ECA&D return periods:
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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. Problem statement. Unrealistic differences in frequency and levels of warnings

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Problem statement

ECA&D return periods: the key to a more uniform warning system for MeteoAlarmIne Wijnant, Andrew Stepek and ECA&D staff at KNMIMeteoAlarm Expert Meeting Vienna April 2011


Problem statement

MeteoAlarm Expert Meeting Vienna April 2011

Problem statement

Unrealistic differences in frequency and levels of warnings

between neighbouring countries


Problem statement1

MeteoAlarm Expert Meeting Vienna April 2011

Problem statement

Unrealistic differences in frequency and levels of warnings

between neighbouring countries


Problem analyses

MeteoAlarm Expert Meeting Vienna April 2011

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


Approach

MeteoAlarm Expert Meeting Vienna April 2011

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


Approach1

MeteoAlarm Expert Meeting Vienna April 2011

Approach

New “pan-European” Meteoalarm guideline with warning

thresholds based on return values associated with

return periods that are not normalised

to 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


Method

MeteoAlarm Expert Meeting Vienna April 2011

Method

Find best link between colour code and return period

We suggest:

(1 year return period → Yellow)

2 year return period → Orange

5 year return period → Red


Method1

MeteoAlarm Expert Meeting Vienna April 2011

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


Method2

MeteoAlarm Expert Meeting Vienna April 2011

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


Method3

MeteoAlarm Expert Meeting Vienna April 2011

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)


Example find seasonal differences

MeteoAlarm Expert Meeting Vienna April 2011

Example: find seasonal differences

  • Summer half year

  • Winter half year: 5 m/s higher


Example find climate regions

MeteoAlarm Expert Meeting Vienna April 2011

Example: find “climate” regions


Example find climate regions1

MeteoAlarm Expert Meeting Vienna April 2011

Example: find “climate” regions

Coastal stations

(< 12 km from open sea)

Inland stations

(> 50 km from open sea)

  • Return value of annual maximum gust [m/s]

  • Distance to coast line [km]


Example find climate regions2

MeteoAlarm Expert Meeting Vienna April 2011

Example: find “climate” regions

Coastal stations

Inland stations

Mountain stations

> 800 m

  • 1 year return value of

  • annual maximum gust [m/s]

  • Station elevation [m]


Example find a trend

MeteoAlarm Expert Meeting Vienna April 2011

Example: find a trend


Data availability

MeteoAlarm Expert Meeting Vienna April 2011

Data availability

Available precipitation amount data

Available wind gust data


Data availability1

MeteoAlarm Expert Meeting Vienna April 2011

Data availability

Available precipitation amount data

Available wind gust data

SUPPORT THE ECA&D DATA COLLECTION EFFORTS !!!


Data availability2

MeteoAlarm Expert Meeting Vienna April 2011

Data availability

ECA&D wind gust data currently only from 8 countries

Data reduction as a result of:

Quality control

(Homogeneity tests)

Completeness requirements


Conclusions 1

MeteoAlarm Expert Meeting Vienna April 2011

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” intounrealistic warning thresholdsfor 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 levelsof warnings between neighbouring countries if warning thresholds are based on uniform return periods


Conclusions 2

MeteoAlarm Expert Meeting Vienna April 2011

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!


Discussion

MeteoAlarm Expert Meeting Vienna April 2011

Discussion

Contact us at: [email protected]


Problem statement

MeteoAlarm Expert Meeting Vienna April 2011


Problem analyses1

MeteoAlarm Expert Meeting Vienna April 2011

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


Results

MeteoAlarm Expert Meeting Vienna April 2011

Results

  • Old and new orangethresholds


Conclusions

MeteoAlarm Expert Meeting Vienna April 2011

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


Summary

MeteoAlarm Expert Meeting Vienna April 2011

Summary

Current guidelines very unrealistic for many countries

Initial 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 thresholds

Regional and maybe seasonal thresholds required


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