利用一个集总式水文模型(CHARM),模拟了不同的气候与土地覆被条件下长江上游梭磨河流域的水量平衡,定量区分气候波动和土地覆被变化对水文影响的“贡献率”。模型模拟的初步结果表明,从20世纪60年代到80年代,径流深增加了45.7mm,其中,由气候波动所引起的年平均径流深的增加占63.9%,由土地覆被变化所引起的径流深的增加占20.8%,其他条件的变化所引起的径流深的增加占15.3%。

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.