Drought-stress modified crop coefficients for estimation of evapotranspiration of spring wheat in the southwest Loess Plateau of China

Abstract

Evapotranspiration (ET) is an important component of the surface water cycle. In this study, we analyzed the differences between the estimated ET using the crop coefficients (k_c) recommended by the Food and Agriculture Organization (FAO) and the measured ET with a lysimeter in Loess Plateau spring wheat (Triticum aestivum L.) from 2010 to 2012. Results showed that ET estimated from FAO-recommended crop coefficients (k_c-FAO) was significantly overestimated (55%) compared with measured ET by lysimeter. Evapotranspiration was sensitive to the relative available water (R_aw), and k_c were strongly dependent on drought stress in semiarid area (p < 0.001). Relative available water dependence of k_c increased with the decrease in R_aw. An improved k_c model based on k_c-FAO integrating drought stress factor was developed, and then an empirical ET model derived from the k_c approach was established based on the Penman–Monteith equation and the improved k_c model. The ET data measured by lysimeter from June of 2004 to May of 2005 were used to validate the proposed ET model. The estimated ET showed satisfactory consistency to measured ET with a linear regression coefficient of 1.01. Evapotranspiration modeling performance derived from the improved k_c model integrating drought stress factor was superior to that derived by k_c-FAO directly in semiarid area.