Abstract
The change in water storage driven by the Three Gorges Project directly affects the terrestrial water migration and redistribution in the Yangtze River Basin (YRB). As a result, a new water balance is established and regional evapotranspiration (ET) fluctuates in the process. In this paper, data from multiple-sources including from the Gravity Recovery and Climate Experiment (GRACE) satellite, land surface models (LSMs), remote sensing, and in-situ observations were used to monitor the temporal and spatial evolution of terrestrial water and estimate changes in ET in the Three Gorges Reservoir (TGR) from 2002 to 2016. Our results showed that GRACE data scaled using the scale factor method significantly improved the signal amplitude and highlighted its spatial differences in the TGR area. Combining GRACE with surface hydrological observations, ET in the TGR area was estimated to have overall change characteristics highly consistent with results from the MOD16 Moderate Resolution Imaging Spectroradiometer (MODIS), and the uncertainties of monthly ET are mainly from TWS changes derived by GRACE uncertainties such as measurement errors and leakage errors. During our study period, the cyclical ET was mainly driven by climate precipitation but short-term (monthly) ET in the TGR area was also directly affected by human-driven water storage. For example, rising water levels in the three water storage stages (2003, 2006, and 2008) caused an abnormal increase in regional ET (up to 22.4 cm/month, 19.2 cm/month and 29.5 cm/month, respectively). Usually, high precipitation will cause increase in ET but the high precipitation during the water release periods (spring and summer) did not have a significant impact on the increased ET due to the water level in the TGR having decreased 30 m in this stage. Our results also indicate that the short-term fluctuations in flooded area and storage capacity of the TGR, i.e., the man-made mass changes in the main branch and tributaries of the Yangtze River, were the main factors that influenced the ET. This further illustrated that a quantitative estimation of changes in the ET in the TGR allows for a deeper understanding of the water balance in the regional land water cycle process as driven by both climate and human factors.
Highlights
Terrestrial water storage (TWS) is the main carrier by which mass circulation, migration, and exchange is accomplished between the earth’s terrestrial, oceanic, and atmospheric systems [1]
The GLDAS forcing precipitation data are extracted from the National Oceanic and Atmospheric Administration (NOAA) and Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP) [49], GLDAS simulates TWS as the summation of soil moistures, snow, and canopy storages through four main land surface models, CLM, Mosaic, Noah, and VIC
Changes in total Gravity Recovery and Climate Experiment (GRACE)-estimated ET were mainly caused by climate and human factors
Summary
Terrestrial water storage (TWS) is the main carrier by which mass circulation, migration, and exchange is accomplished between the earth’s terrestrial, oceanic, and atmospheric systems [1]. Quantitative estimation of the ET in the TGR area will provide an understanding of the state of the water balance in the Three Gorges region and can help with analysis of the regional terrestrial water cycle process and understanding the degree to which it is driven by climatic and human factors. Since the Three Gorges Project was established in 1994 and experimental storage of 175 m (the highest design water level) started in 2008, there have been a series of studies on the significant changes in hydrological cycles that have occurred and their potential impact on climate and environmental variables using different data, methods, and scales [17,18,19,20]. The ET is significantly observable by GRACE data that could be good to consider assimilating the GRACE into the Hydrological model to update their ET estimates
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