Abstract:
Abstract: Analysis of spatio-temporal variability of terrestrial evapotranspiration (ET) over China facilitates understanding the response of water cycle to global climate change and water resources rational allocation. However, large-scale ET estimation methods based on satellite-based observations have some uncertainty. In this study, we firstly validated the accuracy and applicability of ET data from Global Land-surface Evaporation: the Amsterdam Methodology (GLEAM) using in-situ observations from China FLUX at point scale. Secondly, based on water balance model, we also validated the GLEAM ET data over China and Chinese 10 sub-basins using hydrological data at basin scale. In addition, we obtained the 32-year spatio-temporal datasets of terrestrial ET over China from 1980 to 2011 using GLEAM ET data. The research results indicated that: 1) GLEAM ET data were basically reasonable over China after the validation at both point and basin scales. Point scale validation using daily data revealed that GLEAM ET data showed overall comparable daily accuracies. GLEAM ET data showed the highest performance for three Grassland sites, which had the highest CC (correlation coefficient) mean value 0.77 (0.65-0.85) and lower relative bias (RB), root mean squared error (RMSE), mean absolute error (MAE) value. GLEAM ET data showed high performance for forest sites except XSBN site, which had CC mean value 0.66 (0.40-0.85) and had a low performance at XSBN (CC, 0.4, RMSE, 1.14 mm). GLEAM ET data also showed high performance for cropland (CC, 0.68; RB, 11.73%). Validation results at basin scale over 2003-2011 using water balance ET data as a reference indicated reasonable accuracies for GLEAM ET data, especially in Haihe River basin (RB, 16.2%), Yellow River basin (RB, 15.2%) and the Northwest River basin (RB, 9.2%). GLEAM ET value may be greater than precipitation value in oasis or agricultural irrigation area due to the artificial irrigation increased the soil moisture content in relative drought years. 2) GLEAM ET data showed that the climatological annual mean ET value varied spatially from 18 to 1400 mm during the 1980-2011 period over China. Spatial patterns of mean annual ET showed an increase from the northwest to the southeast part with the smallest ET value over Northwest region and the largest ET value over Hainan Island and Taiwan Island. 3) The domain-averaged annual ET over China showed an inter-annual variability ranging from 349.7 to 436.0 mm with the climatological value of 397.5 mm and a significant increasing trend of 12.3 mm per 10 years. 4) The trend in grid-based GLEAM ET over China displayed a prominent spatial variability ranging from -86.5 to 108.7 mm/(10a). The percentage of areas with decreased trends was 28.4%, and the significantly decreased areas was 9.45% of the total, which were mainly distributed in east Nei menggu, west Tibetan plateau (west and northeast Xinjiang, northwest Xizang), south Gansu. The areas with increased trends were 71.6% of the total and the significantly increased regions were 18.2%, which were mainly distributed in south Hebei and northwest Shandong (Haihe River basin), Shandong peninsula in Huai River basin, east Qinghai in the Yellow River basin, east Sichuan, south Shanxi, Hubei, Hunan, Anhui, and Jiangxi (Middle-lower Yangze River), Southeast River basin, Pearl River basin and south Yunnan et al. 5) The trends in grid-based GLEAM ET over China showed a remarkable seasonal cycle with the largest value in summer. The trend in the spring, autumn and winter time ET was not significant. Results from this research probably played an important role in understanding the interaction between climate change and water resources and provided reference and decision making base for China's water resources evaluation and management.