Presented by Guillaume Lacombe at the Regional Conference on Risks and Solutions: Adaptation Frameworks for Water Resources Planning, Development and Management in South Asia, on July 12, 2016, at Hilton, Colombo, Sri Lanka
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Climate change science, knowledge and impacts on water resources in South Asia
1. Climate change science, knowledge
and impacts on water resources in
South Asia
GUILLAUME LACOMBE, PENNAN CHINNASAMY
Regional Conference on Risks and Solutions: Adaptation Frameworks for Water
Resources Planning, Development and Management in South Asia
Colombo, Sri Lanka, 12-13th July 2016
DIAGNOSTIC PAPER 1
2. Objectives
Provide a critical review of climate risks that threaten water resources
in South Asia
Review current situation and future trends influenced by climate
change
Identify knowledge gaps and recommendations to improve
preparedness and reduce vulnerabilities
3. Outline
1. Water resources: variability, trends, and drivers
Climate, hydrology, aquifers and water demand
2. Water resource risks: shortage, excess, and contamination
3. Climate change & water resources: CERTAINTIES & UNCERTAINTIES
Changes in rainfall, temperature, evaporation, and sea level
Consequences on river flow, groundwater recharge, storages and water quality
4. Knowledge gaps and recommendations
4. Water resources in South Asia:
an overview
1. 25% of world’s population, 5% of global water resources,
2. Annual per capita water availability (2,500 m3) below world average
(5,900). Continued decline could reach critical 1,000 m3 in 2025
3. Agriculture: major water consumer (>90% of water abstracted)
4. Growing domestic and industrial demands (e.g. hydropower)
5. Increasing pressure on ecosystems, particularly in downstream areas
1/ water resources
5. Climate influenced
by Indian Ocean
(Southwest
monsoon) and
topography
(Himalayan range)
Contrasted climate conditions
1/ water resources
Peel, Finlayson and
McMahon (University
of Melbourne).
6. 1 Ganges-Brahmaputra-Meghna (GBM)
2 Indus Basin
More than half of South Asia
drained by 2 major river basins
with very different hydrology
1300 km3/year (= 760 mm) mainly from monsoon rain (June-September). High seasonality
Ganges: 20-40% of water resources used (75% aquifers, 25% surface). Low water quality
Brahmaputra largely unexploited (low population and steep terrain). Relatively good water
quality upstream. 800 million tons of sediments transported annually in GBM
200-300 km3/year (= 170-250 mm) mainly supplied by snow melt providing perennial water
supply 75% of water resources used, mainly for irrigation (53% surface; 47% aquifers). High
water stress (<1000 m3/capita.year). 0.44 km3 of sediments carried annually
Other basins: Coastal (Southern India, Sri Lanka) and endorheic (Helmand) basins
1/ water resources
9. 2/ Climate risks
Water excess: floods destroying infrastructures, crops and causing
casualties or diseases
GLOF, flash floods, riverine flood and coastal floods
Water shortage: crop yield declines, hydropower loss, lower industrial
productions and domestic supplies
Rainless periods, low surface and groundwater levels, sediments in storages
Water contamination: diseases, crop yield declines
Sea level rise contaminating coastal aquifers, flux of pollutants and contaminants
induced by drops in water table levels
South Asia concentrates over 40% of
natural disasters recorded globally
2/ climate risks
10. Floods (1 million affected people over last century: 80% in
India and 14% in Bangladesh)
Flash-floods and landslides in
mountains
aggravated by slopes, land-use
changes, settlements in flood-
prone areas
Afghanistan, Northern
Bangladesh, Indu Kush Himalayas
region, e.g. glacial lake outburst
floods (GLOF)
Riverine floods in alluvial plain. Higher vulnerability in flat densely
populated river delta. Aggravated by flat/low terrain, land-use change
Bangladesh (coincidence of flood pulses in GBM system), India, Pakistan, Sri Lanka
GLOF in Nepal
2/ climate risks
(http://www.emdat.be/)
11. Coastal floods mainly
due to cyclones
creating local sea-level
surges
Will worsen in the future
as the sea level rises
Hazard map accounting for sea-
level rise rate, costal slope and
elevation, tidal range, tsunami
arrival height
(Giriraj et al., 2016)
2/ climate risks
12. Water shortages (6.1 million casualties caused by
droughts over last century) (http://www.emdat.be/)
• Low rainfall → lower crop yields, less food
• Semi-arid and arid countries
• Low river flow ← less rainfall, glacier and snow, land-use change, upstream
diversion)
• Indus Basin (Pakistan), GBM in dry season (Bangladesh) and many other countries
• Water-table drawdown ← pumping and reduced groundwater recharge
• Reservoir siltation in erosion-prone environments
• Sediment transport and deposition (e.g. Tarbela dam)
2/ climate risks
13. Saline intrusion in coastal aquifers ← sea level storm surge, flow reduction in river deltas
e.g. Bangladesh, Pakistan
Groundwater level drawdown ← droughts/reduced recharge
mobilization of endogenic contaminants, infiltration of toxic residual from
agriculture/industries
Coastal aquifers in Sri Lanka, alluvial aquifer of the Indus and GBM
Groundwater
contamination
Due to combination of
anthropogenic and
natural dynamics
Climate-related causes:
2/ climate risks
Geoscience Australia
14. 3/ Climate change and water resources
• Global warming alters water
cycle and storages through:
• ↑ temperature and
evaporation
• ↑ sea level
• Modified rainfall patterns
(intensity, frequency,
seasonality)
• … in turn altering streamflow,
sediments, groundwater
recharge and water
storages
3/ climate change
UNFCC
15. • Observed trends and model projections
• Rainfall trends hardly detectable. High variability: seasonal, inter-annual, inter-decadal
• Past: depend on periods, variables, domains, trend tests, statistical significance levels.
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Example of 52-
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• Predictions depend on models & scenarios → need to refer to most updated model
intercomparison CMIP5 (IPCC, 2014)
• Effects on water resources compounded by many other drivers (e.g. water abstraction)
3/ climate change
3/ Climate change and water resources
17. Sea level rise
Observations: Global rate
since 1850s exceeds that
of previous 2,000 years
+2 to +5mm/year along
South Asian coasts since
2000, (Nicholls and
Cazenave, 2010)
• Projections: under all emissions scenarios, future sea level rise likely to
exceed past 3 decades rate. By end of 21st century, sea level higher by 50-
100 cm
3/ climate change
Union of concerned scientists 2015
18. Climate changes & water resource risks:
CERTAINTIES and UNCERTAINTIES…
CERTAINTIES: global warming will induce
1. Heavier rainfall, more frequent and larger inland and coastal floods (cyclones). More
erosion → downstream siltation of reservoirs
2. Earlier monsoon onset (Annamalai et al., 2007) = earlier flood pulse,
3. High-altitude summer melting of glaciers → increased summer runoff followed by
reduction as glaciers shrink (e.g. Indus Basin) (2 + 3 → irrigation water shortages in
summer)
4. Sea level rise → salt contamination of coastal aquifers and coastal floods.
5. Rise in drought severity (heat waves) and crop water stress
3/ climate change
19. UNCERTAINTIES
1. Change in annual and seasonal river flow patterns in snow-fed basins (e.g. Indus)
Rising winter temperature → snow sublimation (=water loss)
Rising winter precipitation → snow accumulation → increased snowmelt in spring
Two counteracting changes, compounded by albedo variations (Archer et al., 2010)
2. Change in seasonal and annual rainfall (cf. IPCC projections)
3. Groundwater recharge depends on distribution of rainfall events (more concentrated
→ higher recharge), rising evapotranspiration (→ less recharge), and river flows
(snowmelt-controlled recharge in Indus vs. monsoon-driven recharge in Ganges)
4. Further uncertainties caused by non-climatic factors: land-use change, soil
degradation, water withdrawals
3/ climate change
Climate changes & water resource risks:
CERTAINTIES and UNCERTAINTIES…
20. To better understand processes
- Ice and snow mass balance influenced by
changes in precipitation, temperature, and
other variables to predict downstream flow
- Sparce monitoring network in >4,500m areas
More hydro-meteorological data from ground measurements
4/ Gaps and
recommendations
Knowledge gaps & recommendations
(Credit: Jane Qiu)
21. More hydro-meteorological data from ground measurements
- Surface-groundwater interactions (quality and quantity), spatial and temporal variations
and drivers to improve management of artificial and natural storages and buffer increased
variability
- Need to increase number of river gauging stations and monitoring wells,
4/ Gaps and
recommendations
Knowledge gaps & recommendations
To better understand processes (cont.):
USGSCircular1139
22. - Sea level rise and land subsidence are difficult
to disentangle: tectonics, compaction,
sedimentation, river embankments limiting
sediment deposition, groundwater abstraction)
- Need to accurately monitor local variation in
sea level changes relative to coast lines
Case of the Ganges-Brahmaputra-Meghna
Delta (Brown and Nicholls, 2015)
To better understand processes (cont.):
4/ Gaps and
recommendations
Knowledge gaps & recommendations
More hydro-meteorological data from ground measurements
23. To improve regional climate projections and hydro(geo)logical forecasts
Kumar et al.
GCM → downscaling → RCM
• GCM cannot capture
local topographic
features influencing fine-
scale precipitation and
temperature
• Hydrological effect of
land-use change (role of
soil in rainfall-runoff
relationship)
4/ Gaps and
recommendations
Knowledge gaps & recommendations
More hydro-meteorological data from ground measurements
24. Improving technics for crop water use
efficiency and water productivity
- parsimonious irrigation (drip
irrigation) adjusted to crops and soils
- limiting water losses (leakages, deep
percolation, evaporation)
- Adjust crop selection to local
weather patterns
- Levelling of irrigated fields
Building capacities, communicating, and coordinating actions
4/ Gaps and
recommendations
Knowledge gaps & recommendations
25. Improve capacity of analysis of remote sensing
products (research centers, flood mitigation
centers)
- To map flood- and drought prone areas,
- To assess and predict water resources in
ungauged areas
4/ Gaps and
recommendations
Knowledge gaps & recommendations
Building capacities, communicating, and coordinating actions
Chinnasamy and Agoramoorthy 2015
Rodell et al 2009
26. Regional approach required for South Asian countries to adapt to climate change
- to tackle regional issues (e.g. large-scale flooding),
- to promote data sharing and coordinate transboundary early warning systems,
- to build capacity in research and development amongst national institutions
4/ Gaps and
recommendations
Knowledge gaps & recommendations
Building capacities, communicating, and coordinating actions
Coordination for improved forecast
dissemination (early warning systems),
from prediction centers to exposed
communities
2/ Rapidly declining groundwater levels and degradation in water quality.
3/ Agriculture sector’s contribution to GDP continues to decline, despite high proportion of workforce and total population directly depending on agriculture.
4/ Species biodiversity are vulnerable to changes in flow seasonality and climate patterns.
Southwest Monsoon brings warm humid air from Indian Ocean, annual rainfall exceeds 2,500mm/year
70%–90% of annual precipitation falls during monsoon June-September. Himalaya generates world highest annual rainfall, due to orographic effects.
Driest countries receive less than a 1/5 of annual amount of rainfall recorded in wettest parts of the region. Low rainfall in Afghanistan and Pakistan due to high mountain range and middle east countries limiting intrusion of weaker monsoon. Most precipitation as snowfall in high elevation areas.
GBM: world second largest basin
Ganges supplied by monsoon rains and snow totalling about 500-1,000mm/year, 5-10% snow and ice-melt. 1/3 of total renewable water resources in Ganges from aquifer. 20%-40% of water resources used in Ganges Basin, mainly for irrigation. Extremely low water quality due to contamination by faecal coliform. Improvement along upper tributaries
Brahmaputra and Meghna supplied mainly by monsoon rains during June-September (up to 10,000mm/year of rainfall). <5% of snow and glacier melt. Largely unexploited in their Indian portion. Due to low population densities upstream of densely populated alluvial plain of Dhaka, water quality is relatively good in upstream part
Indus Basin: ice and snow meltwater represent about 35-40% of mean annual flow because most of rainfall occurs at high elevation as snow. It serves as natural water storage providing perennial water supplies. About 75% of water is withdrawn in irrigation schemes for irrigation mainly by Pakistan (63%) and India (36%) and mainly for irrigation (93%). 53% with surface water and 47% with groundwater. High water stress with water scarcity level below 1000 m3/capita per year.
Saline groundwater in 60% of the Indus Basin Irrigation System. Agriculture and industrial effluents further complicates the situation. High sedimentation rates.
Downstream GBM (i.e. in Bangladesh): alluvial and deltaic deposits form unconfined aquifer with highest recharge rates (>300 mm/year) of South Asia, mainly from rainfall, rather than floods because of heavy monsoon.
Indus Basin: underlained by extensive unconfined aquifer mainly recharged by seepage from rivers and irrigation canals. (low rates: 2mm/y). Deep water table is declining due to high pumping and low recharge.
GBM: world second largest basin
Brahmaputra and Meghna: groundwater quality also characterized in some place by dangerous concentrations of arsenic and fluoride.
Ganges: natural contaminants of growing concerns (arsenic, fluoride etc…).
Indus: High salinity levels.
5th phase of the Coupled Model Inter-comparison Project (CMIP5) (IPCC, 2014). Intermediate RCP4.5 emission scenario and focusing on median projection of CMIP5 (i.e. 50% percentile) over period 2046-2035 (central panel in Figure 4).
Rainfall: Bangladesh, Bhutan, India and Sri Lanka will be exposed to a 10% increase in annual rainfall with greater statistical significance in Sri Lanka. Greatest increases in annual rainfall, reaching 20%, will be observed in southwest India and south Pakistan. In contrast, Afghanistan and Nepal will exhibit rainfall declines down to -10%. An earlier monsoon onset is expect according to the most reliable projections.
The facts that i/ the natural inter-decadal variability of rainfall is of the same magnitude as the projected long-term trend in annual rainfall (cf. hatching in Fig) and ii/ the direction of the projected trends (either positive or negative) change according to the percentiles of the distribution of the CMIP5 ensemble considered, reveal great uncertainty in terms of projected rainfall in South Asia.
Temperature: Future trends in temperature are more reliable and predictable than for rainfall. Rising temperature rates will not be uniform across the continent.
Compared to 20th century, average annual temperatures could rise by more than 2°C in South Asia by the mid-21st century and exceed 3°C by the late-21st century. Lowest increases observed along the coasts of Southern India, Sri Lanka and Bangladesh. Stronger temperature increases will be observed at higher latitudes in Afghanistan, Bhutan, Nepal and Pakistan.
Climate and river flow data for the Upper Indus Basin fall far short of the WMO (1994) recommendation for density in rugged mountainous areas. Recommendation is one gauge per 250 km2. Actual density: 1 gauge per 5000 km2 (and less than one per 10 000 km2 if automatic gauges are excluded)
Gauges are predominantly at valley sites. Only 3 automatic gauges >4000 m, whereas mean elevation of Upper Indus (to Tarbela) is about 4500m. Highest precipitation and melt contribution to runoff is from elevations above this level.
3 countries (Bangladesh, Bhutan and India) advocate that these data be held in a central repository and be made available when needed. Many countries recognize importance of specific disaster monitoring systems, such as monitoring of GLOFs in Bhutan and Nepal.
There is also a wide acceptance of the need to invest in research, including modelling the hydrological effects of climate change, and understanding the linkages between surface and groundwater in the Indo-Gangetic plain if planned conjunctive use is to be effective. In Pakistan’s Punjab, it is necessary to increase the number of monitoring wells to accurately survey the temporal and spatial variations in groundwater levels and better understand their connections with surface water bodies. Hydrological and groundwater modelling should help forecasting variations in groundwater and surface water availability under different aquifer conditions and climatic scenarios.
Climate and river flow data for the Upper Indus Basin fall far short of the WMO (1994) recommendation for density in rugged mountainous areas. Recommendation is one gauge per 250 km2. Actual density: 1 gauge per 5000 km2 (and less than one per 10 000 km2 if automatic gauges are excluded)
Gauges are predominantly at valley sites. Only 3 automatic gauges >4000 m, whereas mean elevation of Upper Indus (to Tarbela) is about 4500m. Highest precipitation and melt contribution to runoff is from elevations above this level.
3 countries (Bangladesh, Bhutan and India) advocate that these data be held in a central repository and be made available when needed. Many countries recognize importance of specific disaster monitoring systems, such as monitoring of GLOFs in Bhutan and Nepal.
There is also a wide acceptance of the need to invest in research, including modelling the hydrological effects of climate change, and understanding the linkages between surface and groundwater in the Indo-Gangetic plain if planned conjunctive use is to be effective. In Pakistan’s Punjab, it is necessary to increase the number of monitoring wells to accurately survey the temporal and spatial variations in groundwater levels and better understand their connections with surface water bodies. Hydrological and groundwater modelling should help forecasting variations in groundwater and surface water availability under different aquifer conditions and climatic scenarios.