Surface Water in Indian Rivers: Perilous or Promising?

By: S R K Mall and Diva Bhatt
With advancements in the science of simulation modelling, climate models have improved their projection capabilities. This can have an important bearing on the future hydrology of flowing surface waters in the current context of climate change.
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With India’s per-capita surface water projections for 2050 placed at 1235 cubic m and 1451 cubic m, respectively, for high and low population growth scenarios, as per Kumar et al’s 2005 paper ‘Water resources of India’, Current Science, the water resources of the nation are clearly under stress.

About 328.726 million hectare (mha) of India’s geographical area is covered by rivers. Of these, 12 are major rivers with individual basins comprising catchments exceeding 10 mha, and cumulatively totalling 252.8 mha. The Ganga-Brahmaputra-Meghna system is the largest among these, with a catchment area comprising 110 mha, and amounting to 60 per cent of India’s total surface water potential. As per a United Nations 2012 report, these rivers are a source of livelihood for more than 70 per cent of India’s population, most of whom are dependent on agriculture for their livelihood.

The southwest monsoon between June and September, and the northeast monsoon between October and November are the main sources of water in the country. The annual precipitation in India stands at 4000 sq km and includes both rainfall and snowfall, as H Pathak et al. have pointed out in their 2014 paper, ‘Climate change and water availability in Indian agriculture: Impacts and adaptation’, published in the Indian Journal of Agricultural Sciences. Presently, more than 45 per cent of India’s average annual precipitation flows away as natural runoff into the sea.

In India, demand for water has already increased manifold due to urbanisation, agricultural expansion, increasing population, rapid industrialisation and economic development. At present, changes in cropping and land use patterns, over exploitation of stored water and changes in irrigation and drainage are modifying the hydrological cycle in many climatic regions and river basins. According to estimates by the Central Water Commission (CWC) made in December 2013, the per capita water availability of the country will drop to 1140 cubic m by 2050 as compared to 1608 cubic m in 2010.

Assessing the potential socio-economic impact involves comparing two future scenarios, one with and one without climate change. Among many of the uncertainties involved regarding assessment of water resources are:

  • The ability of ecosystems to adapt either naturally or through managed intervention to climate change; and,
  • Future increase in population and economic activities and their impact on natural resources systems.
Fig 1: The major river basins of India
Fig 1: The major river basins of India

Both these uncertainties hold good even for surface water resources. It is with ‘robust evidence and high agreement’ that J Cisneros et al., in their 2014 Intergovernmental Panel on Climate Change (IPCC), Working Group II, AR-5 paper, stated that projections regarding reduction in renewable surface water resources in dry subtropical regions will result in “…intensifying competition for water among agriculture, ecosystems, settlements, industry, and energy production, affecting regional water, energy, and food security…”

Table 1: Projected Change in Water Yield for the 17 River Basins of India
Table 1: Projected Change in Water Yield for the 17 River Basins of India

Many of the above mentioned river systems are perennial, while some are seasonal as precipitation over a large part of India is strongly concentrated around the summer monsoon (June to September/October) and the tropical storm season (May to October). This apart, the recent rise in erratic weather patterns has drastically jeopardised river flow regimes. As Stocker et al. (eds.), have stated in their ‘The physical science basis: Working group I, fifth assessment report of IPCC’, in 2013—the climate is changing, and so are both the variables of climate, namely, precipitation and evapotranspiration.

Climate Change

Widespread changes have been observed in extreme temperatures over the last 50 years. Cold days, cold nights and frost extremes have become frequent, just as hot days, hot nights and heat waves have become more common. Global average surface warming is likely to be in the range 0.4-4.8°C with a best estimate of about 3°C, and is very unlikely to be less than 1.5°C, with spatial and temporal changes in rainfall pattern, as per the estimates of Stocker et al. (eds) ibid. Recent measurements undertaken by the National Oceanic and Atmospheric Administration (NOAA) show carbon dioxide concentrations at 402.80 ppm (estimate until June 2015), which is 1.65 ppm higher as compared to the June 2014 level.

It is well known that water resources are inextricably linked to trends in weather patterns, which indicates that global climate change would have serious implications for water resources, as B C Bates et al. have pointed out in ‘Climate change and water’, Technical Paper of IPCC Secretariat 2008. Though both climatic and non-climatic drivers control the regulation of the hydrological cycle, the essay will confine itself to climatic factors alone.

India’s National Water Policy

Under its National Water Mission 2010, the government modified the National Water Policy of 1987. The Mission suggested strategies to tackle water management in keeping with climate change. Encompassing 2.6 per cent of the world’s land area, and saddled with just 4 per cent of the world’s renewable water resources and an ever growing population, India needs to be serious about regularly updating its water management strategies.

A new draft of the National Water Policy (NWP)was sanctioned in 2012 at the 14th meeting of the National Water Board. The NWP aims to take cognizance of the existing water resources of the nation and propose a framework for the creation of a system of laws and institutions for a unified national perspective, as stated in the National Water Policy of India document, 2012, of the Ministry of Water Resources, Government of India.

Simulation Modelling

There have been major improvements in the development and use of simulation models during the last two decades. Thus, current models are better equipped to give us reliable projections in connection to climate change for refined decision making. The ability of models to simulate important aspects of the current atmospheric processes in conjugation to interfaces with the hydrosphere, cryosphere and land surface processes through comparison of simulations with observations has vastly improved.

A number of research studies using simulation modelling have already been conducted for runoff projections for the major river basins. A 2011 study by A K Gosain et al.,‘Climate change impact assessment of water resources of India’, published in Current Science, on India’s 17 river basins (Fig.1) had evaluated the possible impacts of climate change on water resources.

The evaluation was conducted within the uncertainty constraints of climate change predictions for the A1B scenario of PRECIS, a Regional Climate Model (RCM), for near term (2021-2050) and long term (2071-2098) water availability. Providing regional climates for impact studies (PRECIS), is a regional climate model developed by the Hadley Centre of Meteorology, UK and A1B is a future scenario of forcing agents specified in the IPCC special report on emission scenarios (SRES). The cumulative change in water yield for all these river basins (considering both near and long terms) at the end of the long term were estimated to be fairly negative (Table 1).

Estimates of runoff for Brahmaputra in a study conducted by S Ghosh and S Dutta in 2012, ‘Impact of climate change on flood characteristics in Brahmaputra basin using a macro-scale distributed hydrological model’, published in the Journal of Earth System Science were found to be similar to that obtained by Gosain et al. in 2011.

Of course, some researchers have a different opinion as regards the Ganga and Narmada. The estimates by D Raje et al., as revealed in their article on ‘Macro-scale hydrological modelling approach for study of large scale hydrologic impacts under climate change in Indian River basins’, in Hydrological Processes, 2013 indicate an increased runoff in these rivers. These differences could be due to the resolution differences in the set of climate and hydrological models chosen to carry out the projections.

Endnote

With a population count of 1.25 billion occupying a mere 2.6 per cent of the world’s land, and its population projected to outdo all other countries in the world by 2028, India needs to be judicious with its water resources. To sustain its economic growth as against economies like that of China and the US, India will need to embark on path-breaking measures to manage its fast diminishing and deteriorating surface waters. An assessment of the availability of water resources in the context of future national requirements and expected impact of climate change and its variability is critical for relevant national and regional long-term development strategies and sustainable development. For this, science and governance will have to walk hand in hand to take up the challenge of ensuring ‘water security’ for the nation’s inhabitants.

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