Why Fans Matter: Groundwater Abstraction and Decline in Northwestern India

Alexander Densmore, Professor, Institute of Hazard, Risk, and Resilience and Department of Geography, Durham University

India, the largest agricultural user of groundwater in the world, has seen a revolutionary shift from large-scale surface water management to widespread groundwater abstraction in the last 40 years, particularly in the northwestern states of Punjab, Haryana and Rajasthan. As a result, these states are now a hotspot of groundwater depletion, with the largest rate of groundwater loss in any comparable-sized region on Earth. Despite this, there is no integrated view of the aquifer system in northwestern India, no detailed understanding of the decline in groundwater levels, and no regional-scale conceptual framework with which to understand these changes and forecast the evolution of the system.

In this talk, I describe our efforts to address these shortcomings, using the sedimentological and geomorphological framework of the aquifer system as a guide to its behavior. Groundwater in northwestern India is largely hosted within ancient, buried, sandy former river channels deposited by aggrading, avulsive fan systems. To understand the response of this aquifer system to future stresses, we must first understand its geology and geometry – the locations, sizes, and characteristics of the channels, their ages, and their three-dimensional pattern. The geomorphology of the fan systems provides a first-order framework for assembling and relating data on the aquifer system and its properties. In particular, the geomorphological framework determines key aquifer properties, such as the thickness, proportion, and stacking pattern of sandy channel beds. These properties vary in predictable ways across the study area, and this variation can be used to make testable hypotheses about aquifer characteristics in areas with no existing well data or subsurface information. The detailed pattern of water-level change is influenced by this geomorphological framework, in conjunction with district-level patterns of abstraction and recharge. Future large-scale assessments of aquifer characteristics and groundwater sustainability should adopt a similar framework, so that the widest possible range of surface and subsurface data can be integrated and understood.