## 3 Results
### Characteristics of Spatial and Temporal Changes in Drought
#### 3.3.4 Characteristics of Spatial and Temporal Changes in Drought Severity  
The severity of drought reflects the extent of its impact on agricultural production, ecological environment, and other aspects. The assessment of drought severity is crucial in understanding the causes, impacts, and development trends of drought, thereby enablingthe implementation of more effective measures. Figures S7 and S8 illustrate the temporal and spatial evolution of drought severity at different time scales. Overall, the drought severity in the Liaohe Plain, Sanjiang Plain, and Songnen Plain shows a decreasing trend, with the Sanjiang Plain exhibiting the lowest drought severity. In 2009 and 2011, the severity of drought in the three plains was particularly strong, especially in the Sanjiang Plain. Conversely, the Liaohe Plain, Sanjiang Plain, and Songnen Plain exhibited weaker drought severity in 2021, 2008, and 2021, respectively. It can be observed that the Sanjiang Plain and Songnen Plain display more prominent drought characteristics in dry years, while in non-drought years, they exhibit wetter conditions compared to other regions. As can be seen from Figure S8, the trend of change in drought severity is consistent with the trend of change in other drought characteristics, both of which become more pronounced with the increase in time scale. The trend of increasing drought severity is primarily distributed in the northern part of the Northeast, with a slight extension as the time scale increases. Meanwhile, the trend of decreasing drought severity extends from the middle region of the Northeast, particularly in the Songnen Plain and the Sanjiang Plain, towards the south. Overall, the frequency, duration, intensity, and severity of droughts across different land use types exhibited a weakening trend during the period 2008-2023. The drought conditions for the four land use types were most severe in 2011 and lighter in 2018 and 2023. Previous studies have shown that different land use types exhibit varying degrees of sensitivity to drought, thereby eliciting distinct drought responses. These differences arise from the unique structural and physiological characteristics of each vegetation type, such as stomatal conductance and light utilization efficiency [51]. Dry cropland experienced 7.8 times of drought in 2011, with a total of 205 drought days. The intensity and severity values reached \(-1.13\) and \(-234\), respectively. Since 2018, drought conditions in dry cropland have mitigated significantly. However, the frequency, duration, intensity, and severity of droughts occurring in dry cropland have remained at a higher level compared to other land use types. This suggests that dry croplands are more susceptible to droughts [52; 53]. Grasslands exhibited the most significant fluctuations in drought characteristics. In 2011, droughts occurred on average 6.7 times, with a total duration of 182 days, an intensity of \(-1.18\), and a severity of \(-218\). By 2023, only four drought events occurred, with a total duration of 47 days, an intensity of \(-0.81\), and a severity of \(-46\). Grasslands showed the highest sensitivity to drought among all land use types [54]. This high sensitivity is likely attributed to the fact that grassland vegetation types possess shallower root systems and are more dependent on the availability of surface water [55; 56]. Consequently, the rate of change in grasslands is both faster and more pronounced under drought conditions. The response of woodlands and wetlands to drought has remained relatively low. In 2011, they experienced 6.8 and 6.9 drought events, respectively, with total durations of 192 and 188 days, an intensity of -1.18, and severities of -227 and -223, respectively. This indicates that woodlands and wetlands exhibit a weaker response to drought and are more resistant to its effects [52]. The shorter, milder droughts experienced by woodlands are attributed to their deeper root systems compared to other vegetation types.