Depleting groundwater adding to city’s increasing heat

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Depleting groundwater adding to city’s increasing heat

Avishek Sengupta | June 30, 2018 15:25 hrs

GUWAHATI: With the city’s temperatures soaring higher every passing year, besides pollution and irregular monsoon, reports indicate that the depleting groundwater in the city is also one of the reasons for the same.

According to Central Ground Water Board (CGWB) that has its northeast branch at Bethkuchi here, groundwater acts as a natural coolant.

“Consider the groundwater as a natural coolant. It consists mostly of the rainwater that the soil soaks in and it runs underground like a stream. Along with the rainfall cycle, the groundwater level naturally goes up during the summers when it rains and dries up a bit in the winters when the rain is scanty. Hence, when it is hottest in the summers, the groundwater stabilizes the heat that the soil soaks in and cools the environment at night. This balance has been destabilized with the fast depletion of groundwater,” a scientist at CGWB said.

As per a report of the CGWB published in 2013, the groundwater resources in greater Kamrup – Kamrup (Metro) and Kamrup (Rural) districts – is still under ‘Safe’ category. The annual dynamic groundwater resources as in 2009 are estimated to be 1,847.29 million cubic metres while the net annual ground water consumption is 715.97 million cubic metres of which, 43 per cent is renewed every year. But when the rise in water consumption concentrated in the urban areas is considered, the scenario is worrisome, CGWB said.

“The water renewal of the groundwater channels mostly depends on the porousness of the soil. Unlike Kamrup (Rural), about 70 per cent of Kamrup (Metro) has hard-to-penetrate granite rocks while only the Brahmaputra river bank areas consist of porous new and old alluvial soil. Hence, the renewal rate is much lesser. But the consumption here is much higher,” the scientist said.
The consumption, since 1980 till 2010, has increased four times and is expected to further double by 2020.

About 70 per cent of the city is dependent on the groundwater as the Guwahati Municipal Corporation (GMC) is able to provide water to only 30 per cent of the city’s population. While the city waits for its three ambitious water projects – South Central Guwahati, East and West Guwahati water projects – the continued dependence on groundwater is fast depleting the reserve.

While the fast depleting groundwater reserve is an issue, several international reports and NGOs indicate that the heating of the groundwater reserve too adds as an insulator. This was first revealed in a report published by ETH Zurich and further backed in another by Nature Geoscience.

The reports, based on a datasets of 40 years of observation of climate change and groundwater movement, demonstrated that global warming is directly reflected in the groundwater temperatures up to 60 meters below the surface.

“This sets motion to a much more harmful chain of climate change. As the excessive heat in and around the city puts off the prospects of rains, it leads to the further depletion of groundwater,” Parthojyoti Das, an environmental scientist of Aaranyak, said.

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