Abstract: Soil moisture is one of the most important indexes on water resource circular studies and drought monitoring. Based on the soil water balance principle,the point that the main influential factor of the soil moisture was the antecedent effective rainfall under the situation of no irrigation was brought forward. The soil moisture data of Jingzhou in 1982-2006,Suizhou and Macheng in 1993-2006 were used to construct the linear regression equation between the effective rainfall and the soil moisture in the layers of 0-10cm and 10-20cm. The model checking results showed that the accuracy ratio of the forecast to the observed soil moisture was about 85% in the layer of 0-10cm and over 85% in the layer of 10-20cm,while the accuracy rate of the drought monitoring in and winter of 2007 in part areas of Hubei Province was over 93%. Compared with other empirical models,the model could be used without the antecedent soil moisture data,and it had more scope application and higher time-effect,so it was much easier to generalize.

Key words: Effective rainfall, Effective rainfall, Soil moisture, Model, Soil water balance