Trends of Calculated and Simulated Actual Evaporation in the Yangtze River Basin

Abstract

ctual evaporation in the Yangtze River basin is calculated by the complementary relationship approach?that is, the advection?aridity (AA) model with parameter validation from 1961 to 2007?and simulated by the general circulation model (GCM) ECHAM5?Max Planck Institute Ocean Model (MPI-OM) from 1961 to 2000. Trends of annual and seasonal estimated actual evaporation and air temperature, net radiation, saturation vapor pressure deficit, wind speed, and precipitation are examined by the linear regression method and nonparametric Mann?Kendall test. The stepwise regression method is used to analyze the significance to reference evapotranspiration of independent variables.Results show that a significant decreasing trend in annual reference evaporation is caused by a significant decline in wind speed. The annual actual evaporation decreases in the upper and midlower Yangtze reaches; more significantly in the AA model [?9.3 mm (10 yr)?1] than in the GCM [?3.6 mm (10 yr)?1]. Significant negative trends are found in spring and autumn, but they show reverse trends in summer and winter within the two methods, which is caused by the different contributors to the seasonal actual evaporation in the two methods.Decreasing net radiation is the main contributor to annual and spring actual evaporation in the two methods. Decreasing precipitation and net radiation are the main contributors to decreasing autumn actual evaporation in the AA model and the GCM. Increasing net radiation and decreasing precipitation are the main contributors to summer and winter actual evaporation in the GCM. Decreasing net radiation and increasing precipitation are the main contributors to decreasing summer and increasing winter actual evaporation in the AA model.