A framework to develop a watershed pollution load model for semiarid and semihumid areas

Modeling pollutant processes in soil and water is helpful to better understand a pollutant's potential adverse impacts on an environmental system. There are many watershed pollution load models; however, their effectivity is generally poor in semiarid and semihumid areas because of the complexity of hydrological processes and pollutant transport processes. In this paper, a pollution load module was combined with the well-established HIMS (Hydro-Informatic Modelling System) model for the purpose of simulating the processes of pollution generation and transport and quantifying the pollution load in semiarid and semihumid areas. The model has the advantages of a simple structure and low data requirement, and can simulate dissolved and solid-phase nitrogen and phosphorus. As a demonstration, the HIMS-pollution load (HIMS-PL) model was respectively tested for three semiarid and semihumid basins in China-the Liuhe and the Yixunhe River basins, two sub-basins of the Luanhe River basin, and the Chaohe River basin. Model simulations of streamflow and pollution loads at monthly time step accurately matched the observed streamflow (with NSEs 0.77-0.95 and REs 0.53-11.24%) and pollution load (with NSEs 0.54-0.83 and REs 2.45-12.72% for total nitrogen loads and with NSEs 0.51-0.79 and REs 2.22-19.70% for total phosphorus loads). In comparison with HSPF and GWLF models, the HIMS-PL model performed better than the GWLF model in all of the above-mentioned basins and better than the HSPF model in some of the basins. Overall, the proposed model is generally suitable for simulating streamflow and pollution load in semiarid and semihumid regions.