Latest trends in sea level rise and storm surges in Maine Peter A. Slovinsky, Marine Geologist

Transcription

1 Latest trends in sea level rise and storm surges in Maine Peter A. Slovinsky, Marine Geologist Image from Chebeague.org

2 Maine s glacial geology and historic sea level rise trends Current sea level trends in Maine Where might sea levels go in the future? Abrupt sea level change Storm tides and surges in Maine

3 Sea Levels Since the Last Ice Age Sea Level Highstand Sea Level Lowstand Modified from MGS (1999)

4 Think of Maine s historical sea level rise in relation to a foam mattress

5 Think of Maine s historical sea level rise in relation to a foam mattress 13,000 yrs ago 230 feet above present

6 Think of Maine s historical sea level rise in relation to a foam mattress

7 Think of Maine s historical sea level rise in relation to a foam mattress 11,000 yrs ago 195 feet below present

8 Sea Levels Since the Last Ice Age Sea Level Highstand Modern beaches and wetlands form Sea Level Lowstand Modified from MGS (1999)

9 University of Maine Massive adjustments of the crust in response to glaciation historically drove much of Maine s sea level changes

10 What causes the global sea level changes that we are seeing today? Volumetric Increase 10% 50% 40% modified from Griggs, 2001 Thermal Expansion

11 Global Sea Level Rise Driving Factors: Volumetric Increase (melting of land- based ice sheets and glaciers) Glaciers (m of water equivalent thickness) 30 well-studied glaciers have decreased in average thickness by 60 feet

12 Global Sea Level Rise Driving Factors: Thermal Expansion (expansion of the water column due heating) Ocean Heat (10 22 joules) compared with average Global sea level (mm) as difference from 1990 Global sea level rise average over the last century: 1.8 mm/year

13 Global Sea Level Rise Trend Global sea level (mm) as difference from 1990 Global sea level rise average over the last century: 1.8 mm/year (0.7 per decade); last 20 yrs mm/yr (1.3 per decade)

14 Combined independent totals from thermal expansion and glacier/land based ice sheet input match satellite measurements adapted from Figure 3.15a in State of the Climate in 2016

15 Locally, sea level is rising in the long term

16 is rising faster in the short term

17 is rising faster in the short term can rise abruptly

18 Sea level can also change abruptly. Portland saw an average of approximately 5 higher than normal tides in the summer of 2009, and, especially in winter of This was the highest along the whole east coast.

19 Five of the highest monthly sea levels since 1912 occurred in winter 2010

20 Higgins Beach, Scarborough, April 7, 2010 P.A. Slovinsky

21 and is expected to continue to rise Global Mean Sea Level Scenarios to ft Global Mean Sea Level (m) Tide gauge data Satellite data Scenarios 6.6 ft 4.9 ft 3.3 ft 1.6 ft 1.0 ft Adapted from NOAA Technical Report NOS CO- OPS 083, January,

22 and potentially rise higher than global averages. Relative Sea Level Scenarios to ft Relative Sea Level Change (m) Scen Interm Int-High ft 6.0 ft 3.8 ft 1.6 ft 1.0 ft Adapted from using Portland tide gauge and NOAA 2017 regional scenarios for New England.

23 King Tide October 25, 2016 A. Sherwin, MCP Flood Stage = 12 ft MLLW

24 Hourly Readings >= 12 ft MLLW Long Term Mean Last Decade Mean Mean = 3 events/year Mean = 10 events/year Data from NOAA CO- OPS

25 Historic Mean = 53 events/year Mean = 98 events/year Data from NOAA CO- OPS

26 Changes in Annual Flooding Frequency with SLR (using Average) Scenario Flood Stage # times per % of high (ft, MLLW) year tides Existing % +1 ft SLR % +2 ft SLR % Based on this, there could potentially be a tenfold increase in the frequency of flooding in Portland with 1 foot of sea level rise.

27 What about storm tides and storm surges?

28 So what is storm surge and storm tide? Storm surge is an abnormal rise of water generated by a storm, over and above the predicted astronomical tides. Storm surge should not be confused with storm tide, which is defined as the water level rise due to the combination of storm surge and the astronomical tide (NHC).

29 The Battery, NY during Superstorm Sandy Predicted Tide = 1.9 ft NAVD Storm Tide = 11.3 ft NAVD Storm Surge = 9.4 ft Storm Tide Storm Surge Predicted Tide

30 Portland Storm Tides Statistics Recurrence Interval % Annual Chance Storm Tide (ft, MLLW) 1 100% % % % % % 13.7 Highest recorded storm tide was 14.1 feet on 2/7/1978 Updated 11/17/17, P.A. Slovinsky, MGS

31 Portland Storm Tides Statistics Recurrence Interval % Annual Chance Storm Tide (ft, MLLW) 1 100% % % % 13.2 <1 foot difference! 50 2% % 13.7 Highest recorded storm tide was 14.1 feet on 2/7/1978 Updated 11/17/17, P.A. Slovinsky, MGS

32 Top 25 annual water levels ( ) Tide Surge

33 Portland Storm Surge Statistics (at any tide, ) Recurrence Interval % Annual Chance Surge (ft) 1 100% % % % % % 4.8 Highest recorded surge: 3/3/ feet

34 Top 25 annual surges at any tide ( )

35 Portland, Maine s Superstorm Ingredients King Tide, 12 feet MLLW Record Surge (4.8 feet) Resulting water levels of 16.8 feet MLLW, which would be 2.7 feet higher than our historic 1% event (the February 1978 event)

36 16.8 feet 14.1 feet 4.8 feet 2.8 feet 11.3 feet 12.0 feet Blizzard of 1978 Portland Portland, Maine Superstorm

37 Sea Level Rise and Storm Surge Summaries Latest scenarios for SLR (using the intermediate to intermediate high relative scenarios from NOAA 2017): Short Term: approximately ft by 2050 Long Term: 3-6 ft but potentially more by 2100; Sea level rise increases both the frequency and duration of annual tidal and storm- driven flood events. Abrupt short- term sea level changes do occur, and can have significant impacts on storm levels and beach erosion. Maine has been extremely lucky in the past due to its large tidal range, which lowers the probability of a large surge (>4.0 feet) corresponding with a high tide.

38 Thank you! Peter A. Slovinsky, Marine Geologist Maine Geological Survey (207) C. Adams