Sea-level rise: How are we tracking in Wellington region & how will it effect coastal flooding? Dr Rob Bell NIWA, Hamilton

Transcription

1 Sea-level rise: How are we tracking in Wellington region & how will it effect coastal flooding? Dr Rob Bell NIWA, Hamilton

2 Coastal adaptation in NZ: Starting-block issues with sea-level rise Tell us what SLR number to use? Any sign of accelerated SLR? Shouldn t we wait for: o o more certainty from scientists? or a National Environmental Standard? What if SLR is less than anticipated & we overdesign? What is the likelihood of a SLR higher than anticipated? How and when do we start adapting? New vs existing development? Dave Allen, CartoonStock.com

3 Sea-level rise: datums! What we need to adapt to Global projections tide-gauge SLR SLR Relative sea-level rise Earth geo-centre Absolute (eustatic) sea-level rise

4 Source: CSIRO Global average rate: ~0.21 m in 120 years or ~1.8 mm/yr

5 Sea-level fluctuations: climate variability 0.2 m Wellington Vertical Datum: set up in 1953 from 14-yrs data from 1909 to 1946

6 Sea-level fluctuations: climate variability m Monthly mean sea level m

7 Climate variability masks long-term trends 0.8 m years to show appreciable difference 0.18 m historic

8 Climate variability affects short-term trends

9 Hannah & Bell (2012) JGR-C Long-term NZ trends: relative SLR

10 Wellington: relative SL trend Year of Analysis Data used Linear trend Standard deviation (inclusive years) (mm/yr) (mm/yr) 1990 (Hannah,1990) (Hannah,2004) (GWRC report)

11 Relative SLR (1903 to 2008) Auckland 1.5 mm/yr [±0.1] NZ average relative SLR (4 main ports): 1.6 ± 0.1 mm/yr (to 1999) 1.7 ± 0.1 mm/yr (to 2008) Similar to global average of 1.8 mm/yr Wellington 2.03 mm/yr [±0.15] Lyttelton 1.9 mm/yr [±0.1] Dunedin 1.3 mm/yr [±0.1] Hannah (2004) Hannah, Denys & Beavan (2010)

12 Vertical land movement: slow slip events Land subsidence from SSEs in City: -1.7 mm/yr since at least 2000 relative sea-level rise is temporarily(?) 2x the NZ-average rate Source: Denys, Beavan & Hannah (2012): JGR (in prep)

13 Vertical land movement: Lower North Island Source: Beavan & Litchfield (2012): GNS Report 2012/29

14 New Scientist: 22 Oct 2011: Special Report: Climate Change What we do know and what we don t Michael Le Page (2011)

15 SLR tracking relative to a few credible scenarios 1.8 m 1.4 m 1 m 0.7 m MfE(2008) by 2090s by 2115 Mean ( )

16 SLR tracking relative to 2007 IPCC projections 0.8 m by 2090s 0.5 m by 2090s Recent acceleration not significant yet - if sustained to end of decade then it will be Source: Church et al. (2011) Oceanography

17 Guidance on SLR to accommodate

18 NZCPS policies: 1 st port of call 1. Consider climate-change & hazard effects for at least 100 years (Policies 10, 24-25, 27) Need to get beyond the 2100 glass ceiling it s nearly 2012 If starting now, look out to 2115 But Shand study a good start out to Not just SLR other hazards as well (P 24) 3. Different approach for greenfields (Obj 5, P 3, 25) vs existing development (P 27)

19 Planning timeframes: now essential!!

20 Guidance on sea-level rise to accommodate MfE guidance Manual for Local Government in NZ (2008): Largely based on IPCC AR4 but also included some peerreviewed papers ( ) Risk-based approach rather than provide a single value

21 Guidance on sea-level rise to accommodate For planning and decision timeframes out to the 2090 s ( ): 1. a base value sea-level rise of 0.5 m relative to the average be used, along with; 2. an assessment of potential consequences from a range of possible higher sea-level rise values. At the very least, all assessments should consider the consequences of a mean sea-level rise of at least 0.8 m relative to the average. For planning and decision timeframes beyond 2100: For longer planning and decision timeframes beyond the end of this century, we recommend an additional allowance for sea-level rise of 10 mm per year beyond MfE Guidance Manual for Local Government in NZ

22 International SLR planning guidance State SLR guidance Timeframe Queensland 0.8 m 2100 NSW 0.9 m 2100 Victoria 0.8 m 2100 South Australia 1.0 m 2100 West Australia 0.9 m (was 0.38 m) 2110 Tasmania TBD NT TBD UK Env Agency scenarios m 2095 UK Env Agency H ++ scenario* m 2100 Thames Estuary 2100 flood-risk 0.9 m (for timing) 2100 Delta Commission -Netherlands 1.1 m 2100 * for contingency planning & limits on adaptation

23 Some issues with 2008 MfE guidance Councils have generally reduced guidance down to a single number e.g. 0.8 m or even 0.5 m by the 2090s or 2100 A risk-based approach requires knowledge of future impacts local and regional, but provides more flexibility than 1 number Timeframe out to 2090s needs to be extended further to at least 100 years (NZ Coastal Policy Statement) 2115 MfE guidance is perceived as being out of date (behind recent estimates) by some councils and overestimates by others

24 Existing development: Much less room to manoeuvre with rising risk

25 Greenfields vs existing development Existing development: Determining an appropriate mix of staged responses and setbacks with a credible sea-level rise Complex!!! May eventually require retreat New Greenfields development: Risk avoidance and precautionary approach now paramount (NZCPS) but being tested! $4.45M A made-to-order property... where the land extends into the sea...

26 Suggested SLR guidance to councils for now Existing development: Plan generally for a sea-level rise of around 1.0 m by 2115* The Shand report (2012) adopted 0.9 m over a shorter timeframe from 2008 to so reasonably consistent New Greenfields development (e.g. new subdivisions): Plan for m (irrespective of timeframe) as sea level will continue rising for several centuries If the risk is limited in time or isolated, then maybe >1.0 m New development eventually exposed to higher SLR e.g., 2+ metres should also incorporate future-proofing elements into building/design requirements (also co-benefit with improved tsunami protection) Monitor SLR, changes in risk, frequency of events and review Keep eye on vertical land movement if subsidence continues then higher regional SLR projection will be required (barring another quake) * equivalent to 0.8 m by 2090s

27 Circumventing uncertainty in SLR Uncertainty in sea-level rise projections may be around for awhile ice-sheet response is the big science challenge Adaptation of existing development: Pushing SLR values too high for minimum ground levels may lead to maladaptation e.g. distort drainage, aesthetics Coastal hazard setback zones a tried & tested approach Also needs strategic blueprint for the response of vulnerable coastal communities to higher sea levels across all council processes Where possible, adaptation should include staging Revise SLR estimates and hazard setback zones via regular monitoring & review

28 Back to the future: development tuned to tides Present perigean-spring ( king ) high tide: 8% of all high tides exceed it 0.3 m sea-level rise exceeded by 55% of all high tides 0.5 m sea-level rise exceeded by 81% of all high tides

29 Storm-tides will become more frequent increasing occurrence increasing magnitude Drainage issues with more frequent storm-tide levels or inundation events

30 Summary points Signs around NZ now of sea-level rise exacerbating coastal flooding Wellington presently tracking towards 0.8 m (2090s) or 1 m (2115) But could be lower or higher: ±0.5 m by 2115 depends on ice-sheets Avoid foreseeable risk where possible for new or greenfield developments Coastal-storm inundation will be much more frequent incl. high tides Monitor & review check need to switch tracks for forward planning?