## 3 Results
### Drought Evolution Trends and Response to Precipitation  
Drought conditions in the study area have changed over the past decade and a half. This increased climate change could significantly trigger changes in regional attributes, which could lead to greater uncertainty regarding economic development in the region. Different time scales can characterize different moisture features. SPI-30 can reflect detailed changes in moisture deficit, SPI-90 can reflect seasonal changes in moisture deficit, and SPI-180, SPI-270, and SPI-360 can reflect mid-term and long-term changes in moisture deficit. As a crucial grain production base in China, monitoring the precipitation situation during the growing period of crops in the Northeast region is of significant importance. The primary crop-growing areas in the study region are concentrated in the Songnen Plain, the Sanjiang Plain, and the Liaohe Plain (Figure 1).  
In this study, we selected daily CLM3.5 precipitation data with a 2 km spatial resolution in the watershed to calculate the SPI and analyze the evolutionary trends and patterns of drought in the Northeast region (Figure 2). Overall, the SPI at all time scales has shown a consistent wetting trend since 2008, aligning with the results of existing studies [49]. The region has predominantly been free of severe drought, with most events classified as light droughts. Moderate drought conditions were observed in 2011, after which there was a gradual shift towards wetter conditions. As the time scale increases, the fluctuations in the SPI curve tend to flatten out. The frequency of alternating drought and non-drought periods gradually decreases, the durations of different drought events lengthen, and the trend towards wetting becomes more pronounced. This is because small droughts occurring in shorter periods cannot be recognized as the time scale increases.  
The primary cause of drought phenomena is the variation in precipitation. Based on precipitation statistics, we identified 2011 as a low-water year and 2020 as a high-water year. We analyzed the changes in daily precipitation and the SPI during the crop-growing period (May to September) in the three major plains during these high- and low-water years (Figure 3). Overall, the fluctuating trend in the SPI at different time scales is relatively consistent across the plains, both in low-water and high-water years. However, there are differences in the fluctuation amplitude of the SPI. The smaller the time scale, the more pronounced the fluctuations in the SPI, resulting in a higher identification sensitivity to drought and a more sensitive response to drought conditions. Conversely, the larger the time scale, the gentler the fluctuations and the lower the identification sensitivity to drought. At the Liaohe Plain, peak precipitation occurs in late July during low-water years and in late August during high-water years, while peak SPI values are observed in mid-August and mid-September, respectively. In the Sanjiang Plain, precipitation is higher in early June during low-water years, peaking in late August during high-water years, with SPI peaks occurring in mid-June and mid-September. In the Songnen Plain, precipitation is mostly concentrated in mid-July during low-water years and peaks in early September during high-water years, while SPI peaks in early August and mid-September. A lag exists between SPI and precipitation, with this lag being more pronounced in high-water years than in low-water years.