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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 20th century and the first decade of the 21st. 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 20th 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 20th 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 21st 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 1

In Europe, it is estimated that around 65 % of drinking water is extracted from groundwater. Worryingly, groundwater drought events (defined as below normal groundwater levels) pose a threat to water security. Groundwater droughts are caused by seasonal to multi-seasonal or even multi-annual episodes of meteorological drought during which the drought propagates through the river catchment into the groundwater system by mechanisms of pooling, lagging, and lengthening of the drought signals. Recent European drought events in 2010–2012, 2015 and 2017–2018 exhibited spatial coherence across large areas, thus demonstrating the need for transboundary monitoring and analysis of groundwater level fluctuations. However, such monitoring and analysis of groundwater drought at a pan-European scale is currently lacking, and so represents a gap in drought research as well as in water management capability. To address this gap, the European Groundwater Drought Initiative (GDI), a pan-European collaboration, is undertaking a large-scale data synthesis of European groundwater level data. This is being facilitated by the establishment of a new network to co-ordinate groundwater drought research across Europe. This research will deliver the first assessment of spatio-temporal changes in groundwater drought status from ∼1960 to present, and a series of case studies on groundwater drought impacts in selected temperate and semi-arid environments across Europe. Here, we describe the methods used to undertake the continental-scale status assessment, which are more widely applicable to transboundary or large-scale groundwater level analyses also in regions beyond Europe, thereby enhancing groundwater management decisions and securing water supply.