GROUNDWATER ACCUMULATION IN NORTHWEST INDIA AND PAKISTAN IN THE 20TH CENTURY

Northwest India and central Pakistan are vital for food production in South Asia. The region has a long history of major surface and, more recently, groundwater development for irrigation and have become global hotspots of groundwater exploitation. The Gravity Recovery and Climate Experiment (GRACE) satellites, launched in 2002, provide evidence of the scale of groundwater depletion. More recently studies have shown that groundwater depletion is regionally heterogenous and is influenced by a combination of human and climatic factors, including changes in monsoon precipitation and recharge from the regions vast canal network. The areas of most concern for the long-term sustainability of the transboundary aquifer are within the states of Punjab and Haryana in India and Punjab Province in Pakistan.

Recent depletion is set within a much longer history of groundwater level variation spanning the last 150 years. Using a unique long-term dataset, we investigated groundwater level change throughout the 20^th century and the first decade of the 21^st. The dataset contains time-series from 4028 observation wells and includes 110 years of groundwater level data from 1900 to 2010. Our aim was to: 1) examine changes in post-monsoon groundwater levels during the 20^th century and; 2) unravel the influence of canal construction, tubewell development and precipitation on long-term groundwater storage in northwest India and central Pakistan.

We found that for the majority of the 20^th century groundwater levels were rising and estimated net groundwater accumulation of c.350 km³ (150-450 km³). Large scale irrigation development via canal construction played a defining role in groundwater accumulation during the early twentieth century. The groundwater depletion that occurred in the first decade of the 21^st century, and which we estimate at c.75 km³(estimated range: 25-100 km³), was driven by the superimposed effects of low rainfall and large-scale tubewell development. However, between 1970–2000, when large increases in tubewell irrigation began, groundwater levels stabilised as a result of higher than average rainfall. Our study clearly demonstrates that human activity in the early 20^th century increased the total volume of groundwater available prior to the large-scale exploitation that began in the late 20^th century.