Erosive Rainfall and Characteristics Analysis of Sediment Yield on Yellow Soil Area in Karst Mountainous

Erosive rainfall research is the basis of calculation of slope erosion. Because of the short data sequence, it is difficult to draw valid conclusions in previous research on yellow soil area in karst mountainous. Some studies focus on the micro process of observation that can't spread on the large scale application for natural conditions. To establish the erosive rainfall index and its standard for different underlying surface and simulate the condition of watershed rainfall-erosion with relevant background information have important significance to the water erosion prediction of yellow soil area in karst mountainous. Two small watershed are observed separately in the central and western of Guizhou from 2009 to 2013. The data of rainfall and sediment yield for plough, grassland and man-made forest runoff plot are recorded in each watershed. Then the minimum deviation factor of rainfall erosivity and their corresponding precipitation and rainfall intensity standard can be calculated by the runoff plots data. Relative error, elimination rate and loss rate have been used to evaluate the optimal erosive rainfall standard. On the basis of these results, relevant indexes about erosive rainfall and characteristics of sediment yield in different underlying surface were researched. The conclusions of the study can be drawn as follows: 1) The best structure of rainfall erosive agent index is the product of rainfall kinetic energy and maximum 30 min rainfall intensity. Rainfall erosive agent index can be also calculated with the product of rainfall amount and maximum 30 min rainfall intensity. 2) The erosive rainfall index of bare yellow soil should use maximum 30 min rainfall intensity with the value range from 9.6 to 10.2 mm·h-1, and the plough use rainfall amount standard better which is about 15 mm. Soil and water conservation measures can increase erosive rainfall standard apparently. 3) Erosive rainfall account for 36% and 38% of the total rainfall in the central and western of Guizhou for the average year which mainly distribute form May to August. The rainfall erosivity for the average year is about 1 700~1 800(MJ·mm·hm-2·h-1·a-1)which is significantly lower than the red or purple soils on the same latitude. The annual distribution of the slope sediment yield is extremely uneven. A handful of rainstorms course most of the sediment yield. 4) The shrub grassland without human disturbance has the best effect of soil and water conservation. Corn planted with the measure of downslope cultivation can seriously intensify soil erosion. Reduce human disturbance is the key to management in soil and water conservation.