Climate Change and Water Resources in South Asia - Chapter 7 docx

Most of the rivers in South Peninsular India like the Cauvery, the Narmada and theMahanadi are fed through ground water discharges base-flow and are supplemented bythe monsoon rains.. Ta

is likely to be accompanied by a sharp decline in per capita water availability Whileconsumption of 1,000 m3 of water per year and per capita is considered a standard for

“well-being” in the developed world, projection of annual water availability per capita bythe year 2025 for South Asia is a mere 730 m3 This trend is declining in all parts of theworld, including those that are considered to have ample water resources

With the growing recognition of such issues as the possibility of global climate change,

an increasing emphasis on the assessment of future availability of water on various spatialand temporal scales is needed A warmer climate will enhance the hydrological cycle,which implies higher rates of evaporation, and a greater proportion of liquid precipitationcompared to solid precipitation; these physical mechanisms, associated with potentialchanges in precipitation amount and seasonality, will affect soil moisture, ground waterreserves and the frequency of flood or drought episodes The supply of water is limited andgoverned by the renewal processes associated with the global hydrological cycle.Future projections of changes in monsoon rainfall patterns are tenuous in currentlyavailable global climate models Moreover, it has been recognized now that thesuperimposed modes of climatic variability (e.g., El Niño and Southern Oscillation), whichcan disturb mean rainfall patterns on timescales ranging from seasons to decades, areimportant mechanisms to take into account but are not well predicted by the global climatemodels

Water resources will come under increasing pressure in South Asia due to thechanging climate Changes in climatic conditions will affect demand, supply and waterquality In regions that are currently sensitive to water stress (arid and semi-arid regions of

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India), any shortfall in water supply will enhance competition for water use for a widerange of economic, social and environmental applications In the future, larger populationwill lead to heightened demand for irrigation and perhaps industrialization at the expense

of drinking water Disputes over water resources may well be a significant socialconsequence in an environment degraded by pollution and stressed by climate change.7.2 INDIA’S GEOGRAPHY, POPULATION AND WATER NEEDS

India is a land with diverse geographical and climatic endowments This large expanse ofland (with 328 mha gross area) is bounded by the Himalayan range in the North and the sea

on three sides encompasses varied geographical and climatic zones ranging from the hotdesert of Thar in the Northwestern corner to the cold desert of Ladakh in the extremeNorth, the arid region of the Rann of Kutch in the West to the world’s wettest place,Cherrapunji, in the Northeast (Fig 7.1) With the icy continent of Antarctica as its majorneighbor to the South with vast stretch of the Indian Ocean in between, India has theworld’s tallest wall (the Himalayas) on its Northern boundary Adjoining the Himalayasfurther North is the Tibetan plateau that is large, massive and about 5 km high - a giganticslab of rock protruding up to the middle of the troposphere and acting as a large sized heatsource at the mid-tropospheric level Physiographically, India comprises of seven regions,viz., (1) Northern Mountains (the Himalayas), (2) Indo-Gangetic Plains, (3) CentralHighlands, (4) Peninsular Plateau, (5) East Coast, (6) West Coast, and (7) the Islands(Andaman & Nicobar group in the Bay of Bengal and Lakshadweep group in the Arabian

Sea) India also has the world’s largest estuary and mangroves, the Sundarbans in the East

and biologically rich mountain ranges of the Western Ghats along its West Coast Apartfrom this, India is a home to a billion people that is projected to increase to 1.7 billion by

2050 according to the high scenario assuming a fertility rate of 2.1%

The surface water and ground water resources in India play vital roles in agriculture,fisheries, livestock production, forestry, and industrial activity Water and agriculturesectors in India are likely to be most sensitive to monsoon rainfall There have beenconsiderable spatial and temporal variations in rainwater availability in recent years as aresult of observed swing in the onset, continuity and withdrawal patterns of monsoon Thepace of the green revolution seems to have started slowing down due to immense pressure

on India’s land and water resources and indiscriminate addition of restorer inputs such asinorganic fertilizers, pesticides etc and their inefficient use Agriculture’s share in GrossDomestic Product (GDP) of India has also declined recently, thus marking a structuralshift in the composition of the GDP Though traditionally, agriculture accounted fortwo-fifths of the GDP; it accounted for only 31% in 1990-1991 and 25% in 2001 (ADB,2003) India’s GDP has shown robust growth (never less than 5% since 1990-1991) whichsuggests that non-agricultural sectors (particularly the service sector) have grown at theexpense of agriculture However, as in all developing countries, about 72% (2001 Census)

of India’s population still lives in rural areas The main source of income for this majority

is either directly or indirectly dependent on agriculture Hence agricultural progress andstability, which has strong links to availability of water resources, holds the key to ruraland agrarian prosperity in India

7.2.1 KEY DEVELOPMENT SECTORS AND WATER SOURCES

In spite of a spurt in industrial growth and activity in the last 30 years, the livelihood ofmillions of people in rural India is still drawn from the agriculture sector Besides this,

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there are also major linkages between agriculture and industry Agriculture supplies theraw materials for employment-intensive industries It stimulates and sustains industrialoutput through rural household demands for consumer goods and services It influencesindustry through government savings and public investment Besides irrigation supplies,large water reservoirs are also required to generate hydropower But unlike irrigation theconsumptive use of water in this sector is mainly limited to the evaporative losses Many ofthe large reservoirs like Bhakra, Hirakud, Nagarjunasagar, Koyna, Pong, Rihand, Srisailamand Idduki are excellent examples of providing hydropower to the nation and have usheredthe economic growth and prosperity to the region.

Fig 7.1 Topographic Map of India.

The agricultural output is primarily governed by the availability of water making thecountry’s agrarian economy sensitive to the status of water resources and the monsoon inparticular As the monsoons serve not only as a sole provider of water to large areas of

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rainfed cultivation but also remain the primary source of water to recharge the groundwater resources of the country The demands on the water resources in the country, by theseveral sectors are not surprisingly dominated by the agriculture sector In the year 1999,agriculture consumed 85.3% of the water, industry 1.2%, energy sector 0.3% and othersectors 6.4% whereas domestic consumption was 6.6% (GOI, 2000).

The two sources of freshwater are ground water and surface water; of these the riverbasins represent the main source of freshwater in the Indian subcontinent India is giftedwith

a river system involving over 20 major rivers with many tributaries The total annual charge in the rivers that flow in various parts of the country amounts to 1,880 km3yr-1(CWC, 1995) Many of these rivers are perennial though few are seasonal The large riverssuch as the Indus, the Ganges and the Brahmaputra have their origin in the Himalayas andflow throughout the year though their flows significantly reduce during the lean summerperiod (March to May) The Himalayan snow and ice supports three main river systemsviz., Indus, Ganges and Brahmaputra having their average annual stream flow of 206 km2,

dis-488 km2 and 510 km2 respectively Thus, more than 50% of water resources of India arelocated in various tributaries of these three river systems (Fig 7.2) Average water yieldper unit area of the Himalayan Rivers is almost double that of South Peninsular riversystem indicating the importance of snow and glacier melt contribution from highmountains The average intensity of mountain glaciations varies from 3.4% for Indus to3.2% for Ganges and 1.3% for Brahmaputra The tributaries of these river systems showmaximum intensity of glaciations (2.5% to 10.8%) for Indus followed by Ganges (0.4% to10%) and Brahmaputra (0.4% to 4%); the average annual and seasonal flows of thesesystems give a different picture thereby demonstrating that the rainfall contributions aregreater in the Eastern region while the snow and glacier melt contributions are moreimportant in the Western and Central Himalayan region

Most of the rivers in South Peninsular India like the Cauvery, the Narmada and theMahanadi are fed through ground water discharges (base-flow) and are supplemented bythe monsoon rains Therefore, these rivers have very limited flow during the non-monsoonperiod The importance of these rivers lies not just in the size of their basins but also on thequantity of water they can carry The flow rate in these rivers is independent of the watersource of the river and depends upon the precipitation rate in the region Therefore, inspite of being smaller in size, the rivers flowing West have a higher flow rate due to higherprecipitation over that region

Apart from the rivers, the Indian subcontinent is covered by a number of reservoirs,lakes, wetlands, mangroves and ponds During lean season, these reservoirs are the keysource of water For example, a large dam in Mettur over Cauvery River has a 40 m highreservoir with a storage capacity of about 10 km3 The amount of water stored here duringthe monsoon season is released for irrigation under controlled conditions during the dryperiod Even though various types of freshwater bodies are widely distributed across theIndian subcontinent, still the availability of drinking water suggests skewed distribution ofactual supply These water bodies regulate both the quantity and quality of water inaddition to supporting the biota of various species The importance of these water bodies

is apparent from the fact that in the thirteen States, which experienced frequent floods anddrought in the last few years, 50% of the areas of those States are prone to periodicdroughts possibly due to the shrinking or vanishing of these water bodies Many lakes inRajasthan (including the largest lake in Udaipur) have been heavily silted and the waterlevels in the Krishnaraja reservoir in Tamil Nadu on the river Cauvery has gone downrecently due to lack of water input from the upstream region Table 7.1 presents anoverview of the storage capacity of various reservoirs in India

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Table 7.1 Water storage capacity of reservoirs in India

Reservoir’s storage at the end of

monsoon

1998 1999 Reservoirs (number)

Designed capacity (km3)

Storage (km3)

Average of last 10 years (km3)

Current year’s storage as % of

Fig 7.2 Major Rivers of India.

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this unconfined aquifer is massive and has not been brought into utilization in anysystematic manner In fact, a good part of the dry season flow in the river system isaugmented by the flow back of the ground water from the unconfined aquifers in the areaadjoining the Ganges and its tributaries The deep artesian aquifers underlying millions ofacres of alluvia and deltaic cropland in the Ganges basin are believed to be filled withfreshwater to depths as great as 2,000 m The total replenishable ground water resourceavailable in India is currently estimated to be 45.22 million hectare meter/year (mha m/yr).

Of this quantity, 6.933 mha m/yr may be used for drinking and industrial purposes whilethe rest can be used for irrigation Interestingly, almost 80% of domestic waterrequirement in India today is met from ground water sources However, the ground waterresources in several States of India are fast getting depleted primarily due to overextraction and poor recharging facility

7.2.2 THE NEED FOR SUSTAINABLE DEVELOPMENT OF WATER RESOURCESDespite the presence of substantial reserves of water in India, the actual utilizable quantity

is limited and water crisis is seen to be inevitable in the future The annual quantity offreshwater including ground water available in India is currently about 1.88 km3 (CWC,1995) This puts the per capita availability to be about 2,000 m3 i.e., 2x109 liters per personper year and this quantity is further expected to drop to 1,480 m3 in the next decade due toincrease in population coupled with no further augmentation of water resources and alsoits consequent decrease over the same time due to consumption India will reach a state ofwater stress before 2025 when the availability falls below 1,000 m3 This clearly indicatesthe ‘two sided’ effect on water resources - the rise in population will increase the demand

of water leading to faster withdrawal of water and this in turn would reduce the rechargingtime of the water tables As a result, availability of water is bound to reach critical levelssooner or later In this regard the emerging disputes are already indicative of what can beexpected in the future Fights over water have already broken out in between States (Cauveryissue, Narmada problem, Krishna water disputes) Disputes between nations also alreadyexist over sharing of river water between India and Bangladesh over the Ganges water andIndia and Pakistan over the Indus water Water riots have also been reported in Bhavnagarand Rajkot in Gujarat (Ramakrishnan, 1998) This makes it imperative to draw outappropriate action plans and strategies to conserve our water resources and optimizeutilization of water from the various water sources

7.3 CLIMATE OF INDIA

7.3.1 PRESENT CLIMATE AND ITS SPATIAL DIVERSITY

India, a country of subcontinental size, is the largest peninsula in the world and issurrounded by seas on the three sides with an extensive coastline of about 6,000 km.Climatologically, India covers the tropical, sub-tropical and the temperate regimes Thecountry is divided into almost two equal halves by the Tropic of Cancer The Northern halfcutoff from the rest of the continent by the Himalayan range, experiences temperate type

of climate whereas the extreme Southern part of the country falls within the tropicallatitudes The inner Himalayas present sub-polar conditions registering extremely low andeven negative temperatures in winter due to the altitude effect while the presence of theseas on all three sides brings the Southern Peninsular India under direct maritime influencewith low diurnal temperature differences and a very moderate climate The interior of the

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country experiences a continental type of climate with extreme annual temperature swings.The summer temperatures over this region soar and often go beyond 40oC while thetemperature in winter drops radically.

India’s unique geographical configuration gives it the peculiar climate regime withfour seasons Winter season covering the months of December, January and February isfollowed by the summer (pre-monsoon) season extending from March to May India comesunder the sway of the Southwest monsoon season from June to September and then goesthrough post-monsoon season from October to November The basic driving force behindthe monsoons is the thermal contrast between the land and the sea During thepre-monsoon, as the sun progresses Northwards, a simultaneous shift in the convergingzone of the trade winds of the two hemispheres (ITCZ) occurs to the North of thegeographical equator The Southeasterly trades blowing in from the Southern Hemisphereget deflected to the right as they enter the Northern Hemisphere and blow into thesubcontinent from the West Coast bringing with it moisture from the adjoining seas Thismarks the advent of the Southwest monsoon over the subcontinent The point of first entry

of the monsoon in India is the Kerala Coast These Southwesterlies bring rain throughoutthe country, mainly to the South of the monsoon trough As the Southwest monsoonwinds blow over peninsular India they collect more moisture from the Bay of Bengal and,

on striking the Himalayan range in the North, get deflected Westward These deflectedSoutheasterly trades bring rains to the Northern half of the country As the summermonsoon enters from the Southwestern corner of the country, it moves progressively Northand by 15th of July, it covers the entire Indian subcontinent (Fig 7.3) The monsooncirculation over the subcontinent is associated with several synoptic scale events such asthe development of the heat low over Rajasthan in the Northwest India during thepre-monsoon season, the Tibetan high occurring over the Tibet plateau, the Mascarenehigh off the coast of Madagascar and the weakening of the sub-tropical Westerlies overNorth India with the subsequent onset of the tropical Easterly jet stream over thepeninsular India

Towards the end of the monsoon, as the sun begins its journey Southwardthe monsoon starts withdrawing This event is heralded by the reinforcement of thesub-tropical Westerlies over North India The Easterly jet disappears rapidly withthe recession of the monsoons As the Westerly jet stream re-establishes itself South ofthe Himalayas, winter rains start to the Southeast coast near Tamil Nadu in India This isknown as the Northeast or the winter monsoon During the winter months, rain alsooccurs over North India due to the Southward shift of the polar fronts Frontal or extra-tropical cyclones developing over West Asia and the Mediterranean Sea pass throughNorth India during its passage Eastward The presence of the Himalayas weakens thesedisturbances and the temperature contrast of the air masses is also somewhat reducedbecause of which the frontal characteristic of these extra-tropical cyclones is not clearlyevident Since these disturbances have their origin in the West, the rains which result overNorth India is said to be due to the Western disturbances

The long-term average annual rainfall for the country as a whole is 116 cm - thehighest for a land of comparable size in the world But this rainfall is highly variable both intime and space The percentage areal distribution of annual rainfall over India is given in

Table 7.2 below The rainfall is highly variable in time as well The maximum rainfall occurs

in July and August during the four-month (June to September) Southwest monsoonseason There are considerable intra-seasonal and inter-seasonal variations as well Thesummer monsoon rainfall oscillates between active spells with good monsoon (abovenormal) on all India basis and weak spells or the breaks in the monsoon rains when

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deficient to scanty (≤20%) rains occur on all India basis for a few days at a stretch Weakand active spells of the summer monsoon is determined by the position of the monsoontrough extending from the Northwestern end over the Rajasthan desert to the head Bay ofBengal The monsoon trough oscillates either South or North of this normal position overthe Gangetic plains When the trough is to the South or close to the normal position, activespells result and when it is near the foothills, weak monsoon conditions prevail Theaverage seasonal summer monsoon rainfall of India is about 85 cm with a standarddeviation of about ±10% Orissa, East Madhya Pradesh, West Bengal, and theNortheastern States of India, the Western coast and the Ghats receive more than 100 cm ofrainfall during this season The submontane region extending from North Bihar to Jammualso receives more than 100 cm of rainfall The heavy rainfalls in the Northeastern States,West coast and the Ghats and the submontane regions are influenced by the orography.The peninsular India South of 15oN gets less than 50 cm rainfall The lowest rainfall isreceived in the extreme Southeast Peninsula The West and the Northwest regions of thecountry receive about 50 cm of rain in the season The rainfall decreases rapidly to lessthan 10 cm in the West Rajasthan Regions above 50 cm in the season are classified as wetand those less than 50% as dry parts of India.

Fig 7.3 The onset and withdrawal dates of the Southwest monsoon.

The two monsoon seasons (the Southwest monsoon in June to September and theNortheast monsoon in November -December bring forth rains - many a times in intensitiesand amounts sufficient to cause serious floods creating hazardous (and often disastrous)situations Moreover, cyclonic storms in the pre-monsoon months (April-May) and the

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post-monsoon months (October-November) cause large-scale inundation, destruction anddeaths In fact, floods and cyclones are the two major natural disasters, which visit Indiaquite often The adverse impacts of these two natural disasters cannot be assessed merely

in economic terms based on destruction of crops, property and infrastructure becausethe toll of human misery in the form of death, disease, injury, loss of employment,psychological trauma, and above all the set-back to development are too difficult toevaluate

Table 7.2 Areal Distribution (%) of Annual Rainfall over India

Mean Annual Rainfall Corresponding % Area

An annual mean global warming of 0.4°C to 0.8°C has been reported since the late

19th century (IPCC, 2001) Surface temperature records indicate that the 1990s have beenthe warmest decade of the millennium in the Northern Hemisphere and 1998 is thewarmest year (Fig 7.4) The observations also suggest that the atmospheric abundances

of almost all greenhouse gases reached their highest values in recorded history during the

1990s (Nakicenovic et al., 2000) Anthropogenic CO2 emissions due to human activities

are virtually certain to be the dominant factor causing the observed global warming In

India, the analysis of seasonal and annual surface air temperatures (Pant & Kumar, 1997),using the data for 1881-1997, has shown a significant warming trend of 0.57oC perhundred years (Fig 7.5) The warming is found to be mainly contributed by thepost-monsoon and winter seasons The monsoon temperatures do not show a significanttrend in any major part of the country except for a significant negative trend overNorthwest India Similar trends have also been noticed in Pakistan, Nepal, Sri Lanka andBangladesh The rainfall fluctuations in India have been largely random over a century,with no systematic change detectable on either annual or seasonal scale (Fig 7.6).However, areas of increasing trend in the seasonal rainfall have been found along the WestCoast, North Andhra Pradesh and Northwest India and those of decreasing trend overEast Madhya Pradesh, Orissa and Northeast India during recent years (Fig 7.7)

The global warming threat is real and the consequences of the climate changephenomena are many, and alarming The impact of future climatic change may be felt moreseverely in developing countries such as India whose economy is largely dependent onagriculture and is already under stress due to current population increase and associateddemands for energy, freshwater and food In spite of the uncertainties about the precisemagnitude of climate change and its possible impacts particularly on regional scales,measures must be taken to anticipate, prevent or minimize the causes of climate changeand mitigate its adverse effects

7.3.2 IMPACT OF GLOBAL WARMING ON INDIA’S CLIMATE

Besides being the most important determinant of the economic welfare of the country, themonsoon is the predominant source of freshwater required for the rejuvenation of thewater resources after the hot spell of the pre-monsoon season The leading concern today

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is the probable impacts that climate change and global warming might have on the annualcycle of the monsoon and the precipitation pattern A few of the currently availablestate-of-the-art Global Climate Models [CCSR/NIES (Japan), CSIRO (Australia), ECHAM(Germany) and UKMO (England) global climate models] have the ability to simulate themonsoon process realistically enough in order to be able to project the plausible regionalclimate change and its impacts on the long-term cycle of events including monsoons overthe subcontinent (Lal & Harasawa, 2000) These models have been run with realistic

forcing history for the 20th century and allow direct comparison of the model’s response to the observations The combination of the warming effects on a global scale from increasing

Fig 7.5 All-India Mean Annual Surface Air Temperature Anomalies (1881-1997).

Fig 7.4 Monthly global mean temperature anomalies in the year 1998 and the previous warmest year.

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Linear Trend = 0.57 ⬚C/100 yrs

5-Point Gaussian Lowpass Filtered

CO2 and the regional cooling from the direct effect of sulfate aerosols produced a better

agreement with observations of the time evolution of the globally averaged warming andthe patterns of 20th century climate change With the possible effects of future changes of

anthropogenic aerosols as prescribed in the IS92a emission scenario (~1% per year

compound increase of equivalent CO2), the coupled atmosphere-ocean global climate models(A-O GCMs) suggested a global and annual mean warming at 2100 relative to 1990 ofbetween 1oC and 3.5oC (at an average rate of 0.3oC per decade)

Fig 7.6 All-India Summer Monsoon Rainfall Anomalies (1871-1999).

Climate change scenarios for the Indian subcontinent based on an ensemble of results

as inferred from the four A-O GCMs (which have demonstrated some skill in simulatingthe present-day climatology over Indian subcontinent) on annual and seasonal mean basisare presented in Table 7.3 Three future time periods centered around 2020s (2010-2039),2050s (2040-2069) and 2080s (2070-2099) have been considered here for developingscenarios of changes in surface air temperature and precipitation relative to the baselineperiod of 1961-1990 over the Indian subcontinent The projected area-averaged annual

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mean warming is about 2.7oC for the decade 2050s and about 3.8oC for the decade 2080sover the land regions of India as a consequence of increases in atmospheric concentration

of greenhouse gases (Lal & Harasawa, 2001) Under the combined influence ofgreenhouse gas and sulfate aerosols, the surface warming is restricted to only 1.9oC and3.0oC for the decade 2050s and 2080s, respectively In general, the projected warming isfound to be higher during winter than during monsoon The A-O GCMs show highuncertainty in future projections of both winter and summer precipitation over the Indiansubcontinent (with or without aerosol forcing) The magnitude as well as the sign ofprojected changes in monsoon rainfall over the region varies significantly among themodels This is largely attributed to complex feedbacks due to differences in treatment ofground hydrology and cloud-radiation interactions in these models The likely magnitude

of mean sea level rise along the Indian Coastline due to thermal expansion of seawater hasalso been calculated and is included in Table 7.3 Even though the aerosol forcing reducesthe surface warming, its magnitude is still considerable and could substantially impact theIndian subcontinent The inter-model differences over the tropics represent the primarysource of uncertainty in regional projections of simulated precipitation changes in currentA-O GCMs

In order to predict the changes in the seasonal as well as annual variability of themonsoons in response to increases in radiative forcing of the atmosphere, climate changescenarios over Indian subcontinent under the new SRES ‘Marker’ scenarios have alsobeen developed based on the data generated in more recent numerical experiments with

A-O GCM of the CCSR/NIES, Japan (Lal et al., 2001) The new set of emission scenarios

covers a wide range of the main demographic, technological, and economic driving forces

of future global emissions (Nakicenovic et al., 1998) Four ‘Marker’ scenarios (namely

A1, A2, B1 and B2 scenarios) have been identified each of which describes a differentworld evolving through the 21st century and each of which may lead to quite differentgreenhouse gas emission trajectories The scenario B1 projects the most conservativefuture emission of greenhouse gases while A2 scenario is characteristic of scenarios withhigher rates of greenhouse gas emissions in combination with higher sulfur and otheraerosol emissions More recently, the A1 scenario family has been further divided intothree groups that describe alternative directions of technological change in the energy

system (Nakicenovic et al., 2000) The three A1 groups are distinguished by their

technological emphasis: fossil intensive (A1FI), non-fossil energy sources (A1T), or abalance across all sources (A1B) The SRES scenarios exclude the effects of climate changeand climate policies on society and the economy (‘non-intervention’) Most of the recentnumerical experiments with A-O GCMs, however, have not included all the SRESscenarios as yet The projections of regional climate change based on these newer sets of

emission scenarios of greenhouse gases are likely to be more realistic than the IS92a

emission scenario used earlier in transient experiments with A-O GCMs

Over land regions of the Indian subcontinent, the area-averaged annual mean surfacetemperature rise by 2080s is likely to range between 3.5oC and 5.5oC (least in B1 scenarioand maximum in A2 scenario) The area-averaged surface temperature increase during thewinter over India by 2080s would be at least 4oC (B1 scenario) and could reach even 6oC(A2 scenario) During summer monsoon, the warming may range between 2.9oC and 4.6oC(Table 7.4) The projected surface warming is more pronounced during winter than duringsummer monsoon season The spatial distribution of surface warming as a consequence ofincrease in anthropogenic radiative forcing (with respect to 1981-1990) suggests that NorthIndia may experience an annual mean surface warming of 3oC or more by 2050s,depending upon the future trajectory of anthropogenic forcing The spatial pattern of

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temperature change has a large seasonal dependency The model simulates peak warming

of about 3oC over North and Central India in winter Over much of the Southern Peninsula,the warming is likely to be under 2oC during the winter season The surface temperaturerise would be more pronounced over the Northern and Eastern regions of India (~2oC)during the monsoon season

A marginal increase of about 7% to 10% in area-averaged annual mean precipitation

is projected over the Indian subcontinent by 2080s (Table 7.4) A decline of between5% to 25% in area-averaged winter precipitation is likely During the monsoon season, anincrease in area-averaged precipitation of about 10% to 15% over the land regions is

projected Contrary to earlier projections (Lal et al., 1994; 1995), the new simulation

experiments suggest appreciable change in spatial pattern of winter as well as summermonsoon precipitation over land regions of the Indian subcontinent This could beattributed to inclusion of more realistic estimates of regional aerosol concentrations aswell as the indirect radiative forcing due to aerosols A decrease of between 10% and 20%

in winter precipitation over most parts of Central India is simulated for 2050s During themonsoon season, the results suggest an increase of 30% or more in precipitation overNorthwest India by 2050s The Western semi-arid margins of India could receive higherthan normal rainfall in a warmer atmosphere

In order to examine the likely changes in intra-seasonal and inter-annual variability insummer monsoon over Central India (land points only confined to latitudes 18oN and 30oNand longitudes 67oE to 90oE) in response to changes in anthropogenic forcing, we haveanalyzed the simulated daily data for rainfall from 1st May until 30th October (183 days)during each of the 30-year period corresponding to 1970s and 2050s Figure 7.8 depictsthe temporal variation of observed (based on daily rainfall data averaged for 10 CentralIndian stations during the period 1966-1990) as well as simulated (1961-1990) daily values

of total rainfall averaged over Central India from 1st May till 30th October for each yearsalong with daily mean for the selected period (thick line) The rainfall maxima coincideswith the peak monsoon activity over the region around mid-July The seasonal total ofsimulated daily rainfall is marginally higher (by 4.9%) as compared to observed rainfallwhile the intensity of simulated daily rainfall is only two-thirds of the observed over thecentral plains of India This could be attributed to far more number of rainy days in modelsimulation as against observations The year-to-year variability in monsoon rainfallsimulated by the model (as inferred from the standard deviation of area-averaged monsoonrainfall for 30-year period) is significantly low (only 42% of the observed) relative toobserved rainfall variability The temporal variations of simulated daily total rainfallaveraged over Central India during the years 2036-2065 in each of the four SRES ‘Marker’scenarios are depicted in Figure 7.9 A comparison of Figure 7.8 with Figure 7.9 revealsmany aspects of plausible changes in Indian summer monsoon activity over the centralplains of India The standard deviation of future projections of area-averaged monsoonrainfall centered around 2050s is not significantly different in each of the four scenariosrelative to that simulated for the present-day atmosphere This implies that theyear-to-year variability in Central India rainfall during the monsoon season may notsignificantly change in the future More intense rainfall spells are, however, simulated overthe land regions of the Indian subcontinent in the future (relative to that simulated for thepresent-day atmosphere) thus increasing the probability of extreme rainfall events in awarmer atmosphere

It is interesting to note here that there are no appreciable shifts in rainfall maximaduring July-August (located at about 20oN) in the temporal variation of simulated monthlymean precipitation over the region in any of the four ‘Marker’ scenarios The Northward

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Table 7.4 Climate Change Projections* for Indian subcontinent under the new SRES Marker Emission Scenarios

* Based on CCSR/NIES Model Experiments; Area-averaged for land regions only.

advancement of monsoon rains over India with the progression of the season thereforeseems quite robust A detailed analysis of the daily rainfall data suggests that, under A1and A2 scenarios, while the model still simulates the first spell of intense rainfall appearingover the Southern most part of India (5oN to 10oN) during the first week of June on anaverage, the spread of simulated onset date at 10oN (based on the criteria that rainfall at allgrid points along 10oN in the region is 3 mm day-1 or more for at least three consecutivedays) extends from 24th May to 11th June during the 30-year period centered around 2050sagainst between 29th May and 8th June during the 30-year period of the present dayatmosphere This implies the possibility of enhanced variability in the date of onset ofsummer monsoon over Central India in a warmer atmosphere.

Fig 7.8 Temporal variation of observed as well as (1961-1990) daily values of total rainfall averaged over Central India from 1 st May till 30 th October The thick line depicts daily mean for the selected period.

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Utility of precipitation primarily depends upon its spatial as well as its temporaldistribution Uniform precipitation over a larger area is more useful than its occurrenceconcentrating over a smaller region and also, precipitation occurring over a larger timeperiod would be more effectively utilized rather than, when it occurs within a short timespan Therefore, the projected changes in the precipitation pattern over the Indiansubcontinent as presented above come as bad news for the water resource sector On thefirst count, the decrease in the winter precipitation would reduce the total seasonalprecipitation being received during December, January and February implying a greaterwater stress On the second count, intense rain occurring over fewer days, which otherthan implying increased frequency of floods will also mean that much of the rain would belost as direct runoff resulting in reduced ground water recharging potential.

Fig 7.9 The temporal variations of simulated daily total rainfall averaged over Central India during 2036-2065 in each of the four SRES ‘Marker’ scenarios.

7.4.1 PERIODICITY AND OCCURENCE

Rain gauge records of the Indian monsoon are available for over a century In 1910, SirGilbert Walker, the then Director General of the India Meteorological Department, usedgauge records since 1840 to describe the variability of Indian monsoons The analyses ofthe rainfall records of the monsoon trends have continued till this day These analyses have

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yielded a 30-year cyclicity of the Indian monsoons It was observed that drought as well asflood years occurred in runs rather than scattered randomly through the years Walker inhis study found two periods of greatest rainfall deficiency, 1843-1860 and 1895-1907 Thelatter period extended till about 1920 This period was then followed by a remarkably lowfrequency of droughts for the next 30 years or so Droughts became once more common inthe 1960s Of the 14 major drought years in the 85-year record, 8 occurred in the first30-year period (1891-1920) whereas there was only one in the second 30-year period(1921-1950) In the 25-year period from 1951-1981, five major drought years wererecorded In 1972 and 1979 deficient rainfall (about 25% below normal) was recorded inone-half to two-thirds of India’s plains In 1994, monsoon rainfall was deficient (bybetween 20% and 43%) in 10 of the 31 meteorological subdivisions of India Gujarat,West Rajasthan, Tamil Nadu and Kerala had deficient monsoon rainfall during the year

1999 Apart from the inherent 30-year cyclicity of the Indian monsoons, droughts havebeen found to be more frequent during the years following El Niño-Southern Oscillation(ENSO) events At least half the severe failures of the Indian summer monsoon since 1871

have occurred during the El Niño years (Webster et al., 1998) In the event of enhanced

anomalous warming of the Eastern Equatorial Pacific Ocean such as that observed duringthe 1997-1998 El Niño, the higher frequency of drought conditions is possible

Floods and cyclones are the natural disasters where excess of water (rains) creates thehavoc in India In case of floods, the swollen rivers with overflowing banks do the damage

in floodplains Of late, flooding or water logging is becoming a major problem in urban andmetropolitan areas Cyclonic storms pose a hazard mainly in coastal regions (more on theEast Coast as compared to the West Coast) but no place in the country is free from floods(even Rajasthan suffers from floods and flooding) although floodplains of rivers andcyclone-affected coastal regions are most prone to floods While cyclone is a naturaldisaster in the full sense of the term, flood problem (including flooding) has been seriouslyaggravated by human activities such as overgrazing, deforestation, soil erosion andsiltation On the average, the area actually affected by floods every year in India is of theorder of 10 mha of which about half is cropland In fact, the area prone to floods in Indiahas been estimated to be of the order of 40 mha Persistent occurrence of rainfall over anarea already soaked with rain or intense rainfall often results in flood Excess water in ariver, due to heavy and/or persistent rains in the catchment area or the upper regions of theriver system also create flood downstream Absence or lack of adequate drainage in anyarea will aggravate the flooding Flash floods occur due to high rate of water flow as alsodue to poor permeability of the soil Areas with hardpan just below the surface of the soilare more prone to floods as water fails to seep down to the deeper layers

As is evident, floods and drought occurring in India are closely associated with thenature and extent of the summer monsoon The inter-annual fluctuations in the summermonsoon rainfall over India are sufficiently large to cause devastating floods or seriousdroughts Though floods are often caused by tropical depressions and cyclones, these

cyclones are not a part of the monsoons per se Severe tropical cyclones generally develop

during the pre-monsoon or post-monsoon season (generally defined cyclone seasons areOctober-November and March-June) The Eastern Coast of India along Bengal, Orissaand Andhra Pradesh are prone to such tropical cyclones These cyclones cause devastatingcoastal floods, which often take the proportion of national disasters A case in point would

be the super cyclone that hit the Orissa Coast on 29th October 1999 with wind speed ofabout 260 kmph and heavy rains causing severe floods This cyclone ranked highest in thedamage caused in terms of both life and property As per the information received from theState Relief Commissioner’s Office in Bhubaneshwar (CDBI Special Issue No 15, 1999),

172 I MPLICATIONS F OR I NDIA ’ S W ATER R ESOURCES

9,885 people lost their lives; 2,142 people were injured; 370,297 cattle heads perished and1,617,000 hectares of paddy field and 33,000 hectares of other crops were damaged.Several villages had been completely wiped out and over a million made homeless withstorm-surge of height 9 m above astronomical tide level at Paradip, which penetrated

35 km inland Many of the tropical cyclones move inland and may even reach as far inland

as Nepal though at a much reduced intensity Sometimes these cyclones stagnate over aregion as the Orissa super cyclone did (it was more or less stationary with slightSouthward drift over the region after making landfall) and it is these cyclones that causemaximum damage to life and destruction to the existing infrastructure

7.4.2 IMPACT OF GLOBAL WARMING ON FLOODS AND DROUGHTS

Several recent studies (Kitoh et al., 1997; Lal et al., 2000) suggest an increase in the

inter-annual variability of daily precipitation in the Asian summer monsoon with increasinggreenhouse gas concentrations in the atmosphere An examination of the frequencydistribution of daily monsoon rainfall over India in the model-simulated data has suggested

(Lal et al., 2000) that the intensity of extreme rainfall events are likely to be higher in

future as a consequence of increased convective activity during the summer monsoonperiod suggesting thereby the possibility of more frequent flash floods in parts of India,Nepal and Bangladesh

Some of the most pronounced year-to-year variability in climate features and theextreme weather events (such as cyclones) in many parts of Asia have been linked toENSO events The analysis of data generated in several A-O GCMs indicate that, as globaltemperatures increase due to increasing greenhouse gases, the Pacific climate will tend tomore resemble an El Niño-like state (Meehl & Washington, 1996; Knutson & Manabe,

1998; Mitchell et al., 1995; Timmermann et al., 1999; Boer et al., 1999) Collins (1999)

finds an increased frequency of ENSO events and a shift in their seasonal cycle in a warmeratmosphere, so that the maximum occurs between August and October rather than aroundJanuary as currently observed Meehl & Washington (1996) suggest that future seasonalprecipitation extremes associated with a given ENSO event are likely to be more intense inTropical Indian Ocean region; anomalously wet areas could become wetter andanomalously dry areas become drier during future ENSO events During ENSO, a cyclone

in tropical oceans has more than 40% chance of being a severe one (Lander, 1994).The role of sea surface temperature in the genesis and intensification of tropicalcyclones has been well demonstrated, for example, by Gray (1979), Emanuel (1988) andSaunders & Harris (1997) One of the necessary (but not sufficient) conditions for tropicalcyclone formation in the North Indian Ocean is that the sea surface should have a minimumtemperature of about 28oC Analysis of sea surface temperature in the Bay of Bengalduring the period 1951-1997 suggests that the sea surface temperatures have beenincreasing here since 1951 Observational records suggest that, while there has been arising trend in all-India mean surface air temperature, the numbers of monsoon depressionsand tropical cyclones forming over the Bay of Bengal and Arabian Sea exhibits decliningtrends since 1970 (Fig 7.10)

There have been a number of studies that have considered likely changes in tropical

cyclones (Knutson et al., 1998; Henderson-Sellers et al., 1998; Royer et al., 1998; Krishnamurti et al., 1998) Some of these studies suggest an increase in tropical storm

Fig 7.10 Trends in all-India mean surface temperature anomaly and number of monsoondepressions and cyclones in Indian Seas.

intensity (wind speed) The relationship between cyclone intensity (maximum sustainedwind speed) and sea surface temperature is well discussed in literature (Emanuel, 1987;1999) A possible increase in cyclone intensity of 10%-20% for a rise in sea surfacetemperature of 2oC to 4oC relative to the threshold temperature of 28oC is very likely.Thus, while there is no evidence that tropical cyclone frequency may change, the availabledata strongly suggests that an increase in its intensity is most probable

Storm-surges are generated by the winds and the atmospheric pressure changesassociated with cyclones At low latitude land-locked locations such as the Bay of Bengal,the tropical cyclones are the major cause of storm-surges Any increase in sea surfacetemperature is likely to cause greater convective activity, leading to an increase in wind

174 I MPLICATIONS F OR I NDIA ’ S W ATER R ESOURCES

speed The stress exerted by wind on water underneath is proportional to the square of thewind velocity Amplification in storm-surge heights should result from the occurrence ofstronger winds and low pressures associated with tropical storms Thus, an increase in seasurface temperature due to climate change should lead to higher storm-surges and anenhanced risk of coastal disasters along the East Coast of India.

7.4.3 IMPACT OF FLOODS AND DROUGHTS ON HUMAN SOCIETY AND

DEVELOPMENT

When drawing a comparison between the flood and drought events, it is seen that ruralcommunities suffer less from floods than from droughts because good crops can be grownafter the water recedes (depends on timing of flow and crop calendar) Flood deposits silt,thereby adding organic matter and nutrients to the soil They also recharge the aquifersthereby improving the ground water availability However, impacts of these events onhuman and animal populations vary according to the nature and severity of the calamity.Most problems relate to the availability of food, safe drinking water and shelter The extent

of the disasters was evident in the four episodes - (a) the 1977 typhoon in Andhra Pradeshclaimed nearly 10,000 lives, (b) 1978-1979 floods in Uttar Pradesh, Bihar and WestBengal damaged 18 mha of cropped land, destroyed nearly 4 million hutments and took atoll of 2,800 human lives and about 200,000 cattles, (c) 1979-1980 drought in large areas

of Northern and Eastern India that affected more than 38 mha of cropped areas andendangered the lives of 130 million cattles and more than 200 million people, and (d) 1999super cyclone in Orissa which claimed nearly 10,000 human lives and damaged about1,617,000 hectares of paddy field and 33,000 hectares of other crops

Looking into the flood damage scenario of the country as shown in Table 7.5, it isobserved that the flood damage is mainly related to the damage of land and cropped areaand shows an upward trend during the three decades starting from 1953 The mostdamaged areas belong mainly to the States falling within the Ganges and the Brahmaputrabasin Ranks have been assigned to the different States according to the magnitude ofaverage annual damage to crops, population and land (Table 7.6) The States located in themountainous regions in Jammu and Kashmir, Himachal Pradesh, Nagaland, Manipurand other hilly States are least affected by floods The damage to land, cropped areas,population, property and livestock depends on the geomorphology of the area as well aspopulation distribution Damage to population is more in the areas where the populationdensity of the floodplains is higher such as in the Gangetic plains

In order to assess drought conditions in the country, the area-averaged Southwestmonsoon rainfall for the country as a whole and the percentage of the country receivingdeficient rainfall during the monsoon season are considered According to the intensity,drought in India may be declared as all India drought, severe all India drought andphenomenal all India drought There have been 17 incidents of all India droughts in thiscentury, 8 severe all India droughts and 3 phenomenal droughts The drought of 1987 wasdeclared as a phenomenal of all India’s droughts The worst affected were the threemeteorological subdivisions of Saurashtra, Kutch and Diu (departure from normal rainfallwas -74%), West Rajasthan (departure from normal rainfall was -74%), Haryana and Delhi(departure from normal rainfall was -67%) As many as 18 subdivisions had rainfalldepartures between -20% and -60% during this year Based on the data in the report of theNational Commission on Agriculture and additional data from the Central WaterCommission of the Government of India, Bagchi (1991) identified 100 districts in the

13 States in India as drought prone which are detailed in Table 7.7

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