## 3 Results
### Comparison of Nonstationary and Stationary Drought Characteristics in China  
Figure 5 shows the percentage of the differences in drought characteristics estimated using the NSPEI index and SPEI. The differences are represented as \(\frac{DrouChar_{NSPEI}-DrouChar_{SPEI}}{DrouChar_{NSPEI}}\times 100\%\); the values of the drought characteristics estimated by the SPEI are subtracted from those of the drought characteristics (duration and severity) estimated by the NSPEI as a percentage of the drought characteristics estimated by the  
Figure 4: Changes in location and scale (\(\mu\), \(\sigma\)) parameters for the nonstationary model. 1 indicates a trend that passes the 95% confidence test, and 0 indicates either no trend or one that does not pass the 95% confidence level. (**a**) distribution parameter change class in spring–summer season; (**b**) distribution parameter change class in fall–winter season. SPEI. Positive values imply an under-estimation of the drought conditions by the current stationary index and vice versa. Figure 5 shows that in many areas of China, the results of the SPEI and NSPEI are the same (shown in white). The differences in these indices were concentrated between \(-15\) and \(15\%\), and these differences were spatially dispersed. Overall, the differences between the stationary SPEI and NSPEI values for the drought durations were minor, and there was no obvious spatial pattern. For drought severity, drought assessment generally remained consistent in the east during the spring-summer season, while in sporadic areas, such as the YRB2, Eastern SRB2, and PRB, there was over-estimation of drought severity under the stationary SPEI. The same results could be found in the fall-winter season, except for a more visible underestimation of drought severity in the southeast and the HRB1. The most significant difference in drought evaluation between the nonstationary and stationary models was found in Northwest China, that is, the CRB. The under-estimation of drought by the stationary SPEI in this region was particularly evident during the spring-summer season, while the over-estimation in the eastern sheet and northern ribbon regions could also be observed. In the fall-winter season, the over-estimated area expanded, and the under-estimated area decreased. This may be due to the decrease in precipitation and increase in evapotranspiration during the spring-summer seasons in the region, while there was no significant change in precipitation and reduced or no evapotranspiration during the fall-winter seasons (Supplementary Figures S1 and S2). Figures 6-9 show the probability densities of drought characteristics (duration and severity) evaluated using the SPEI and NSPEI under the classification of different changes in the distribution parameters (\(\mu\), \(\sigma\)) in different river basins during the spring-summer and fall-winter seasons for all the grid points. Figure 6 shows the results of the durations for the spring-summer season. The results of the NSPEI and SPEI assessment only varied in the distribution of durations; there was no probability bias. As mentioned in the previous section, the results of the nonstationary and stationary models were essentially indistinguishable for the case wherein the distribution parameters presented (0, 0) variations. For the (1, 1) class, the nonstationary index identified more durations in all the river basins  
Figure 5: Percentage of differences in drought characteristics under NSPEI and SPEI. (**a_1**) shows the duration in the spring–summer seasons; (**a_2**) shows the severity in the spring–summer seasons; (**b_1**) shows the duration in the fall–winter seasons; (**b_2**) shows the severity in the fall–winter seasons. than the stationary index did. There were only a few grid points where only the scale parameter changed (class of (0, 1)), and the drought durations identified by the NSPEI and SPEI were similar. Variations in the (1,0) class were identified only at grid points close to Northwestern China, such as CRB, YRB2, YRB1, and SRB2.