## 3 Results
### ET and Related Variables in Beijing Sponge City  
Based on the Sentinel-2-derived LCC and LAI data, we conducted daily simulations for June 2018 at 10m resolution using the PML-V2 model with daily climate forcing data from CMFD v1.0. Figure 5 presents the spatial patterns of simulated monthly ET and GPP averaged over the daily output for June 2018. Lakes and rivers have the highest ET (\(\geq\)8 mm d\({}^{-1}\)) due to the full water supply for evaporation in Summer. There is no GPP in lakes and rivers as simulated by PML-V2. The vegetation production activities are strongest in mixed forests and croplands, with the GPP ranging from 8 to 16 gC m\({}^{-2}\) d\({}^{-1}\) (Figure 5b). In these mixed forests and croplands, the ET is also high (4-6 mm d\({}^{-1}\)), where the plant transpiration (Ec) plays a dominant role with ratios of Ec to ET larger than 0.8 (Figure 6a). In addition, the impervious surfaces have very small ET (<2 mm d\({}^{-1}\)) and GPP (<4 gC m\({}^{-2}\) d\({}^{-1}\)), indicating both Ec and soil evaporation (Es) are very small in these areas. The grasslands have 2-4 mm d\({}^{-1}\) of ET and 4-8 gC m\({}^{-2}\) d\({}^{-1}\) of GPP in the sponge city (Figure 5), where the ratio Ec/ET are 0.5-0.7 (Figure 6a). Figure 4: Vegetation index at 10m resolution for Beijing Sponge City. (**a**) NDVI and (**b**) LAI (m\({}^{2}\) m\({}^{-2}\)) for June 2018 derived from the Sentinel-2. In summary, on average, for the whole sponge city, we find that the LAI in June 2018 is 0.83 m\({}^{2}\) m\({}^{-2}\); the ET is about 1.6 mm d\({}^{-1}\); the GPP is 2.8 gC m\({}^{-2}\) d\({}^{-1}\). Table 2 further gives the evaluation for different districts in the sponge city. It shows that the central areas (i.e., Xicheng and Dongcheng districts) have the smallest LAI (0.66-0.7 m\({}^{2}\) m\({}^{-2}\)), ET (-1.61 mm d\({}^{-1}\)) and GPP (2.36-2.44 gC m\({}^{-2}\) d\({}^{-1}\)), while the western areas (i.e., Shijingshan and Haidian districts) have the highest LAI (0.93-1.05 m\({}^{2}\) m\({}^{-2}\)), ET (-1.65 mm d\({}^{-1}\)) and GPP (3.10-3.53 gC m\({}^{-2}\) d\({}^{-1}\)). Figure 5: ET and GPP at 10m resolution for Beijing Sponge City estimated using the PML-V2 model and Sentinel-2 data. (**a**) Monthly ET (mm d\({}^{-1}\)) in June 2018; (**b**) Monthly GPP (gC m\({}^{-2}\) d\({}^{-1}\)) in June 2018. We further investigate how ET changes spatially with increasing LAI for June 2018. It is shown that the fraction Ec/ET increases with LAI for the three vegetation types (grassland, mixed forest and cropland) in the sponge city (Figure 6b). The Ec/ET for mixed forests increase from 0.4 (LAI = 0.5) to 0.8 (LAI \(>\) 3), while Ec/ET for grasslands and croplands show higher values, increasing from 0.6 (LAI = 0.5) to 0.9 (LAI \(>\) 3). The ratio ET/LAI represents the amount of water loss per unit LAI. In Figure 6c, we can find that ET/LAI for mixed forests and some grassland parks show the lowest ET/LAI (0.8-1.2), while impervious surfaces have the highest ET/LAI, with about 2-3 times larger values (2.4-3.6). The ET/LAI for the major vegetation types (grassland, mixed forest and cropland) decrease with LAI increase (Figure 6d); with LAI increasing from 0.5 to 5.0, the ET/LAI for mixed forests decrease from 2.0 to 0.6, and ET/LAI for grasslands and croplands from 3.0 to 1.0. This result indicates that grasslands and croplands have much higher water consumption per unit LAI than mixed forests. Fractional contributions of other ET components to ET have been estimated (Figure 7). Soil evaporation (Es) contributes a relatively small fraction (\(\leq\)0.2) due to a very small fraction of bare lands and large vegetation coverage in mixed forests, grasslands and