km km ~ m

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1 ~ JO UR N AL O F M O UN TAIN SCIEN CE Vol. 29 No. 5 pp561 ~ 565 Sept SWAT 30% ~ 40% 35% ~ 40% 5% P343 A km km ~ m Landsat TM % 11% 8% 67% 2% Received date Foundation item National Nature Science Foundation of China Biography Cheng Genwei male research professor engaged in the research on hydrology and ecology. E - mail gwcheng@ imde. ac. cn

2 Fig. 1 The location of the Suomo watershed A. B. C. D. E. F. G. H. I. J. K. L. M. N. A. subtropical evergreen broadleaved B. subtropical evergreen deciduous C. Fabris D. hard evergreen broadleaved E. spruce and birch mixed forest L. temperate zone coniferous forest M. subtropical coniferous forest N. Larix potaninii 2 Fig. 2 Comparison of water conservation of typical forest types in upper Yangtze river mm > mm > mm > mm > mm > mm > mm > mm mm ~ mm 3 p < mm > mm > mm > mm > mm > mm > Fig. 3 Relationship between litterfall and its water capacity

3 5 563 Fig Comparison of observed and simulated hydrographs for Suomo river S1 SWAT 6 SWAT 0% - 2 S SCS 22% CN Curve Number - 3 S3 40% S % - DEM C max SWAT C max CN a SWAT 5 SWAT a - 40 a S1 7 a m 3 /s S m 3 /s S m 3 /s S4 320 m 3 /s CN 250 m 3 /s S1 1 a S2

4 % ~ 40% 5 Fig. 5 Flood frequency distributions for different forest coverage of Suomo watershed 3 a S3 4 a S4 5 a 5 S4 S % S3 S4 5% S2 S3 20 a 40 a 6. 8% 9% 10 a 10. 6% ~ 19. 3% 500 ~ S km 2 35% S2 S3 30% ~ 40% 100% 5% 35% ~ 40% % 5% References 1 Conway D. Understanding the hydrological impacts of land-cover and 3 Cheng Genwei. An approach to the relationship between runoff char October 2000 Background Paper No. 1. FAO Rome acters and forest in the basin of Sichuan J et aquae Sinica J % ~ 40% protective forest system J 80% 50% Fig The flood detention-storage effects of forest ecosystem and the optimal forest coverage land-use change J. IHDP Update No Calder I. Land use impacts on water resources G / /Land - Water Linkages in Rural Watersheds. Electronic Workshop 18 September. Acta conservation soli Cheng Genwei. The quantitative indexes of the ecological effects of. J. of Soil and water conservation 1991

5 5 565 J Cheng Genwei Zhong Xianghao He Yucheng. The reviews and recent progress in forest hydrology J. Exploration of Nature J. J Arnold J G Srinivasan R Muttiah R S et al. Large area hydrologic modeling and assessment Part I model development J. Journal of the American Water Resources Association Sun G Riekerk H Comerford N B. Modeling the Hydrologic Impacts of Forest Harvesting on Florida Flatwoods J. Journal of the A- merican Water Resources Association Chen Junfeng Li Xioubing. Simulation of hydrological response to land-cover changes J. J. appl. Ecol Shi Peili Wu Bo Cheng Genwei. Water retention capacity evaluation of main forest vegetation types in the upper Yangtze basin J. J. of Natural Resources J Simulation of Forest Impacts to the Flood Frequency Characteristics of Mountainous River in South-western China CHENG Genwei 1 SHI Peili 2 TIAN Yu 1 1. Institute of Mountain Hazards & Environment CAS Chengdu China 2. Institute of Geography Science and Resources CAS Beijing China Abstract Forest logging or reforestation will singnificantly influent the generation condition of hydrographes. The flood peaks and total volume may change with the variation of forest coverage. But it is hard to selecte a proper method to evaluate this impact quantitatively. In the paper a distributed hydrological mathematical model SWAT is used to simulate the hydrographies of the Shuomo River south-western China. The flood frequency curves are derived from the modeled flood events by this model. Based on the frequency analyses of flood events for different forest coverages one can find that the reducing rate of flood peak is about 35% at the most advantaged forest condition. The main part of flood reducing effect is come down with forest ratio in 30% - 40%. It has only 5% difference in flood reducing effect comparing with the most possible forest coverage 100%. These results mean that the optimal forest ratio for south-western China is between 30% - 40%. This criterion can be application in the planning of ecological rehabilitation engineering. Key words forest change flood features impact evaluation