S

Bangladesh’s coastal vulnerability

under climate change

BanD-AID

M. Becker1, F. Papa1,2, S. Calmant1, V. Ballu3, M. Karpytchev3,

L. Testut1, P. Valty4, F. Hossain5, C. Shum6, A. Liibusk6, Z. Khan7

1. IRD/LEGOS, France

2. IFCWS, IRD-IISc, India

3. CNRS/LIENSs, France

4. IGN/LAREG, France

5. U. Washington, USA

6. Ohio State U., USA

7. IWM, Bangladesh

Our Common Future under Climate Change (CFCC), 7 -10 July 2015, Paris

BanD-AID: Build an Earth Analysis & Prediction System based on space sensors to reduce Bangladesh coastal vulnerability from sea-level rise hazards under climate change.

http://www.belmont-bandaid.org

Delta: Natural state

Eustatic sea level rise 2100 projection IPCC AR5

Withdrawal of groundwater and hydrocarbon

Sediment

Ground Ocean

River influence

subsidence

Sediment trapping by dams and reservoirs

Relative sea level rise

+12-100 mm/yr

+2-10 mm/yr

+8-40 mm/yr

+2-50 mm/yr

Perturbations

Coastal subsidence and relative sea level rise

Relative sea level rise in Bangladesh ?

©C. Ashleigh

120 155

204 195

33 40 56 53

2000 2020 2040 2060 2080 2100

40 million (≈26% of total)

+900 people/km2

Population in delta

Projections (million)

United Nations

Bangladesh pop.

Delta pop.

Which data and tools can be used ?

Mathematical Sea level Reconstruction derived

from satellite altimetry or Ocean general circulation models (OGCMs) and tide gauges.

Relative sea level rise in Bangladesh ?

Satellite altimetry

Sea surface

Tide Gauge Station

GPS Receiver

Crust

Tide Gauges (or Sea Level Gauges)

X TRIBENI

Sea level variability

India : Hooghly River & Tide Gauges

CALCUTTA

DIAMOND HAR.

SAUGOR

GANGRA

HALDIA

TRIBENI

Tide gauges (PSMSL)

X TRIBENI m

m (

+off

set)

Monthly variations of sea level in the Indian side of the Bengal Delta,

the Hooghly River

6 TG along the Hooghly River with time series of ~30-35 years are

available at monthly time scale. The larger seasonality amplitude moving

northward is linked to the river hydrology influence.

India:

Hooghly

river

CALCUTTA

DIAMOND HAR.

SAUGOR

GANGRA

HALDIA

TRIBENI

Dipole Mode Index Tropical Indian Ocean east-west temperature gradient

+IOD +IOD +IOD +IOD +IOD

El Niño

+IOD

+IOD +El niño = dry year

Tide gauges (PSMSL) 12-month moving average

Hardinge discharge

X TRIBENI m

3/s

m

m (

+off

set)

Bangladesh: tide gauges and altimetry Seasonal sea level

Tide gauge (PSMSL)

Altimetry (AVISO)

Common period of time (1993-2012 ), fair/good agreement with ρ>0.85

Hiron Point

Khepupara

Charchanga

Chittagong

Cox’s Bazar

Bangladesh: Tide Gauges/Reconstruction Interannual sea level

v

CHARCHANGA 1979-1998

KHEPURARA 1977-2000

Tide gauge (TG)

Church et al. (2004) TG+ EOF altimetry

Hamlington et al. (2011) TG+ CEOF altimetry

Wenzel et al. (2014) TGNN+ EOF altimetry

Meyssignac et al. (2012, updated)

TG+ EOFREG SODA

TG+ EOFREG GECCO

TG+ EOFREG altimetry

TG+ EOFREG ORAS

Mean

The reconstructions provide an opportunity to compare sea level over the past 60 years. Limitations imposed by : - tide gauge sampling back through time - non-stationarity of satellite altimetry For the Bay of Bengal, our analysis shows that Messignac et al., “SODA” product compares best with TGs (not used to construct the product)

Bangladesh: tide gauges/altimetry/reconstruction Interannual sea level variability

Tide gauge (PSMSL)

Altimetry (AVISO) Reconstruction (Meyssignac et al. 2012, SODA)

24-month moving average

Sea level trends (mm/yr p<0.01)

1960-2012 2.6±0.1

1993-2012 3.4±0.4; 2.8 ±0.3

1983-2002 3.5±0.4; 3.3 ±0.6

Mean globally 1960-2012 = 1.7 mm/year

24-month moving average

Sea level trends (mm/yr p<0.01)

1960-2012

2.6±0.1 1993-2012

3.4±0.4; 2.8 ±0.3 1983-2002

3.5±0.4; 3.3 ±0.6

Sea level trends (mm/yr p<0.01)

1960-2012 2.6±0.1

1993-2012 5.2±0.4; 2.6 ±0.3

TG: no significant trend

Sea level + land motion

24-month moving average

Bangladesh: tide gauges/altimetry/reconstruction Interannual sea level variability

Tide gauge (PSMSL)

Altimetry (AVISO) Reconstruction (Meyssignac et al. 2012, SODA)

Mean globally 1960-2012 = 1.7 mm/year

http://www.belmont-bandaid.org

Understanding relative sea level variability

GPS stations collocated with tide gauge

We have installed 6 GPS/TG

stations since 2013 (green dots)

Conclusions and Outlook

•In Bangladesh, relative sea level rise in combination with land

subsidence resulting from groundwater pumping, sediment load

and/or tectonic motion.

•The separation of the relative sea level change into individual

contributors is important.

influences from hydrology and steric changes ?

•GPS stations, collocated with long-term tide gauge, are crucial

information for the understanding of relative sea level variability.

•BanD-AID field works: to quantify the vertical land motion with GPS

campaign, and calibrate satellite data for sea-level measurements.

Eroded rice field banks, Hatia Island, Bangladesh