Lecture 4. Climate change and the

integrated coastal system. Wednesday

25 July 2007

ESPA Deltas Project

Coastal ecosystems, governance and poverty:

A case study of managing the Ganga-Brahmaputra- Meghna Delta in a

changing world

Changing Socio-economics and Climate Conditions and their impact on flows and Nitrogen flux in GBM Rivers:

Implications for policy, people and livelihoods in Bangladesh

Rajiv Sinha1, Paul Whitehead2, Sananda Sarkar1 and Emily Barbour2

1Indian Institute of Technology Kanpur

2University of Oxford

Key Questions and Motivation

– Societal Importance to Stakeholders and affects Poverty Alleviation

– Freshwater supply for domestic, agriculture, aquaculture are essential to people’s livelihoods

– Flows and Nutrient loads stimulate estuarine ecosystems, supporting fish stocks, which contribute significantly the economy of Bangladesh

– Upstream alterations, as well as the local impacts of climate change are very significant to many stakeholders in Bangladesh at the local, regional and government levels

The Ganga-Brahmaputra Basin and GBM Delta • How will future socio-economic change combined with climate change in

the Ganga basin impact flows and nutrient fluxes into the GBM Delta? • How can management and policy interventions reduce these impacts?

Ganga Dispersal

System

3

Himalaya

GBM delta

Ganga Basin

Bengal fan

(Courtesy: Steve Goodbred)

River Length 2510 km (29th) Basin area 980,000 km2 (18th) Mean height 890 m (14th) Depositional area 28% (4th) Suspended load 524 Mt/yr (2nd) Dissolved load 75 Mt/yr (8th)

(Source: Hovius, 1998)

Brahmaputra basin

Climatic & Socio-Economic Trends - IPCC 2014 Strategy

SSPs – Shared Socio-economic Pathways

• Population changes

• Sewage treatment works capacity and design for water quality control

• Water demands for irrigation and public supply

• Atmospheric nitrogen deposition

• Landuse changes

• Water transfer plans

-40.0

-20.0

0.0

20.0

40.0

60.0

80.0

100.0

120.0

20

11

20

21

20

31

20

41

20

51

20

61

20

71

20

81

20

91

% change

year

UNDP Population Centre Trends (India)

Q0 – Moderately warmer/wetter Q8 – warmer/drier Q16 – warmer/wetter

Climate Scenarios

Integrated Catchment Model (INCA)

• Can account for diffuse and point sources of pollution, land use change and climate change

• Successfully applied to over 50 catchments including Ganges main stream

PLOT

HILLSLOPE &SUBCATCHMENT

CATCHMENT

(Hydrology, Nitrogen, Phosphorus, Sediments, Carbon, Metals and Ecology)

The INCA-N NITROGEN Model Process Pathways

Source: P.G. Whitehead et al./The Science of the Total Environment 210/211 (1998) 547-558

INCA reach divisions for Ganga basin

7

Major Cities and Point Source Pollution

Reach Structure: Ganga Model

Total 70 reaches Ganga – 21 reaches Yamuna – 10 reaches Other tributaries – 39 reaches

Tributary confluence Sampling/monitoring point Effluent input/abstraction

Modelled Sub-Catchments in Ganga

Detailed Land Use Mapping

(Based on NRSC, Hyderabad)

26 classes aggregated into 6 classes for INCA

UK Met Office GCM- RCM (25km grid- calibrated spatially and in time)

10

Q0 – Moderately warmer/wetter Q8 – warmer/drier Q16 – warmer/wetter

Climate Scenarios

Inputs for INCA Model

Simulated data for 1981-2000 using PERSiST Model (Daily time series data)

Model Calibration - flow gauges on the Ganga River system

GA04 Kachla

GA05 Ankinghat

GA06 Kanpur

GA07 Garh

Hardinge Bridge Bangladesh

Calibration of N Flux

At Kanpur (Reach GA06) At Beharampore (Reach GA19)

13

Estimated Flows, Nitrate and Ammonia at Farakka

Blue – 1990s Red – 2050s Green – 2090s

Climate Scenario Q0

Flow Nitrate Ammonium

• No major shift in timing of monsoon season, peak flows change • Nitrate and Ammonia follow the dilution trend due to increased flows

Effects of SSPs on Ganga Flow and Water Quality (Climate Scenario Q16)

Blue – BaU; Red – MS; Green – LS; Dotted – baseline 1990s

Flow Nitrate Ammonium

• No major difference in flows (no major change in irrigation flows & water transfers simulated) • Large reduction in N and NO3 under MS scenario – reflects improved effluent treatment,

implications for river ecology and reduced nitrogen load into Bangladesh (similar results for P)

3 Climate Scenarios and 3 SSPs

For 2090s

=> SSPs have minimal effect on GBM mean flows

Similar analysis for Meghna and Brahmaputra

• Monsoon season shortened in Q16 but flows increased, more floods

• Minimum flows are significantly affected

• N and NO3 conc. Reflect temp patterns and dilution effects

Water Infrastructure Major Transfer Plans (River Interlinking project)

• Impact of water transfers on flows is very significant • 22% reduction in peak flows for 2090s; 48% reduction in low flows for 2090s • => Large scale impact on delta ecosystem

Model assumptions: 20% diversion from Ganga; 30% from Brahmaputra

Conclusions 1. INCA model simulates the spatial and temporal complexity of

flows and N-flux in a large river system. 2. Significant climatic shift with increased temperatures and

change precipitation could have significant impact on flows, increasing peak flows and frequent droughts.

3. Socio Economic Changes could have a large effect on flows during droughts where increased irrigation will reduce low flows, plus impact of Water Transfers could be very significant in the GB delta.

4. Clean up of the Ganga River will reduce Nitrogen (and Phosphorus) fluxes into Bangladesh.

5. Process based model of the GBM rivers can now be used to evaluate alternative policies in more detail (e.g. dam effects, different agricultural strategies, point source pollution, different Ganga Clean up strategies etc.).

Thanks to ESPA Directorate, NERC, ESRC and DFID for their support