Groundwater is the world’s most mined and primary resource for sustaining agricultural, industrial, and domestic activities in many arid and semiarid regions globally (V. Steenbergen et al. 2015; W. Yin et al. 2018). Groundwater supplies over 2 billion people globally with domestic and agricultural water, especially in dry regions, making it crucial for agriculture and domestic use (Ukasha et al., 2023). Groundwater is vital for rivers because it maintains a steady base flow during dry times (Kahil et al., 2018). It functions as a natural buffer against floods and droughts and supports ecosystems (Wada et al., 2010). Global groundwater faces stress from over-extraction, climate-change and depletion. Examples of aquifers that are being depleted by intensive agriculture are the North China Plain and the Ogallala Aquifer (Gong et al., 2018; Scanlon et al., 2012). However, the over-extraction of groundwater and the imbalance between water recharge and discharge has led to a decrease in groundwater levels over the last few decades. The Bangkok Basin's land subsidence demonstrates the geological effects of excessive groundwater extraction (Bremard, 2022). The continuous abstractions, in high quantities, can adversely affect the overall water balance when the average value consistently exceeds the recharge over a long period (Cheema et al., 2014). Sustainable management of groundwater resources is therefore very important for food security and the betterment of the livelihoods of the large population living in rural areas (K. Ahmed et al., 2019). One of the biggest issues in groundwater management is comprehending spatiotemporal dynamics. According to (Munagapati et al., 2021), it is critical to take fluctuations in groundwater storage into account. The impact of human-induced alterations on dynamics is highlighted by (Fan et al., 2013). These insights highlight the necessity of advanced methodologies and a holistic approach in sustainable groundwater management.
Pakistan, the sixth most populated country, has been among those most at risk from the negative effects of climate change (Dars et al., 2021). Under climate change and increasing water demands, groundwater depletion has become regional and global threats for water security, which is an indispensable target to achieving sustainable developments of human society and ecosystems, especially in arid and semiarid regions where groundwater is a major water source (Hu et al., 2019). Understanding the spatio-temporal variations in groundwater storage is essential for effective groundwater management and sustainable resource planning. Pakistan’s diverse hydrological landscape, couples with challenges of climate variability and rapid population growth, necessitates comprehensive and accurate insights into groundwater dynamics. The spatio-temporal variations in groundwater storage across Pakistan are missing. Groundwater is indeed a valuable resource in Pakistan, that is essential for supplying domestic, industrial, and agricultural demands. Pakistan’s primary water sources are surface water and groundwater, but unfortunately, the country’s water storage has been severely strained by the agricultural and industrial sectors excessive water use due to hasty growth in population (Nadeem et al., 2023). The agricultural sector is the largest user of groundwater for agricultural production in Pakistan (Iqbal et al., 2017). In Pakistan, more than 60% of the population utilizes groundwater for drinking purpose (Solangi et al., 2017). Pakistan faces water scarcity problem in the last decades due to increased water demands (Memon et al., 2020). The long-term viability of Pakistan's groundwater resources has come under scrutiny in light of this circumstance. As we fulfil the current water demands, it is crucial to properly regulate groundwater use to protect this priceless resource for future generations.
In-situ observations and modelling are used to study spatio-temporal dynamics of the groundwater (Frappart et al., 2019); however, these methods have drawbacks such as restricted coverage and resource limits (Castellazzi et al., 2016; Lin et al., 2019). The limited coverage and resource limits of in-situ observations provide challenges, and the simplifications and uncertainties in modelling of complicated groundwater dynamics may impose restraints. On the other hand, remote sensing provides continuous global scale observations and sometimes with no too little cost. In addition to conventional techniques, remote sensing is an essential instrument for comprehending dynamic Earth processes, despite obstacles such as resolution trade-offs. Advancements in remote sensing present viable approaches to tracking and assessing groundwater supplies on a regional basis (Adams et al., 2022). Specifically, the Gravity Recovery and Climate Experiment (GRACE) satellite mission offers a means of measuring variations in Earth's gravity field, which have been used to evaluate spatiotemporal variations in groundwater storage in different regions of the world (Su et al. 2020; Ali et al. 2022; Akhtar et al. 2022). The goal of the dedicated satellite project GRACE is to map the Earth's gravity field every thirty days at a spatial resolution of 400–40,000 km (Tapley et al., 2004). The Total Water Storage Anomaly (TWSA), which includes Surface Water Storage (SWS), Soil Moisture Storage (SMS), and Groundwater Storage (GWS), is evaluated using GRACE which provides insights into surface water, soil moisture, and groundwater dynamics for water resource management by using gravity variations to estimate changes in TWSA. The GRACE mission uses Earth's gravitational field measurements to monitor monthly changes in terrestrial water storage, potentially filling the observational gap in regional water storage change (Strassberg et al., 2009).
According to available research, a mix of anthropogenic activities like groundwater extraction and natural factors like climatic fluctuation, affect Pakistan's groundwater storage changes. But, there are still gaps and groundwater monitoring and analysis at province-level is limited and hence this study as a GRACE-based GWS will provide an integrated assessment to groundwater variations in the provinces. The main goal of this study is to investigate the spatiotemporal groundwater storage variations in an agro-ecologically diverse Pakistan from 2003 to 2022. Understanding the spatiotemporal groundwater variations in Pakistan is essential for ensuring water security, enhancing agricultural practices, adapting to climate change, protecting ecosystems, reducing the impact of natural disasters, guiding urban planning, and developing efficient policies. This study will enhance the understanding of groundwater dynamics and contribute to sustainable water resource management in Pakistan. Mainly focus at the provincial levels, provincial groundwater analysis offers a focused comprehension of regional differences, fits well with administrative frameworks, enables regional resource management, improves collaboration with local partners for practical solutions and uniquely aligns with the National Water Policy, by focusing on regional dynamics, study’s analysis supports decentralized water management, echoing the policy's call for tailored provincial strategies. This study serves as a vital baseline for policy formulation and decision-making, contributing directly to the policy's emphasis on provincial autonomy in developing integrated water resource management (IWRM) approaches.