Impacts of Land Use and Climate Change on Flood Season Runoff in Tropical Islands

To analyze the impacts of land use and climate change on flood season runoff in tropical island regions, we selected the middle and lower reaches of the Nandu River basin in Hainan, a tropical river area, as the study area. We employed the SWAT model to simulate flood season runoff changes under different scenarios. Results indicate that, under the land use change scenario, converting cropland or planted forest land to natural forest land in the watershed reduces both the average monthly runoff and its variance during the flood season. Conversely, converting planted forest land to cropland increases these two parameters. The runoff generation capacity of cropland is larger than that of planted forest land and natural forest land in descending order. Under the climate change scenario, the average monthly runoff and its variance during flood season in the basin are directly proportional to rainfall and inversely proportional to temperature. Particularly, the flood season average monthly runoff changes at Longtang Station are more susceptible to climate change. In the integrated scenario, compared with the base period, the increment of average monthly runoff and its variance due to climate change significantly outweighs the decrease caused by land use change. Longtang Station shows higher sensitivity to climate change.