| The Minjiang River valley (MRV) is the first key tributary of the Yangtze River, which functions as an important area for ecological screen in the upper reaches of the Yangtze River and economic development in Sichuan. The ecological safety of the Minjiang River valley is vitally important in ensuring economic development of Sichuan and in guarantying ecological safety in the Yangtze River valley. However, its serious water and soil loss is bringing a series of problems in both economic development and ecological safety in this region.Based on remote sensing data of 1995 and 2000 of the MRV and field investigation in 2005, changes of soil erosion and their driving factors in the MRV was studied. Based on the Markov model, the evolution of soil loss between 2005 and 2025 was predicted. Meanwhile, some countermeasures were suggested for integrity of project in controlling soil erosion in the study area. The results were shown as follows:(1) A total area of soil erosion in the MRV in 2000 was 19907.7km~2, among which water-caused erosion rated 88.24%, and the area of freezing-thawing erosion was 3326.28 km~2 and that of wind erosion was 5.34 km~2. Compared with the situation in 1995, the soil erosion rate was decreased by 0.81% and its total area was 369.6km~2, among which freezing-thawing erosion shared an area of 326.26 km~2 and the wind erosion shared 0.55km~2. As for different erosion levels, the area of light erosion was increased by 148.99km~2. Totally, soil loss in the Minjiang River valley amounted to 89.4325 million ton under an average modulus of 1966 t/km~2.a in 2000.(2) Based on Chinese Criterion for soil erosion classification, the MRV could be categorized into three regions, which were named as moderate water-caused region in the upper reaches, light water-caused soil erosion region in the middle reaches and moderate water-caused soil erosion region in the lower reaches. Soil erosion rate in the three regions was 52.88%, 21.7% and 50.04% respectively in 2000. Compared with those in 1995, the erosion rate was reduced 0.2%, 5.08% and 3.6% respectively.(3) Through forecast by application of the Markov model, the soil erosion area in the MRV from 2005 to 2025 was in a descending trend, by an area decrease of 1452.87 km~2 and by an amount of 3.1736 million tons every five years.(4) Driving forces for soil erosion in the MRV could be diagnosed as both natural factors and human factors. On basis of comprehensive analysis of precipitation changes, land use changes, population density, vegetation coverage, GDP (per thousand Yuan RMB), the results suggested that rainfall erosivity contributed more than other factors at an effect coefficient of 0.71 whereas while forest coverage increased by 1%, average soil erosion modulus would reduce by 53 t/km~2.a. Moreover, regression analysis showed that relationship of between erosion area and the area of forestland and grassland was in a significant linear depiction, that between erosion area and cropland area was in a significant quadratic depiction, that between soil erosion area, soil erosion quantity and GDP was in an exponential depiction, and that between soil erosion area, soil erosion quantity and population density was in a significant power depiction.(5) For sake of integrated controlling of soil erosion in the Minjiang River valley, regionalization and an optimum regime should be firstly formulated on the basis of existing problem probing and sustainable management objectives. Due to the complexity of soil erosion changes in the Minjiang River valley, the priority region and the key region for soil erosion control were mainly in the upper reaches, and the countermeasures were suggested as farming slope harnessing, ecosystem restoring and protecting, mountain hazards control, soil loss monitoring and preventing and even some more reforms in administrative policies.
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