Sensitivity analysis of the evaporation module of the E-DiGOR model

Abstract

Sensitivity analysis of the soil-water-evaporation module of the E-DiGOR (Evaporation and Drainage investigations at Ground of Ordinary Rainfed-areas) model is presented. The model outputs were generated using measured climatic data and soil properties. The first-order sensitivity formulas were derived to compute relative sensitivity coefficients. A change in the net solar radiation significantly affected potential evaporation from bare soils estimated by the Penman-Monteith equation. The sensitivity coefficients were positive, with a mean value of 0.82. The sensitivity of potential soil evaporation to soil heat flux was lower during the summer months and higher during the winter. The gradient of saturated vapour pressure–temperature curve increased or decreased the potential evaporation rates because of the occurrence of the gradient variable in both the numerator and denominator of the equation. Increases in the vapour pressure deficit increased the evaporation and its effect was more pronounced in the winter. In the case of aerodynamic resistance, the coefficients were constantly negative, and became more negative in the winter, which means a negative correlation between the input and output. In Aydın's equation, the dependent variable (actual soil evaporation) was initially very sensitive to a change in the water potential of a wet soil. The sensitivity decreased progressively during the drying period. The coefficients related to the absolute values of soil water potential were constantly negative, with a mean value of -0.19. The sensitivity of actual soil evaporation to air-dry water potential remained low in the wet soil and was higher in the drier soil. The sensitivity coefficient to measure the impact of potential evaporation on actual evaporation did not change during the study. According to Aydın and Uygur's equation, potential soil evaporation greatly affected the output (soil water potential) in the wet soils. In Kelvin's equation, increases in air temperature increased the absolute value of water potential at air-dryness. The sensitivity coefficients, owing to relative humidity, showed a great deal of fluctuation.