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ESSD: Revealing the spatial and temporal variation of actual evapotranspiration over the Tibetan Plateau (2001-2018)

Recently, the research team of Prof. MA Yaoming (corresponding author) and Dr. HAN Cunbo (first author), published an article entitled "Long-term variations in actual evapotranspiration over the Tibetan Plateau" in Earth System Science Data (IF=11.33). The dataset of this article includes the monthly actual evapotranspiration of the Tibetan Plateau at a spatial resolution of 0.1 degree. The dataset is based on the satellite remote sensing data (MODIS) and reanalysis meteorological data (CMFD), and is calculated by the surface energy balance system model (SEBS). The National Tibetan Plateau/Third Pole Environment Data Center (https://data.tpdc.ac.cn/en/), as the data warehouse for the paper, has released the corresponding dataset online and is openly available to users.

Actual terrestrial evapotranspiration (ET) is the sum of water vapor flux transmitted from land surface and vegetation to the atmosphere, mainly including soil and water surface evaporation, vegetation canopy interception precipitation or dew evaporation, vegetation transpiration and ice and snow sublimation. It is the main process of energy and water exchange between surface and atmosphere, and has a profound impact on the physical, chemical and biological processes of the Earth's surface, and it is the key process of earth's multi cycle interaction. Globally, about 60% of precipitation is returned to the atmosphere through ET. Therefore, it is the second largest component of land water cycle after precipitation, and it is also an important component of global energy and water cycle. In the past few decades, great changes have taken place in the climate and environment of the Tibetan Plateau. The increase of temperature, humidity and vegetation will cause the changes of ET. Therefore, accurate quantification of the climatic state and spatial and temporal characteristics of ET is very important to understand the current situation and variation characteristics of water cycle and the allocation of water resources in the Tibetan Plateau.

In order to obtain the real situation of ET on the Tibetan Plateau, the research team of Prof. Ma established a comprehensive observation and research station for earth atmosphere interaction on a variety of typical underlying surfaces of the plateau, realizing long-term continuous observation of energy and water exchange between earth and atmosphere. Based on the observation data, an algorithm for effective aerodynamic roughness length had been introduced into the SEBS model to parameterize subgrid-scale topographical form drag. Then, using the improved SEBS model, combined with MODIS satellite remote sensing data and CMFD meteorological reanalysis data, the monthly average ET of the Tibetan Plateau from 2001 to 2018 is calculated. Validation against data from six eddy-covariance monitoring sites yielded root-mean-square errors ranging from 9.3 to 14.5 mm per month and correlation coefficients exceeding 0.9.

The total evapotranspiration from the terrestrial surface of the Tibetan Plateau was 1238.3±57.6 km3 yr⁻¹. However, there are great spatial differences in its annual variation trend (Fig. 1). The annual ET increased significantly at a rate of 2.62 mm yr⁻¹ (p<0.05) in the eastern sector of the Tibetan Plateau (longitude >90∘ E) but decreased significantly at a rate of −5.52 mm yr⁻¹ (p<0.05) in the western sector of the Tibetan Plateau (longitude <90∘ E). In addition, the decreases in annual ET were pronounced in the spring and summer seasons, while almost no trends were detected in the autumn and winter seasons (Fig. 2). The estimated ET product presented in this study is useful for an improved understanding of changes in energy and water cycle on the Tibetan Plateau.

This research has been supported by the Second Tibetan Plateau Scientific Expedition and Research (STEP) program (grant no. 2019QZKK0103), the Strategic Priority Research Program of the Chinese Academy of Sciences (grant no. XDA20060101), and the National Natural Science Foundation of China (grant nos. 91837208, 41705005, and 41830650).

Fig 1. Spatial distribution of annual ET linear trend on the Tibetan Plateau from 2001 to 2018. The stippling indicates the trends that pass the t test (p<0.05).

Fig 2. Spatial distributions of seasonal ET linear trends on the Tibetan Plateau from 2001 to 2018: (a) annual, (b) spring, (c) summer, (d) autumn, (e) winter. The stippling indicates the trends that pass the t test (p<0.05).

Article:

Han, C., Ma, Y., Wang, B., Zhong, L., Ma, W., Chen, X., & Su, Z. (2021). Long-term variations in actual evapotranspiration over the Tibetan Plateau. Earth System Science Data, 13(7), 3513–3524. https://doi.org/10.5194/essd-13-3513-2021.

Data available at:

https://data.tpdc.ac.cn/en/data/5a0d2e28-ebc6-4ea4-8ce4-a7f2897c8ee6/（DOI: 10.11888/Hydro.tpdc.270995）

Reprinted from the website of the Institute of Tibetan Plateau Research, Chinese Academy of Sciences (http://www.itpcas.ac.cn/new_kycg/new_kyjz/202107/t20210725_6147408.html).