Spatiotemporal water dynamics and micro-administrative (Hobli) scale storage variations in the coastal area of Mangaluru Taluk, India: a geospatial approach for sustainable water management

ABSTRACT The Mangaluru coastal region of India faces increasing water management challenges due to rapid urbanisation, industrial growth, and climatic variability. This research investigates spatiotemporal variations in Terrestrial Water Storage (TWS) and Groundwater Storage (GWS) over two decades (2003–2022) using Gravity Recovery and Climate Experiment (GRACE) data integrated within the Google Earth Engine (GEE) platform. Trends were analysed at the hobli (micro-administrative) level using the Modified Mann–Kendall (MMK) test, Innovative Trend Analysis (ITA), and Empirical Orthogonal Function (EOF) with Principal Component Analysis (PCA). In-situ groundwater monitoring well data (2000–2019) were incorporated to validate satellite estimates. Results reveal significant seasonal variability: winter and post-monsoon generally exhibit increasing storage, while pre-monsoon and monsoon often show declines. Lag correlation analysis indicates delayed responses of +2 years during recharge seasons, reflecting hydrogeological controls. Well data confirm long-term groundwater depletion, with fluctuations rising from 9.41 mbgl in 2000 to 16.8 mbgl in 2019. Land-use change and rising water demand further exacerbate pre-monsoon scarcity. The integrated analysis highlights the complementary role of satellite and ground observations in capturing storage variability. Findings underscore the need for hobli-level monitoring and adaptive water management strategies to ensure sustainability in rapidly urbanising coastal regions.