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