Journal of Resources and Ecology ›› 2021, Vol. 12 ›› Issue (3): 305-318.DOI: 10.5814/j.issn.1674-764x.2021.03.001

• Forest and Grassland Ecosystem •     Next Articles

The Bowen Ratio of an Alpine Grassland in Three-River Headwaters, Qinghai-Tibet Plateau, from 2001 to 2018

ZHAO Xuanlan1,2, WANG Junbang1,*(), YE Hui3, MUHAMMAD Amir1,2, WANG Shaoqiang1   

  1. 1.National Ecosystem Science Data Center, Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China
    2.University of Chinese Academy of Sciences, Beijing 100049, China
    3.College of Tourism and Geography, JiuJiang University, Jiujiang, Jiangxi 332005, China
  • Received:2020-08-02 Accepted:2020-10-20 Online:2021-05-30 Published:2021-07-30
  • Contact: WANG Junbang
  • About author:ZHAO Xuanlan, E-mail: zhaoxl.17s@igsnrr.ac.cn
  • Supported by:
    The National Key Basic Research and Development Program(2017YFC0503803);The National Natural Science Foundation of China(31971507);Qinghai Province Science and Technology Program(2018-ZJ-T09);CAS-Qinghai Province Joint Program on Three-River Headwaters National Park(YHZX-2020-07)

Abstract:

The Bowen ratio (β) is used to quantify heat transfer from the land surface into the air, which is becoming a hot topic in research on the biogeophysical effects of land use and cover changes. The Three-River Headwaters (TRH), as a sensitive and fragile region, was selected as the study area. The β for 2001-2018 was estimated from the evapotranspiration product (ETMOD16) of MODIS and the net radiation of the land surface through the albedo from GLASS. The ETMOD16 data were evaluated against the observation data (ETOBS) at two alpine grassland flux towers obtained from ChinaFLUX. The interannual trend of the β was analyzed by multiple linear regression (MLR) and structure model (SEM) with the multiple factors of precipitation, temperature, humidity, albedo, and normalized difference vegetation index (NDVI, MOD09Q1). The results show that the ETMOD16 values were significantly correlated with ETOBS, with a correlation coefficient above 0.70 (P < 0.01) for the two sites. In 2001-2018, the regional mean β was 2.52 ± 0.77 for the whole grassland, and its spatial distribution gradually increased from the eastern to western region. The interannual β showed a downward trend with a slope of -0.025 and a multiple regression coefficient (R 2) of 0.21 (P = 0.056). Most of the variability (51%) in the interannual β can be explained by the linear regression of the above multiple factors, and the temperature plays a dominant role for the whole region. The SEM analysis further shows that an increasing NDVI results in a decreasing albedo with a path coefficient of -0.57, because the albedo was negatively correlated with NDVI (R 2 = 0.52, P < 0.01), which indicates a negative and indirect effect on β from vegetation restoration. An obvious warming climate was found to prompt more evapotranspiration, and restoring vegetation makes the land surface receive more radiation, which both resulted in a decreasing trend in the annual β. This study revealed the biogeophysical mechanisms of vegetation restoration under a changing climate, and demonstrated the Bowen ratio can be applied as an indicator of climate-regulating functions in ecosystem assessments.

Key words: alpine grassland, Bowen ratio, Three-River Headwaters, MODIS, evapotranspiration