chronological variations, complex tectonic framework, climatological dissimilarities, and various hydrochemical conditions lead to the complicated behavior of
the groundwater system in India (Jha 2007).
The various rock formations with distinctive hydrogeological characteristics act
as different aquifer systems of various dimensions (CGWB 2017). Based on the
hydrogeological characteristics, the whole country has been categorized into 14 Principal Aquifer Systems and 42 Major Aquifers by the Central Groundwater Board of
India (CGWB 2011). Alluvium is the most important aquifer system, covering a
maximum area of about 30% of the entire country in the Indus–Ganga–Brahmaputra
basin areas. Around 20% of the area of the country is covered by banded gneissic
complex (BGC) and gneiss aquifers, which are accessible in almost all the peninsular
states as well as the Himalayan states. The basalt aquifer, sandstone aquifer, shale
aquifer, and limestone aquifer cover about 16%, 8%, 7%, and 2% of the area of the
country, respectively. The rest (17%) of the entire area of India is covered by other
aquifers: schist, granite, quartzite, charnockite, khondalite, laterites, and intrusive
(Fig. 6.2).
Following GEC-2015 norms, the CGWB have estimated total annual groundwater recharge for the entire country as 432 billion cubic meters (BCM). After
subtracting the total natural discharge of 39 BCM, the total annual extractable
groundwater resources of the whole country have been estimated as 393 BCM
(CGWB 2019a). Monsoon rainfall has been assessed as the main source of groundwater recharge, contributing about 58% (251.9 BCM) to total annual groundwater
recharge. Overall, 67% (288.2 BCM) of annual groundwater recharge occurs from
annual rainfall, both in monsoon and non-monsoon periods, and 33% (143.6 BCM)
of annual recharge is caused from other sources: canal seepage, return flow from
irrigation, recharge from tanks, ponds, and water conservation structures. Unit
recharge of groundwater (meters) is higher (>0.25 m) in the Indus–Ganga–Brahmaputra alluvial belt in north, east, and northeast India covering the Punjab, Haryana,
Uttar Pradesh, Bihar, and West Bengal states and the valley areas of the northeastern
states from the occurrences of sufficient rainfall and the presence of recharge
supportive unconsolidated alluvial formations. In the coastal alluvial belt, particularly on the east coast, recharge intensity is also higher. However, in western India,
central India, and major parts of peninsular India, annual groundwater recharge is
lower (<0.25 m) because less rainfall occurs and the hard rock terrain is unfavorable
for infiltration (Tables 6.2 and 6.3).
Currently, groundwater depletion has become a major threat to the country,
caused by its overextraction for irrigation and domestic purposes. As per estimation
of CGWB, 248.69 BCM groundwater was extracted in India in 2017, about 89%
(221.5 BCM) of which is utilized for irrigation (CGWB 2019a). Currently
(2014–2015), groundwater contributes to irrigation of 42.9 million hectares
(ha) (63%) net irrigated area of the country whereas in 1950–1951 only 5.9 million
ha (29%) agricultural land was irrigated from this source (Fig. 6.3, Table 6.4). So,
within the span of 65 years, the groundwater-dependent net irrigated area of the
country has increased more than sevenfold and the proportion of groundwater
irrigation to total irrigated area has essentially doubled. This rapid acceleration of
groundwater use for irrigation purposes is facilitated by the huge improvement in
6 Impact of Climate Change on Groundwater Resource of India: A Geographical. . .
133
the groundwater system in India (Jha 2007).
The various rock formations with distinctive hydrogeological characteristics act
as different aquifer systems of various dimensions (CGWB 2017). Based on the
hydrogeological characteristics, the whole country has been categorized into 14 Principal Aquifer Systems and 42 Major Aquifers by the Central Groundwater Board of
India (CGWB 2011). Alluvium is the most important aquifer system, covering a
maximum area of about 30% of the entire country in the Indus–Ganga–Brahmaputra
basin areas. Around 20% of the area of the country is covered by banded gneissic
complex (BGC) and gneiss aquifers, which are accessible in almost all the peninsular
states as well as the Himalayan states. The basalt aquifer, sandstone aquifer, shale
aquifer, and limestone aquifer cover about 16%, 8%, 7%, and 2% of the area of the
country, respectively. The rest (17%) of the entire area of India is covered by other
aquifers: schist, granite, quartzite, charnockite, khondalite, laterites, and intrusive
(Fig. 6.2).
Following GEC-2015 norms, the CGWB have estimated total annual groundwater recharge for the entire country as 432 billion cubic meters (BCM). After
subtracting the total natural discharge of 39 BCM, the total annual extractable
groundwater resources of the whole country have been estimated as 393 BCM
(CGWB 2019a). Monsoon rainfall has been assessed as the main source of groundwater recharge, contributing about 58% (251.9 BCM) to total annual groundwater
recharge. Overall, 67% (288.2 BCM) of annual groundwater recharge occurs from
annual rainfall, both in monsoon and non-monsoon periods, and 33% (143.6 BCM)
of annual recharge is caused from other sources: canal seepage, return flow from
irrigation, recharge from tanks, ponds, and water conservation structures. Unit
recharge of groundwater (meters) is higher (>0.25 m) in the Indus–Ganga–Brahmaputra alluvial belt in north, east, and northeast India covering the Punjab, Haryana,
Uttar Pradesh, Bihar, and West Bengal states and the valley areas of the northeastern
states from the occurrences of sufficient rainfall and the presence of recharge
supportive unconsolidated alluvial formations. In the coastal alluvial belt, particularly on the east coast, recharge intensity is also higher. However, in western India,
central India, and major parts of peninsular India, annual groundwater recharge is
lower (<0.25 m) because less rainfall occurs and the hard rock terrain is unfavorable
for infiltration (Tables 6.2 and 6.3).
Currently, groundwater depletion has become a major threat to the country,
caused by its overextraction for irrigation and domestic purposes. As per estimation
of CGWB, 248.69 BCM groundwater was extracted in India in 2017, about 89%
(221.5 BCM) of which is utilized for irrigation (CGWB 2019a). Currently
(2014–2015), groundwater contributes to irrigation of 42.9 million hectares
(ha) (63%) net irrigated area of the country whereas in 1950–1951 only 5.9 million
ha (29%) agricultural land was irrigated from this source (Fig. 6.3, Table 6.4). So,
within the span of 65 years, the groundwater-dependent net irrigated area of the
country has increased more than sevenfold and the proportion of groundwater
irrigation to total irrigated area has essentially doubled. This rapid acceleration of
groundwater use for irrigation purposes is facilitated by the huge improvement in
6 Impact of Climate Change on Groundwater Resource of India: A Geographical. . .
133