This study investigates the water balance of the Yangtze River Basin (YRB) during 2003-2012 using the Tropical Rainfall Measuring Mission precipitation, the Moderate Resolution Imaging Spectroradiometer evapotranspiration and the Gravity Recovery and Climate Experiment total water storage change. The bias, absolute error and correlation coefficient are used to quantify water balance performances at monthly and annual time steps. The results show that the absolute error in the YRB water balance was 18.1 mm/month and 152.5 mm/yr at monthly and annual time steps accounting for 20% and 14% of YRB precipitation, respectively. The three satellite products were combined through a water balance equation to estimate monthly and annual stream flow, which was in error by 19.4 mm/month and 76.7 mm/yr, accounting for 22% and 7% of YRB precipitation, respectively. Trends in YRB water balance components at annual time steps obtained from satellite products were in the range 83-318% of the corresponding trends from alternative datasets (e.g., ground-based measurements, land-surface modelling, etc.), which performed significantly better than monthly time series. The results indicate that the YRB water balance can be evaluated using multiple satellite products to a reasonable accuracy at annual time steps.

Abstract:Reference evapotranspiration (ET 0 ) is a crucial parameter for hydrological modeling, land-atmospheric interaction investigations and agricultural irrigation management. This study investigated changes in ET 0 and attributed those changes to climate variations in a coastal area (Zhejiang province) of China by a numerical experiment method. The results indicated that annual ET 0 increased significantly (p < 0.05) at a rate of 1.58 mm·year −1 from 1973 to 2013, which was mainly caused by an obvious increase in ET 0 in spring. Air temperature and water vapor pressure deficits increased significantly (p < 0.05) at rates of 0.04 • C·year −1 and 0.005 kPa·year −1 , respectively, at an annual time scale during the study period, while wind speed and solar radiation decreased significantly (p < 0.05) at rates of −0.01 m/s·year −1 and −3.94 MJ·m −2 ·day −1 ·year −1 , respectively. The contributions of changes in air temperature, wind speed, water vapor pressure deficits and solar radiation to increases in ET 0 were 0.39, −0.56, 2.62 and −0.61 mm·year −1 , respectively. The decrease in wind speed and solar radiation negatively affected the increase in ET 0 , which was offset by the positive effects of the air temperature and water vapor pressure deficits increase, where the water vapor pressure deficits was the dominant factor in increasing ET 0 in the coastal area. Moreover, the impact of topography on ET 0 was further discussed. ET 0 changes at plain stations were approximately 5.4 times those at hill stations, which may be due to the impact of a large water body and the augment of surface roughness from intense human activities in the well-developed plain area. The results are helpful for investigating spatial and temporal changes in the evaporative demand for well-developed regions under energy-limited conditions.

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