Soil hydraulic properties in arid regimes are essential to evaluate drying processes of soil; however, in-situ measurements of the properties are time-consuming and difficult to execute. We investigated the characteristics of semi-derivatives (half order fractional derivatives) of soil water variation in drying obtained from finite difference solutions. The semi-derivatives of soil water change in dry layers, where gravitational effects on soil water movement were negligible, were almost linearly related to the vertical gradients of the soil water profiles. The coefficient of linearity agreed well with square root of the soil water diffusivity. Initial and boundary conditions had few effects on the result. Based on the characteristics of the semi-derivative, soil water diffusivity in-situ was estimated using soil water contents measured by the time domain reflectometry at two depths. Application of the fractional derivative to estimate soil water evaporation rate, soil thermal diffusivity, and heat flow in soil will also be discussed.