The mega-drivers of global change

Transcription

1 Impact of Global change on Landslide hazard and Risk: with reference to New Zealand. Elements at risk Vulnerability Exposure to Hazard III Convegno Nazionale AIGeo In Honour of Mario PANIZZA Modena and Alta Val Badia, Italy September 2009 Increased landslide risk and losses Michael Crozier Landslide activity School of Geography, Environment and Earth Sciences Victoria University of Wellington Physical susceptibility Triggering activity Number of disasters The mega-drivers of global change Population growth increase resource demand Increased wealth - increase in demand per person Increase wealth and technology - increased resource exploitation and geomorphic change Urbanisation and the concrete environment Climate change All lead to increased impact on geomorphic systems 1

2 Number of natural events Increasing impacts because of changes to the physical process (A & B) and changes to human vulnerability or physical susceptibility reducing the damage threshold (C) Billions World population growth Damage thresholds Less Developed Regions More Developed Regions Source: United Nations, World Population Prospects: The 2004 Revision (medium scenario), Cendrero et al. (2006), make the link: Population increase can turn events into catastrophes Population exposed Population + wealth + technology. Frequency and/ or intensity of catastrophic events and damage per event catastrophe 1, disaster event 100,000 10,000 1,000 Data from Guzzetti & Tonelli (2004) Variation of the physical event GDP-world US$ million (2001) 2

3 But is it that simple? What is the reality of globalisation? Does the economic benefit in one country result of degradation and increased risk in another? Cendrero et al. (2006), make the link: Population + wealth + technology. Frequency and/ or intensity of catastrophic events and damage per event BUT not always: technology can reduce risk Building damage Kobe earthquake Geomorphic Source: What is the geomorphic footprint of urbanisation QUARRIES MINES RIVERS COASTS E.G: Geomorphic footprint Madrid: >30m3/person/year (Cendrero et al. 2006) 3

4 The threshold storm rainfall required to produce significant landsliding within the Wellington urban area is 150 mm compared with a threshold of mm for surrounding natural slopes Urban areas are dependent on crtical facilities and lifelines for their existence. The implications of lifeline disruption by landslides are enhanced in urban areas The Wellington fault Increasing exposure to both rainfall and seismically triggered landslides from urban sprawl (Hufschmidt and Crozier 2008) Wellington fault 4

5 The landslide sites are in-filled drainage lines they are evacuated by landslides in heavy rain The area of urban development also has a history of landlsiding 5

6 August 2005 August 2006 Increasing exposure due to life style choices Increasing susceptibility through resource exploitation July 2004 In using our rivers we change them: we need to understand those changes to safeguard the benefits we receive Mining waste Damming Irrigation abstractions Aggregate removal Channel modification Stop banks 6

7 Landslides from Mining: OK Tedi gold and copper, Papua New Guinea Pyroclastic and lahar deposits fill valleys but demand for aggregates has removed the material. It no longer reaches the coast protective dunes are depleted and coastal erosion results -Indonesia Sediment deposits at the head of reservoirs can lead to flooding while down stream of the dam, channel incision may occur, leading to destabilisation of structures and bank slumping 7

8 Channel degradation from sediment starvation downstream of a dam: increases bank height and slope Increased susceptibility by deforestation and farming practices Most of the forest in NZ was cleared by Europeans between 1870 and 1920 Deforestation in New Zealand has increased erosion rates up to 7 times the rate under the natural cover, principally by increased soil landsliding. New Zealand had forest covering 85% of the country - 75% of that has been removed mostly in the last 150 years Deforestation in New Zealand has increased runoff by possibly 28% NB: the most extreme IPCC predictions for New Zealand predict a max increase in runoff of 15% by

9 Bola 1998 Gisborne, 2002 Trustrum Wairoa, 1977 Wairarapa, 1977 Even young forest can reduce landsliding Adapted from Scarf (1982) and Bosch and Hewlett (1982) Increased water yield from deforestation 9

10 Inreased runoff can cause flooding and destabilise channels NIWA 2007 Royal Society wellington Overgrazing can lead to pipe formation and gullying Overgrazing leading to tunnel/gully development Pipe exits: Moeraki 10

11 Geomorphic significance of Humaninduced erosion: Indirect impacts climate change the accumulation of post-settlement alluvium on large flood plains(12,600m M a-1 ) is producing the greatest geomorphic changes being experienced on earth - far exceeding inputs from Pleistocene glaciations or from current alpine erosion Wilkinson and McElroy (2007) By the end of this century, increases in the rates of erosion could be in the order of 25-50% Goudie (2006) Increase in triggering activity Global surface temp Wellington annual rain Mean annual rainfall at different locations and return period of landslide events, NZ (Hicks, 1985) El Nino Southern Oscillation If 1500 mm annual rainfall increases 8%, return period drops from 6.26 y to 5.04 y 11

12 Daily rainfall (mm) Landslide area ratio Number of landslides Increase in area of landsliding with rainfall : Wairoa 14 2:Kamanachi : Fujioka 4: Neo Storm Rainfall (mm) 1: Eyles & Eyles (1982); 2,3,4: Omura & Hicks (1991) scenario rain 70 actual rain number of landslides 50 scenario rain required 40 rain required 1996 model Antecedent water status landslide triggering model re-run with climate change scenario (8% increase in daily rainfalls), Wellington 15/06/ /06/1996 1/07/1996 9/07/ /07/ /07/1996 2/08/ /08/ Will climate change produce more landslides? Low resolution downscaling results make this difficult to answer. But Intuitively yes Deteriorating alpine permafrost, glacial de-buttressing - yes 4 modelling studies 1 yes ; 2 no, 1 can t tell problems: what extent will increased temp and wind increase evapotranspiration to offset increased rainfall? Water must enter faster than it drains but constraint is often not rainfall intensity but infiltration capacity and hydraulic conductivity Availability of susceptible sites is a constraint: availability of material, critical depth, & slope geometry Difficulty separating human from natural enhancement. Observational evidence suggests an increase in landslide activity but in the same types of sites So avoidance and adaptation are possible strategies Will Human activity produce more landslides? YES 12

13 Conclusions Human impacts on geomorphic systems are unavoidable. They have increased landslide susceptibility and landslide activity Human impacts are increasing in intensity with increased resource demand per person, fuelled by urbanisation, and because of population growth - increased landslide activity and losses are inevitable. We have appropriate models, and paleoenvironmental studies, to suggest that climate change will affect landslide activity. Predicting the extent of this awaits higher resolution downscaling. Systems behaviour is complex: one impact can set off a chain reaction of downstream unintended consequences. If we understand system behaviour we can predict and minimise the adverse impacts. Geomorphologists have an important role to play in planning, engineering, and the development of environmental policy REFERENCES Bosch, J. M., Hewlett, J. D., A review of catchment experiments to determine the effect of vegetation changes on water yield and evapotranspiration. Journal of Hydrology 55, Cendrero, A., Redmondo, J., Bonachea, J., Rivas, V., and Soto, J., Sensitivity of landscape evolution and geomorphic processes to direct and indirect human influence. Geogr. Fis. Dinam. Quat 26: Eyles, R. J., Eyles, G. O., Recognition of storm damage events. Proceedings of Eleventh New Zealand Geography Conference, Wellington 1981, Hicks, D. L., A way to estimate the frequency of rainfall-induced mass movement. Journal of Hydrology (New Zealand) 33 (1), Hufschmidt, G., Crozier, M J., Evolution of natural risk: analysing changing landslide hazard in Wellington, Aotearoa / New Zealand. Natural Hazards 45, Omura, H., Hicks, D., Probability of landslides in hill country. In: Bell, D. H. (Ed.). Landslides. Proceedings of the Sixth International Symposium on Landslides, Christchurch, Balkema, Rotterdam, Scarf, F., Water yield and land use. In: D.J. Moore (Ed.). Catchment Management for Optimum Use of Land and Water Resources. Documents from an ESCAP Seminar, Part 2 New Zealand Contributions. Water and Soil Miscellaneous Publication No 46. Water and Soil Division, New Zealand Ministry of Works and Development, Wellington,