e-Journal Earth Science India, Vol. I (III), 2008, pp. 138-147 http://www.earthscienceindia.info/

Climate Change and its Future Impact on the Indo-Gangetic Plain (IGP)

H. S. Saini Geological Survey of India, Faridabad Email: [email protected]

Abstract

The Indo-Gangetic plain (IGP) is an environmentally sensitive, socially significant and economically strategic domain of India where landscape, hydrology and fertility are threatened by climate warming and anthropogenic pressure. Irregular availability of water is going to be the biggest hazard in future. In case of increased water supply, the piedmont zone and river lowlands are threatened by erosion and sedimentation while in case of decreased water supply, the upland surface is endangered by salinization, desertification and drying-up of aquifers. Decline in food production will be the major problem. In order to make assessments of the environmental changes, concerted efforts should be initiated to understand the geological past and model the future. A pre-requisite is to develop a high resolution history of climate variations and their impact on landscape and ecology from the geological and historical records of IGP during the past 25 ka. Such data can help in the evaluation of forecasting scenarios, and thereby assist in developing mitigation plans regarding the environment. Artificially induced recycling the water can be one of the possible ways to maintain a minimum availability of water.

Introduction

A major concern stands emphasized further after the release of the assessment reports of the Intergovernmental Panel on Climate Change (IPCC) in February and May 2007. It is difficult to ignore the scientific conclusions drawn in the reports for the globe in general and India in particular. Today, an ordinary person is aware of the extreme events of unseasonal rains, monsoonal drought and rapid temperature fluctuations. He interprets them as the advance indications of an impending change in climate. Climate is not changing for the first time. It has changed several times in the geological past. The most recent of such changes were during the Quaternary period, which began with a major cooling of the earth’s environment about 1.8 m.y. ago. Since then, there have been nine phases of cooling when glacial masses on the earth advanced significantly. The warm intervals between successive glaciations too had pulses of cooling. We live in the interglacial period i.e. Holocene. Since its inception, around 11,000 years ago, it has witnessed six climatic changes (Mayewski et al., 2004). Among them, the last spell of cooling known as little Ice Age, between 15th and 19th Century, and the last spell of warming Medieval Warm Epoch between10th and 13/14th centaury are historically known (Wigley et al, 1981, Lamb, 1982).

Human societies have suffered enormously due to climatic changes but ultimately most were able to adjust by changing their life style and migrating to the hospitable areas. Few centuries back, the impact of climate was not so severe because the population was less, it lived in small groups and economic stakes were low. Their migration to the fertile areas was easier because large areas on the earth were yet to be habited. Today, the societies have grown tremendously and are anchored in areas that are difficult to abandon because of the high economic stakes. Most of the habitable land is occupied. So if a population is forced to migrate under the pressure of global warming, there is not much place left for resettlement.

In the past the earth’s climate changed due to natural reasons. Milankovitch effect, plate tectonics and rise of mountain chains are considered as the major driving

e-Journal Earth Science India, Vol. I (III), pp. 138-147 http://www.earthscienceindia.info/

forces (Ruddiman and Kutzbach, 1989; Ruddiman, 2001). But the present cause of global warming is, in part, manmade due to the increased concentration of carbon dioxide in the atmosphere (IPCC, 2007). The fear of environmental ‘losses’ has stimulated the world to strategize the reduction of carbon emission in the atmosphere. Our past actions have already perturbed the earth climate system, and the impact of which is inevitable in future. The projected global warming has the potential to change the course of history, if not tackled in right earnest.

Today, the scientific community faces two primary tasks: a) to stabilize and reduce the carbon dioxide build-up in the atmosphere and b) to develop the hazard specific mitigation measures so that the earth’s surface can sustain the societies. For the first task, affordable technologies have to be evolved and dependence on fossil fuel to be minimized in energy and transport sectors. This topic, however, is beyond the scope of this article. The second task requires the acquisition of specific knowledge about the types of hazard likely to develop, delineation of areas to be affected by them and working out suitable mitigation strategies for each one of them.

The Indian Scene

The Indian landmass consists of three physiographic domains; the Himalayas, Indo-Gangetic Plain (IGP), and Peninsular Shield (Fig.1). The Himalaya is the highest domain of rugged topography with deep valleys and high hill ranges. It is a tectonically active terrain shaped by the dissection of crystalline and sedimentary ranges by glacial, glacio-fluvial and fluvial agencies. It houses several hundred glaciers that feed and maintain the perennial flow of the Indus, Ganga and Brahmputra systems and is the main contributor of detrital loads to rivers landscaping the IGP, deltas and sub-marine floors. Erosion of its landforms plays an important role in the carbon contribution to atmosphere and has a direct bearing on the global climate change (Raymo and Ruddiman,1992).

The Indo-Gangetic Plain is a 400-800 km wide, low relief, east-west zone between the Himalaya in the north and the Peninsula in the south (Fig.1). It is a sinking basin that came in to being about 50 Ma ago due to epiorogenic movements of Himalaya and was subsequently filled up by the sediments deposited by northerly and southerly drainage under the influence of climate changes, mainly from the Middle Miocene (Rowley 1996).

The present surface configuration of IGP was fashioned about 100 ka BP (Gibling et al., 2005). Its western part - the Punjab and Haryana Plains, constitute the Indus regime which has a southwesterly master slope and is drained by a perennial Satluj system in the extreme west and by short rain- fed, southerly –southwesterly flowing, ephemeral streams like Ghagghar and Markanda in the east. A subordinate system of northerly flowing seasonal streams namely Krishnawati and Sahibi originating from the northern part of Aravali ranges drain this regime from the south although they carry only a small sediment load from the adjoining alluvial-aeolian plain. This is an arid to semi-arid, water-starved region with annual precipitation of 300-600mm and an evaporation of 1200 mm. In spite of the dry climate, a network of canals sustains the intensive cultivation of the entire surface. Natural forest is absent. Groundwater is fresh and shallow in the vicinity of canals but saline and deep near the margin of the Thar Desert. The surface is densely populated and cultivated.

e-Journal Earth Science India, Vol. I (III), pp. 138-147 http://www.earthscienceindia.info/

Fig.1: (A) Regional Goggle image of the northern part of India and its surrounding showing Himalayas, Indigangetic plain and northern part of Peninsula. The white patches in Himalayas are glaciers (B) Figure of the above image showing drainage pattern in Punjab Haryana and Ganga plains

The area east of the Yamuna river constitutes the Ganga basin which has a sub-humid to humid climate with 600-1000mm of average rainfall. Unlike Haryana – Punjab plain, it has a well developed drainage of Himalayan-fed, southeasterly flowing perennial system of Ganga and its tributaries like Yamuna, Ramganga, and Kosi. It also has some streams like Gomti, Sai etc which originate in the piedmont and are fed by rain and groundwater. A prominent northerly flowing river system consisting of Betwa, Chambal and Son originating from the northern margin of peninsula join the Yamuna and Ganga rivers in the southern part of the Ganga plain (Kumar et al., 1996). The IGP can be divided into three major geomorphic units namely, piedmont, central alluvial plain and marginal alluvial plain (Singh, 1996; Kar et al., 1997). Some of the important hazards mapped in IGP are shown in Fig.2. Piedmont is a narrow, forested, zone of gravelly-muddy sediments along the Himalayan foothills affected by gully erosion. Rivers passing from the Himalayas shed their coarse sediment load in this zone and multiply their channels in braided fashion. The central alluvial plain is 200-400 Km wide stretch with gradual southerly and SE slope in Ganga plain and SW slope in Haryana- Punjab plain. The rivers have 2-8km wide valleys forming distinct lowlands, about 2-10m lower than the adjoining upland. The lowland valleys have flat terraces (T1 and T2) and channel

e-Journal Earth Science India, Vol. I (III), pp. 138-147 http://www.earthscienceindia.info/

bars. The regional upland surface is the master plain which is extensively cultivated and habited. Sand ridges, lakes, depressions and ponds are main landforms while soils salinity, flooding, riverine erosion are the main hazards in the Ganga plain and desertification and ground water salinity in the Punjab and Haryana Plains (Saini et al., 2001), (Fig. 2). The marginal alluvial plain is a northerly sloping zone which was formed by the deposits of the northerly drainages from the peninsula. In Haryana, this zone is poorly defined due to the overlapping by aeolian deposits.

Fig.2: Map of parts of Indo-Gangetic plain showing important hazards. (1. Soil erosion, 2. Flooding, 3. Soil salinity, 4. Desertification, 5.water logging, 6. Hard rock exposures.)

IGP is critical

The importance of IGP is due to its high population density and agricultural production. Its climate is controlled by the monsoon rains. Since IGP is strongly connected to the tectonics and climate of Himalaya, any changes in these factors are liable to adversely affect the hydrology, soil fertility, food production and settlement pattern of IGP. Moreover, its proximity to Thar Desert is another cause of concern as the processes of sand movement can force undesirable modifications in the landscape of IGP under varying conditions of temperature and rainfall.

Besides natural threats, the IGP is also overstressed due to over exploitation of the land and water resources. The cultivable land is replaced by urbanization leading to increase in waste production. It can be concluded that IGP is under the twin threat of increasing population and climate change.

e-Journal Earth Science India, Vol. I (III), pp. 138-147 http://www.earthscienceindia.info/

Climate Change and Associated Hazards

One of the primary concerns of climate shift is whether precipitation will decrease or increase in a given region? This will decide whether the potential hazards will be due to excessive availability of water or scarcity of water. The traditional model indicates that evaporation and humidity will increase due to warming. However, the warm air will hold the water for long duration that will delay and slow down the precipitation. On the contrary, some recent studies indicate that global warming could increase the precipitation by about 20% (Wentz and Schabel, 2000, Wentz et al., 2007). Assuming that precipitation and temperature will change, we can anticipate rapid as well as slow hazards in the IGP that may nucleate in Himalaya as well as in the IGP. Rapid hazards like flood, erosion and deposition will possibly accompany the increased precipitation while slow hazard like soil -salinization, desertification, drought, ground water subsidence, shrinkage of water bodies and diminished flow in rivers will follow when precipitation is decreased. Both can lead to change in the boundary conditions of landforms, land-water and vegetation. Our concern is how and when the land and water systems in IGP will respond to these variations. Studies have shown that the impacts of climate controlled short and long-term changes on landscape and river systems could be predicted (Moll et al., 2000, Veldkamp and Tebbans, 2001, Boggart et al., 2003). In the context of IGP, we need to examine such changes during the last glacial and present interglacial period (i.e. 25 ka) to know how landscape, ecology and hydrological systems were affected when the water supply to IGP decreased and increased.

It may be assumed that initially the warming will trigger melting of glaciers and snow in Himalaya and a change in precipitation mode from snowfall to rainfall. It will increase the availability of water leading to accelerate erosion of the Himalayan landforms and production of detritus that may increase the sediment storage in the valley. A close example of this situation in the past can be taken from the hypsithermal event of Holocene, around 8-6 ka BP, when fluvial erosion filled up to 80m of the valleys with regoliths, which were also subsequently transported downstream (Pratt et al., 2002). But it takes few hundred years to complete the cycle because there is a response time for landscape elements and geological agencies to adjust to the new conditions. The IGP and its river valleys will possibly shift towards changed conditions of sediment load, river flow velocity and discharge.

Traditionally, our societal and agricultural needs, conservation and exploitation pattern of water are adapted to the existing monsoonal climate and adjusted with the seasonal behavior of river flow and sub-surface aquifers. After debouching the alluvial plain, the piedmont zone would be the first target of fluvial erosion due to its sloping topography and loose lithology. It is already affected by the gully erosion (Fig. 2) which is likely to be intensified under accelerated flow velocity leading to the extension of badland and loss of forest land. Further downstream, in the central alluvial plain where slope is gentler, deposition of fresh sediment layers in the lowlands may occur. In fact the maximum sedimentary growth of IGP has taken place during the earlier wet interstadials in Late Quaternary as megafans near the Himalayan front and as channel and flood plain deposits in the down stream (Shukla et al., 2001, Kar et al., 1997). The lowlands are few hundred meters to more than 10 kilometer wide tortuous surfaces on either side of the Himalayan mountain-fed rivers. Though less populated, these surfaces are preferred for agriculture on account of fine textured soil, proximity with the perennial water source and fresh quality of shallow ground water. These are stabilized surface in which the cultivation pattern has evolved through centuries of experience. Fresh sedimentation due to change in the hydrodynamics of the rivers would lead to landscape modification in this terrain element and is likely to affect the cultivation style.

e-Journal Earth Science India, Vol. I (III), pp. 138-147 http://www.earthscienceindia.info/

In second scenario, when precipitation is decreased, the western part of IGP i.e. Haryana –Punjab plains, adjacent to the Thar desert become the most vulnerable sector because it is already a water scarce region with history of drought and desertification. It has undergone a major phase of desertification around 16ka BP when large dunes were deposited up to Delhi (Glennie et al., 2002) followed by several pulses of humid and semi-arid climate( Enzel et al.,1999; Saini et al., 2005). These plains are sensitive to even smaller changes in climate and respond much quicker than the desert core. Rainfall at the eastern limit of Thar is around 300mm and 600mm in the latitude of Delhi. If we assume that rainfall decreases by 300mm, it will account for an average of 50% reduction, which is sufficient to transform the area into an arid zone. In the Ganga plain, east of Delhi, where rainfall is between 600-1400mm, a decrease of 300mm rainfall will not change the climatic zone and thus effects will be marginal.

The Haryana –Punjab plain becomes more critical in the light of past events. This area was once a site of the famous Indus valley civilization, when Harappan culture flourished in the Ghagghar-Hakara basin. Hundreds of cultural mounds scattered in northwestern Haryana and southeastern Punjab are testimony that a large population lived on these plains. The exact cause of the downfall of civilization is debatable; however increased aridity, drought, soil salinisation and desertification are cited as the possible causes (Bakliwal and Grover, 1980; Mishra, 1984; Sahai, 1999). The downfall is estimated around 200BC. There is also a growing volume of opinion on the existence of a mighty river named “Vedic Saraswati” in this region that flowed from Himalaya to Arabian sea and later disappeared due to tectonic disturbances and climate change (Wilhelmy, 1999; Oldham, 1999; Roy and Jakhar, 2001). Although a complete chronology of events and precise evidence of the cause of decimation of civilization and the Saraswati river are yet to be established, however, it is evident that the area has witnessed medium to large scale changes in landscape and the climatic variations which appear to be one of the major factors. In the event of a decrease in rainfall in future, there are strong possibilities of the Thar Desert to spread over this region, thereby changing the landscape, and making the land uncultivable.

Even a rise in temperature by 20o C can lead to a fall in farm production between 4 and 34% (IPCC, 2007). The soil salinity, already prevalent in the plains of Haryana, Punjab and western Uttar Pradesh, is bound to extend over the marginally saline areas reducing the availability of agricultural land. This will put additional stress on the already declining water table. The groundwater exploitation is likely to be intensified and consequently the water stressed areas will become water scarce. It can lead to change in river habit from gainer to contributor as shown in Fig.3 of Yamuna river in Faridabad district, U.P.

e-Journal Earth Science India, Vol. I (III), pp. 138-147 http://www.earthscienceindia.info/

Fig.3: The change in the water table in the surrounding of Yamuna river south of Delhi (Faridabad district, U.P.). The excessive withdrawal of ground water has changed the nature of Yamuna River from an affluent to influent river.

What can be done?

It is difficult to predict how exactly the warming will affect people in different regions of the globe. In the IGP changing environments have the potential to decrease the productive capabilities. We may have to deal with two kinds of situations: when water resource increases and second when water resource decreases. A possible approach is to model the behavior of IGP under conditions of excess and deficit water. For this we could seek past analogues based on the environmental changes in the last ~ 25ka time slice in the Himalaya and IGP and to analyze past responses of land, water and vegetation to such changes. The task will involve the collection, collation and synthesis of basin wise stratigraphic records, proxies of rainfall and temperature, so that the pattern of monsoon variation in time and space could be reconstructed. This will help in setting up and testing future hypothesis on landscape response to the fluctuations in climatic parameters as well as in identifying the areas according to their vulnerability to different kinds of hazards. Based upon these inputs, management plan(s) for storage, distribution and conservation of water could be attempted; and appropriate modifications in cropping pattern and new techniques for land use, and irrigation evolved.

There are several conventional approaches like construction of reservoirs, water harvesting, and water recycling which on a limited scale are employed for short term management of water resources. Under global warming scenario, such approaches may require re-assessment. Today, a large part of the river water flows unutilized to the sea and it may not be practical to store it in reservoirs which have their own adverse impact on the environment. The ideal situation will be to have a regular supply of water through precipitation. Is it possible to ‘store’ the excess water of Himalayan rivers back in the atmosphere and then facilitate its re-precipitation? It amounts to creating an artificial climatic domain by changing the circulation pattern and enriching the moisture content of air. One possible way is to increase evaporation of the water from water

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surplus areas through plantation, increase moisture in the atmosphere and receive it back as precipitation. This approach includes identification of water surplus areas i.e. pumping zones, afforestation of suitable plant species i.e. transpiration surface, and understanding of the atmospheric circulation so as to know whether the evaporated water can be re-precipitated in the areas of interest. In this way a large proportion of water can be retained in the IGP before it goes to the sea. There are good chances that the increased moisture content of air may bring good rains over the IGP. The concept is highly preliminary and speculative but has the potential to address the problem of future water shortages. The need is to make institutionalized efforts with shared expertise and focused approach. Presently there is no such institution, though sporadic and un- coordinated investigations on hydrology, agriculture and geology are being undertaken by various individuals and groups.

Acknowledgements: I wish to record my gratefulness to Prof. S.K.Tandon, University of Delhi who nucleated the thought of preserving the sustenance of IGP as a social surface under changing environments. The idea was refined by several discussions with my colleagues, Dr. N. C. Pant, S.A.I Mujtaba and R. K. Khorana of the Geological Survey of India. There could be several deficiencies in the write up as it is just a spark in the hazy horizon of understanding. I also wish to thank Sri D.D. Bhattacharya, whose consistent efforts made me complete the manuscript. The efforts put in by an anonymous reviver are thankfully acknowledged.

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