eca&d return periods: the key to a more uniform warning system for meteoalarm ine wijnant,...

ECA&D return periods: the key to a more

uniform warning system for MeteoAlarm

Ine Wijnant, Andrew Stepek and ECA&D staff at KNMI

MeteoAlarm Expert Meeting Vienna April 2011


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Problem statement

Unrealistic differences in frequency and levels of warnings between neighbouring countries


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Problem statement

Unrealistic differences in frequency and levels of warnings between neighbouring countries


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Problem analyses

Current Meteoalarm guideline:

•Difficult to find information (also on warning thresholds of individual countries)

•Normalisation (return period per 300.000 km²) ”translates” into unrealistic warning thresholds for small and big countries


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Approach

•Return periods are not only a measure of the likelihood of an event, but also a measure of how extreme the event is compared to local climate conditions

•Associated return values are therefore a very useful indication of the possible danger of the event and its impact on society


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Approach

New “pan-European” Meteoalarm guideline with warning thresholds based on return values associated with return periods that are not normalisedto a standard country size of 300.000 km²:

Return values are a good measure of likelihood and impact (and therefore of distruption and danger)

Return values do not change abruptly at country borders (uniform warning system)

Use statistics to account for population density differences


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Method

Find best link between colour code and return period

We suggest:(1 year return period → Yellow)2 year return period → Orange5 year return period → Red


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Method

Translate return values based on station data into warning thresholds

We suggest:•Regional thresholds•Seasonal thresholds•Use statistics to account for differences in population

density


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Method

Make use of ECA&D !!(http://eca.knmi.nl)

• Long time series of daily data• More than 3600 stations in

63 countries• 12 elements: precipitation

amount, temperature (min, max, mean), sunshine, sea level pressure, snow depth, humidity, cloud cover and wind (speed, gust, direction)

• Tools to help analyse extreme events and climate change

3606 stations in ECA&D


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Method

Use tools in ECA&D to:

•Calculate return values that match with return periods of 1, 2, 5, 10 and 50 years

•Calculate return values for a specific month or season (seasonal thresholds)

•Analyse climate change (trend maps)•Choose “climate” regions (regional thresholds)


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Example: find seasonal differences

Summer half year Winter half year: 5 m/s higher


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Example: find “climate” regions


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Coastal stations (< 12 km from open sea)Inland stations (> 50 km from open sea)

15

20

25

30

35

40

45

50

-50 0 50 100 150 200 250 300

Ret

urn

valu

e of

ann

ual m

axim

um w

ind

gust

[m/s

] ii

1 year

10 year

Distance to coast line [km]

Retu

rn v

alu

e o

f annual

maxim

um

gust

[m

/s]


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Coastal stations Inland stations Mountain stations > 800 m

15

18

21

24

27

30

33

36

39

-10 190 390 590 790 990 1190 1390

1 ye

ar r

etur

n va

lue

of a

nnua

l m

axim

um w

ind

gust

[m

/s]

Station elevation [m]

1 y

ear

retu

rn v

alu

e o

f an

nu

al m

axim

um

gu

st [

m/s

]


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Example: find a trend


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Data availability

Available precipitation amount data Available wind gust data


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Data availability

Available precipitation amount data Available wind gust data

SUPPORT THE ECA&D DATA COLLECTION EFFORTS !!!


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Data availability

ECA&D wind gust data currently only from 8 countries

Data reduction as a result of: Quality control (Homogeneity tests) Completeness requirements

Country Stations with QC gust data

Stations with return values

TheNetherlands

60 23

Norway 53 13

Germany 52 37

Ireland 23 12

Spain 11 7

Estonia 2 2

Luxembourg

1 0

Hungary 1 0


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Conclusions (1)

•Return value are not only a good indication of likeliness, but also of the possible danger or impact on society of the extreme event

•Normalisation (return period per 300.000 km²) ”translates” into unrealistic warning thresholds for small and big countries

•More information on guidelines and warning thresholds on www.meteoalarm.eu would make the MeteoAlarm warning system more transparant for users

•No more unrealistic differences in frequency and levels of warnings between neighbouring countries if warning thresholds are based on uniform return periods


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Conclusions (2)

•Best link between color code and return period: 1, 2 and 5 years for code yellow, orange and red

•Regional and seasonal thresholds may be required•Use statistics to account for differences in population

density•ECA&D very useful tool to calculate return values and

to find seasonal differences, climate regions and trends•But ECA&D needs data!


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Discussion

Contact us at: [email protected]


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Problem analyses

CODE RED WARNINGS:

Current guideline: less than 1 time a year per 300.000 km²

For a county like Malta (~ 300 km²) this means: less than 300/300000 times a year = less than 1/1000 times a year = less than once in 1000 years!

For a county like France (~ 650.000 km²): about 2 times a year


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Results

Old and new orange thresholds

Norway

Netherlands

Spain Germany

Ireland

Coast 32 m/s (-)

30 m/s (28 and 33 for winter)

26 m/s (25)

35 m/s (29)

40 m/s (30)

Inland 23 m/s (-)

27 m/s (28)

- 27 m/s (29)

30 m/s (30)

Moun-tain

- - - 43 m/s (29)

-


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Conclusions

Most of the current thresholds should be changed

Current thresholds for coastal and mountainous stations need to be changed the most

Current thresholds are mostly too low, only a few of the current code red thresholds are too high


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Summary

Current guidelines very unrealistic for many countriesInitial proposal new guidelines based on:

1 year return period for yellow 2 year return period for orange 5 year return period for red

New guidelines require significant changes for most of the current thresholdsRegional and maybe seasonal thresholds required

eca&d return periods: the key to a more uniform warning system for meteoalarm ine wijnant,...

Documents

ecad return periods

climate change3606 stations

unrealistic warning

climate regionsexample

dangerreturn values

open seainland stations

local climate conditions

ecad data collection