# Spatiotemporal Variations in Vegetation Canopy Interception in China Based on a Revised Gash Model
## 4 Discussion  
The validation results of the revised Gash model (Figure 2) meant that the model performed well in estimating canopy interception at the regional scale compared with other products and in-situ measurements [30; 32]. The model results revealed that the Ic and Ir in China during the last two decades were 166.55 mm and 22%, respectively (Figure 3), which are in line with the values obtained in previous related studies [54; 55]. For example, [PERSON] et al. [56] conducted a review study by collecting canopy interception data from 86 studies conducted in 47 different research sites located in China and concluded that the Ic and Ir were 209.8 mm and 25.5%, respectively. The results published in this paper are slightly higher than those in present study, which may be due to the scale gaps of different methods. The interception data used in [PERSON] et al. [56] was based on rainfall event at site scale, and thereby analyzed by the meta-analysis method. Moreover, our study found that the Ir in the coniferous and broadleaved mixed forest in temperate zone of China was 34.56 \(\pm\) 6.58%, which was close to the result of [PERSON] et al. [56] (i.e., 35.00 \(\pm\) 10.50%). Despite the slight differences, the simulated results of canopy interception in the present study were generally in line with those of previous studies. The results revealed a significant decreasing spatial pattern of the mean annual canopy interception from Southeastern to Northwestern regions in China (Figure 3). This pattern was mainly determined by the spatial distributions of precipitation and vegetation types [4; 6]. From Southeast to Northwest, precipitation significantly decreased with the effect of the monsoon climate [57]. In addition, the vegetation type changed from  
Figure 9: Dominant environmental factors affecting canopy interception in China. P: precipitation; NDVI: normal difference vegetation index; T: temperature; WS: wind speed; RH: relative humidity; SR: solar radiation. I: cold temperate coniferous forest; II: temperate mixed forest; III: deciduous broadleaved forest; IV: subtropical evergreen broad-leaved forest; V: tropical rain forest; VI: temperate steppe; VII: temperate desert; VIII: alpine vegetation of Qinghai-Tibet Plateau. tropical or subtropical forest to temperate steppe or temperate desert (Figure 1), which are characterized by a sparser canopy structure that can retain less rainwater [58]. A similar spatial pattern was also detected in the ratio of interception to precipitation (Figure 3b), except for the cold temperate coniferous forest, which exhibited a relatively higher interception ratio but lower canopy interception. This was mainly because coniferous plants generally present a higher total plant leaf area due to their needle leaf form [4; 59]. [PERSON] et al. [52] collected data on 68 woody plant species worldwide and found that the Ir in needle leaf form was significantly higher than in broad leaf or pinnate leaf forms. At the temporal scale, the mean annual canopy interception in China increased significantly from 2000 to 2018 (Figure 5) at a rate of 1.79 mm yr\({}^{-1}\) (\(p<0.01\)). This increasing trend was most pronounced during the 2000-2009 periods (Figures 5 and 6), with a rate of 1.79 mm yr\({}^{-1}\) (\(p<0.01\)). This phenomenon was also reflected in the interception changes observed in most vegetation types (Figure 7,II,IV-VI,VIII). For instance, in the temperate steppe, the increases in canopy interception were significantly more pronounced between 2000 and 2009, but the trend almost stabilized or even decreased during the 2010-2018 period (Figure 7 VI). The subtropical evergreen broad-leaved forest and tropical monsoon forest (Figure 7 IV,V), the two vegetation types with the highest canopy interception in China, also experienced a significant increasing trend of canopy interception. In addition, [PERSON] et al. [38] estimated that the mean annual canopy interception gradually increased from 2004 to 2016 in Guangdong Province, China.