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Climate change science, knowledge and impacts on water resources in South Asia
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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
Web Master at International Water Management Institute (IWMI)
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Climate change science, knowledge and impacts on water resources in South Asia
- 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
- 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
- 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
- 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
- Climate influenced by Indian Ocean (Southwest monsoon) and topography (Himalayan range) Contrasted climate conditions 1/ water resources Peel, Finlayson and McMahon (University of Melbourne).
- 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
- Recharge rates (Mukherjee et al., 2016) Aquifers 1/ water resources
- Groundwater contamination (Mukherjee et al., 2016) 1/ water resources Aquifers
- 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
- 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/)
- 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
- 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
- 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
- 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
- • 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. 0 200 400 600 800 1000 1200 1953 1955 1957 1959 1961 1963 1965 1967 1969 1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 mm/year 0 200 400 600 800 1000 1200 1953 1955 1957 1959 1961 1963 1965 1967 1969 1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 mm/year 16 years Example of 52- year time series • 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
- Rainfall Temperature 3/ climate change 5th phase of the Coupled Model Inter-comparison Project (CMIP5) (IPCC, 2014)
- 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
- 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
- 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…
- 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)
- 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
- - 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
- 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
- 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
- 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
- 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
- Thank you for your attention…
Editor's Notes
- 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.