Study On The Affects On Surface Runoff Of Different Types Of Forest In Jianfengling, Hainan Island

In order to explore the water conservation function of tropical rainforest ecosystem, this paper did a quantitative study on a tropical rain forest named Hainan Jianfengling based on the observations of its rainfall and runoff from2007-2008through position monitoring and statistical analysis. It focused on analysis of the characteristics of rainfall and surface runoff; effect of flood control and drought relief of different types of forests during both the dry and rainy season; the impacts of different rainfall intensity on the surface runoff; the impacts of rainfall factors on surface runoff of different vegetation types. The results showed that:(1)The rainfall varies significantly by different months. The perception of the wettest month is500mm more than the driest season. Jianfengling Forest has a significant seasonal climate as the rainfall of dry season accounted for only10-20%of annual rainfall while the rainy season accounts for80-90%. Surface runoff lags about a month than the rainfall while the magnitude of change of the surface runoff is found to be smaller than that of the rainfall.(2)Jianfengling tropical rain forest has a water storage function of11660-18031m3per hectare during the rainy season. The water storage capacity of different forest types in the rainy season ranks from highest to lowest are:tropical montane secondary rain forest> original montane rain forest>lowland rain forest. The drought relief function of secondary forest is slightly better than the original forest in the dry season while that of the lowland rain forest is not significant.(3)The intensity of rainfall also affects the surface runoff. The impacts gradually reduce from extreme rain to light rain. The average increase of the runoff as follows:extreme rain228.3%; torrential rain178.4%; violent rain128.9%; heavy rain50.6%, moderate rain8.7%; light rain2.5%.(4) The impact of rainfall factors on the surface runoff varies according to different vegetation types. First, bivariate correlation analysis showed that the degree of correlation between rainfall factors and surface runoff as follows:rainfall> rainfall duration> rainfall of early three days>30min rainfall intensity> average rainfall intensity. The correlation between runoff and rainfall as well as rainfall duration is highly significant which indicates that heavy precipitation is more prone to follow a heavy surface runoff. Second, principal component analysis showed that the factors of rainfall, rainfall duration and average rainfall intensity all play a significant role in the change of the surface runoff and have a accumulated contribution of91.49%to the variation of all five factors. Regression analysis between the three principal factors and the surface rainfall showed a linear relationship and a high degree fitting.