气候变化和人类活动对吴起土壤侵蚀的影响

通过分析GIMMS和SPOT VEGETATION的NDVI数据，1997年和2007年TM卫星数据，以及吴起降水、径流、输沙量等资料，利用相关分析，回归分析，并建立数学模型，得出结论。发现吴起1999-2007年9 a中NDVI增加了24.4%，退耕前后NDVI比较，冬季的变化较小，植被生长季节的4-10月NDVI有明显的差值，平均相差0.039，9月相差最为明显，达到0.062，其次是5月、10月和8月。与1997年相比，到2007年吴起县有75.15%耕地不再耕种，退出的耕地主要变为草地、林地和果园；林草覆盖率增加显著，由1997年的37.06%提高到2007年的80.60%；高坡度耕地绝大部分实现退耕，>25°的坡耕地80%～90%实现了退耕；低植被覆盖度的土地面积在大幅度减少，相反高植被覆盖度的土地面积在大幅度增加，退耕还林（草）的成绩是显著的，生态环境有了明显的改善。模型计算表明，退耕还林工程产生了较明显的水土保持效益，平均减水效益32%，减沙效益53.6%，土壤侵蚀明显降低。人类活动因素的贡献率远大于降水因素。

Effect of Climate Change and Human Activities on Soil Erosion in Wuqi

Regression analysis and establishing mathematical model by use of correlation analysis after analyzing the data on NDVI of GIMMS and SPOT VEGETATION, TM satellite data in 1997 and 2007, precipitation, runoff and sediment discharge, and draw the conclusion that the NDVI increased by 24. 4% in the 9 years from 1999 to 2007 in Wuqi. There has obvious advantage in Aprail-October vegetation growing season, and with less change in winter by compared NDVI before and after farmland. The mean differences is 0. 039, it is 0. 062 in September, and is the most obvious, next came the May, October and August. Compared to 1997, with 75.15% of cultivated land is no longer farmed in 2007 in Wuqi. The withdrawal of the main arable land into grassland, woodland and orchards, forest coverage increased significantly, to 80.60% in 2007 from 37.06% in 1997 ;high slope cultivated land most returned, the 80%～90% of slope(>25°) land returned;low vegetation coverage of the land area reduced greatly, on the contrary, high vegetation coverage of the land area apparently increased, the achievement of returning farmland to forest (grass) is remarkable, the marked improvement in the ecological environment. Model calculations show that returning farmland to forest project produced a more obvious benefits of soil and water conservation, the average benefits of water reduction is 32%, it is 53.6% of sand reduction and, soil erosion decreased significantly. The contribution of human activities factor is much greater than precipitation.