# GRACE/GFO and Swarm Observation Analysis of the 2023-2024 Extreme Drought in the Amazon River Basin
## 6 Conclusions  
In this study, we employed comprehensive data comprising satellite gravity measurements, extreme climate, and atmosphere movement to conduct a holistic analysis of the 2023 extreme drought in the ARB. Our investigation dissected the drought's formation through multifaceted lenses: extreme climatic, atmospheric movement, water vapor transport dynamics, and anthropogenic influences. The key findings are summarized as follows. 1. This extreme drought, ranked as the fourth-most severe in the ARB since 2003, exhibited a six-month duration with a drought peak of \(-\)1.29 and a drought severity index of \(-\)5.62. Initiating in the northwestern subregion, the drought propagated eastward and southward, eventually encompassing the entire basin. The eastern sector suffered the most pronounced impacts, characterized by the largest depletion of TWS. 2. Spatially, the 2023 drought's footprint mirrored that of the 2015-2016 event, yet featured distinct temporal-severity metrics: it had the longest duration and highest severity in the basin's eastern domain alongside the most significant water storage deficit in that region. While the 2015-2016 drought exhibited greater overall severity, both events recorded comparable peak drought indices: the former endured for 14 months, contrasting with the 2023 drought's six-month duration. 3. The direct causes of the drought are reduced PRE and increased temperatures. However, this drought is closely linked to the El Nino event that occurred in June 2023. The El Nino event led to an abnormal intensification of atmospheric descending movements in the ARB by altering the Walker circulation, thereby resulting in reduced PRE and rising temperatures. Additionally, extensive deforestation of the Amazon rainforest due to human activities has also contributed to and exacerbated drought severity. The GRACE/GFO satellites, which monitor TWSC via gravity field variations, have a spatial resolution of \(\sim\)330 km. This coarse resolution hinders their ability to resolve fine-scale hydrological dynamics in the ARB's complex topography, including Andean slopes, alluvial plains, and floodplains, where groundwater recharge, soil moisture, and transpiration exhibit heterogeneous drought responses. Additionally, the 21-year data(2002-present) are insufficient to characterize multi-decadal climate modes (e.g., the 60- to 80-year Atlantic Meridional Mode), limiting our ability to distinguish long-term drought trends from short-term anomalies. To address these constraints, future research will focus on two key initiatives: (1) spatial downscaling: employ deep learning to integrate high-resolution hydrometeorological data, enhancing GRACE TWSC resolution from 330 km to <50 km to capture subregional drought processes; and (2) temporal extension: use deep learning algorithms with long-term precipitation and temperature records to reconstruct pre-2002 TWSC data, extending the data to better resolve climate mode cycles. Additionally, quantifying the contributions of individual drought drivers--an unresolved challenge in hydrology--will be a critical focus for subsequent studies, bridging gaps in mechanistic understanding and predictive capabilities. Our research results have transformed the previous simple analysis of observational data. By integrating multidisciplinary data, we have achieved a closed-loop study of drought events encompassing observation verification, mechanism analysis, and process reconstruction. This provides a multidimensional evidence chain for understanding the dynamics of terrestrial water storage under extreme climate events and also offers a new perspective and method for drought research based on satellite gravity data. Conceptualization, L.C. and J.Z. ; methodology, L.C. ; data curation, J.Z. ; writing--original draft preparation, L.C. ; writing--review and editing, L.C. and C.Y. ; visualization, Y.L. ([PERSON]); supervision, J.M. ; project administration, Y.L. ([PERSON]); funding acquisition, Z.Z.