## 3 Results
### Characteristics of Spatial and Temporal Changes in Drought  
The increased frequency of droughs is widely recognized as a direct consequence of global warming. Understanding this increase is crucial in comprehending and responding to climate change, developing water resource management plans, and assessing the agricultural, ecological, and socio-economic impacts of droughs. In this study, we utilized SPI data from 2008 to 2023 to analyze the spatial and temporal evolution trends and patterns in drought frequency in Northeast China across different time scales (Figures 4 and 5).  
Figure 2: Trends in 30\(-\), 60\(-\), 90\(-\), 180\(-\), 270\(-\), and 360\(-\)day SPI, 2008–2023. Areas with negative SPI values are denoted by red coloration, whereas regions exhibiting positive SPI values are indicated in blue.  
Figure 4: Changes in drought frequency at different time scales and trends in precipitation in the three plains, 2008–2023. (a) Liaohe Plain, (b) Sanjiang Plain, and (c) Songnen Plain.  
Figure 3: SPI and precipitation for three plains from May to September in high- and low-water years. (a,b) Low- and high-water years for the Liaohe Plain, respectively; (c,d) low- and high-water years for the Sanjiang Plain, respectively; (e,f) low- and high-water years for the Songnen Plain, respectively.  
Overall, Figure 4 indicates that the annual precipitation in the three plains has shown an increasing trend since 2008, followed by a decreasing trend, which aligns more closely with the trend in drought frequency across different time scales. However, there are differences in drought frequency identification across various time scales. The larger the time scale, the coarser the identification of drought, meaning it can only detect drought occurrences over longer periods. Consequently, as the time scale increases, the frequency of identified drought occurrences decreases. Drought frequency also varies across the plains, with the Liaohe Plain experiencing a relatively high frequency of droughts and the Sanjiang Plain and Songnen Plain experiencing lower frequencies. For the Liaohe Plain, the highest drought frequency was recorded in 2011, with 10 times, mostly short-term droughts. In 2009, the region saw eight drought events, with a relatively higher proportion of medium-term droughts. In contrast, the Liaohe Plain had the lowest frequency of drought in 2021, with most droughts occurring in the short term and fewer medium-to-long-term droughts. The Sanjiang Plain had the highest frequency of drought in 2010, with more droughts in the medium and long term compared to other years. The Sanjiang Plain experienced the lowest frequency of drought in 2023, with fewer droughts occurring in the medium and long term. The Songnen Plain had the highest drought frequency in 2009, with more droughts occurring in the medium to long term. In contrast, the Songnen Plain had a lower drought frequency in 2021, with more droughts occurring in the short term.  
On the spatial scale, the trend of drought change in the Northeast region tends to flatten out as the time scale increases. At different time scales, SPI-30 and SPI-60, similar to the seasonal time scale SPI-90, exhibit a relatively clear trend of decreasing drought frequency, primarily concentrated in the Songnen Plain and the Sanjiang Plain. In contrast, the SPI-180, SPI-270, and SPI-360 scales show relative stability, with only a slight increase in drought frequency in the northern part of Northeast China and the western part of the Sanjiang Plain. Thus, while short-term and seasonal droughts in the Northeast have decreased in frequency, changes in medium- and long-term droughts are less pronounced.  
Figure 5: Spatial trends in drought frequency at 30-, 60-, 90-, 180-, 270-, and 360-day time scales in Northeast China, 2008–2023.