22 Surface Water Resources: Vulnerability and Resilience

 Objectives

Spatio-temporal changes in surface water configuration: Increased sedimentation and stream migration, increased runoff, water logging, land subsidence, declining water tables and emerging problems.

Introduction

Water is absolutely essential for sustaining life on earth. It has a unique place among all the planet’s renewable resources. It is vital for food production, economic development and for general well being. Water resources of a country are one of its vital assets. Water is truly unique as there is no substitute for this resource. The Earth can be perceived as a water planet as about 71 per cent of the Earth’s surface is covered with water. The oceans hold about 96.5 per cent of all Earth’s water. Water also exists in the air as water vapour, in rivers and lakes, in icecaps and glaciers, in the ground as soil moisture and in aquifers, and even in human beings and other organisms. Water is never still and our planet’s water supply is constantly moving from one place to another and from one form to another through the ‘water cycle’. The vast majority of water on the Earth’s surface, over 96 per cent, is saline water found in the oceans. The freshwater resources, such as water falling as precipitation and moving into streams, rivers, lakes and groundwater, provide us with the water needed for everyday use. However, there is much more freshwater stored in the ground than there is in liquid form on the surface.

Where is Earth’s water located?

The total volume of water on Earth is about 1400 million km3 of which only 2.5 per cent, or about 35 million km3, is freshwater. Most freshwater occurs in the form of permanent ice or snow, located in Antarctica and Greenland, and in deep groundwater aquifers. The principal sources of water for human use are lakes, rivers, soil moisture and relatively shallow groundwater basins. The usable portion of these sources is only about 200,000 km3 of water-less than 1 per cent of all freshwater and only 0.01 per cent of all water on Earth. Much of this available water is located far from human populations, further complicating issues of water use.

The replenishment of freshwater depends on evaporation from the surface of the oceans. About 505,000 km3, or a layer 1.4 metre, evaporates from the oceans annually. Another 72,000 km3 evaporates from the land. About 80 per cent of all precipitation (around 458,000 km3 per year) falls on the oceans and the remaining 119,000 km3/year on land. The difference between precipitation on land surfaces and evaporation from those surfaces (i.e. 119,000 km3 minus 72000 km3 annually) is run-off and groundwater recharge which is approximately 47,000 km3 annually (Gleick 1993). The figure shows the estimate of the average annual water balance of major continental areas, including precipitation, evaporation and run-off. More than one half of all run-off occurs in Asia and South America, and a large fraction occurs in a single river, the Amazon, which carries more than 6000 km3 of water a year (Shiklomanov 1999).

Table 1: Estimate of Global Water Distribution

Source: Shiklomanov, 1993.

Note: Percentages may not sum to 100 per cent due to rounding.

Distribution of World’s Freshwater Resources

Glaciers and icecaps cover about 10 per cent of the world’s landmass. These are concentrated in Greenland and Antarctica and containing more than 70 per cent of the world’s freshwater. Unfortunately, most of these resources are located far from human habitation and are not readily accessible for our use. According to the United States Geological Survey (USGS), “ 96 per cent of the world’s frozen freshwater is at the South and North poles, with the remaining 4 per cent spread over 550,000 km2 of glaciers and mountainous icecaps measuring about 180,000 km3” (UNEP, 1992). Groundwater is by far the most abundant and readily available source of freshwater, followed by lakes, reservoirs, rivers and wetlands. Groundwater represents over 90 per cent of the world’s readily available freshwater resource (Boswinkel, 2000). Most freshwater lakes are located at high altitudes, with nearly 50 percent of the world’s lakes located in Canada alone. Many lakes, especially those in arid regions, become salty through evaporation. Reservoirs are artificial lakes, produced by constructing physical barriers across flowing rivers, which allow the water to pool and be used for various purposes. The volume of water stored in reservoirs worldwide is estimated at 4286 km3 (Groombridge and Jenkins, 1998). Wetlands are other significant sources of freshwater which include swamps, bogs, marshes, mires, lagoons and floodplains. The 10 largest wetlands in the world by area are: West Siberian Lowlands, Amazon River, Hudson Bay Lowlands, Pantanal, Upper Nile River, Chari-Logone River, Hudson Bay Lowlands in the South Pacific, Congo River, Upper Mackenzie River and North America prairie potholes. The total global area of wetlands is estimated at ~2900000 km2 (Groombridge and Jenkins 1998).

Figure 1: World’s Freshwater Sources

Source: Shiklomanov, 1993.

Figure 2: Location of World’s Freshwater

Source: Shiklomanov, 1993.

   Water Cycle

Without water, the other nutrients cycles would not exist in their present forms; and current forms of life on the earth, which consists mostly of water-containing cells and tissues, cannot not exist. The hydrologic cycle or water cycle collects, purifies and distributes the earth’s fixed supply of water. The main processes in this water recycling and purifying cycle are:

§    Evaporation: the conversion of water into water vapour

§  Transpiration: evaporation from the leaves of water extracted from soil by roots and transported throughout the plant

§   Condensation: conversion of water vapour into droplets of liquid water

§    Precipitation: rain, sleet, hail and snow

§    Infiltration: movement of water into soil

§   Percolation: downward flow of water through soil and permeable rock formations to groundwater storage areas called aquifers

§   Runoff: down-slope surface movement back to the sea to resume the cycle.

The water cycle is powered by energy from the sun and by gravity. Incoming solar energy evaporates water from oceans, streams, lakes, soil and vegetation. About 84 per cent of water vapour in the atmosphere comes from the ocean and the rest comes from land. The capacity of air to hold water vapour depends on its temperature. Warm air can hold more water vapour than cold air. Winds and air masses transport water vapour over various parts of the earth’s surface, often over long distances. Falling temperatures cause the water vapour to condense into tiny droplets that form clouds or fog. For precipitation to occur, air must contain condensation nuclei which are tiny particles on which droplets of water vapour can collect. Volcanic ash, soil dust, smoke, sea salts and particulate matter (emitted by factories, coal-burning power plants and vehicles) are sources of such particles. The temperature at which condensation occurs is called the dew point. Some of the fresh water returning to the earth’s surface as precipitation gets locked in glaciers. Most of the precipitation falling on terrestrial ecosystems becomes surface runoff, flowing into streams and lakes which eventually carry water back to the oceans where it can be evaporated to begin the cycle again. Water not only replenishes streams and lakes, surface runoff also causes soil erosion and moves soil and weathered rock fragments from one place to another. Some of the water returning to the land soaks into or infiltrates the soil and porous rocks and then percolates downward, dissolving minerals from porous rocks on the way. This water gets stored in the pores and cracks of rocks. Where the pores are joined, a network of water channels allows water to flow through the porous rock. Such water laden rock is called an aquifer and the level of earth’s land crust to which it is filled is called the water table. This underground water flows slowly downhill through rock pores and seeps out into streams and lakes or comes out in springs. Eventually, this water evaporates or reaches the sea to continue the cycle. Throughout the hydrologic cycle, many natural processes act to purify water. Evaporation and subsequent precipitation act as a natural distillation process that removes impurities dissolved in water. As water flows above ground through streams and lakes and below ground in aquifers, it is naturally filtered and purified by chemical and biological processes. Thus, the hydrological cycle also acts as a cycle of natural renewal of water quality.

Water is transported in different forms within the hydrological cycle or water cycle. Shiklomanov in Gleick (1993) estimates that each year about 502800 km3 of water evaporates over the oceans and seas, 90 per cent of which (458000 km3) returns directly to the oceans through precipitation, while the remainder (44800 km3) falls over land. With evapotranspiration totalling about 74200 km3, the total volume in the terrestrial hydrological cycle is about 119000 km3. About 35 per cent of this, or 44800 km3, is returned to the oceans as run-off from rivers, groundwater and glaciers. A considerable portion of river flow and groundwater percolation never reaches the ocean, having evaporated in internal runoff areas or inland basins lacking an outlet to the ocean. However, some groundwater that bypasses the river systems reaches the oceans. Annually the hydrological cycle circulates nearly 577000 km3 of water (Gleick, 1993).

Figure 3: World’s Water Cycle

Source: Shiklomanov, 1999.

Figure 4: Availability of Freshwater- 2000

Water Resources in India

     With the increasing population of India, there is an ever-growing demand for water resources. On an average, India receives annual precipitation (including snowfall) of about 4000 km3. However, there exist considerable spatial and temporal variations in the distribution of rainfall across the country. Consequently, the availability of water also varies considerably. It is estimated that out of the 4000 km3 water, 1869 km3 is average annual potential flow in rivers available as water resources. Out of this total available water resource, only 1123 km3 is potentially usable (i.e. 690 km3 from surface water resources and 433 km3 from ground water resources).

Table 2: Water Availability Facts at a Glance

India, with a geographical area of about 329 million hectares, can be divided into seven well defined physiographic regions. These include, the Northern Mountains comprising the mighty Himalayan ranges; the Great Plains traversed by the Indus, Ganga and Brahmaputra river systems; the Central Highlands, consisting of a wide belt of hills running east-west between the Great Plains and the Deccan plateau; the Peninsular Plateaus; the East Coast; the West Coast; and the islands comprising Lakshadweep in Arabian Sea and Andaman and Nicobar group of islands in the Bay of Bengal. India has a variety of climatic zones which range from extremes of heat to extremes of cold; from extreme aridity and negligible rainfall to excessive humidity and torrential rainfall. Most of the rainfall in India takes place under the influence of South West monsoon between June to September except in Tamil Nadu where it is under the influence of North-East monsoon during October and November. The average rainfall is about 1215 mm. However, there is considerable spatial variation in rainfall which ranges from less than 100 mm in the western Rajasthan to more than 2500 mm in North-Eastern areas.

Table 3: India’s Water Resources

Source: Water Resources at a Glance 2011 Report, CWC, New Delhi,

(http://www.cwc.nic.in)

India is also blessed with many rivers. A river basin, also called catchment area of the river, is the area from which the rain will flow into that particular river; and the shape and size of the river basin is determined by the topography of the area. River basin is considered as the basic hydrological unit for planning and development of water resources. There are 12 major river basins with catchment area of 20000 km2 and above. The total catchment area of these rivers is 25.3 lakh km2. The largest river basin is the Ganga-Brahmaputra-Meghna with catchment area of about 11.0 lakh km2 (more than 43 per cent of the catchment area of all the major rivers in the country). The other major river basins with catchment area more than 1.0 lakh km2 are Indus, Mahanadi, Godavari and Krishna. There are 46 medium river basins with catchment areas ranging between 2000 and 20000 km2. The total catchment area of medium river basins is about 2.5 lakh km2. All these river basins cover about 81 per cent of the geographical area of the country.

Table 4: List of Basin Name and Area

Source: India-WRIS (http://www.india-wris.nrsc.gov.in)

Problems of Surface Water Resources

Water is an essential part of any ecosystem. Any changes in the availability and quality of water would have devastating effects on the natural environment. Climate change is fuelled both by emissions and the degradation of the world’s natural environment. Increasing number and intensity of natural disasters are direct results of the degrading environment. Climate change is often blamed for the increasing number of floods and droughts. Our natural environment has the capacity to cope with pollution and degradation to a certain extent. But when this capacity is exceeded, it can result in irreparable contamination, which in turn can lead to destruction of ecosystems. Surface water resources are renewable but only within clear limits. Water resources also vary over space and time, as there are vast differences in the availability of water resources in various parts of the world and huge differences in the amount of seasonal and annual precipitation.

Our water resources are facing rapid pollution, mostly due to human waste (with 2 million tons a day disposed of in watercourses), industrial wastes and chemicals, and agricultural pesticides and fertilizers. Over the last 200 years, human activities such as urban and industrial development and intensification of agricultural practices had unprecedented effects on the water bodies. There are global problems such as heavy metals, regional problems like acid rain and much more localized ones such as groundwater contamination. In many places groundwater has become contaminated as a result of leakage from storage tanks, mine tailings and accidental spillages (Herbert and Kovar, 1998).

Organic Pollutants: “Organic material from domestic sewage, municipal waste and agro-industrial effluent is the most widespread pollutant globally” (UNEP, 1991). These pollutants are discharged untreated into rivers, lakes and aquifers contaminating the water bodies. Densely populated parts of Asia, Africa and South America are mostly affected from this type of pollution. This organic material also has high concentrations of nutrients, particularly nitrogen and phosphorus. Increase in these nutrients cause eutrophication of lakes and reservoirs which in turn promotes abnormal plant growth and depleting oxygen levels. Nitrogen levels have also risen due to the increased use of nitrogen containing fertilizers in agriculture. There is a matter of concern as nitrate concentrations in large numbers of sources of surface water and groundwater exceed the WHO guideline of 10 milligrams per litre. In many parts of the world, heavy metal concentrations in river water have risen due to leaching from waste dumps, mine drainage and melting (Meybeck, 1998). Concentrations of organic micro-pollutants from the use of pesticides, industrial solvents and other materials have also increased.

In India, River Ganga originates from the source glacier Gangotri in northern India extending to a length of 2525 km and basin area over 1 million km2. Over the course of time, River Ganga has become a site of environmental catastrophe. Poor sanitation, untreated urban sewage, improper waste management by industries and disposal of solid corpses along its banks has led to severe environmental stress. Nearly, all sewage from the nearby habitations goes directly into the river. “Further 260 million litres of industrial wastes, runoff from 6 million tons of fertilizers and 9000 tons of pesticides used in agriculture within the basin enters into the river” (Singh et.al, 2004).

Acidification of Water Bodies: Acidification occurs when the capacity of the soil or water bodies to resist or neutralize acidifying atmospheric deposition begins to decline. Acidifying compounds may fall to the ground with rain or snow as wet deposition, or in the form of particles or gases as dry deposition. If acid deposition rates increase consistently, ecosystems can eventually lose their neutralizing capacity completely. Acidification of surface water was a serious problem for the developed world during 1960s and 1970s, particularly in Scandinavia, western and central Europe and in the north-east of North America. However, sulphur emissions in these regions decreased and the acid rain problem diminished. Acidification mostly affects aquatic life which generally cannot survive with pH levels below

5. Higher acidity also raises concentrations of metals in drinking water. Acidification is likely to continue in countries and regions with increasing industrialization. For the developing world, increasing salinity is a serious form of water pollution. Arid and semi-arid regions often suffer from increased salinity as a result of poor drainage, fine grain size and high evaporation rates which lead to concentration of salts in the soil.

Sedimentation: Most rivers carry sediment in the form of suspended load and bed load. This sediment load is adjusted to the flow regime of the river over time. Increasing or decreasing sediment load can change the flow regime of rivers and cause problems in the downstream region. Affects of sedimentation include: reduction of reservoir volumes due to siltation, the scouring of river channels and the deposition of sediment in them, threatening flood protection measures, fisheries and other forms of aquatic life. River diversions, including dams, can produce some of these effects on sediment. “The world total of suspended sediment transported to the oceans is reported to be as high as 51.1 billion tons per year” (Walling and Webb, 1996).

Salinisation: The term ‘salinity’ refers to the concentrations of salts in water or soils. Salinity can take three forms, classified by their causes: primary salinity (also called natural salinity); secondary salinity (also called dryland salinity), and tertiary salinity (also called irrigation salinity). Small amounts of dissolved salts in natural waters are vital for the life of aquatic plants and animals. However, changes in salinity can often lead to drastic alterations in marine and aquatic ecosystems. Banerjee (2013) provides with some important evidence that the climate change and the resultant events have led to changes in the levels of salinity in Indian Sundarbans. Over the past two decades, increase in the melt-water of the Gangotri Glacier in the Himalayan ranges due to global-warming, Farakka barrage discharges and sea level rise have accelerated such changes. Observations of salinity over a period of 23 years (1990-2012) showed a significant long-term variation. This study showed that, increasing melting of Himalayan ice might have decreased the salinity at the mouth of the Ganges River, where it meets the oceanic waters at the western end of the deltaic complex of the Indian Sundarbans.

Water-related disasters: According to World Water Report (2003) during the time period of 1991 and 2000, over 665,000 people died in 2,557 natural disasters, 90 per cent of which were water-related events. The vast majority of victims (97 per cent) were from developing countries (IFRC, 2001). “Growing concentrations of people and increased infrastructure in vulnerable areas such as coasts and flood plains and on marginal lands mean that more people are at risk” (Abramovitz, 2001). Asia has fared particularly badly, with roughly 40 per cent of all disasters taking place on the continent. Each event leaves thousands of communities more vulnerable to the next disaster. Hence, people are barely able to recover from one disaster before the next catastrophe strikes. Worldwide, floods were the most reported disaster event; the year 2000 saw 153 flood events alone, some of the worst taking place in Mozambique and along the length of the Mekong River (South-East Asia), while in terms of loss of life, droughts claimed the greatest number of victims. According to the United Nations, at least 41 million people in Bangladesh, India and Nepal have been directly affected by flooding and landslides resulting from the monsoon rains, which usually begin in June and last until September.

Figure 5: Flood Prone Areas in India

Water Stress in India: India has made significant improvements in both the availability and quality of municipal drinking water systems over the past decades. Still, water resources are under severe stress due to the rapidly increasing population. Additionally, rapid growth in India’s urban areas has made the governments initiatives go in vain in providing safe and adequate water to everyone. Regardless of improvements in drinking water, many other water sources are contaminated with pollutants, and over 21 per cent of the country’s diseases are water-related. Concerns have been raised that India actually lacks adequate replenishable water resources for longer periods of time. India’s aquifers are currently considered replenishable, but the Water Development Rates are also very high in various parts of the country. As a large grain producing country, use of water for agricultural purposes is very high in our country.

Figure 7: Water Stress in India

Source: www.indiawatertool.in

World Resource Institute estimates depict that 54 per cent of India’s total area is facing high to extremely high water stress and almost 600 million people are at higher risk of surface-water supply disruptions. Groundwater levels are also declining across India. “Of the 4,000 wells captured in the IWT 2.0 showing statistically significant trends, 54 percent dropped over the past seven years, with 16 per cent declining by more than 1 meter (3.2 feet) per year”. Farmers in arid areas and areas with irregular rainfall depend heavily on groundwater for irrigation. Government subsidies on the farmers’ electrical pumps and lack of existing limit to water use have resulted in widespread pattern of excessive water use. North-western India is most vulnerable. “Of the 550 wells studied in the region, 58 per cent have declining groundwater levels”. At the same time, as much as “130,600,000 people live in districts where at least one pollutant exceeded national safety standards in 2011”. And more than 20 million people lived in the eight districts where at least three pollutants exceeded safe limits.

   Conclusion

Keeping in mind the current trends, India is set to become a water scarce country in the not too distant future. A rapidly increasing population with ever-increasing demand for water coupled with increasing pollution, over-use in farming activities, high levels of groundwater exploitation, inadequate governance and poor infrastructure have severely stressed our water resources. This uneven distribution of the precipitation results in highly uneven distribution of available water resources, which leads to floods and drought affecting vast areas of the country. Utilising scientific structural and non-structural measures can prove significant in mitigating floods and droughts. There is a need for better management of existing water storages to increase the availability of water resources. At the same time, we can create additional storages by constructing small, medium and large sized dams keeping in mind the economical, environmental and social aspects. The availability of water resources may be further enhanced by rejuvenation of dying lakes, ponds and tanks and increasing the artificial means of groundwater recharge. Inter-basin transfer of water can be a crucial measure for mitigating the problems of the surplus and deficit basins. Due to rapid industrialization and increasing use of fertilizers and pesticides, the quality of surface and groundwater resources is deteriorating. The movement of pollutants in the rivers, lakes and groundwater aquifers needs to be regulated. In this regard, regular water quality monitoring programme can go a long way in identifying the areas prone to poor water quality. For maintaining the quality of freshwater, water quality management strategies are required to be evolved and implemented.