Spatial-temporal Change Of Extreme Precipitation And Their Effects On Relation Of Runoff And Sediment In Yanhe Basin

With the aggravation of global climate change, the frequency and intensity of extreme precipitation events are increasing. The Loess Plateau is the sensitive area with global climate change, and the most serious area of soil erosion in the world. Extreme precipitation is the important factor affects the soil erosion in this region. Human activity, especially the returning farmland to forest and grassland, has the important influence on the soil erosion and changes of the runoff and sediment in this region. What is the trend of extreme precipitation in the Loess Plateau? does the effect of extreme precipitation on the variation of soil erosion and runoff and sediment change with the returning farmland to forest and grassland in this region. Based on the above scientific questions, the paper choose the Yanhe Basin in Loess Hilly and gully region as the research object, analyzed the temporal and spatial variation of 10 stations 12 extreme precipitation indexes from 1970 to 2010 in the Yanhe Basin. In order to clarify the influence of extreme precipitation and revegetation on changs of water and sediment in the Yanhe. Specific conclusions were as follows:the paper analysed spatial and temporal variation of the extreme precipitation intensity, frequency and extent of wet and dry characteristics analysis of the Yanhe Basin, nearly 40 years(1970 to 2010). Extreme precipitation intensity, such as PRCPTOT, R95 p, Rx1 day, Rx5 day, SD II and D showed no significant change in the trend, but showed significantly increasing trend after 2000. The characteristics of extreme precipitation frequency, R25 showed an increasing trend from 1970 to 2010, while R50 decreased, but the M-K trend test is not significant. The two indexes showed an increase trend after 2000. The wet and dry characteristics of extreme precipitation, the trend of CWD(1970 to 2000) decreased, but increased after 2000. The CDD were not significant, but the change was significantly reduced after 2000.By the Pettitt change point detection method, detected mutations of runoff and sediment transport of Yanhe. Taking this mutation as the boundary, analysed the influence of extreme precipitation on runoff and sediment load. The pettitt change detection showed that the mutation of runoff and sediment discharge change in 1996. The cumulative curve and double cumulative curve method results showed, extreme rainstorm had significant linear correlation with runoff and sediment, extreme rainstorm had direct impact on runoff and sediment yield; extreme rainstorm had no obvious linear relation with runoff and sediment from1996 to 2010. Human activities especially returning to forest and grassland was an important factor of runoff and sediment load variation.