Increasing population and accelerated urbanization puts additional stress on water resources. The deterioration of water resources (river pollution, depletion and contamination of ground water) is accelerated by demographic pressure. In case of growing cities, migration of people from smaller cities adds to further increase in population and stress on resource availability in urban areas.

Human activities such as fossil fuel burning, deforestation, agricultural activities, land use changes, industrial processes and transportation etc. are releasing greenhouse gases into the atmosphere. Rising levels of greenhouse gases are projected to cause climate change. The IPCC Third Assessment Report gives an estimate that the global temperature will rise by about 1.4-5.8°C by the year 2100. It is based on current emission trends and assumes that no efforts are made to limit greenhouse gas emissions. This projected rate of change is larger than any climate change experienced over the last 10,000 years.

The most widely discussed potential impact of climate change is the impact on water supply and demand. The potential changes in water supplies would result directly from the changes in runoff and the levels of rivers, lakes, and aquifers. Hydrological and water management analyses of plausible changes in climate predicts that precipitation in certain parts of the world may go up whereas in other parts it may decrease, thus affecting the amount of water that could be reliably supplied.

Reduced water supplies would place additional stress on people, agriculture, and the environment. Regional water supplies, particularly in developing countries, will be stressed in the 21st century. Climate change will exacerbate the stresses caused by pollution and by growing populations and economies. The most vulnerable regions are arid and semi-arid areas, some low-lying coasts, deltas, and small islands.

A case study was carried out to assess the sensitivity of water availability in the city of Delhi to growing pressures such as population, urbanization and climate change. The findings of this study are summarized below.

Delhi receives a normal rainfall of 610 mm per year in about 27 rainy days and the unutilized rainwater runoff is 193 MCM (Million Cubic Meters). The city is mainly supplied by surface water from the Yamuna and the dam on the Beas, which is a tributary of the river Indus. Surface water, contributes to over 86% of Delhi’s total water supply. Yamuna, a perennial river, provides the major share of this supply. Other sources of water supply to Delhi, through different inter-state arrangements, include the Himalayan rivers and sub-surface sources like tube wells etc. Of the water allocation from the Yamuna, 282 MCM flows unutilized. Total groundwater availability is of the order of 290 MCM per year. Underground water represents only approximately 11 per cent of the Delhi’s water resources.

New Delhi Municipal Council (NDMC), Municipal Corporation of Delhi (MCD), and Delhi Jal Board (DJB) are the major agencies handling surface water supply in Delhi. Issues related to ground water extraction are looked after by Central Ground Water Board (CGWD). In view of the water shortages in Delhi, particularly during summer seasons, some private agencies have also started supplying water to the residents in several colonies through water tankers.

The Delhi Jal Board is responsible for production of drinking water and distribution in the areas under the control of the Municipal Corporation of Delhi. It supplies water in bulk to NDMC and Delhi Cantonment Board for further distribution in their respective areas. The Board is also responsible for the collection, treatment and disposal of wastewater or sewage in the capital. According to estimates of a study by the end of 9th Five Year Plan i.e. by 2002 water requirement in Delhi would be 945 MGD.

Underground water resources are limited and diminishing. The water table has decreased by 2 to 4 m (up to a maximum of 8 m) between 1983 and 1994. Sub-soil water has also been polluted. Salinity and over-exploitation of the resources have affected groundwater availability in different parts of the city. Inadequate and intermittent supply of piped water has led to unchecked exploitation of the ground water resources. According to a study, the existing groundwater levels in the different administrative blocks show a decline of 2–30 m. However, there is a scope for further groundwater development in the Yamuna flood plain area and in some other areas of the National Capital Territory.

Delhi, on an average, receives about 610 mm rainfall. About 80 per cent of the season’s rainfall is received during the months of July, August and September. The year 2002, not being fortunate enough for Delhi, has fetched only a little more than 400 mm of rainwater, a deficit of approximately 33 per cent. The failure of the monsoon this year has just added pressure to this fast-depleting resource.

Delhi is experiencing an increasing pressure to meet demand for its water resources. Growing urbanization, improvements in living standards, exploding population are some of the contributing factors. The city, at the moment, requires 3,324 million liters of water a day (MLD) while what it gets stands closer to 2,034 MLD. Average water consumption in Delhi is estimated at being 240 liters per capita per day (lpcd), which is the highest in the country. The large-scale extraction of groundwater is a result of this widening gap between the demand and supply of water. On the other hand, serious doubts are also being raised about both the quality and quantity of groundwater.

In recent years, the treatment capacities have increased from 42 MGD (million gallons per day) in 1951 to the current production level of 600 MGD to meet the increased demand for water. Despite this, the average current shortfall is about 200 MGD (as calculated using the Delhi Jal Board’s supply norms and average losses estimated at 15%).

The capital already faces a groundwater crisis. Now with a paltry monsoon providing nearly a third less than the average rainfall to Delhi, the crisis will only be aggravated without intensive measures for water conservation or rainwater harvesting are seriously undertaken.

According to the Central Ground Water Board, the current groundwater level varies from 15 to 20 meter below the ground, which previously used to be around 8 to 10 meter. Interaction with Central Ground Water Board (CGWB) officials has revealed that, there are more than 1.5 to 2 lakh private tube wells in Delhi, fetching great quantities of water on a regular basis from the ground reserve and thus causing groundwater depletion. In view of the fast depleting groundwater reserves, Ground Water Board along with PWD and FID has started several groundwater recharging projects.

Rooftop rainwater harvesting is also being given a lot of thrust and several colonies have already, started implementing different mechanisms of water harvesting. However, there is a long way to go. The deficiencies in water availability will further become serious due to the rising temperature of the earth surface and resulting changes in water supply and demand patterns.

Water Availability in a Warming World

Analysis of annual temperature data of Delhi for last 17 years shows an increasing trend. The seasonal temperature trend for summer or pre-monsoon has been shown in figure; it is an upward trend.

The figure also shows water demand and supply trend over the past 50 years. It is observed that water deficit is increasing over the years. Increase in the water deficit may be due to population growth, urbanization, and industrialization of the city.

The increase in temperature will further alter the water demand and supply patterns. With increase in temperature the demand of water for various usages goes up whereas the supply does not show any increase thus widening the gap between water supply and demand.

Global climate change portends shifts in water demand and availability which may damage or cause inter-sectoral water reallocation in water short regions. An increase in temperature will cause an increase in water demand for irrigation and municipal use, but would also increase evaporation, lowering runoff and in turn ground water recharge. The overall results indicate that changes in climatic conditions reduce water resource availability and increase water demand. Reduced water availability or increased water demand caused by climate change could exacerbate regional water scarcity.

Reduced water supplies would place additional stress on people, agriculture, and the environment. Climate change will exacerbate the stresses caused by pollution and by growing populations and economies. The impact of climate change on water resources depends not only on changes in the volume, timing and quality of stream flow and recharge, but also on system characteristics, the changing pressures on the system, how the management of the system evolves, and what adaptations to climate change are implemented.