## 3 Results
### Ecological Response to Flash Droughts  
Figure 7 elucidates the spatial distribution of the GPP response rates to two distinct categories of flash drought events across the Songnen Plain from 2002 to 2022. It can be observed that water deficit- and high-temperature-driven flash drought showed similar spatial dynamics, with a pronounced concentration in the northwest as opposed to the southeast. Within this framework, areas exhibiting a high response rate to water scarcity droughts are extensively distributed, showcasing an average response rate of 76%, and nearly 47% of this terrain is characterized by a response rate exceeding 80%. Conversely, regions affected by heatwave-driven droughts are more localized, maintaining an average response rate of 70%, with 37% of these areas exhibiting response rates above 80%.  
In comparison to GPP, WUE provides a more refined reflection of the ecosystem's water-carbon interplay in reaction to flash drought phenomena. Figure 8 delineates the normalized anomalies of WUE and its underlying variant (uWUE) amidst the onset and amelioration of flash drought conditions, illustrating that positive standardized anomalies of uWUE surpass those of WUE during both the escalation and recuperation phases. Notably, both WUE and uWUE register significant negative anomalies throughout the escalation of both drought types. Spatially, the negative standardized anomalies of WUE associated with water scarcity are predominantly concentrated in the northern reaches of the Songnen Plain and notably within Qiqihar and Daqing cities during the escalation phase (Figure 8a), extending into the northern and central zones during the recuperation phase (Figure 8b). In contrast, heatwave-driven anomalies are centrally and westerly focused during the escalation phase, showcasing a more confined distribution but with heightened positive anomalies (Figure 8c), and during the recuperation phase, negative anomalies are primarily localized in the central and western regions (Figure 8d).  
When juxtaposing uWUE's anomalies against those of WUE, it becomes evident that water scarcity flash droughts exhibit superior overall performance during the escalation phase (Figure 8e), with the recuperation phase witnessing more pronounced and geographically concentrated positive anomalies within the western sector of the Songnen Plain (Figure 8f). The spatial distribution of uWUE anomalies during the heatwave-driven escalation phase mirrors that of WUE (Figure 8g), albeit with an expanded distribution of positive anomalies during the recuperation phase (Figure 8h). Moreover, an examination reveals that positive anomalies of WUE and uWUE are more prevalent during heatwave-driven droughts compared to water scarcity ones, indicating a swifter GPP response to the former drought type. Throughout the drought recuperation phase, certain locales, including the Qiqihar and Songyuan areas, persist with negative anomalies in WUE and uWUE, signaling a diminished ecological resilience within the vegetation of these regions.  
Figure 7: The spatial distribution of the GPP response rates to (**a**) water deficit- and (**b**) heatwave-driven flash drought events across the Songnen Plain from 2002 to 2022.  
These findings suggest a gradual erosion of the ecological self-regulatory capacity in these areas, exacerbated by the protracted duration of drought events.