Veränderliches Küstenklima - die vergangenen und zukünftigen 100 Jahre Hans von Storch Institute für Küstenforschung GKSS, Geesthacht Tagung "Marsch: Natur, Geschichte und Gegenwart“, Oldenburg am 4. Juni 2004 Institut für Historische Küstenforschung und dem Marschenrat in Wilhelmshaven

Klima, Küstenklima Klima ist die Statistik des Wetters, nicht “durchschnittliches Wetter” (gibt’s nicht). Alle „Wetter“variablen - in Atmosphäre, Ozean und anderen Klimakomponenten. Besonderes Interesse: Variablen und Kennstatistiken mit Bedeutung für Gesellschaft. Küsten: Wind, Seegang, Wasserstand, und deren Extreme.

Windklimaänderungen Schwierig festzustellen, weil die Messmethoden sich ändern. (Früher: subjektiv visuell, heute instrumentell) Schwierig festzustellen, weil die unmittelbare Umgebung von Bedeutung ist. Fast alle langen Winddatensätze sind inhomogen, d.h. spiegeln nicht nur Änderungen des Windklimas wieder sondern auch andere Faktoren (Beobachtungsmethode & - dichte, lokale Änderungen) Historische Analysen à la de Kraker wichtig.

Scheinbare Änderungen der Sturmstatistik 10-jährige Mittel der jährlichen Häufig-keiten von Starkwind-ereignissen (Wind-stärken von mehr als 7) in Hamburg. Scheinbare Änderungen der Sturmstatistik Sichere Tornados Vermutete Tornados Sonstige schwere Sturmereignisse Tschechien Dobrovolny & Bràzdil, 2001

Öffentliche Aufmerksamkeit Klima wird fast immer als schlechter werdend wahrgenommen. Jahreszeiten weniger zuverlässig, stärkere Extreme, speziell mehr/schwerere Stürme.

Estimated losses due to hurricanes (1850-2000) impacting 2000 insured values in the US. Gross Loss ($Millions) - 10,000 20,000 30,000 40,000 50,000 1850 1860 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 Historic Annual Aggregate Loss Historic AAL ($3,571 Million) 20-Year Moving Average Year Actual insured losses Richard Muir-Wood, pers. comm.

Sturmtätigkeit, 1800-1900-1950-2000

Hurricanes im nördlichen Atlantik, 1944-1994

stormproxies 1820-2001 Storm proxies, derived from local air pressure readings Lars Bärring, pers. comm.

Hasse Alexandersson, pers comm

Hasse Alexandersson, pers comm

C/year Stormcount 1958-2001 t   t   Weisse , pers. comm. Linearer Trend Stuerme in Anzahl/Jahr ermittelt fuer den Zeitraum 1958-2001.  alle Stuerme >= Bft 8 (17.2m/s)   Relativer Trend, d.h. Aenderungen relativ zum langjaehrigen Mittelwert. beachte, dass der bei schweren Stuermen oft nur 1-3 betraegt. Signifikanz wurde mit Hilfe Mann-Kendall Test getestet. Da wo die Nullhypothese "kein Trend" mit 5% Irrtumswahrsch. verworfen werden muss wurde das 95% Konfidenzintervall "D" fuer den Trend "x" geplottet (x-D <= x <= x+ D)

IPCC summary IPCC statement to changing extratropical storminess... p.33: “...There is no compelling evidence to indicate that the characteristics of tropical and extra-tropical storms have changed...” “...Owing to incomplete data and conflicting analyses, it is uncertain as to whether there have been any long-term and large-scale increases in the intensity and frequency of extra-tropical cyclones in the Northern Hemisphere ...”

sea level

Nordseewasserstand im Holozän

1910-1990 contributions to global sea level rise. IPCC summary IPCC, 2001

Perzentile der Abweichungen vom Wintermittel Den Helder Wintermittel Wintermittel Perzentile der Abweichungen vom Wintermittel

Significant wave height

90%ile, reconstructed in WASA project 1955-1993 trend, [cm/year] Günther et al., 1998

Ocean wave height reconstruction Weisse, pers. comm. Ocean wave height reconstruction Solid: HIPOCAS RCM/NCEP reconstruction Dashed: WASA/DNMI SLP reconstruction Red: Local observations 50%, 90%, 95% and 99%iles. Oben Trends jaehrliche 99% Percentil sig. Wellenhoehe, Punkte: geplante Windparks, Kreuz: Nordseeboje (Beobachtungen),

wave energy

30 year mean estimated wave energy impinging on the west coast of Jutland, derived from WASA wave reconstruction (1955-93) and statistical extrapolation backward until 1900, and empirical downscaling from 200 year control global climate simulation („T42 control“) and, empirical downscaling from 150 year climate change global simulation („T42 transient“) Pfizenmayer, 2002

1958-2002 assessment Storminess – there was a trend towards more intense/frequent storm in the NE Atlantic, North Sea and Baltic Sea since 1960. In most areas, this trend has reversed in the most recent years. A comparison with historical records does not indicate systematic recent changes towards more intense/frequent storms. Before 1960, there was a decrease of storminess, see WASA project. Storm surges have shown a slight increase in the past 40 years in the eastern part of the North Sea. This is mainly due to an increase of the mean sea level (circulation) in the North Sea. (up to 2 mm/year) Wave heights have increased only in the Southern North Sea in a systematic manner in the past 40 years (99%iles: 2 cm /year); wave energy along the west coast of Jutland seemingly increased beyond the level of normal range of variability (local detection of climate change).

External Forcing – Future Scenarios IPCC SRES A2 and B2 emissions scenarios A2 very heterogeneous world continuously increasing population strengthened regional cultural identities slow economic development B2 slower population growth intermediate levels of economic development more accent on environ- mental protection THE IPCC…scenarios corresponding to different storylines assume diff. Emission scenarios. The main scenario characteristics are described in the Box. A2 assumes..… B2 assumes… with ….and … producing therefore lower emissions and less future warming than A2

Hemispheric Warming and Storms Hemispheric mean Air temperature and storm indices Hemispheric Warming and Storms Both storm indices together with the temperature are displayed here from 1550 until the year 2140 for the first pair of simulations. For the NH we see a shift to the N for the future scenario but no Increase in storm intensity. For the SH we have a shift together with an increase of intensity. (smoothed by 11-yr running means) Fischer-Bruns, pers. comm.

Kennzahl für Sturmhäufigkeit (8 Bft und mehr) im Nordatlantik, wie dargestellt in einer langen Klimasimulation der letzten 450 Jahre, samt einem Ausblick für die kommenden 100 Jahre (A2) Fischer-Bruns, pers. comm.

Index of galeday frequency for both winter hemispheres Storm Intensity Index of galeday frequency for both winter hemispheres Change for NAtl and NPac relative to pre-industrial phases Here again the same graph. Over the whole NH the index is constant, but how does it look like for the two different NH storm tracks, in the NA and the NP?? The figure below reveals that we have an increase of storm frequency in the Natl region, but a decrease in the Npac!! It is worth while to go more into detail here, but we haven’t done yet. NAtl (90W-30E) NPac (150E-90W) Fischer-Bruns, pers. comm.

SREs emission scenarios: Impact on global sea level IPCC, 2001 SREs emission scenarios: Impact on global sea level

Run of the TRIM surge-model with a series of RCM forcing GCM (CTL: 1961 - 1990) (A2: 2071 - 2100) series of RCM runs Run of the TRIM surge-model with a series of RCM forcing SLP & wind components dynamical downscaling of water level / North European shelf sea Woth, pers.comm.

A2 - CTL: changes in 99 % - iles of wind speed (6 hourly, DJF): west wind sector selected (247.5 to 292.5 deg) HIRHAM RCAO REMO5 CLM Woth, pers.comm.

Mean (30 year) of winter maximum surge levels (significance level: 95%) dotted lines: limits of stat. significance (95%) of differences in surge Keep in mind, that increase in sea level height due to thermal expansion is not taken into account! Surge [m] Near coastal model cells Woth, pers.comm.

Projections for the future / surge meteorological forcing: HIRHAM / RCA Differences in inter-annual percentiles of surge / A2 - CTL: HIRHAM Differences in inter-annual percentiles of surge / A2 - CTL: RCA Woth, pers.comm.

Scenarios – plausible but not necessarily probable future developments The scenarios indicate for the North Sea – increases of at the end of the 21st century: higher wind percentiles of up to 0.5-2 m/s. mean sea level, 10-90 cm storm surge levels, of up to 20-40 cm in the 99%iles significant wave height of up to 0.5 m.