Impacts Of Picea Crassifolia Forest On Runoff In Pailugou Watershed Of Qilian Mountains

Based on the hydrological processes of mountains in temperate zone, the hydrological processes model TOPOG was improved, which is designed on the environment conditions of tropic regions. In order to image snowmelt process, a module about snow and snowmelt was joined in TOPOG model. Then, the calibration and validation of TOPOG model was done using the meteorological and hydrological data measured at the outlet of the watershed in 2001 and 2002. The error of daily runoff simulated by TOPOG was less than 0.41 mm/d and 11%. Thus it can simulate the runoff of the small watershed. To find out the impacts of the amount of forest (Picea crassifolia) on the runoff generation of Qilian Mts., 23 vegetation scenarios (Picea forest cover ratio varies from 0.41% to 46.33%) were modeled by TOPOG model. Besides, in order to find out the hydrological impacts of forest spatial distribution, three scenarios of forest spatial distribution, i.e. higher position (the Picea forest distributes in the elevation of 3100-3300 m), medium position (the Picea forest distributes in the elevation of 2850-3050m) and lower position (the Picea forest distributes in the elevation of 2650-2800m) were made and simulated.The results suggest that:1. The hydrological effects of forest area When the forest cover ratio increases from 0.41% to 46.33%, the annual runoff is decreased from 196.58 mm/yr to 78.89 mm/yr. Their relationship is following: where x is the forest cover ratio (%), y is the annual runoff (mm/yr), the correlation coefficient R is 0.95. When the forest cover ratio increases 1%, the peak flow decreases by about 1% compared with no forest in the wateshed.2. The hydrological effects of forest distributionWhen the location of Picea forest is higher, the annual runoff will be lower. But this effect is slight such that the annul runoff varies from 162.90 mm/yr to 166.65 mm/yr when Picea forest with the cover ratio of 16 % distributes in the elevation of 2600-3300 m. The forest distribution strongly affects on the peak flow. For example, the mean highest peak flow of one year is 0.3749 m3/s and varies by 4.65 % when the Picea forest with the cover ratio of 16% distributes in 2650-3300 m.