Inter-comparison
Project, Phase 5 (CMIP5) and the CMIP5 atmosphere-only
counterparts (AMIP5). The use of HadAM3P allows for huge
ensembles to be computed relatively fast, thereby providing
unique insights into the dynamics of extremes. The analysis
focuses on mid Northern Latitudes (primarily Europe) during
winter, and is compared with ERA-Interim reanalysis.
The tri-modal Atlantic eddy-driven jet distribution is remarkably
well captured in HadAM3P, but not so in the CMIP5 or
AMIP5 multi-model mean, although individual models fare
better. The well known underestimation of blocking in the
Atlantic region is apparent in CMIP5 and AMIP5, and also,
to a lesser extent, in HadAM3P. Pacific blocking features
are well produced in all modeling initiatives. Blocking duration
is biased towards models reproducing too many shortlived
events in all three modelling systems. Associated storm
tracks are too zonal over the Atlantic in the CMIP5 and
AMIP5 ensembles, but better simulated in HadAM3P with
the exception of being too weak over Western Europe. In all
cases, the CMIP5 and AMIP5 performances were almost
identical, suggesting that the biases in atmospheric modes
considered here are not strongly coupled to SSTs, and perhaps
other model characteristics such as resolution are more
important. For event attribution studies, it is recommended
that rather than taking statistics over the entire CMIP5 or
AMIP5 available models, only models capable of producing
the relevant dynamical phenomena be employed.


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Re: Extreme weather event attribution
« Reply #1 on: January 03, 2017, 12:47:32 AM »
Yes, Some Extreme Weather Can Be Blamed on Climate Change

Article on attribution science in Scientific American.

Scientific American spoke with Friederike Otto, deputy director of the Environmental Change Institute at the University of Oxford, about how attribution science works and why it’s a critical part of helping communities prepare for and adapt to climate change.
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Re: Extreme weather event attribution
« Reply #2 on: January 03, 2017, 06:02:30 PM »
Title: New technique predicts frequency of heavy precipitation with global warming


Now MIT scientists have found that such extreme precipitation events in California should become more frequent as the Earth's climate warms over this century. The researchers developed a new technique that predicts the frequency of local, extreme rainfall events by identifying telltale large-scale patterns in atmospheric data.

Referenced paper:
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Re: Extreme weather event attribution
« Reply #3 on: November 16, 2018, 06:12:13 PM »
It seems like precipitation follows the power law

Half of the World's Annual Precipitation Falls In Just 12 Days

An analysis of rainfall measured at weather stations across the globe between 1999 and 2014 found that the median time it took for half of a year's precipitation to fall was just 12 days. A quarter of annual precipitation fell in just six days, and three-quarters fell in 27 days.

These results are published in Geophysical Research Letters, a journal of the American Geophysical Union.

To look forward, the scientists used simulations from 36 of the world's leading climate models that had data for daily precipitation. Then they pinpointed what the climate model projections for the last 16 years of this century would translate to for the individual observation stations.

They found that total annual precipitation at the observation stations increased slightly in the model runs, but the additional precipitation did not fall evenly. Instead, half of the extra rain and snow fell over just six days.

This contributed to total precipitation also falling more unevenly than it does today, with half of a year's total precipitation falling in just 11 days by 2100, compared to 12 in the current climate.

"While climate models generally project just a small increase in rain in general, we find this increase comes as a handful of events with much more rain and, therefore, could result in more negative impacts, including flooding," Pendergrass said. "We need to take this into account when we think about how to prepare for the future."

Open Access: Angeline G. Pendergrass et al, The Uneven Nature of Daily Precipitation and Its Change, Geophysical Research Letters (2018)

The change in precipitation in response to warming is more uneven than present‐day precipitation, and it occurs primarily during events often considered extreme.

In contrast to temperature, where climate change can be thought of as a simple shift of the distribution, the shape of the distribution of precipitation changes with warming so that the heaviest events make up a larger fraction of total precipitation. The uneven nature of precipitation increase could exacerbate impacts like flooding and drought. Rather than assuming more rain in general, society needs to take measures to deal with little change most of the time and a handful of events with much more rain.
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