New Advances of Space Gravimetry in Climate and Hydrology Studies

Dear Colleagues,

Space gravity emerged as an operational science with the launch of the GRACE mission on 17 March 2002. This mission was a worldwide success, making it possible to measure the Earth's variable gravity field in great detail. It has also made it possible to monitor continental waters and the hydrological cycles of the world's largest water basins. This variable field, once transformed into equivalent water height, made it possible to monitor continental and oceanic waters and the hydrological cycles of the world's largest drainage basins. This mission ended in 2017 and was replaced on 22 May 2022 by GRACE FOLLOW-ON, which had very similar characteristics. If we cannot improve the accuracy of the measurements, we can try to improve spatial resolution by replacing classic spherical harmonic functions with local functions such as mascon or Slepian functions.

The results obtained in this field are quite impressive. We propose showing the most recent and innovative advances in the field, whether for storm monitoring, intermediate-scale catchment areas or groundwater monitoring.

The aim of this Special Issue is to highlight innovative approaches that combine different remote sensing missions with gravimetry missions (GRACE/ GRACE-FO) to improve our understanding of global hydro-climatic phenomena.

This involves several innovations to improve the spatial resolution (Li et al., 2017; Ramillien et al., 2021; Kvas et al., 2024) and/or temporal resolution (Eiker et al., 2020). These improvements can also incorporate approaches based on AI techniques (Ali et al., 2024).

These contributions should lead to a better understanding of hydro-climatic phenomena (storms, droughts, floods, sea level rise, steric sea level, etc.), which are strongly impacted by climate change, both in terms of intensity and recurrence. The forecasts and warning systems associated with these phenomena could also be pointed out.

Another important point is the integration of these data into global hydrological models, such as for oceanic hydrology (ocean circulation (OGCMs), hydrodynamic modelling (FVCOM; Chen et al., 2006)); for continental hydrology (WGHM (Döll et al., 1997) or GLDAS (Rodell et al., 2004)); or, more recently, HydroPY (Stake et Hagemann, 2021) to improve the estimation of river discharges, which are often overestimated (Heinicke et al., 2024).

Therefore, we welcome articles that address, but are not limited to, the following topics:

• GRACE (FO) local solutions;
• GRACE (FO) improvements using AI systems;
• Ocean circulation;
• Hydrodynamic models;
• Sea level rise;
• Extreme hydro-climatic events;
• Continental hydrology;
• Climate change;
• Floods and droughts;
• Groundwater monitoring;
• Warning systems.

Dr. José Darrozes
Dr. Guillaume Ramillien
Dr. Lucia Seoane
Guest Editors

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