3.4.2. Standard Deviation (SD)

To analyze the significance of the inconsistencies between the four products, we first computed the 90%, 95%, and 99% percentile of standard deviation (Figure 14). The 99% percentile SD (red color) mainly occurs in southern Tibet (Region A in Figure 14), western Sichuan with mixed forest and grass land cover types (region B in Figure 14), and Taiwan (region C in Figure 14) with mainly broadleaf and needleleaf forest; the 95% percentile SD (green color) mostly occurs in southern provinces in temperate climate zones with mixed forest and savannas biomes, and 90% percentile SD (blue color) mainly occurs in eastern Sichuan province in a cold climate zone with mainly grass.

We extracted three 99% percentile SD typical regions according to pixel density and geographic location (Tibet, Sichuan, and Taiwan (regions A, B, and C)), then calculated the minimum, maximum, median, mean, 25% and 75% quartile values for each product and the boxplots (Figure 15). Because GLASS LAI performs best in direct validation, we set GLASS LAI as the benchmark. For the Tibetan region (region A), the main reason for the difference could be due to GLOBMAP LAI, whose mean value is quite high compared with the other three products. For the Sichuan region (region B), the main reason for the difference can also be attributed to GLOBMAP and MODIS LAI, as the mean GLOBMAP LAI is a little high while MODIS LAI is a little low with an LAI difference of 0.5 m2/m2 between them. Also, for the Taiwan region (region C), the difference may be because of the high deviation of GLOBMAP.

**Figure 14.** Percentile distribution of standard deviation of four LAI climatologies over China. Blue represents 90% percentile level, green represents 95% percentile level, and red represents 99% percentile level.

**Figure 15.** LAI boxplots of typical regions: (**a**) region A; (**b**) region B; (**c**) region C; (**d**) region D.

We then counted the proportion of each land cover type at 99%, 95%, and 90% percentile SD (Table 6). At the 99% percentile SD level, evergreen needleleaf forest, woody savannas, and mixed forest have the highest proportion with 32.87%, 16.71%, and 11%, respectively. At 95% and 90% percentile SD levels, evergreen needleleaf forest, woody savanna, and savanna have the highest proportion. Thus, from the perspective of standard deviation, the LAI discrepancy can attribute to evergreen needleleaf forest, savannas, and mixed forest.


**Table 6.** Pixel proportion of different biome types at three standard deviation percentiles.

Similarly, we counted the proportion of each climate type at three percentile SD levels (Table 7). At 99% and 95% percentile SD levels, temperate hot summer/no dry season, temperate warm summer/dry winter, and temperate dry hot summer climate types are the top three, and at 90% percentile SD level, temperate dry hot summer, temperate warm summer/dry winter and cold dry winter/warm summer climate types have the highest proportion.

**Table 7.** Pixel proportion of different climate types at three standard deviation percentiles.

