Toward reasonable and efficient simulations: A distributed model based on improved mechanism and confluence algorithm

Adequate description of phosphorus processes and high computational demand are core challenges in watershed modeling. In this study, a distributed model was developed, including rainfall-runoff module, erosion module, soil enrichment-loss module, watershed confluence-dissipation module, and river transmission module. To improve the efficiency of the distributed model, the recursive algorithms and Hash Tables are used. Besides, the Colloidal Phosphorus (CP) module was also added as its fate differs from Dissolved P (DP) and Particulate P (PP). The erosion module and soil P enrichment and loss module are modified based on the loss equations of colloids and CP with pH. The case stuty in the Three Gorges Reservoir area of China shows that the R 2 and NSE of the distributed model are greater than 0.4, indicating a good model performance. Compared with traditional models, the developed model has been improved in terms of computational efficiency and P process description. Compared with forward confluence method, the running time of new model is reduced from 6 s to 0.5 s. Also its calibration time was 66′4′’, 40′8′’ and 25′3′’ at a grid scale of 30 m, 40 m and 50 m, respectively. Compared to conventional two-phase model that can misestimate P loss, the new model can provide reasonable results. The developed model provides a methodological basis for precise simulation and prevention of non-point source pollution.