## 5 Conclusions  
This study, utilizing the NNsm reanalysis dataset, investigated the occurrence, impact, and types of flash droughts in the Songnen Plain from 2002 to 2022, alongside the terrestrial ecosystems' responses. Our findings highlight the urgent need for targeted drought management strategies and further research in this critical area. Below are our main conclusions:  
(1) We find an increased frequency and uneven spatial distribution of flash droughts in the Songnen Plain. The increasing frequency of flash droughts with more than seven occurrences was mainly distributed in Baicheng and Songyuan in Jilin and Suihua and Wuchang in Heilongjiang. Flash droughts exhibited a widespread but uneven spatial coverage, with the average duration of 28-30 days.  
(2) The region experiences a higher incidence of water scarcity flash droughts and longer durations of heatwave-driven droughts. Both types exhibit a fluctuating upward trend, with water scarcity flash droughts increasing at a faster rate.  
(3) The ecosystems show varying responses to these flash droughts in the Songnen Plain. Heatwave-driven flash droughts, predominantly occurring around the Songhua River coast, elicit a slower response rate with weak resilience across most areas. Conversely, ecosystems are more sensitive to heatwave-driven flash droughts, with GPP responding more rapidly compared to water scarcity flash droughts.  
(4) There is a noticeable spatial difference in WUE between the development and recovery periods of both flash drought types. Heatwave-driven flash droughts mainly occurred alongside the river, while water scarcity flash droughts are more prevalent in the semi-arid regions of western Jilin.  
These findings underscore the complexity of flash drought phenomena and their profound impact on the Songnen Plain's ecosystems. They call for enhanced monitoring and adaptive management strategies to mitigate the adverse effects of such droughts. Future research should focus on the long-term ecological impacts, effective drought prediction models, and comparative studies with other regions facing similar challenges. Implementing sustainable water management practices and developing resilient agricultural systems are crucial steps toward mitigating the impacts of flash droughts in the Songnen Plain and similar ecosystems worldwide.  
Conceptualization, J.S., Y.W. and M.C.; methodology, Q.Z.; software, J.S.; validation, Q.Z. and Q.M.; formal analysis, L.J., J.S. and Q.M.; investigation, L.J. and Q.Z.; resources, Y.W.; data curation, Q.M.; writing--original draft preparation, J.S. and Y.W.; writing--review and editing, M.C. and G.Z.; visualization, C.D., G.Z. and Q.M.; supervision, M.C. and Y.W.; project administration, Y.W.; funding acquisition, Y.W. and G.Z. All authors have read and agreed to the published version of the manuscript.  
This work was supported by The National Key Research and Development Program of China (2021 YFC3200203), the National Natural Science Foundation of China (421010514, 422070881, U2243230 and 42371169), the Postdoctoral Science Foundation of China (2021M693155 and 2022M723129), and the Strategic Priority Research Program of the Chinese Academy of Sciences and China (XDA28020501 and XDA28100105).  
The data presented in this study are available upon request from the corresponding author. The data are not publicly available due to privacy.  
We would like to sincerely acknowledge and express our deep appreciation to the editor and to three anonymous referees for their thorough review of this work.  
The authors declare no conflicts of interest.