## 4 Discussion  
### Spatio-Temporal Analysis of Flash Drought Events  
A significant number of flash drought events were detected in our study area. In comparison to other papers, the overall count of flash drought events in our study area was higher. The reason behind this might be that we selected a large area, while another reason might be that we chose an area with only forest vegetation in northeastern China. The flash drought in northeast China is influenced by dense vegetation. Dense vegetation can increase water stress by pumping more water from the soil and increase rates of evapotranspiration, which change the soil moisture level, and that increases the probability and severity of flash droughts in these regions. Similarly, the vegetation greenness also intensifies the flash drought [50]. It was found to have a considerable impact on the occurrence of flash droughts in locations such as the Great Plains and the western regions of the United States, as demonstrated by various studies [51]. The percentages of area affected by the flash drought are ranked as follows: GKM > CM > LKM. These results demonstrate the variability in the flash drought events in our research region. To understand the characteristics of flash drought, we employed an analysis based on their frequency and duration as these are vital features of any drought events. In the case of these characteristics, we did not observe much spatial variation. This can also be justified on the basis of our research area as it was selected within only forested regions. Considering this, we can assume that the results would be different if we had chosen multiple land covers. Based on the definition we used for the identification of frequency, we found that some areas experienced a flash drought once during this time frame, while others experienced it twice. A study in northeast China found an average frequency of about three times [52]. In addition to considering the actual humidity limitations and the quick development of flash droughts, the flash drought events' duration should also be considered by researchers [53] as the impacts on the ecosystem much depend on the duration of drought. While following [29], we kept the threshold of the flash drought duration at a minimum 15 days. According to this, the total duration of major flash drought events in our study varied from 20 to 55 days, where the average duration over all the study area from 2000 to 2020 was about 22 days (4.4 pentads). Our findings were almost consistent with other findings, where the average duration in northeast China was 4.48 pentads [36]. In another research study, the duration reached up to 36 days in the northeastern part of China [54]. We focused on how much area was affected by flash drought within our selected study area and we found out that with the passing of years, less area was influenced between 2000 and 2020. Our findings was consistent with the findings of [55], where they also observed the area affected by flash drought was decreasing in northeast China. While looking at the trend in the area affected by flash drought in the three mountain areas, the trend in the CM was little bit different in comparison to the GKM and LKM. There might be several factors being influenced by its climate variability, soil type, vegetation and land cover, which need to be investigated more [56]. Similar to our result, flash drought events primarily occur between April and October in others study also, with a focus on the plant-growing seasons [57; 58]. Even though flash drought is more frequent in dry regions throughout the year, it is more common in the northeast and northern China (moist) areas during the plant growth season [54]. Along with this, the flash droughts in the Wei River basin also mainly occur in spring (March-May) and summer (June-August) [50]. The primary cause of flash droughts is a lack of precipitation, which is common during growing seasons and makes the soil dry, especially in regions that are vulnerable to flash drought events [7].