Numerical difference in soil water between vertically stratified and homoge-nized soil profiles

For many land surface process models, soil moisture is described quantitatively by assuming that its vertical distribution is uniform and that the upper soil texture is representative of the whole soil profile. There are differences in soil moisture between stratified and homogenous soils, which have been little documented so far in research. By setting up three stratified soil groups with different soil hydraulic conductivity combinations and using the upper soils as representative of the soil profiles of the three stratified soil groups, one-dimensional soil water movement model was established to analyze the differences in soil moisture. At the same time, the sensitivities of five parameters (including saturated hydraulic conductivity, saturated water content, residual moisture content, pore size distribution and particle shape) to the differences in leakage and water storage between stratified and homogenous soils were analyzed. It was found that:1) soil water profile simulated by the one-dimensional soil water movement model was consistent with that simulated by Yeh Analytical Solution and also that by Water Transformation Dynamical Processes Experimental Device (WATDPED) experiment. This proved that the model was reliable irrespective of whether root water uptake was considered or not. 2) The greater the difference in saturated hydraulic conductivity between upper and lower soils, the greater the difference in hydrological variables of homogeneous and stratified soils. When saturated hydraulic conductivity of the upper soil was 1.5 times that of the lower soil, the difference in soil mois-ture distribution between stratified and homogeneous soils was less than 0.05 cm³·cm^-3. When it was 3.3 times, the differences in soil moisture, leakage and water storage were 0.15 cm³·cm^-3, 20 cm and 5 cm, respectively. 3) Compared with the lower layer of stratified soil, water holding capacity of the lower layer of homogeneous soil was lower and with water outflow was faster, which resulted in lower moisture distribution, higher leakage and lower storage capacity in lower layer of homogeneous soil. 4) Soil particle shape (n) was the most sensitive parameter to leakage. Then pore size distribution was the most sensitive parameter to water storage, followed by soil particle shape n. In reality, if upper and lower soil saturated hydraulic conductivities differed largely, homogeneous treatment induced significant errors, differing greatly from actual soil moisture distribution in the layers. This heavily affected the accurate estimation of soil moisture, which required a realistic consideration of the use of this practice.