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

MeteoAlarm Expert Meeting Vienna April 2011 Problem statement Unrealistic differences in frequency and levels of warnings between neighbouring countries

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

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

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

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

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

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

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)

MeteoAlarm Expert Meeting Vienna April 2011 Example: find seasonal differences • Summer half year • Winter half year: 5 m/s higher

MeteoAlarm Expert Meeting Vienna April 2011 Example: find “climate” regions

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]

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]

MeteoAlarm Expert Meeting Vienna April 2011 Example: find a trend

MeteoAlarm Expert Meeting Vienna April 2011 Data availability Available precipitation amount data Available wind gust data

MeteoAlarm Expert Meeting Vienna April 2011 Data availability Available precipitation amount data Available wind gust data SUPPORT THE ECA&D DATA COLLECTION EFFORTS !!!

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

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

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!

MeteoAlarm Expert Meeting Vienna April 2011 Discussion Contact us at: eca@knmi.nl

MeteoAlarm Expert Meeting Vienna April 2011

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

MeteoAlarm Expert Meeting Vienna April 2011 Results • Old and new orangethresholds

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

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

Problem statement