Scenarios for the NI coast in the 21 st Century

Transcription

1 Scenarios for the NI coast in the 21 st Century Prof Julian Orford Geography, Archaeology & Palaeoecology Queen s University, Belfast

2 Challenging perspective Living by the coast is good for your health! (Wheeler et al., 2013 I want to identify why it could be the opposite in the 21 st C! However, Shoreline Planning could minimise this change.

3 21 st Century NI SCENARIOS First estimates Para 1.4: Future trends in weather patterns predict sea level rise. Scientific evidence attributes this trend to global warming and climate change. Para 2.4: The CC Risk Assessment indicates that increased flooding and coastal erosion affecting people, properties (including built heritage) and infrastructure: and increased coastal squeeze and coastal evolution affecting beaches, intertidal areas, grazing marshes etc. are potentially significant threats for Northern Ireland from a changing climate. (From 2013 Revised Draft PPS 15 Planning and Flood Risk based on Defra s 2012 Climate Change Risk Assessment)

4 GLOBAL SEA LEVEL RISE: HOW ARE WE DOING SO FAR? (IPCC 5th Assessment, 2013) Instrumentation: Satellite altimetry Historical record: salt marsh and tide gauges SLR rate: 3.25mm/yr Note historical trend is rising to match altimetry

5 WHAT HAS BEEN HAPPENING IN NI? Belfast Harbour: 20 th Century Monthly Mean Sea Level (Orford and Murdy, 2012) Long term 20 th Century SLR rate: ± c 0.5mm/yr Short term SLR rate: ± c 2mm/yr

6 FUTURE GLOBAL SEA LEVEL RISE (IPCC 5 th Assessment, 2013) Overall mean rise: 59cm Mean rise rate: 6.5mm/yr Conservative estimate

7 UNCERTAINTY OF FUTURE SLR: Concerns for <2x mean SLR estimates by MEAN SL CHANGE (IPCC 5 th Assessment, 2013) Low Medium Low Blue: Temperature projections Medium High High Red: RF scenario projections 8 Experimental studies

8 CHANGING VERTICAL REACH OF THE SEA (1) Surge = temporary rise in water level due to storms (Orford and Murdy, 2012) Maximum annual surge at Belfast Harbour (Orford and Murdy, 2012)

9 CHANGING VERTICAL REACH OF THE SEA (2) Extreme Water Level (EWL) Tidal elevation + surge = EWL Annual maximum EWL + associated peak surge, Belfast Harbour (Orford and Murdy, 2012)

10 CHANGING VERTICAL REACH OF THE SEA (3) CHARACTERISING EXTREME VERTICAL REACH OF THE SEA Use the Observed Return Period (RP) of EWL ~ 1:N yr Belfast Harbour RP: Orford and Murdy 2012 Important: RP value for given elevation, as mean sea level

11 CHANGING VERTICAL REACH OF THE SEA (4) To assess changes in RP, future SLR estimates are needed SEA LEVEL RISE SCENARIOS: Belfast Harbour Projections (UKCP 09) based on 4th IPCC ASSESSMENT (2007) By 2100 using 3 EMISSION SCENARIOS: H: 39cm SLR M: 30cm SLR L: 23cm SLR

12 CHANGING VERTICAL REACH OF THE SEA (5a) Effect of rising sea-level on RP for north NI coast Portrush 20 year record RP 1:200 (Defra, 2012) 30 cm 1:10yr SLR 59 cm 1:<1yr 100 cm 10x per yr Malin Head 50 year record RP 1:100 (Orford et al., 2007) HWS: 1.8m OD Dublin BY 2050AD current 1:100 year event level could reoccur 1:5 years (HIGH) and 1:20 years (MED). By 2100AD, current 1:100 year event might re-occur 1:1 year By 2100AD 1:100 year could reach m OD (MED), possible to reach m OD (HIGH)

13 CHANGING VERTICAL REACH OF THE SEA (5b): Effect of rising sea-level on RP for East NI Coast Bangor 20 year record - RP 1:200 (Defra, 2012) 30cm 1:12yr SLR 59cm 1:<2yr 100cm 2x per yr Belfast Harbour 100 yr record - RP 1:100 (Orford & Murdy 2012) HWS: 1.5m OD Belfast. 1:100 is at 2.68m OD Belfast By 2100AD current 1:100 year event might re-occur 1:5 year By 2100AD current 1:100 year event likely to reach 2.92m (MED) to 3m (HIGH). Using UKCP 09 By 2100AD 1:100 year event likely to reach 3.2m (MED) to 3.5m OD (HIGH). Using IPCC 2013

14 THE ONSHORE REACH OF RISING SEA LEVEL: THE BRUUN RULE a simple budgetary model of beach profile response to sea level change RESULT: RISING SEA LEVEL FORCES COASTAL EROSION

15 MODELLED IRISH COASTAL RECESSION RATES (m/yr) Based on the Bruun Rule (Carter 1990)

16 IMPACT OF SEA LEVEL RISE (1) INTEGRATED PHYSICAL and CULTURAL VULNERABILITY (eastern NI Coast) (Orford & MacFadden, 2003) Probability assessment of functional change (500m coastal units) given: 30cm Sea Level Rise Modelling breaking wave height of extreme SE storm % coast showing likelihood of functional change >High: 49% Moderate: 28.4% <Low: 22.6% Fair Head Whitehead Belfast Lough Orlock Pt St John s Pt St John s Pt - Cranfield Pt

17 IMPACT OF SEA LEVEL RISE (2) Changing sediment pathways and cells: Sources-Corridors-Sinks along the Ards Orford & Bowden 1983 As SLR then: Cell boundaries likely to shift longshore Relative dimensions of cells likely to change Given degree of coastal protection, then coastal squeeze will likely force reduction of beach dimensions (by 40%: Defra 2012)

18 UNDERSTANDING HAZARDOUS COASTS Lack of appreciation of sediment pathways Sink: beach and dune deposition Source area: cliff erosion SE Co. Down

19 IMPACT OF SEA LEVEL RISE (3) STRANGFORD LOUGH OF THE FUTURE? (Orford et al., 2007) c.1m rise in sea-level (SL) = significant loss of tidal mudflats (habitats) Steep lough-shore slopes and coastal walls = coastal squeeze Seal haul outs and nesting shingle beaches lost under SL rise Saltmarsh losses as onshore transition potential lost with rapid SL rise +squeeze Increased winter storms and surges = increased overtopping threatening roads, and undermining defences

20 IMPACT OF SEA LEVEL RISE (4) MURLOUGH NNR OF THE FUTURE? Sea-level rise would lead to between m landward dune erosion. Dune erosion rate depends on rate of sea-level rise Longshore storage capacity of sand dependent on rate of sea-level rise Inner Bay flooding leading to saltmarsh losses on west side, though possible growth on eastern side Flood pressure on new build in Dundrum

21 ESTIMATED ROI LOSSES WITH 1m SLR (Devoy, 2008) IMPACT NUMBER/VALUE PROPORTION VULNERABILITY People affected < % Med (1-10%) People at risk Floods) Capital Value loss (total loss/gnp) < :100 flood c. US$170M (agric land value) C8/1000 Low (<10/1000) c.0.2% GNP Low (<1%) Dry land loss <230km2 <0.3% Total area Low (<3%) Wetland loss c. 800km2 c. 30% Wetland area Protection/adaptat ion costs (ROI only) Potential $420M/yr Likely $10M/yr c. 0.6% GNP c. 0.02% GNP High (10-30%) High (0.25-1%) Low (<0.05%) (Vulnerability Classes: Watson et al., 1996)

22 ESTIMATES OF UPGRADING EXISTING COASTAL PROTECTION COSTS GIVEN 1M SLR Current costs (Devoy, 1992) Coast (km) Defence (km) Cost to bring SOP to meet 1m SL rise Total ( ) Low coast Urban coast Harbour Beach Britain M 2536M 624M 1164M 6222M Ireland M 336M 39M 0 437M

23 WHAT ARE THE OPTIONS FOR COASTAL SOCIETY FACED WITH SUCH PHYSICAL CHANGES IGNORE THE MESSAGE and live in ignorance until the next major event(s) MORE and BIGGER COASTAL DEFENCES but not for all the coast. Q. of sustainability RETREAT FROM THE SHORELINE: where and how? To make/ take the option choice requires Shoreline Planning.

24 CONCLUSIONS The Coastal Zone is hazardous and likely to be more so, during the 21 st century Coasts likely to be the most dynamic changing NI physical environment Given future SLR by 2012, the current 1:200 yr EWL RP likely to drop to 1: <10 yr, with new 1:200 EWL between 3-4m OD major protection issues. A conservative 30cm RSL will be associated with major beach and soft cliff retreat, but uncertainty due to lack of baseline data. Sediment pathways likely to change - more erosion and loss of beaches. 50% NI coast likely to experience significant functional change. Shoreline re-alignment likely to be the dominant planning response. Living by the coast is likely to be injurious to our economic health. Shoreline Planning is the major tool for mediating between society and these future physical coastal changes.