EGU2020-4494, updated on 12 Jun 2020
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Observed canopy evapotranspiration enhancement of green patches in Chinese metropolis

Jiacheng Zhao and Xiang Zhao
Jiacheng Zhao and Xiang Zhao
  • State Key Laboratory of Remote Sensing Science, Jointly Sponsored by Beijing Normal University and Institute of Remote Sensing and Digital Earth of Chinese Academy of Sciences, Faculty of Geographical Science, Beijing Normal University, Beijing, China

With the acceleration of urbanization, the canopy evapotranspiration (ET) of vegetation plays an increasingly important role in urban surface energy and water budget [1-2]. A reasonable assessment of urban vegetation ET requires not only the estimation of high-resolution ET but long-term monitoring due to high heterogeneity of city, especially that of metropolis, and changeable land management policy. The study takes advantages of Google Earth Engine (GEE) platform to investigate how canopy ET of green patches in Chinese metropolis, represented by Beijing, changes from 1984 to 2018. Typical green patches including city park, community green belt, large area lawns etc. in study area were manually vectored on GEE based on a thorough examination of historic high-resolution google earth images and thermal images. Using a simple Taylor skill fusion method by Yao et al. [3], 853 cloudless Landsat 5/8 surface reflectance images were used to retrieve long-time series ET for each green patch identified with 30 m spatial resolution. Time series analysis combined with robust regression were employed for trend detection. Results indicated that the ET of green patches in Beijing significantly increased from 1984 at a mean rate of 18.05 ± 4.21 W/m2/10 year (r2 = 0.42, p < 0.001). However, such enhancement varied in different green patch type. This talk will graphically depict the spatial pattern of enhanced green patch ET, explore their changes over long-term urbanization and the potential cooling capacity for urban heat island alleviation.



[1] Grimmond, C. S. B. and Oke, T. R., 1991. An evapotranspiration‐interception model for urban areas. Water Resources Research, 27(7): 1739-1755.

[2] Chen, X., et al., 2019. Canopy transpiration and its cooling effect of three urban tree species in a subtropical city- Guangzhou, China. Urban Forestry & Urban Greening (43): 126368.

[3] Yao, Y. J. et al., 2017. Estimation of high-resolution terrestrial evapotranspiration from Landsat data using a simple Taylor skill fusion method. Journal of Hydrology (553): 508-526.

How to cite: Zhao, J. and Zhao, X.: Observed canopy evapotranspiration enhancement of green patches in Chinese metropolis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4494,, 2020

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Display material version 1 – uploaded on 03 May 2020
  • CC1: Comment on EGU2020-4494, Stenka Vulova, 07 May 2020

    Interesting study - I am also interesting in estimating evapotranspiration in an urban environment. How well does the Yao Taylor skill fusion method work in an urban area? Did you validate the evapotranspiration? Did you use optical data in addition to Land Surface Temperature?

    • AC1: Reply to CC1, Jiacheng Zhao, 07 May 2020

      Thanks for your reply!

      The method is still the remote sensing-based Penman-Monteith algorithm. Hence, all the input data used is from the Landsat imagery (e.g., NDVI) and some other reanalysis climate data (e.g., temperature, wind speed). To be exact, the observed canopy enhancement refers to the evapotranspiration (ET) of tree canopies in urban areas. I'm not sure the difference you mentioned between ET estimation of natural lands and an urban environment. Are you referring to the irrigation effect on the urban trees?

    • AC2: Reply to CC1, Jiacheng Zhao, 07 May 2020

      Unfortunately, the method is only validated in some flux tower sites and not tested yet in urban areas.