The Impact of Reforestation Induced Land Cover Change (1990-2017) on Flash Flood Peak Discharge Using HEC-HMS Hydrological Model and Satellite Observations: A study in Data Scarce Tributary of Sichuan Basin, China

The Grain to Green Program (GTGP) and the Natural Forest Conservation Program (NFCP) have had a substantial impact on land use and land cover (LULC) in China. This study investigates the effect of these conservation programs on flood peak discharge in an ungauged mountainous catchment in southwestern China and used a series of Landsat images ranging from 1990 to 2017 and Hydrological model. We conducted a supervised classification of Landsat images (1990, 2000, 2008 and 2017) using the Maximum Likelihood Classifier (MLC) algorithm to generate historical LULC maps. A physically based model, the Hydrologic Modeling System (HEC-HMS) was used to quantify the isolated impact of land cover changes on peak discharge while keeping other model inputs constant. The results indicate that between 1990 and 2017, the catchment area of forest (15.69%) and built-up areas (8.1%) increased and agricultural land (-23.74%) decreased. The simulation results for various LULC changes scenarios indicate that flood peak discharge have decreased to different degrees (up to -6.3%) compared to the baseline scenario. At the sub-basin scale, the peak discharge further decreased up to -19.9%. The sensitivity analyses indicated the forest cover as the main land cover type responsible for flood peak reduction. Moreover, the effect on peak discharge of land cover changes was more significant for small to moderate rainfall than for extreme storm events. Thus, the land cover changes influenced by the GTGP and NFCP certainly exerted a negative effects on flood peak discharge in the catchment outlet. Although, more data is needed for model validation, the findings of this study demonstrated that the implementation of GTGP and NFCP helped in reducing flood hazards in the study catchment. Furthermore, this study would provide support in conservation policies formulation.