## 3 Results
### Temporal Variation Characteristics of TCWV in China
#### 3.2.2 Monthly, Seasonal Variation Characteristics and Abrupt Change Analysis of TCWV in China  
The monthly change of TCWV in China from September 2002 to February 2022 was analyzed. As shown in Figure 5a, its distribution is a slightly positive 'bell-shaped' curve. The TCW gradually increased from January (9.58 kg/m\({}^{2}\)), reached the peak in July (32.37 kg/m\({}^{2}\)), then slightly decreased to 31.38 kg/m\({}^{2}\) in August, and then gradually decreased after September. The TCWV of China is mainly concentrated from May to September, and the total TCWV in these five months is 139.96 kg/m\({}^{2}\), accounting for about 59.90% of the annual TCW. The TCWV in the other seven months is relatively low, among which January, February and December are all below 11 kg/m\({}^{2}\), which are 9.58 kg/m\({}^{2}\), 10.89 g/m\({}^{2}\) and 10.77 kg/m\({}^{2}\), respectively. The seasonal change of TCWV in of China from 2003 to 2021 was analyzed, and the seasonal variation of TCWV was shown in Figure 5b. It can be seen from Figure 5b that the TCWV in summer fluctuated around 30 kg/m\({}^{2}\), with a multi-year average of 30.73 kg/m\({}^{2}\). The annual averages of TCWV in spring and winter were 17.16 kg/m\({}^{2}\) and 10.52 kg/m\({}^{2}\), respectively. Therefore, it is concluded that the TCWV is most abundant in summer, relatively less in autumn and spring, and the least in winter, and the annual variation of TCWV in each season shows irregular changes.  
Figure 4: Interannual variation trend. (**a**) Trend analysis of TCW. (**b**) Trend analysis of TAS. (**c**) M-K mutation analysis.  
The M-K mutation test method was used to test the seasonal average TCWV in China, and the UF and UB curves of the M-K mutation test were drawn. The M-K statistical curve (Figure 6a) of the winter TCWV in China was analyzed. The UF was greater than 0 after 2005, indicating that the winter TCWV showed an increasing trend after 2005. The UF and UB curves have intersections in 2015 and 2017, respectively, and the corresponding UF values are greater than 0 and between the two critical lines, but it cannot be stated which intersection is the mutation point of the TCWV rise in winter. The M-K statistical curve of the spring TCWV (Figure 6b) showed that the UF curve of spring TCWV in China was greater than 0 after 2015, indicating that the spring TCWV showed an increasing trend after 2015. The UF and UB curves had an intersection point during 2015, corresponding to the UF value between the two critical lines, indicating that the spring TCWV had a mutation in 2015. From the M-K statistical curve of TCWV in summer (Figure 6c), the UF curve showed an increasing trend, and the increasing trend was obvious, and the UF value was greater than 1.96 after 2016, indicating that the increasing trend of average TCWV in summer was obvious. The UF and UB curves had an intersection point in 2011 and the UF value was between the two critical lines, indicating that the TCWV had a mutation in the summer of 2011. It can be seen from Figure 6d that the UF of TCWV in autumn in China was greater than 0 after 2005, indicating that the average TCWV in autumn gradually increased after 2005. The UF and UB curves had multiple intersections from 2007 to 2015, and the corresponding UF values were greater than 0, although it cannot be determined which point is the mutation point.