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

MeteoAlarm Expert Meeting Vienna April Problem statement Unrealistic differences in frequency and levels of warnings between neighbouring countries

MeteoAlarm Expert Meeting Vienna April Problem statement Unrealistic differences in frequency and levels of warnings between neighbouring countries

MeteoAlarm Expert Meeting Vienna April Problem analyses Current Meteoalarm guideline: Difficult to find information (also on warning thresholds of individual countries) Normalisation (return period per km²) ”translates” into unrealistic warning thresholds for small and big countries

MeteoAlarm Expert Meeting Vienna April 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

MeteoAlarm Expert Meeting Vienna April 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 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

MeteoAlarm Expert Meeting Vienna April 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

MeteoAlarm Expert Meeting Vienna April 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

MeteoAlarm Expert Meeting Vienna April Method Make use of ECA&D !! ( 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

MeteoAlarm Expert Meeting Vienna April 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)

MeteoAlarm Expert Meeting Vienna April Example: find seasonal differences Summer half year Winter half year: 5 m/s higher

MeteoAlarm Expert Meeting Vienna April Example: find “climate” regions

MeteoAlarm Expert Meeting Vienna April Example: find “climate” regions Coastal stations (< 12 km from open sea) Inland stations (> 50 km from open sea) Distance to coast line [km] Return value of annual maximum gust [m/s]

MeteoAlarm Expert Meeting Vienna April Example: find “climate” regions Coastal stations Inland stations Mountain stations > 800 m Station elevation [m] 1 year return value of annual maximum gust [m/s]

MeteoAlarm Expert Meeting Vienna April Example: find a trend

MeteoAlarm Expert Meeting Vienna April Data availability Available precipitation amount data Available wind gust data

MeteoAlarm Expert Meeting Vienna April Data availability Available precipitation amount data Available wind gust data SUPPORT THE ECA&D DATA COLLECTION EFFORTS !!!

MeteoAlarm Expert Meeting Vienna April Data availability ECA&D wind gust data currently only from 8 countries Data reduction as a result of: Quality control (Homogeneity tests) Completeness requirements CountryStations with QC gust data Stations with return values The Netherlands 6023 Norway5313 Germany5237 Ireland2312 Spain117 Estonia22 Luxembourg10 Hungary10

MeteoAlarm Expert Meeting Vienna April 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 km²) ”translates” into unrealistic warning thresholds for small and big countries More information on guidelines and warning thresholds on 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

MeteoAlarm Expert Meeting Vienna April 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!

MeteoAlarm Expert Meeting Vienna April Discussion Contact us at:

MeteoAlarm Expert Meeting Vienna April

MeteoAlarm Expert Meeting Vienna April Problem analyses CODE RED WARNINGS: Current guideline: less than 1 time a year per km² For a county like Malta (~ 300 km²) this means: less than 300/ times a year = less than 1/1000 times a year = less than once in 1000 years! For a county like France (~ km²): about 2 times a year

MeteoAlarm Expert Meeting Vienna April Results Old and new orange thresholds NorwayNetherlandsSpainGermanyIreland Coast32 m/s (-) 30 m/s (28 and 33 for winter) 26 m/s (25) 35 m/s (29) 40 m/s (30) Inland23 m/s (-) 27 m/s (28) -27 m/s (29) 30 m/s (30) Moun- tain m/s (29) -

MeteoAlarm Expert Meeting Vienna April 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

MeteoAlarm Expert Meeting Vienna April 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