the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
A global terrestrial evapotranspiration product based on the three-temperature model with fewer input parameters and no calibration requirement
- 1Shenzhen Engineering Laboratory for Water Desalinization with Renewable Energy, School of Environment and Energy, Peking University, Shenzhen, 518055, PR China
- 2Department of Earth and Environmental Sciences, Data Science Institute, Columbia University, New York, NY 10027, America
- 3Max Planck Institute for Biogeochemistry, Hans-Knöll-Str. 10, Jena, 07745, Germany
- 4Shenzhen Investment Holdings Co., LTD, Shenzhen, 518048, PR China
- 5School of Civil Engineering, Sun Yat-Sen University, Guangzhou, 510275, PR China
- 6Department Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, 519082, PR China
- 1Shenzhen Engineering Laboratory for Water Desalinization with Renewable Energy, School of Environment and Energy, Peking University, Shenzhen, 518055, PR China
- 2Department of Earth and Environmental Sciences, Data Science Institute, Columbia University, New York, NY 10027, America
- 3Max Planck Institute for Biogeochemistry, Hans-Knöll-Str. 10, Jena, 07745, Germany
- 4Shenzhen Investment Holdings Co., LTD, Shenzhen, 518048, PR China
- 5School of Civil Engineering, Sun Yat-Sen University, Guangzhou, 510275, PR China
- 6Department Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, 519082, PR China
Abstract. Accurate global terrestrial evapotranspiration (ET) estimation is essential to better understand Earth’s energy and water cycles. Although several global ET products exist, recent studies indicate that ET estimates exhibit high uncertainty. With the increasing trend of extreme climate hazards (e.g., droughts and heat waves), accurate ET estimation under extreme conditions remains challenging. To overcome these challenges, we used 3-hour and 0.25° Global Land Data Assimilation System (GLDAS) datasets (net radiation, land surface temperature (LST), and air temperature) and three-temperature (3T) model, without resistance and parameter calibration, in global terrestrial ET product development. The results demonstrated that the 3T model-based ET product agreed well with both global eddy covariance (EC) tower (root mean square error (RMSE) = 24.9 mm month-1) and basin-scale water balance observations (RMSE =116.0 mm yr-1). The 3T model-based global terrestrial ET product was comparable to other common ET products, i.e., MOD16, P-LSH, PML, GLEAM, GLDAS, and Fluxcom, retrieved from various models, but the 3T model performed better under extreme weather conditions in croplands than did the GLDAS, attaining 9.0–20 % RMSE reduction. The proposed ET product could provide periodic and large-scale information to support water cycle-related studies. The dataset is freely available at the Science Data Bank (http://doi.org/10.57760/sciencedb.o00014.00001, Xiong et al., 2022).
Leiyu Yu et al.
Status: open (until 19 Jul 2022)
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RC1: 'Comment on essd-2022-171', Anonymous Referee #1, 04 Jun 2022
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This manuscript addresses a useful but challenging topic. Although there are many remotely sensed global or regional evapotranspiration (ET) datasets, their performances varied across different biomes or regions due to high uncertainty exist in ET estimates. The current manuscript provides a good try to retrieve a land ET product in 2001-2020 using a three-temperature model without resistance and parameter calibration, which is different from the available ET products generated by methods including Penman–Monteith equation-based and surface-energy-balance-residual-based methods. The validation performed at different scales sound good. The intent of the manuscript is worthy and significant, and the topic generally fits the scope of the Earth System Science Data. The manuscript is well-written, and the methods, results, and discussion are clearly presented. Seeing the potential of this, I am in general supportive of publication after minor revision.
Specific comments.
The numbers in front of the comments indicate page and line number.
- It may be better to clearly state the temporal resolution and duration of the product.
- Please add the data points used for validation.
- “the energy balance product” is better changed to “the ET product”.
- PMLv2 → PML. Missing a PT-based ET product, GLASS.
- Fluxcom also has no value in some arid regions.
- It is better to provide a journal article as the thesis may not be available.
- “G equals to 0.315Rn” may be misleading.
- The subscript l is not consist with those in equations 10 and 11.
- Order of the section title was wrong as well as the following section. The authors should proof read the manuscript to avoid such mistakes.
- TWSC is better replaced with ΔS. In L171, it is better to use annual TWSC.
- Typos (the unit). The authors should proof read the manuscript to avoid such mistakes.
- The value 133 mm/yr was from what data?
- It seems the ET should be removed.
- PMLv2 looks curious. “v2” may be the version number, suggesting delete it across the entire manuscript but remain a statement somewhere.
- It is better to clearly state that the EC datasets are the same as those used in figure 2.
- Texts in the figures are too small to read. I suggest the authors enlarge these texts to improve their quality and readability.
- What does “PFT” mean? Please consider define such abbreviation.
- “the whiskers indicate the extreme values” should be “the whiskers indicate the outlier values”.
- Area of the Antarctica should be wrong.
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CC1: 'Comment on essd-2022-171', Shaoyang He, 09 Jun 2022
reply
This manuscript describes an actual evapotranspiration dataset with high spatial resolution, no parameter calibration, and good accuracy, which is particularly important in the context of increased extreme climate hazards. However, this paper needs to further verify the accuracy of its product, which will be more appropriate.
- Based on the Conclusion part, it seems the authors produced ET with a resolution of 3-hour. However, the current validations against the observed ET and ET from water balance are mostly at the monthly or annual scales. For this reason, it is not clear the accuracy of the 3-hour ET data. Therefore, it is suggested that the new product have validations against the observed ET at the 3-hour scale.
- In addition, the authors claim that the new ET product has a good accuracy compared with other ET products. Yet, such a conclusion is also mostly based on the validations at the monthly or annual scales. It is appropriate to compare with other ET products at the 3-hour scale, such as GLDAS and ERA5.
Therefore, it will be more rigorous to add content for validations against observation data of 3-hour and comparison with other ET products at the 3-hour scale.
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RC2: 'Comment on essd-2022-171', Anonymous Referee #2, 18 Jun 2022
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This manuscript uses the classic 3T model to generate global terrestrial evapotranspiration (ET) product at 0.25 degree resolution and 3hour temporal resolution. I am glad to see the 3T model has been expended to a global scale. The authors also tested their estimates against flux observations at a monthly scale and water balance ET estimates at an annual scale. Overall, the paper is well written, and the key message is get crossed. Having said that, I have some major concerns on the method applied to the global scale, and validation processes. Follows are the key concerns:
- The author grouped the climate regimes into 5 groups according to Koppen-geiger climate classification, then assumes the means of reference net radiation values of the soil and vegetation components are similar within the same group of samples. I am afraid that the classification is too coarse, which will result in large uncertainty in estimating the two important parameters. I think the more details should be exhibited and the uncertainty should be quantified.
- The validation of the 3T products is a bit weird. The benefit to use the 3-T model is to detect ET variation in a short period of time. Considering that the 3-T products has been run at 3-hour temporal scale, its robustness should be demonstrated at 3-hour or daily scale at least. Currently, the authors focused their validations against flux measurements at a monthly scale, which is too coarse to be acceptable.
- Calculation of water balance ET can be improved. The authors used GLDAS forcing data to drive the 3T model. However, the calculation of water balance ET relies on another precipitation product GPCC. I think the authors need to test the consistency between GLDAS precipitation and GPCC precipitation. In addition, I encourage the authors not only test its performance at a mean annual scale, but also need to test its interannual variability. This will demonstrate its full strength.
In conclusion, the authors had a good attempt to generate global ET product based on the 3T model. However, its robustness has not been fully demonstrated. There are numerous ET products available across the globe. The readers will wonder why this one should be deserved to be published in ESSD. To demonstrate its strength, I suggest the authors put more efforts for validations in arid semi-arid regions and in short period of time. They can show some particular case under extreme drought conditions, i.e. comparing its performance with others in the extreme climatic conditions.
Leiyu Yu et al.
Data sets
A global terrestrial evapotranspiration product based on three-temperature model from 2001 to 2020 Yujiu Xiong; Leiyu Yu; Guo Yu Qiu; Chunhua Yan; Wenli Zhao; Zhendong Zou; Jinshan Ding; Longjun Qin http://doi.org/10.57760/sciencedb.o00014.00001
Leiyu Yu et al.
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