On the other hand, different regions of India are now facing several problems in
respect to the chemical composition of groundwater and its suitability for drinking
purposes and irrigation uses (Singh 2015). Arsenic contamination is prevalent in the
Ganga–Brahmaputra basin; high levels of fluoride, salinity, nitrate, chlorides, and
iron are encountered in several areas; and microbial contamination affects shallow
aquifers throughout the country (CGWB 2011; Singh 2015; Singh et al. 2017). In
2015, of 720 districts in India, EC (salinity), chloride, fluoride, iron, arsenic, and
nitrate concentrations in groundwater of shallow aquifers beyond the permissible
limits of the BIS standard is found in districts 166, 86, 191, 276, 27, and 337, respectively (CGWB 2018). The overall groundwater quality of this country is slowly but
surely declining everywhere because of contamination, overexploitation, or both,
associated with urban, industrial, and agricultural activities (CPCB 2008).
Potential Impact of Climate Change on Groundwater
The recent global trend of climate change, leading to changes in precipitation,
temperature, and evapotranspiration rate, exhibits its deep impact on the quantity
and quality of both surface and subsurface water (Panwar and Chakrapani 2013;
Green 2016). The relationship between changes in climatic variables and groundwater is considered more complicated than its relationship with surface water as
residence time of groundwater can range from days to tens of thousands of years,
which postpone and diffuse the effects of climate change (Holman 2006; IPCC 2007;
Chen et al. 2004; Green 2016). However, as part of the hydrological cycle it can be
predicted that changes in precipitation pattern and evapotranspiration rate will affect
the groundwater system through alteration in the process of recharge potentiality
because of changes in the nature of interactions between groundwater and surface
water systems and changes in groundwater use (Kumar 2014).
Todd divided the subsurface occurrence of groundwater into two zones: zone of
aeration and zone of saturation (Todd 1980). The zone of aeration consists of
interstices that are occupied partially by water and partially by air. In contrast, in
the zone of saturation all interstices are filled with water and hydrostatic pressure
(Todd 1980). The possible impacts of the changing patterns of climatic variables are
dominant on these two vertical layers of groundwater in different geographical
settings.
Vadose water occurs in the zone of aeration, which may be further subdivided
into the soil water zone, intermediate vadose zone, and capillary zone (Todd 1980).
Broadly, less infiltration, high evapotranspiration, and high runoff have a great
negative impact in the water availability of this upper part of the vadose zone,
which may be termed the soil water zone (Panwar and Chakrapani 2013).
Increase in surface temperature leads to a rise in groundwater temperature, which
affects pore water chemistry, residence time, and volume of water in matrix and
fractures, finally determining the composition of groundwater (Glassley et al. 2003;
Panwar and Chakrapani 2013). The effects vary from aquifer to aquifer, and region
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S. Mukhopadhyay and A. K. Mandal
respect to the chemical composition of groundwater and its suitability for drinking
purposes and irrigation uses (Singh 2015). Arsenic contamination is prevalent in the
Ganga–Brahmaputra basin; high levels of fluoride, salinity, nitrate, chlorides, and
iron are encountered in several areas; and microbial contamination affects shallow
aquifers throughout the country (CGWB 2011; Singh 2015; Singh et al. 2017). In
2015, of 720 districts in India, EC (salinity), chloride, fluoride, iron, arsenic, and
nitrate concentrations in groundwater of shallow aquifers beyond the permissible
limits of the BIS standard is found in districts 166, 86, 191, 276, 27, and 337, respectively (CGWB 2018). The overall groundwater quality of this country is slowly but
surely declining everywhere because of contamination, overexploitation, or both,
associated with urban, industrial, and agricultural activities (CPCB 2008).
Potential Impact of Climate Change on Groundwater
The recent global trend of climate change, leading to changes in precipitation,
temperature, and evapotranspiration rate, exhibits its deep impact on the quantity
and quality of both surface and subsurface water (Panwar and Chakrapani 2013;
Green 2016). The relationship between changes in climatic variables and groundwater is considered more complicated than its relationship with surface water as
residence time of groundwater can range from days to tens of thousands of years,
which postpone and diffuse the effects of climate change (Holman 2006; IPCC 2007;
Chen et al. 2004; Green 2016). However, as part of the hydrological cycle it can be
predicted that changes in precipitation pattern and evapotranspiration rate will affect
the groundwater system through alteration in the process of recharge potentiality
because of changes in the nature of interactions between groundwater and surface
water systems and changes in groundwater use (Kumar 2014).
Todd divided the subsurface occurrence of groundwater into two zones: zone of
aeration and zone of saturation (Todd 1980). The zone of aeration consists of
interstices that are occupied partially by water and partially by air. In contrast, in
the zone of saturation all interstices are filled with water and hydrostatic pressure
(Todd 1980). The possible impacts of the changing patterns of climatic variables are
dominant on these two vertical layers of groundwater in different geographical
settings.
Vadose water occurs in the zone of aeration, which may be further subdivided
into the soil water zone, intermediate vadose zone, and capillary zone (Todd 1980).
Broadly, less infiltration, high evapotranspiration, and high runoff have a great
negative impact in the water availability of this upper part of the vadose zone,
which may be termed the soil water zone (Panwar and Chakrapani 2013).
Increase in surface temperature leads to a rise in groundwater temperature, which
affects pore water chemistry, residence time, and volume of water in matrix and
fractures, finally determining the composition of groundwater (Glassley et al. 2003;
Panwar and Chakrapani 2013). The effects vary from aquifer to aquifer, and region
146
S. Mukhopadhyay and A. K. Mandal