Flood response to urban expansion in the Lushui River Basin

This study used a cellular automata Markov model (CA–Markov) to predict future urban expansion scenarios in the Lushui River Basin and a Hydrological Simulation Program-Fortran flood model (HSPF) to simulate the flood process. Flood trends were analyzed based on both measured and simulated data, and the flood response to urban expansion was characterized. This study had four main conclusions. (1) The HSPF and CA–Markov models accurately simulated flood processes and urban expansion in Lushui River Basin. (2) The area of construction land in the basin has continued to increase since 1980. Based on current development rules, 22% of the basin will be construction land by 2048. Therefore, land-use planning policies must be strengthened, and the utilization of rural lands must be increased, to help slow the growth of constructed land areas. (3) Urban expansion in the Lushui River Basin has increased the flood runoff depth by about 1–3% and peak discharge by about 6–18%. The magnitude of the impact was related to the return period of the flood: Floods with a shorter return period are more strongly impacted by urban expansion. (4) Compared with the current development model, the three future scenarios for 2048, obtained after strengthening land-use planning policies, all have the effect of reducing floods. Integrating scattered villages, ensuring basic farmland areas, and returning some farmlands to forests most significantly reduced flood impact.