# Spatiotemporal Variations in Vegetation Canopy Interception in China Based on a Revised Gash Model
## 3 Results
### Temporal Variation of Canopy Interception in China  
The mean annual canopy interception in China significantly increased from 2000 to 2018 (Figure 5), at a rate of 1.79 mm yr\({}^{-1}\) (\(p\)! 0.01). The increasing trend was more pronounced during the 2000-2009 period, with rates of 3.34 mm yr\({}^{-1}\) (\(p\)! 0.01), despite a decrease down to 1.14 mm yr\({}^{-1}\) observed from 2009 to 2018. In terms of seasonal patterns, canopy interception in summer not only accounted for the largest proportion of annual interception but it also obviously increased, especially between 2000 and 2009, at a rate of 2.26 mm yr\({}^{-1}\) (\(p\)! 0.01). Canopy interception in spring also increased significantly (\(p\)! 0.01), causing a certain impact on annual interception.  
Figure 2: Comparison of (**a**) canopy interception (Ic) between the revised Gash model and PML_V2 product and (**b**) ratio of canopy interception to precipitation (Ir) between the revised Gash model and in-situ measurement.  
Figure 4: The canopy interception (Ic) and ratio of interception to precipitation (Ir) of eight vegetation types present in China. The histogram and point plot mean the Ic and Ir, respectively. I: cold temperate, coniferous forest; II: temperate mixed forest; III: deciduous broad-leaved forest; IV: subtropical, evergreen broad-leaved forest; V: tropical rain forest; VI: temperate steppe; VII: temperate desert; VIII: alpine vegetation of Qinghai-Tibet Plateau.  
Figure 3: Spatial patterns of mean annual (**a**) canopy interception (Ic) and (**b**) the ratio of interception to precipitation (Ir) from 2000 to 2018. I: cold temperate coniferous forest; II: temperate mixed forest; III: deciduous broad-leaved forest; IV: subtropical evergreen broad-leaved forest; V: tropical rain forest; VI: temperate steppe; VII: temperate desert; VIII: alpine vegetation of Qinghai-Tibet Plateau.  
The results of the MK test (Figure 6a) showed that in many regions canopy interception displayed an increasing trend during the 2000-2009 period, especially in Northeastern China and in the Loess Plateau, where the increase was significant (\(p<0.01\)). During the 2009-2018 period, the temporal variations were not obvious, except in Southern China (Figure 6b), where a significant increasing trend (\(p<0.01\)) was detected.  
Figure 5: Interannual variations of the mean canopy interception in China from 2000 to 2018.  
Figure 6: Spatial distribution of MK test in canopy interception in China (**a**) from 2000 to 2009 and (**b**) from 2010 to 2018. I: cold temperateiferous forest; II: temperate mixed forest; III: deciduous broad-leaved forest; IV: subtropical evergreen broad-leaved forest; V: tropical rain forest; VI: temperate steppe; VII: temperate desert; VIII: alpine vegetation of Qinghai-Tibet Plateau.  
In particular, except for the deciduous broad-leaved forest and temperate desert vegetation, the other six vegetation types almost displayed a significant increasing trend (\(p<0.01\)) of canopy interception during the 2000-2018 period (Figure 7,II,IV-VI,VIII). Among them, the cold temperate coniferous forest and the temperate steppe showed a significantly higher increasing rate (\(p<0.01\)) of canopy interception between 2000 and 2009 than between 2009 and 2018 (Figure 7,VI), while the remaining four types displayed a significant increasing trend (\(p<0.01\)) during the whole period. Similar with the mean annual value, the canopy interception in summer dominated the most proportion of the annual interception in almost all the vegetation types (Figure S1).  
Figure 7: Interannual variations of canopy interception of eight vegetation types from 2000 to 2018.