Abstract: To effectively obtain the parameters to reflect the process of water movement in soil, a hydrodynamic parameter inversion model was proposed based on an improvd butterfly optimization algorithm (IBOA). Building upon the theoretical framework of soil water movement equations, firstly, the butterfly optimization algorithm (BOA) was used to find the optimal solution through the combination of global search and local search, and the switching probability in the BOA was obtained through the random walk algorithm, so as to improve the situation that the algorithm was easy to fall into the local optimum. Secondly, the improved algorithm was applied to the data under the conditions of using HYDRUS-1D to simulate the uniform distribution of unsaturated soil moisture in the initial water content. At last, the appropriate objective function was selected and the improved butterfly optimization algorithm was used for inversion. The results showed that the average relative error of the parameter inversion value of the improve butterfly optimization algorithm was 0.22%~3.60%, which could better invert soil hydrodynamic parameters. The improved butterfly optimization algorithm could effectively improve the accuracy of the estimated parameters and obtain high-quality global optimal solutions.

Key words: butterfly optimization algorithm, random walk algorithm, soil hydrodynamic parameters, objective function