# Impacts of Drought and Heatwave on the Vegetation and Ecosystem in the Yangtze River Basin in 2022
## 3 Results
### The Response of Vegetation and Ecosystem to the 2022 Drought and Heatwave
As an indicator of vegetation photosynthetic rates, SIF better reflects changes in GPP compared to NDVI in terms of both the degree of response and temporal alignment. This can partly explain the conclusion that SIF is more capable of capturing vegetation photosynthesis compared to NDVI. However, in terms of the timing and duration of response, NDVI is more agile in capturing the onset and duration of extreme environmental conditions compared to SIF. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Month** & **ANDVI** & **ASIF** & **AGPP** & **ANEE** \\ \hline January & 5.552 & 12.19048 & \(-\)2.03061 & 20.7616 \\ February & \(-\)1.41054 & \(-\)4.51962 & \(-\)14.14507 & \(-\)23.81739 \\ March & 1.88785 & 19.41702 & 24.68247 & 7.75961 \\ April & 1.26141 & 11.02048 & 5.93509 & \(-\)17.01419 \\ May & 1.47964 & 6.63404 & \(-\)4.70174 & 75.78726 \\ June & 0.65554 & 3.84533 & \(-\)1.02022 & 1.71822 \\ July & \(-\)0.58247 & 4.13018 & 24.58137 & 71.41891 \\ August & \(-\)4.16176 & \(-\)2.17843 & \(-\)2.39262 & 1.40614 \\ September & \(-\)4.35804 & \(-\)8.66621 & \(-\)4.01513 & \(-\)45.23306 \\ October & \(-\)2.46817 & 0.86978 & \(-\)17.39621 & \(-\)3.3217 \\ November & 1.47221 & 12.20108 & 10.10721 & 53.46793 \\ December & \(-\)0.84992 & \(-\)1.02301 & \(-\)4.70653 & \(-\)21.94149 \\ \hline \hline \end{tabular} In this table, the units of all numbers are %.  
\end{table} 
Table 5: The change percentages of NDVI, SIF, GPP, and NEE for the year 2022 compared to the average values from 2018 to 2021. Red indicates an increase in the monthly average compared to the mean for the base years (2018–2021), while blue indicates a decrease. Figure 6: The seasonal cycles of different soil moisture metrics: (**a**) NDVI (unitless), (**c**) SIF (unitless), (**e**) GPP (gC m\({}^{-2}\) d\({}^{-1}\)), and (**g**) NEE (gC m\({}^{-2}\) d\({}^{-1}\)). The corresponding change percentages for the  
year 2022 compared to the average values from 2018 to 2021 are shown in (**b**) NDVI (unitless), (**d**) SIF (unitless), (**f**) GPP (gC m\({}^{-2}\) d\({}^{-1}\)), and (**h**) NEE (gC m\({}^{-2}\) d\({}^{-1}\)). In (**a**,**c**,**e**,**g**), the black line represents the monthly average for 2022, and the red line represents the monthly average value from 2018 to 2021. In (**b**,**d**,**f**,**h**), the blue part represents the proportion of value in 2022 that exceeds the average from 2018 to 2021, while the red part represents the proportion of value in 2022 that falls below the average from 2018 to 2021. Figure 6g showed that in a typical year, the NEE value reached its lowest point in August (\(-\)1.38), but in 2022, it started to significantly decrease below the average level of the reference year from June, reaching its lowest point in July (\(-\)1.74) (Table 4). However, there was a notable increase in NEE during the midterm of the drought and heatwave period in August and September, reversing from negative to positive and showing an increase compared to the typical year (Figure 6h). Despite the significant decrease in NEE values compared to the average of the reference year during the early stage of the drought and heatwave, the NEE value in 2022 turned positive earlier, even exceeding that of the reference year. This clearly indicated that the ecosystem carbon balance has been affected by the drought and heatwave. Figure 7a-h depicted similar spatial distributions of NDVI and SIF anomalies, with prominent negative anomalies concentrated in the southeastern region, particularly in August and September. While widespread negative anomalies in SIF occurred relatively late, manifesting in a large-scale pattern in the central and eastern regions by October (Figure 7g), NDVI had already established this pattern as early as August and sustained it through September (Figure 7b,c). In comparison, the abnormal distribution of GPP appeared relatively independent, with a global positive anomaly prevailing in July (Figure 7i).