Outline. Extreme sea levels: past and future. Tropical cyclones 12/07/2013. North Sea Storm Surge of Understanding of coastal extremes

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1 Outline Extreme sea levels: past and future Svetlana Jevrejeva National Oceanography Centre, Liverpool, UK Introduction Changes in extreme sea levels in the recent past ( progress and limitation in understanding) observations modelling Future projections by 2 Extreme sea levels in warming climate Conclusion Historical evidence of changes in extreme sea levels North Sea Storm Surge of s 879 January 3 February, 953 Countries: Netherlands, Belgium and UK Water level exceeded 5.6 metres in some locations Fatalities: 2,55 illed Damages: 9% of total Dutch farmland flooded, 3, animals drowned, and 47,3 buildings damaged Sea Palling, Norfol, UK ( Feb 953) Photos from Environmental Agency, UK Oosterscheldeering and Rotterdam barriers (part of Delta wors, The Netherlands) Tropical cyclones Understanding of coastal extremes Bay of Bengal Major Surges 737 3, illed 864, 876, , 97 3, (tide plus 6m surge) 28 3, (Nargis, $ billion (USD)) Extreme sea level North Atlantic hurricane Mid latitude and tropical cyclone tracs Hurricane Katrina, 25 Fatalities:,833 Damage: $8 billion (USD) Probability density function for extreme sea levels

2 Extreme sea levels (Past) Global extreme sea levels From Menéndez and Woodworth, 2 Do we experience more extremes sea levels in recent past? Are there any lins between mean sea level rise and extreme sea levels? From Menéndez and Woodworth (2) Challenges with observational data sets: Lac of global representation Very limited data in Southern hemisphere Most sensitive areas - little data Data on extremes harder to find than mean sea level Homogeneity issue Are there any trends in extreme sea levels? Are there any changes in frequency of extreme sea levels? Menéndez and Woodworth, 2 Estimated trends in (top) annual 99th percentile of sea level, (bottom) 99th percentile reduced to medians. Only trends at a confidence level above 95% are shown in color: red for positive trends and blue for negative trends. Figure Menéndez and Woodworth, 2. Estimated changes in the frequency of extreme sea level events for the total elevation time series and (b) for the time series with the annual median removed. Changes are the annual percentage of increase/decrease in the occurrence of extreme events relative to the average occurrence rate. Blac dots indicate trends with a level of significance below 5%. Regional extreme sea levels Short summary about change in past extreme sea levels Marcos, Tsimplis, and Shaw, 29 Questions were: Do we observe more extremes sea levels in recent past? Are there any lins between mean sea level rise and extreme sea levels? Correlations of winter NAO with (a, b, c) observed extremes and (d, e, f) hindcast data index for (top) the 5th percentile, (middle) the 99.9th percentile, and (bottom) the 99.9th percentile with the median subtracted. Only correlations statistically significant at the 5% confidence level are plotted. 2

3 Sea level extremes by 2 Modelling of extreme sea levels Prediction is very difficult, especially if it s about the future (NielsBohr, Danish ihnobel Prize winning physicist, ) Observations Modelling of components Sea level rise and changes in return period Projections using CMIP3 outputs UK Climate Projections science report: Marine & coastal projections, 29 Emanuel et al, 28 Are there any lins between global warming and an increase of extreme sea levels? Hurricanes Saffir Simpson Hurricane Scale Category Wind speeds Five 57 mph, 252 m/h Four 3 56 mph, m/h Three 29 mph, m/h Two 96 mph, m/h One mph, 9 53 m/h Additional classifications Main Development Region (MDR) Tropical storm Tropical depression mph, 63 8 m/h <38 mph, <62 m/h 3

4 Motivation Data Historical hurricane observations (e.g. PDI, ACE, number of tropical cyclones..) give conflicting information on past trends in number and intensity of hurricanes Climate models suggest that warming will reduce/increase frequency of hurricances (Knutsen et al, 28/Emanuel et al, 28) There is no agreement between scientists about the lin to the global/local temeprature (or SST, or SST in MDR) Storm surges are the most harmful aspect of hurricanes and the measure of storm surge intensity would therefore be a good candidate measure of hurricane activity Grinsted et al, 22 Storm surge index Grinsted et al, 22 Grinsted et al, 22 f x x x e ( x) e x for m(,, ) e ( x ) for and otherwise How does Katrina change in lielihood with T? Range of observations ( a T ) e s ( a T ) ( a s T ) Non stationary GEV fitting to surge time series Relationship between return period and global average temperature for Katrina magnitude (and greater) events. Shading is 5 95% confidence interval Grinsted et al, 22 4

5 Estimated return periods for mean global T now (98 2) and.2c warmer A warming of.2 C corresponds roughly the warming projected under the RCP4.5 scenario by 2 Relative increase in frequency associated with.2c warming Number of Katrina magnitude surge events per decade (b) for RCP45 projected changes in temperatures change. Confidence interval ( %). Grinsted et al, 23 Conclusion Extreme sea levels will change by 2 due to sea level rise There is no agreement in increase/decrease in tropical cycloneactivityandchangesin and changes in mid latitudecyclone tracs Some empirical models suggest a greatly increased hurricane activity (storm surges) in a warmer world, doubling of Katrina events during the 2 th century Global warming ~.2C results in 2 8 fold increase of Katrina magnitude events 5