effects of climate change on the activity of landslides ... · rainfall thresholds:...

J.-P. Malet1, A. Remaître1, Y. Durand2, P. Etchevers2, M. Déqué2,

S. Bégueria-Portuguès3, L.P.H. van Beek4

1. School and Observatory of Earth Sciences, CNRS, University of Strasbourg, Strasbourg, France

2. Météo-France, Centre d’Etude de la Neige, Saint-Martin d’Hères, France 3. CSIC, Estacion Experimental Aula Dei, Zaragoza, Spain 4. Faculty of Geosciences, Utrecht University, Utrecht, The Netherlands

EFFECTS OF CLIMATE CHANGE ON THE ACTIVITY OF LANDSLIDES:

EXAMPLES IN THE SOUTH FRENCH ALPS

EGU’08: European Geosciences Union, Vienna, 14-18 April 2008

Climate and atmosphere chemistry

Freezing and thawing

Mechanical properties

Gravity

Landslides

Rockfalls

Weathering

Hydro(geo)logy

Geometry and geomorphology

Geology

Topography

Infiltration

Groundwater

Active tectonics and earthquake Human activity

Landslides are very diverse in types and can show highly variable behaviour in time and space according to internal and external factors

LANDSLIDES CAUSES AND FACTORS

Frequency of landslide reactivation in the Ubaye Valley (South French Alps; Buma, 2000)

RESEARH QUESTION #1

Global Circulation Models (GCMs) predict changes in intra-annual variability of climate: e.g. rainfall intensity, rainfall amounts, air temperature, distribution snow/rain, …… but with many uncertainties

Can we propose a methodology to evaluate the consequence of these changes

on landslide frequency / intensity … also including information on uncertainties?

Can we identify changes in landslide hazard (susceptibility, frequency, magnitude) and landslide risks (vulnerability, costs) associated to climate and landuse change scenarios? What indicators to express these possible changes?

(modified from Glade & Crozier, 2005)

RESEARH QUESTION #2

TWO PROJECTS ON THESE RESEARCH QUESTIONS

2007-2010

Changing pattern of landslide risks as a response to global changes in mountain areas

2011-2013

Effects of climate change on landslide processes

Effects of climate change on landslide hazard/risk

CLIMATE CHANGE AND LANDSLIDE FREQUENCY

• Analysis of the climate-landslide relationship in a eco-region of 20x30 km for the recent time (period 1950 2005) and the near future (period 2069 2099)

• Analysis of some landslide types specific of the study area: - Rotational or translational shallow slides occurring in moraine deposits - Deep-seated complex landslides occurring in weathered marls

Proposed methodology

• Characterization of past events

• Prediction of high-resolution meteorological time series (observed and changed climate)

• Prediction of landslide hydrology and slope stability with a process-based model

Assumptions and hypotheses

• Possibility to represent the temporal pattern of landslide hydrology/stability with a simple PBM - Initial conditions defined from probability functions of observed field parameters (moisture contents, GWLs, etc) - Boundary conditions issued from downscaled meteorological parameters (time series)

RESEARCH AREA: THE UBAYE VALLEY

Predisposing geomorphologic and climatic factors • High energy relief: slope gradients of 20° - 40° • Climate: dry-intra Alpine zone with a Mediterranean influence - High inter-annual rainfall variability (735mm 400mm; 1928-2005) - Mean annual temperature: 7.5° ± 1.3°; 1920-2005) - Presence of a snowpack on the upper slopes (> 1900m) for 4 to 6 months • Geology: black marls covered by moraine deposits

high hazard with permanent landslide activity

Super-Sauze mudslide

Rotational slide in the Poche torrent

Marseille Nice

Lyon

Landslide inventory maps: Barcelonnette

Barcelonnette – landslide catalogue : 1740 - 2010

Barcelonnette – inventory: aerial photo-interpretation

LANDSLIDE INVENTORY

CLIMATE-LANDSLIDE RELATIONSHIPS (1928-2005)

Archive investigation and dendrochronological analyses at several time scales - Annual time scale: periods of landslide activity are correlated to excess yearly rainfall amounts, but landslide events are also observed in relatively dry periods - Daily time scale: 2 types of climate situations Type A: heavy daily rain (shallow slides) Type B: heavy 30-day rain (deep-seated slides)

Climate classification: analysis of synoptic weather situations (e.g. example of Eastern type of circulation (convective storms)

Analysis of landslide triggering factors

TRIGGERING FACTORS

Calculations based on the rainfall intensity threshold method (Caine, 1980; Montgomery et al., 2000) The rainfall intensity is based on the total amount of rainfall for a given duration (1h; 2h; 6h; 12h; 24h), which may trigger or reactivate a landslide

Rainfall thresholds: intensity-duration approach applied in Barcelonnette

Peak intensity associated to debris flows and mudslides triggering

Seasonal occurrence of landslides in the Barcelonnette basin

Remaître & Malet (2012) . Trrggering conditions of landslides in the Barcelonnette Basin (subm. to Geomorphology)

-> Events characterized by high rainfall intensity and short episode duration (i.e. mostly the result of localized convective storms) will trigger mostly debris flows and shallow slides in relatively permeable soils (e.g. moraines, scree slopes or poorly sorted slope deposits). -> Long rainfall periods characterized by low to moderate average and peak rainfall intensity (i.e. the result of multiple and successive storms during a period of several weeks or months) can trigger/reactivate shallow and deep-seated landslides in low permeability soils and rocks (e.g., black marls, clay-rich material).

Analysis of landslide triggering factors

TRIGGERING FACTORS

EFFECTS OF CLIMATE CHANGE ON LANDSLIDE FREQUENCY

Methodology: - Basic idea: Meteorological variables downscaled from

GCMs are used as input conditions for the slope models

- Land surface meteorological parameters (slope scale) and snowpack properties are modelled for the reference climate and a ‘changed’ climate

- Hydrology and slope stability are modelled for the reference and ‘changed’ climate

Climate modelling and downscaling at meso-scale (region)

Dataset: station (observed) data • Network of six meteo stations with

daily precipitation data in the Barcelonnette area

• Summer Pndq0.9 computed for each station

• Gridded data, 0.035º resolution (aprox. 4 km)

• Model CMCC-CM1 (downscaling driven by ECHAM4-REMO GCM/RCM)

• Radiative / emmission scenarios: CMIP5 (control), RCP4.5/RCP8.5 (future)

• Periods: reference (1965–2000) and future (2011–2050, 2051-2100)

Dataset: GCM data

1. Scoccimarro E., S. Gualdi, A. Bellucci, A. Sanna, P.G. Fogli, E. Manzini, M. Vichi, P. Oddo, and A. Navarra, 2011: Effects of Tropical Cyclones on Ocean Heat Transport in a High Resolution Coupled General Circulation Model. Journal of Climate, 24, 4368-4384.

Example: precipitation field in Barcelonnette of 1st January 1965

CLIMATE MODELLING – MESO-SCALE

Italy

France

- Downscaling of the climate change scenario with the ARPEGES-IFS model of Météo-France and the appropriate disaggregation procedure established for the reference climate:

Main characteristics of the ‘changed’ climate for Southeast France: - higher temperature in summer - more rainy winters - drier summers - decrease in soil water content except for elevation > 1700m

Daily temperature

Daily rainfall

Climate modelling and downscaling at meso-scale (region)

CLIMATE MODELLING – MESO-SCALE

Climate modelling and downscaling at the micro-scale (slope): simulation of meteorological surface parameters (1h-data) for 2 periods of 30 years

- Identification of an appropriate disaggregation procedure (perturbation method):

Use of SAFRAN meteorological model (Durand

et al., 1993) to spatialize meteorological parameters according to estimations of general circulation fields, climate classifications (synoptic weather types) and slope configurations (elevation, aspect, etc).

Time series of air temperature, air humidity,

wind speed, rain and snow precipitation, long-wave radiation, direct and scattered solar radiation, infra-red atmospheric radiation, cloudiness.

- Good agreement of the observed & simulated datasets at a daily time scale.

RAIN

CLIMATE MODELLING – SLOPE SCALE

0,0

200,0

400,0

600,0

800,0

1000,0

1200,0

XX71 XX72 XX73 XX74 XX75 XX76 XX77 XX78 XX79 XX80 XX81 XX82 XX83 XX84 XX85 XX86 XX87 XX88 XX89 XX90 XX91 XX92 XX93 XX94 XX95 XX96 XX97 XX98 XX99 XX00

Year

ly r

ainf

all (

mm

)

Yearly rainfall (2071-2100) Yearly rainfall (1971-2000) Moving average 5 yrs (2071-2100) Moving average 5 yrs (1971-2000)

Example of meteorological parameter database: yearly rainfall at the Barcelonnette station for the past (1971-2000) and the future (2071-2100)

Climate modelling and downscaling at the micro-scale (slope): simulation of meteorological surface parameters (1h-data) for 2 periods of 30 years


Differences between the observed and ‘changed’ climate at the slope scale:

Rise in average annual temperature from 2.4° to 6.2° in relation to elevation

Distribution of temperature shifted to extreme values

Small increase in liquid precipitation Decrease in solid precipitation Snowpack properties

Use of the CROCUS snow model Drastic decrease in snow depths at 1800m No decrease at 2100m

1800m


PROCESS-BASED MODELING OF SLOPE HYDROLOGY/STABILITY

Hydrologic model ‘STARWARS’ (van Beek, 2002) - Dynamic modelling of soil matrix suction and water levels in order to compute pore water pressures - Input parameters: precipitation, temperature, net radiation, geometrical & hydrological characteristics

Hillslope stability model (Malet, 2005) - Limit-equilibrium approach (yielding by plastic failure) - Mohr-Coulomb failure criterion - Janbu force diagram (to account for non-uniformly distributed forces through the soil mass) - Input parameters: soil suction & GWLs, geotechnical parameters

Coupling of hydrology & slope stability / dynamic spatially-explicit approach

MODEL VALIDATION & PERFORMANCE

Model performance tested at the local scale: Super-Sauze mudslide (Malet et al., 2005)

Simulated hydrology (GWL) at 2 locations (upper, lower part of the mudslide) – 2 years

IMPACTS ON SLOPE HYDROLOGY/STABILITY

Application on 2 landslide types: - North-facing slope: Super-Sauze mudslide,

deep-seated flow-like landslide in marls

- South-facing slope: Boisivre rotational slide, shallow slump characterized by a morainic cover on top of weathered marls

Modelling of slope hydrology


Definition of initial conditions from probability density functions of observed soil hydrological variables

Daily groundwater level distribution functions Daily soil moisture distribution functions

Boundary conditions: simulated meteorological parameters (for the reference and the changed climate)


Modelling of slope hydrology: results - Daily groundwater levels simulated at the toe of the landslides: General decrease in GWLs and amounts of water storage in the soils North-facing slopes & deep-seated mudslides: lowering of GWL of ca. 0.5-1m caused by

small changes in yearly rainfall amounts (the decrease in snow depth is balanced by higher amounts of liquid rainfalls)

South-facing slopes & shallow slides: lowering of GWL of ca. 2-3 m caused by a decrease in soil moisture in the unsaturated zone (higher PET in the ‘changed’ climate)

Mudslide: Super-Sauze

Shallow slide: Boisivre


Slope stability - Calculation of the frequency of

unstable cells (eg. a frequency of 0.5 indicates that 50% of the calculation cells have a safety factor value lower than 1.1)

- General decrease in landslide activity with the ‘changed’ climate

Important for the shallow slides Less important for the mudslides

- Important issue: parts of the landslides might still fail or be reactivated with the ‘changed’ climate, though a decrease in unstable cells of 10-20% is simulated

Mudslide: Super-Sauze

Shallow slide: Boisivre

CONCLUSIONS

• Assumptions: Hypothesis on the landslide mechanism Use of a model validated at the field scale Hypothesis on the probability functions of the input time series

• For the hypothesized ‘changed’ climate, and given the uncertainties of the climate & slope hydrology models, the impact simulations indicate: On the South-facing slopes, an important reduction of slope instability for shallow slides On the North-facing slopes, a limited reduction of slope instability for mudslides

Process-based models of slope hydrology/stability allow to assess the impacts of climate change on landslide frequency

• More understanding of local landslide activity (long-term monitoring) is needed for reliable forecasts • No systematic ‘rule’: each landslide has its pattern of activity according to its geomorphological, geological, hydrogeological and mechanical context

Trends in impact of climate change on slope stability are established for the region

BUT:

ON-GOING RESEARCH ACTIVITIES

Definition of time series & maps of actual/changing predisposing/triggering factors Creation of actual and ‘changed’ landslide hazard maps

Definition of ‘changed’ maps of landcover and socio-economic factors Creation of actual and ‘changed’ landslide risks maps



Indicators of changes Maps

Definition of ‘changed’ maps of landcover and socio-economic factors Creation of actual and ‘changed’ landslide risks maps




Application of the methodology to several study cases Trièves region Isère, France Waidhoffen/Ybbs, Lower Austria, Austria Fella River, Venetia Region, Italy Nehohoui catchment, Buzau County, Romania Szymbarck region, Krakow, Poland

EC-MCITN Project: Changes in hydro-meteorological risks as analyzed by a new generation of scientists

Thank you for your attention!

effects of climate change on the activity of landslides ... · rainfall thresholds:...

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