## 4 Discussion  
This study used WT to extract the seasonal terms of GNSS and GRACE displacement time series and analyzed the phase, amplitude, and CC of 24 stations in the Sichuan-Yunnan region. Precipitation data was also considered for analysis. The three data types showed notable seasonal variability and a certain correlation, but with clear systematic differences. First, the GRACE results intuitively responded to changes in the surface loading within the study area, especially the vertical component, which was negatively correlated with changes in the surface mass. Referring to the U component in Figure 8b, precipitation in April was found to gradually increase with the beginning of the rainy season, and crustal displacement gradually changed from a positive maximum value to a negative maximum value due to load application. As precipitation reduced towards the end of the rainy season, surface uplift occurred, and similar changes occurred in the horizontal component. The difference between the two phases may be because precipitation records an instantaneous change, while GRACE records long-term cumulative changes in surface load. Consequently, the maximum displacement of the GRACE-stacked mean seasonal term (DOY: 254) was 50 d (1.7 months) later than the peak precipitation. Second, the GNSS amplitude was greater than that of GRACE in both horizontal and vertical components, indicating that stations were not only affected by regional load as monitored by GRACE, but also by local factors to some extent. Thus, GRACE could not effectively resolve this problem due to the local variations in the estimation accuracy. Moreover, the periods and phases of GRACE and GNSS differed largely in the horizontal component, but marginally in the vertical component, indicating that the horizontal resolution of GRACE was lower than its vertical resolution [10]. In the vertical component, the stacked mean seasonal correlation coefficients of GRACE and GNSS were as high as 0.92, but the GNSS phase occurred 29 days later than that the GRACE phase, and their troughs were 20 days apart. This may be because the instantaneous hydrological loading deformation caused by precipitation was recorded simultaneously by both GRACE and GNSS, but changes in pore pressure in the subsurface medium caused by water diffusion were detected at different times [30]. If the pore pressure increases or decreases, pore volume may increase or decrease, accompanied by an increase or a decrease in the horizontal displacement of the surface, which can be recorded only by GNSS, consequently, leading to changes in the amplitude and phase. Pore pressure changes cause changes in the properties of the subsurface medium and cause differences in the seismic wave velocity changes from the GRACE phase. [PERSON] et al. [30] indicated that the seasonal variation of seismic wave velocity occurs approximately 20 days later than the high phase of equivalent water table, which also supports this view. The horizontal component was strongly correlated between GNSS and GRACE, indicating that the actual GNSS seasonal deformation is more complicated in the horizontal component and cannot be explained well by a single load accumulation model. Third, on comparing the results of different GNSS stations, high or low differences in the coordinate time series of stations were observed, indicating that GNSS is not only affected by large-scale non-structural factors but also considerably by local observation environments. For example, for non-single load areas around the observation stations, multiple loads usually increase the amplitude of the vertical component, but they may offset the amplitude and deviate the phase in the horizontal direction [10]; therefore, consistency between stations was better in the vertical direction, whereas larger differences were observed in the horizontal direction.