Spatio-temporal analysis of hydrometeorological variables for terrestrial and groundwater storage assessment

Abstract

Groundwater is a vital resource supporting various sectors such as agriculture, industry, and drinking water supplies. Gravity Recovery and Climate Experiment (GRACE) and its follow-on (GRACE-FO) can accurately assess variations in terrestrial water storage (TWS) at a regional scale, exhibiting precise measurements of spatio-temporal variations. This study aims to integrate GRACE/GRACE-FO and hydrometeorological variables to understand groundwater storage trends in Pakistan from 2002 to 2023. Precipitation, soil moisture, temperature, potential evapotranspiration, snow water equivalent, and Normalized Difference Vegetation Index (NDVI) are examined to understand the fluctuations in groundwater storage (GWS). Google Earth Engine (GEE) has been used for data collection and pixel-based Sen's slope analysis. The analysis revealed a consistent decline in terrestrial and groundwater storage in Pakistan over the study period. The soil moisture levels and snow water equivalent have decreased, while the levels of NDVI and precipitation have increased. Between 2002 and 2010, the study area experienced variations in TWS, while after 2012, the region faced severe water scarcity as the TWS decreased to 36 cm over the past 22 years. Trend analysis indicates a significant decline in groundwater storage (GWS) in Punjab province's highly urbanized and irrigated areas, averaging −1.41 cm per year. In contrast, the northern and coastal regions of the study area are experiencing an upward trend in GWS. Additionally, ground validation has been performed, yielding an R² value of 0.31. These findings emphasize the urgent need for effective urbanization policies and informed groundwater management. Implementing water conservation strategies in agriculture is essential to tackle water scarcity throughout Pakistan.