The occurrence of rainfall in a changing climate - Natural ...

The occurrence of rainfall
in a changing climate
FREE: Flood Risk from Extreme Events
UK Natural Environment Research Council
Tim Osborn and Douglas Maraun, Maraun,
UEA
Nathan Gillett, Gillett,
now at CCCMA, Canada
Henning Rust, Rust,
Potsdam, Germany
(via a British Council -- DAAD grant)
www.cru.uea.ac.uk

Some of the questions we addressed…
addressed
(with a focus on the UK)
• How have “extreme” precipitation events changed?
• Can we explain some of these variations?
• Can climate models simulate “extreme” precipitation
realistically over the UK?
e.g. geographic patterns, seasonal patterns, links
with atmospheric circulation
www.cru.uea.ac.uk

How have “extreme extreme” (in this case “heavy heavy”) )
precipitation events changes?
Ten years ago…
Fraction of each season’s precipitation provided by “HEAVY” category events
Average UK time series
www.cru.uea.ac.uk
Osborn et al. (2000)

Our new results…
www.cru.uea.ac.uk
Maraun et al. (2008)

How have “extreme extreme” (in this case “heavy heavy”) )
precipitation events changes?
Ten years ago…
Fraction of each season’s precipitation provided by “HEAVY” category events
Average UK time series
www.cru.uea.ac.uk
Osborn et al. (2000)

Our new results…
www.cru.uea.ac.uk
Maraun et al. (2008)

www.cru.uea.ac.uk
MAM
Maraun et al. (2008)

www.cru.uea.ac.uk
SON
Maraun et al. (2008)

Identification of changing
precipitation extremes..
• Maraun et al. (2009)
• Rust et al. (2009)
– Seasonally-dependent extreme value
(GEV) model
10-year return value
(mm/day)
January

Identification of changing
precipitation extremes..
• Maraun et al. (2009)
• Rust et al. (2009)
– Seasonally-dependent extreme value
(GEV) model
10-year return value
(mm/day)
February
Min

Identification of changing
precipitation extremes..
• Maraun et al. (2009)
• Rust et al. (2009)
– Seasonally-dependent extreme value
(GEV) model
10-year return value
(mm/day)
March

Identification of changing
precipitation extremes..
• Maraun et al. (2009)
• Rust et al. (2009)
– Seasonally-dependent extreme value
(GEV) model
10-year return value
(mm/day)
April
Min

Identification of changing
precipitation extremes..
• Maraun et al. (2009)
• Rust et al. (2009)
– Seasonally-dependent extreme value
(GEV) model
10-year return value
(mm/day)
May
Min
Min

Identification of changing
precipitation extremes..
• Maraun et al. (2009)
• Rust et al. (2009)
– Seasonally-dependent extreme value
(GEV) model
10-year return value
(mm/day)
June

Identification of changing
precipitation extremes..
• Maraun et al. (2009)
• Rust et al. (2009)
– Seasonally-dependent extreme value
(GEV) model
10-year return value
(mm/day)
July

Identification of changing
precipitation extremes..
• Maraun et al. (2009)
• Rust et al. (2009)
– Seasonally-dependent extreme value
(GEV) model
10-year return value
(mm/day)
August

Identification of changing
precipitation extremes..
• Maraun et al. (2009)
• Rust et al. (2009)
– Seasonally-dependent extreme value
(GEV) model
10-year return value
(mm/day)
September
Max

Identification of changing
precipitation extremes..
• Maraun et al. (2009)
• Rust et al. (2009)
– Seasonally-dependent extreme value
(GEV) model
10-year return value
(mm/day)
October
Max

Identification of changing
precipitation extremes..
• Maraun et al. (2009)
• Rust et al. (2009)
– Seasonally-dependent extreme value
(GEV) model
10-year return value
(mm/day)
November

Identification of changing
precipitation extremes..
• Maraun et al. (2009)
• Rust et al. (2009)
– Seasonally-dependent extreme value
(GEV) model
10-year return value
(mm/day)
December
Max
Max

Identification of changing
precipitation extremes..
• Maraun et al. (2009)
• Rust et al. (2009)
– Seasonally-dependent extreme value
(GEV) model
10-year return value
(mm/day)
January

Identification of changing
precipitation extremes..
• Maraun et al. (2009)
• Rust et al. (2009)
– Seasonally-dependent extreme value
(GEV) model
10-year return value
(mm/day)
February
Min

Identification of changing
precipitation extremes..
• Maraun et al. (2009)
• Rust et al. (2009)
– Seasonally-dependent extreme value
(GEV) model
10-year return value
(mm/day)
March

Can we explain some of these variations?
• Maraun et al. (2010a,b)
– Extended the seasonally-dependent extreme value (GEV) model
to also depend upon three metrics of atmospheric circulation
– VGLM (Vector Generalized Linear Model), with the parameters of
the GEV modelled as functions of air flow indices, seasonality
and location

Dependence of GEV location parameter on air flow indices
Most extreme when strong flow from the WSW
Most extreme when high vorticity flow (depression/front)

Can regional climate models simulate “extreme extreme”
precipitation “realistically realistically” over the UK?
– A harsher test of model performance than simply evaluating longterm
means
– RCM needs to perform well in a range of synoptic situations,
generating orographic, frontal and convective precipitation
– We have evaluated 14 RCMs from the ENSEMBLES project – these
are models currently being used for informing climate policy and
adaptation policy

• Example: relationship between air flow strength and mean
magnitude of monthly precipitation maxima
UKMO obs EOBS KNMI RACMO RCM

Summary and papers
• Maraun et et al. al. (2008, Int. Int. J. J. Climatol.) Climatol.
– Observed increase in UK heavy rain in SON, DJF, MAM; no change in JJA
• Maraun et et al. al. (2009, Int. Int. J. J. Climatol.) Climatol. ) & Rust et et al. al. (2009, EPJST) EPJST
– Seasonal cycle in UK precipitation extreme value return levels
• Maraun et et al. al. (2010a, Extremes) Extremes)
& Maraun et et al. al. (2010b, Clim. Clim. Dyn.) Dyn.
– Extreme value model conditioned on atmospheric circulation for UK
• Maraun et et al. al. (to be submitted to Clim. Clim. Dyn.) Dyn.
– Evaluating ENSEMBLES RCM ability to simulate UK precipitation extreme
values, seasonality and influence of atmospheric circulation
• Maraun et et al. al. (2010c, Rev. Rev. Geophys) Geophys
– Review of precipitation downscaling and modelling at fine scales, arising from
an international workshop in April 2009 with colleagues from other NERC
FREE projects

www.cru.uea.ac.uk