**4. Discussion**

In this study, we applied a water-carbon coupling model (PML-V2) with the use of Sentinel-2 LAI and land use and cover data and with surface meteorological forcing data as the input to estimate urban ET and its components at 10m resolution for the Beijing Sponge City. Our results indicate that the current vegetation coverage for the Beijing Sponge City is still at a low level (only with mean LAI<1m<sup>2</sup> m<sup>−</sup><sup>2</sup> in June 2018), and the city gains relatively limited benefits from urban ecosystem services.

Eddy covariance measurements to study evaporation from urban ecosystems [24,25] generally helped us to understand the combined evaporation from all land cover types, lacking the capability to divide individual contributions from such as impervious surfaces (roofs, roads and plazas, etc.) and vegetated areas (bare soil, forests, grasslands and croplands, etc.). For different land cover classes, by using an advanced water-carbon coupling ET model driven by Sentinel-2 LAI, we find that lakes and rivers have the highest ET (≥8 mm <sup>d</sup>−1), followed by mixed forests and croplands (ET is 4–6 mm d−<sup>1</sup> and LAI is 2–3 m<sup>2</sup> m<sup>−</sup>2), where the plant transpiration (Ec) plays the dominant role (>80%), then grasslands have 2–4 mm d−<sup>1</sup> of ET, where the LAI is 1~2 m<sup>2</sup> m<sup>−</sup>2, while impervious surfaces have smallest ET (<2.0 mm <sup>d</sup>−1). In most impervious areas, the impervious surface evaporation (Eu) contributes 20-30% of ET, which is larger than the estimate (18%) from previous studies [4]. We have shown that another 40–50% of ET in impervious areas are contributed by plant transpiration (Ec) due to the small fractional area covered by greenbelts with trees and grassland (LAI is 0.5–1.0 m<sup>2</sup> m<sup>−</sup>2). This study did not consider water vapor conversion from human water use activities, which also contributes to the impervious evaporation from building indoor water use [25].
