Question.
Discuss the availability of water resources in the country and the factors that determine its spatial distribution.
(NCERT class 12 geography, India People and Economy, Chapter -6 Water resources)
Answer.
India has about 2.45 percent of the world's surface area, 4 percent of the world's water resources, and about 16 percent of the world's population. India receives an average annual rainfall of 118 cm. The total water availability in India from rainfall should be about 4000 cubic km per year. However, due to topography and other constraints, the total usable water resources in the country are only 1122 cubic km out of 4000 cubic km. Out of 1122 cubic km, 690 cubic km of surface water and 432 cubic km of groundwater can be used. There is more surface water available for use than groundwater.
Water resources in India can be classified into three parts:
- surface water resources.
- Groundwater resources.
- Lagoon and Backwater
Surface water resources;
There are four major sources of surface water in India - rivers, lakes, ponds, and tanks. On average, about 1869 cubic km of water flows through the rivers annually. However, due to topography and other constraints, only 690 cubic km of surface water is available for use. Rain and glacial water (eg Himalayan rivers are perennial in nature) are the major sources of water availability in rivers. Himalayan rivers such as the Indus, the Ganges, and the Brahmaputra are perennial in nature, have more rainfall in their basins than other regions, and have large catchment areas, so these rivers have a large annual flow of water.
The Ganges and Brahmaputra basins hold about 46 percent of India's total replenishable water.
Groundwater resources;
The total replenishable annual groundwater resources in the country are about 432 cubic km. Plains such as northern plains and coastal plains are reservoirs of alluvial soils, so they are good for groundwater recharge as rainwater seeps through alluvial soils easily. Therefore, more groundwater is available in the plains than in the plateaus.
Lagoon and backwaters;
Due to the indented nature of the coastline in some states such as Kerala, Odisha, and West Bengal, the lagoon and backwaters have vast water resources which are mainly used for fish farming, and for irrigation purposes for some crops such as paddy and coconut. The lagoon and backwater are salines in nature.
Water resources in India are not evenly distributed, India's water resources are mainly dependent on monsoon rainfall, and monsoon rainfall across India varies in spatially, duration, and intensity.
The following are the factors that determine the spatial distribution of water resources:
- Uneven distribution of rainfall.
- Relief and topography.
- The perennial nature of the river.
- Availability of lagoons and backwaters.
Rain is the main source of water resources in India. Although India's average annual rainfall is about 118 cm, there is great variation in rainfall, both temporal and spatial. Some areas receive heavy rainfall such as Meghalaya (the annual rainfall in Mawsynram is 1187 cm) and some regions receive very little rainfall such as the western part of the Rajasthan region (about 12 to 30 cm are annual). Thus variability in rainfall causes variability in water resources in India.
Relief and topography are also major deciding factors for the uneven distribution of water resources in the country. Plains are good for groundwater recharging as they have deep alluvial deposits that allow surface water to percolate easily into the ground and plains are easily waterlogged, giving more time to seep into the ground. Therefore, groundwater is easily available in plain areas whereas plateauing areas and hilly areas are not favorable conditions for groundwater recharge, so only surface water is available in plateau and hilly areas.
Himalayan rivers are of perennial nature (water flows throughout the year) so in the northern plains, water is available throughout the year, while the peninsular river is seasonal in nature, except during the rainy season, there is a shortage of water in peninsular India.
Some states like Kerala, Gujarat, Odisha, and West Bengal have lagoon and backwater resources that can be used for various purposes like fish farming and irrigation for paddy and coconut, hence these areas have their own distinct advantage.
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