# GRACE/GFO and Swarm Observation Analysis of the 2023-2024 Extreme Drought in the Amazon River Basin
## 4 Results
### Drought Process
Figures 9 and 10 show the whole process of the spatiotemporal evolution of this extreme drought and the area percentage, respectively, of the droughts at different levels. In June 2023, most regions in the ARB were in non-drought, and only a few regions in the north and south were in drought, but most of them were light drought (D1, Figure 9a). Starting from July 2023, large regions of drought appeared in the east and north. The DAR had reached 38% (regional drought), and it was mainly composed of light and moderate droughts (D1 and D2, Figure 9b). In August 2023, the drought continued to develop, and the DAR expanded to 45.82%, which was close to the critical point (50%, territorial drought). Its influence had almost covered most of the east and north (Figure 9c). By September 2023, this drought finally evolved into a territorial drought (60%), covering all regions except the southeast. The exceptional drought (D5, 1.67%) occurred in the northwest (Figure 9d). In October 2023, the drought area continued to expand (69%, territorial drought) and the drought severity regions began to shift from the east to the west (Figure 9e). In November 2023, the DAR of drought reached its peak (93%), and only a very small region in the south was not affected by the drought. The drought severities in the north were \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Event**} & \multirow{2}{*}{**Time Span**} & **Duration** & \multicolumn{3}{c}{**GRACE-DSI**} & \multirow{2}{*}{**Previous Studies**} \\  & & **(Months)** & **Peak** & **Average** & **Drought** & **Validation (Y/N)** \\ \hline
1 & 200506–200510 & 5 & \(-0.88\) & \(-0.75\) & \(-3.75\) & Y [61] \\
2 & 201004–201101 & 10 & \(-1.15\) & \(-0.86\) & \(-8.64\) & Y [18] \\
3 & 201511–201612 & 14 & \(-1.66\) & \(-1.06\) & \(-14.79\) & Y [28] \\
4 & 201709–201805 & 9 & \(-1.10\) & \(-0.74\) & \(-6.67\) & Y [29] \\
5 & 202009–202011 & 3 & \(-0.85\) & \(-0.69\) & \(-2.07\) & Y [62] \\
6 & 202309–202402 & 6 & \(-1.29\) & \(-0.94\) & \(-5.62\) & Y \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Summary table of drought events. Figure 8: Time series of the monthly GRACE-DSI and P-ET in the ARB during January 2003 and February 2024.  
still higher than that in the south, and the extreme and exceptional droughts (D4 and D5) had begun to spread to the south: their area percentages were 4% and 25%, respectively (Figure 9f). In December 2023, the region severely affected by the drought had obviously shifted. The drought in the east began to gradually subside and the drought severity in the north began to weaken, while the drought severity in the southeastern suddenly increased. The exceptional drought (D5) was mainly concentrated here, and its area percentage reached 8% (Figure 9g). In January 2024, both the DAR and drought severity had subsided to varying degrees. The DAR decreased by 3%. The area percentage of the extreme and exceptional droughts (D4 and D5) decreased by 18% and 7%, respectively, and they were shrinking to the south (Figure 9h). In February 2024, the DAR shrunk further (74%), and the drought was dominated by moderate drought (D2). The extreme and exceptional droughts (D4 and D5) had shrunk significantly, but they were still concentrated in the southeast (Figure 9i). Figure 10: Percentages of different drought severity in the ARB during June 2023 and February 2024. Figure 9: Spatiotemporal distribution of drought in the ARB during June 2023 and February 2024. We compared the drought characteristics of the three extreme droughts in the study period with those of the current drought (Figure 11). In this drought, the drought duration shows a spatial distribution characterized by a long duration in the northeast and a short one in the southwest, with the longest drought duration in the northeast and parts of southwest (6 months) and only 1 month in a small part of the south (Figure 11d). This is similar to the spatial distribution of drought duration for the 2015-2016 drought, but the 2015-2016 drought had a longer duration (Figure 11b).