Ht t t d t Hot temperatures and storm surgggges: Modelling ... · Ht t t d t Hot temperatures and storm surgggges: Modelling the change of ... Henk van den Brink, Gerrit ... Henk

H t t t d t Hot temperatures and storm surges: Modelling the change of g g g

climate extremesAndreas SterlAndreas Sterl

KNMI, De Bilt, Netherlands

• Climate system• Climate changeg• Climate modelling• Climate extremes

• Hot temperatures• North Sea storm surges

Andreas Sterl, SEAMOCS, Malta, 17.03.2009

gHenk van den Brink, Gerrit Burgers, Henk Dijkstra, Reindert Haarsma,Wilco Hazeleger, Erik van Meijgaard, Camiel Severeijns, Hans de Vries

Climate – what’s that?

Climate = statistics of weatherClimate statistics of weather

Weather = state of atmosphereWeather = state of atmosphere at a particular time

“Climate is what you expect, weather is what you get”


The climate systemThe climate system

AR4 FAQ 1 2 Fi 1


AR4, FAQ 1.2, Fig. 1

How does the climate system How does the climate system work?

• short-wave radiation (sun) heats (tropics)

• atmosphere and ocean transport heat poleward (modulated by continents)poleward (modulated by continents)

l di ti i t l• long-wave radiation into space cools


Radiative forcing


AR4, FAQ 1.1, Fig. 1

Greenhouse effect

Outgoing longwave radiation is Outgoing longwave radiation is absorbed in the atmosphere and radiated back to the surfaceradiated back to the surface.

without: T = 15°Cwithout: Tglob = -15 C observed: Tglob =

15°C+15°C


Greenhouse gases

only 1 % of atmosphereH O 70 % < f db k ( 2 )• H2O 70 %

• CO2 15 %<= feedback (~2x)

• CH4 )• N2O ) 5 %2 )• Ozone, …)• (clouds 10 %) <= feedback (?)• (clouds 10 %) <= feedback (?)


(van Dorland, 1999, p. 17/18)

The past 159 yearsThe past 159 years


Increasing

GHG COGHG concent

CO2

ra-tions CH4

N2O

SO4


(IPCC, 2001, Fig. SPM-2) ++++

Sim lationsSimulations<= multi model, all forcings multi model, all forcings

M lti d l t l f i

AR4, Fig. 9.5

Multi model, natural forcings =>


Projectionsj

• Scenarios “How will the world change?”

• Scenarios => CO2 emissions and concentrationsconcentrations

CO• CO2 concentrations => climate


Emission scenariosEmission scenarios

TAR, SPM Fig. 5


ESSENCEESSENCE

• ECHAM5/MPI-OMECHAM5/MPI OM

• observed GHG’s – SRES A1b

• 1950 – 2100

• 17 runs => good statistics


Global mean temperature

blue: ESSENCEred: HadCRUT3+14.3


Temperature trend


Precipitationp


The N-year return value - 1

• value that on average occurs once per N years

( ) ⎪⎫⎪⎧ ⎤⎡ ⎞⎛ −− ξ

μx/1

years• obtained by fitting a GEV to annual maxima (x):

( )⎪⎭

⎪⎬⎫

⎪⎩

⎪⎨⎧

⎥⎦

⎤⎢⎣

⎡⎟⎠⎞

⎜⎝⎛ −

−σμxξ+=xG 1exp

(x):

⎪⎭⎪⎩ ⎦⎣ ⎠⎝

μ: locationμσ: scaleξ: shape


The N-year return value - 2⎫⎧ ξ/1

( )⎪⎭

⎪⎬⎫

⎪⎩

⎪⎨⎧

⎥⎦

⎤⎢⎣

⎡⎟⎠⎞

⎜⎝⎛ −

−− ξ

σμxξ+=xG

/1

1exp⎪⎭⎪⎩ ⎦⎣ ⎠⎝ σ

defined for 01 >μxξ+ ⎟⎞

⎜⎛ −defined for 01 >σ

ξ+ ⎟⎠

⎜⎝

=> bounded by xmax = μ-σ/ξ for ξ < 0

return time T(x) for level x is 1-1/T(x) percentile:

( ) ( )xG=xT−1

1


( )xG1

Example: NetherlandsExample: Netherlands



ΔΔμ


ΔΔσ


ΔTΔT100


TΔT100 / ΔTmean


Model biasT100(ESS)-T100(ERA-40)



Dutch Delta Committee:

What is the effect of global warming on

• maximum wind speed• maximum wind speed• wind directions• wave heights• storm surge levels?

ApproachApproach

• KNMI'06 scenarios• other literature• other literature• Essence + WAQUA


E WAQUAEssence + WAQUAEssenceEssence• ECHAM5/MPI-OMECHAM5/MPI OM• 17-member ensemble• 1950-2100, SRES A1b

WAQUA• storm surge model• storm surge model• Northwest European shelf• 8 km x 8 km• output every 10 minutesoutput every 10 minutes


Will the wind change ?Will the wind change ?ERA-401971-20002071-2100


Extreme windsExtreme winds


ESSENCE winds


Uncertainty present-day water levelswater levels


Future water levelsFuture water levels


Other stationsOther stations


l iConclusions

large ensemble => good statistical basisbasistemperature extremes increase faster than the means faster than the means ...... and may reach dangerous levels within this centurywithin this centuryno change of surge heights along th D t h t b t the Dutch coast, but ...... sea level increases



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Ht t t d t Hot temperatures and storm surgggges: Modelling ... · Ht t t d t Hot temperatures and storm surgggges: Modelling the change of ... Henk van den Brink, Gerrit ... Henk