Groundwater depletion causing reduction of baseflow triggering Ganges river summer drying.

Area of Science:

• Hydrology and Water Resource Management
• Environmental Science
• Geosciences

Background:

• Recent decades show declining water levels in the lower Ganges River during pre-monsoon summers.
• Observed river water level depletion rates range from -0.5 to -38.1 cm/year (1999-2013).
• This phenomenon is particularly pronounced in lower Indian reaches of the Ganges (Ganga) River.

Purpose of the Study:

• To investigate the relationship between Ganges River depletion and groundwater changes.
• To quantify the reduction in groundwater baseflow contributing to the river.
• To assess the implications of reduced river water availability for the region's population and environment.

Main Methods:

• Analysis of river water level data to determine depletion rates.
• Estimation of groundwater storage changes in the Gangetic aquifers.
• Calculation of baseflow reduction from the 1970s to 2016.

Main Results:

• Ganges River depletion is directly linked to groundwater storage depletion in the Gangetic aquifers (-0.30 ± 0.07 cm/year).
• Groundwater baseflow in lower Ganges reaches has decreased by approximately 59% since the 1970s.
• 2016 baseflow was estimated at ~1.0 × 10^6 m³/d, down from ~2.4 × 10^6 m³/d in the 1970s.

Conclusions:

• Reduced groundwater baseflow is the primary driver of declining Ganges River levels.
• The net reduction in river water poses a significant threat to domestic supply, irrigation, transport, and ecology.
• Water security for over 100 million people is jeopardized, impacting food production and highlighting regional vulnerability.