## 3 Results
### Temporal and Spatial Patterns of Drought Characteristics in 1982-1998 and 1999-2015  
We observed that both the annual drought duration and drought intensity series changed abruptly at approximately 1998 across the entire period (Figure 5). Specifically, the drought duration showed a slight increasing trend before 1998, but this trend was subsequently reversed in 1999-2015, with a significantly (\(p<0.1\)) decreasing trend by 2 months per decade (Figure 5a). The absolute values of drought intensity exhibited a slight decrease before 1998 but a strong decrease afterward, with a 6.5 times larger trend (Figure 5b). Figure 6 showed the TDD maps for each selected period (1982-1998 and 1999-2015). During the 1982-1998 period, more than 19.14% of the study areas had TDDs longer than 50 months, and these areas were located mainly in northwestern Canada, the eastern United States, northern Kazakhstan, and a large part of central and eastern Russia (Figure 6a). However, during the 1999-2015 period, the number of high-level TDD areas (TDD >50 months) decreased considerably and accounted for only about 11% of the study area. The high-level TDD areas in 1999-2015 were located mainly in intersection regions, such as North America and Canada, northern Inner Mongolia, eastern China, and scattered locations in Russia (Figure 6b). In addition, by calculating the difference in TDD between these two selected periods, we found that the percentage of TDD areas that had decreased accounted for 60.2% of the total study area, with more than 27.5% of the pixels showing a decrease of more than 14 months (Figure 6c,e). The distribution of these areas (TDD with a decrease of >14 months) closely coincided with the distribution of high-level TDD (>50 months) areas in 1982-1998 (Figure 6a,c). Figure 4: Spatial patterns of SPEI and its standard deviation during 1982–1998 and 1999–2015. (**a,b**) the spatial patterns of SPEI during 1982–1998 and 1999–2015, respectively; (**c,d**) the spatial patterns of standard deviation of SPEI during 1982–1998 and 1999–2015, respectively. Figure 3: Changing trend of annual (**a**) precipitation, (**b**) temperature, and (**c**) SPEI during 1982–1998 and 1999–2015, respectively. Each year value was averaged of all pixels during the growing season. The blue line is the linear fit of 1982–1998; and the red line is the linear fit of 1999–2015. Overall, the mean TDD decreased from 39.03 months in 1982-1998 to 34.23 months in 1999-2015 (Figure 6d). However, we also found that about 13% of the pixels experienced a pronounced increase (>14 months) in TDD and that these areas were mainly located in low latitudes in the study area, such as northern Mongolia, northeastern China, and the eastern United States (Figure 6c,e). Differences in the TDI maps between the 1982-1998 and 1999-2015 periods were shown in Figure 7; the more negative the TDI value was, the more often the area was affected by high-severity droughts. The results showed that more than 64.8% of areas exhibited an increased TDI and that 23.5% of the pixels of the TDI increased by more than 16 (Figure 7c,e). In addition, it is worth noting that the mean TDI increased from \(-\)30.12 in 1982-1998 to \(-\)25.0 in 1999-2015 (Figure 7d), which further indicates that the effects of the drought were alleviated after 1998. Spatially, the TDI maps showed a roughly similar spatial pattern as the TDD during the two study periods because they are connected. The proportion of high-level drought intensity (TDI \(<\)\(-\)44) areas decreased from 13.2% in 1982-1998 to 6.7% in 1999-2015 in the study areas (Figure 7a,b), and these high-level drought intensity areas were concentrated mainly in eastern and middle Russia, northeastern China, and northern Kazakhstan during the 1999-2015 period. Figure 5: Inter-annual variations of (**a**) drought duration and (**b**) absolute value of drought intensity during 1982–1998 and 1999–2015. Each year value was averaged of all pixels. The blue line is the linear fit of 1982–1998; and the red line is the linear fit of 1999–2015.