Simulation of the impact of climate fluctuation and land-cover changes on annual runoff in the Suomo Basin

Abstract

Forest degradation has been widely acknowledged to be the main cause for the 1998 Yangtze River flooding. Of the two crucial reasons of for flooding,climate fluctuation and land-cover change,which one on earth acted as the leading factor? In order to probe this issue, the Suomo Basin on the upper reaches of the Yangtze River was chosen as a study area. About forty years' climate fluctuation and land-cover changes in the Suomo Basin were analyzed in this paper. Precipitation deceased by 19.3 mm from the 1960s to the 1970s and increased by 61.2 mm from the 1970s to the 1990s. According to three decades land-cover maps, the primary land-cover changes are that forestland turned into sparse and shrub by forestland, and the shrubby and sparse forestland turned into grassland. Forestland deceased by 12% from 1970 to 1986. A dump hydrological model, CHARM (Climate and Human Activities-sensitive Runoff Model), was adopted to simulate the impact of climate fluctuation and land-cover changes on runoff discharge and to divide their contributions to annual runoff. From the 1960s to the 1980s, runoff depth increased by 45.7 mm. Among them, 63.9% was caused by climate fluctuation, 20.8% was the result of the land-cover changes and the remaining 15.3% was system error. In other words, 1/5-runoff change was caused by land-cover change and 3/5-runoff change was caused by climate fluctuation. From this simulated conclusion, we can get an elementary explanation about the Yangtze River flooding in 1998. Possibly it is climate fluctuation,rather than forest degradation that is the leading factor for the flood.