Climate change impacts on Salt water intrusion in Coastal Bangladesh

Dr. Fulco Ludwig Earth System Science Group

Wageningen University 27 January 2016

Ganges

Brahmaputra

Meghna

GBM BASINS The GBM Basins drain 1.72 Mi km2 area 93% of the area outside Bangladesh 75-80% of flow in 5 months of monsoon

Saltwater intrusion is caused by a combination of sea level rise and reduction of dry season river flows

Dis

char

ge

(m2/

s)

Water Supply for the city of Khulna

§ Khulna is the 3rd largest of Bangladesh § Local water is saline during the dry season § Only deep groundwater can be used for drinking water § Large parts of the Khulna residents drink saline water

during part of the year § ADB and Japanese gvt wanted to invest 250 million US$

in a new drinking water plant § The question is where to build to plant and where to get

the water from and will this be affected by climate change

Salt intrusion in May in Southwest Bangladesh

Modelling framework to assess future salt intrusion

Future Sea Level Rise – end of 21st Century – From IPCC AR5

IPCC 2013

0 SLR 32 cm SLR 88 cm SLR

Impact of SLR on Salinity Intrusion

Hiron Point

Bay of Bengal

Mongla

Khulna

Movement of 5 ppt Salinity line

Source: IWM

Climate change impact on flow of the Ganges under 2 degree warming

-­‐60%

-­‐40%

-­‐20%

0%

20%

40%

60%

80%

100%

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Change  in  Ganges  Flow

 Com

pared  to  

1985

-­‐200

5  (%

)

CNRM  RCP8.5  (2035-­‐2055) SMHI  RCP8.5  (2029-­‐2049)

Reduction in flow in May when salt intrusion is highest

Climate change impact on salt water intrusion

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Salinity

 (PPT)

Atharobanki  R:  Avge.  Salinity  in  RCP  8.5  Scenario  RCP  8.5  (2029-­‐2049) Base  (1985-­‐2005) RCP  8.5  +  Gorai  Dredging2 degree warming Gorai dreding + 2 degree warming

Where to develop the drinking water plant

Conclusions

§ Combined reduced dry season river flows and sea level rise result in large scale increases in salt water intrusion

§ Salt intrusion is likely to increase in the future in Southwest Bangladesh unless dramatic infrastructure measures are taken

§ Water intake for drinking water supply near Khulna is not suitable due to increasing salt water intrusion

§ This study recommends Mollarhat as intake point due to low salinity

§ In addition a reservoir can be developed