Groundwater resources in the Indo-Gangetic Basin : resilience to climate change and abstraction

Groundwater within the Indo‐Gangetic Basin (IGB) alluvial aquifer system forms one of the
world’s most important and heavily exploited reservoirs of freshwater. In this study we
have examined the groundwater system through the lens of its resilience to change – both
from the impact of climate change and increases in abstraction. This has led to the
development of a series of new maps for the IGB aquifer, building on existing datasets held
in Pakistan, India, Nepal and Bangladesh, a review of approximately 500 reports and papers,
and three targeted field studies on under‐researched topics within the region. The major
findings of the study are described below.
The IGB groundwater system
1. The IGB alluvial aquifer system comprises a large volume of heterogeneous
unconsolidated sediment in a complex environmental setting. Annual rainfall varies
from <25 mm per annum in southern Pakistan to > 2000mm in the Bengal basin, and the
system is dissected by the major river systems of the Indus, Ganges and Brahmaputra.
The groundwater system has been modified by the introduction of large scale canal
irrigation schemes using water from the Indus and Ganges since the 19th and early 20th
centuries.
2. High yielding tubewells can be sustained in most parts of the alluvial aquifer system;
permeability is often in the range of 10 – 60 m/d and specific yield (the drainable
porosity) varies from 5 – 20%, making it highly productive.
3. High salinity and elevated arsenic concentrations exist in parts of the basin limiting the
usefulness of the groundwater resource. Saline water predominates in the Lower Indus,
and near to the coast in the Bengal Delta, and is also a major concern in the Middle
Ganges and Upper Ganges (covering much of the Punjab Region in Pakistan, southern
Punjab, Haryana and parts of Uttar Pradesh in India). Arsenic severely impacts the
development of shallow groundwater in the fluvial influenced deltaic area of the Bengal
Basin.
4. Recharge to the IGB aquifer system is substantial and dynamic, controlled by monsoonal
rainfall, leakage from canals, river infiltration and irrigation returns. Recharge from
rainfall can occur even with low annual rainfall (350 mm) and appears to dominate
where rainfall is higher (> 750 mm). Canal leakage is also highly significant and
constitutes the largest proportion of groundwater recharge in the drier parts of the
aquifer, partially mitigating the effects of abstraction on groundwater storage.
5. Deep groundwater (>150 m) in the Bengal basin has strategic value for water supply,
health and economic development. Excessive abstraction poses a greater threat to the
quality of this deep groundwater than climate change. Heavy pumping may induce the
downward migration of arsenic in parts of Bangladesh, and of saline water in coastal
regions, but field evidence and modelling both suggest that deep groundwater
abstraction for public water supply in southern Bangladesh is in general secure against
widespread ingress of arsenic and saline water for at least 100 years.