Study On Characteristics Of Rainfall Redistribution By Pinus Tabulaeformis Water Protection Forest In Miyun Reservoir

With the investigation data on the climate characteristics and water conservative forest resources of Beijing Miyun reservoir catchment aera, the approach of water balance based on canopy and litter was adopted to divide the hydrological course of the water protection forest into rainfall interception, stemflow, throughfall, water absorption for litter and ground runoff., and deal with a systematic research on the characteristics of the first distribution of precipitation and the redistribution of net rainfall.Based on rainfall data of Miyun reservoir catchment aera from 1999 to 2006, the characters of rainfall were analysed. It showed that the annual rainfall is various (the annual average rainfall is 660 mm), and the precipitation in wet years is 5.8 times that of dry years. The distribution of precipitation during the year is uneven, and 80 to 85 percent of the annual precipitation concentrated in the flood season (June to September). < 20mm / d of the small and medium sized rainfall accounts for total rain day of 64%.The characteristics of distribution of precipitation by Pinus tabulaeformis plantation in Miyun reservoir catchment aera were studied in the point of dynamic view. It was found that the intercepted water, stemflow and throughfall accounted for rainfall of 16.66%, 80.79%, and 2.55% respectively over the same period in the first distribution of precipitation; interceped water by litter, ground runoff, infiltration accounted for net rainfall of 4.29%, 0.12%, and 95.59% in the redistribution of net rainfall. Throughfall and stemflow have a positive-linear relationship with rainfall, and the percentage of throughfall and stemflow increase with rainfall. There is relationship between the rainfall and canopy interception as a power function. The interception increases with rainfall, and the percentage of interception decreases with rainfall contrarily, dropping down quickly during the initial rainfall period, then slowly, and finally reaching the canopy-saturated state.Through the survey and collection of litter form and experiments of water holding characteristics in Pinus tabulaeformis plantation, some characteristics parameter of forest hydrology were gained, such as the litter quality is 7.00t/hm~2 and 5.00t/hm~2 of non-decomposing litter layer and semi-decomposing litter layer, and the maximum interception per gram dry litter is 160g and 260g. All of these mainly depend on semi-decomposing organic layer. With the increase in rainfall, the capacity of litter interception boost up, but it will be no longer increase with rainfall increasing at a certain moment when the largest interception comes forth.The generation of runoff in wood land is affected by rainfall and the intensity of rainfall. Runoff emerges more easily in uncropped field than in wood land.Wood land have better capability in soil and water conservation.