A framework for surface water and groundwater modeling by multiple satellites.

A comprehensive understanding of renewable water resources, including surface water and groundwater, is crucial for human sustenance, societal advancement, and ecosystem well-being at both local and global levels. Remote sensing technology offers an opportunity to rapidly and conveniently monitor inland water resources on a large scale. This study presents a framework for modeling water storage changes by integrating data from multiple satellites. Specifically, the GRACE and GRACE-FO gravity satellites are utilized to observe changes in terrestrial water storage (TWS), while the Landsat multispectral and ICESat / ICESat-2 altimetry satellites are employed to simulate changes in surface water storage (SWS). Groundwater changes are calculated by subtracting SWS and soil moisture storage (SM) from TWS, with SM data obtained from GLDAS 2.1. The innovation of this framework lies in the improved simulation of surface water, facilitated by the fine resolution of ICESat-2, enabling the establishment of an area-elevation relationship for very small water bodies (< 1 km²). This framework does not account for variations in river channel storage, making it suitable for regions where river discharge can be disregarded. The framework is applied to four provinces or cities in the North China Plain, where water scarcity constrains the demand of drinking water, irrigation, and environment. The study reveals a decrease in TWS from 2002 to 2020 in the study area. Although surface water increased following the operation of the Middle Route of the South-to-North Water Diversion Project in December 2014, groundwater continued to decline until 2020 and remained stable from 2020 to 2022. This study represents the first use of 4-year ICESat-2 data to monitor water bodies of all sizes (from <1 km² to >100 km²). Leveraging the exceptional capability of ICESat-2 data in modeling small water bodies, this study advances the prospect of achieving a comprehensive simulation of inland water resources.