Study On Spatial Variability Of Precipitation Of Different Spatial And Temporal Scales On Loess Plateau

Water is the most sensitive ecological element on the Loess Plateau. The temporal and spatial variation and the distribution of precipitation is an important factor on the Loess Plateau ecosystem where there was a lack of water resource, so precipitation become an important input variable of ecological, hydrological and soil erosion simulation. The temporal and spatial variability of precipitation has been a hot research topic. The spatial patterns of precipitation variability, which has great significance on regional precipitation simulation and water and sediment process assessment, is important to natural revegetation, plantation construction and the ecological environment management. The purpose of this study was to analyze the characteristics of the spatial variability of precipitation in the Loess Plateau and to determine the precipitation homogeneous space of different temporal and spatial scales. This helps to determine the scale and range of the impact of the precipitation and provide the basic information for research and practice in the relative field.Three different spatial scales which were the Loess Plateau, Dali River watershed and Chabagou watershed were taken as study area, and traditional statistical methods and Geostatistics was used to determine precipitation homogeneous space of different temporal and spatial scales. First, annual precipitation data (from1959to1985) from56hydrological stations and monthly precipitation data (from1960to1985) from34meteorological stations were used to analyze spatial variability of precipitation of different time scales on Loess Plateau.Second, breakpoint rainfall data (from1959to1969) in Dali River watershed and Chabagou watershed were used to analyze spatial variability of precipitation parameters of different spatial scales.The main results of this paper are as follows: Spatial variability of precipitation of different time scales on Loess Plateau:(1) both of the coefficient of variation of annual precipitation and monthly precipitation were between0.1and1, which suggested moderate variability; most of coefficient of variation of station maximum daily precipitation were greater than1, which suggested strong variability; most of the coefficient of variation of daily precipitation (5%probability) were between0.1and1,while a small amount were greater than1.(2) the average and minimum homogeneous range of precipitation of different time scales in descending order were yearly,daily and monthly; the average range of annual precipitation was495.8km, and the smallest homogeneous range was142km; the average range of monthly precipitation was256.5km, and the smallest homogeneous range was12.2km; the average range of station maximum daily precipitation was451.2km, and the smallest homogeneous range was41km; the average range of daily precipitation (5%probability) was408km, and the smallest homogeneous range was42km. The homogeneous space of annual, monthly and daily precipitation varied greatly which meant that the interpolation needed to use the smallest homogeneous range.(3) Moran’s I correlation distance of annual precipitation was concentrated in280-300km; Moran’s I correlation distance of monthly precipitation was concentrated in80-160.3km; Moran’s I correlation distance of station maximum daily precipitation were between250to333.3km; Moran’s I correlation distance of daily precipitation (5%probability) were between200to250km. Moran’s I correlation distance of different time scales in descending order were yearly,daily and monthly.Spatial variability of rainfall event parameters of different spatial scales:(1) spatial variability of precipitation:most of the coefficient of variation of event precipitation of Dali River and Chabagou watershed were between0.1to1, which suggested moderate variability. The range of precipitation of Dali River watershed was evenly distributed which indicated that event precipitation varied greatly, and the smallest homogeneous range was7.3km; while the range of precipitation of Chabagou watershed was concentrated in18-19km which accounted for60%of the total. Moran’s I correlation distance of precipitation of Dali River watershed were between11to34.1km, and the average of Moran’s I correlation distance was22.3km; while Moran’s I correlation distance of precipitation of Chabagou watershed were between2.7to9.1km, and the average of Moran’s I correlation distance was5.7km.(2) spatial variability of duration of rainfall:most of the coefficient of variation of duration of rainfall of Dali River and Chabagou watershed were between0.1to1, which suggested moderate variability. The range of duration of rainfall of Dali River watershed was concentrated in85-105km; while the distribution of the range of duration of rainfall of Chabagou watershed was more dispersed.(3) spatial variability of average rainfall intensity:55percent of the coefficient of variation of average rainfall intensity of Dali River were between0.1to1which suggested moderate variability, and45percent of the coefficient of variation were greater than1which suggested strong variability. While most of the coefficients of variation of average rainfall intensity of Chabagou watershed were between0.1to1which suggested moderate variability. The range of average rainfall intensity of Dali River watershed was concentrated in10-30km; while the distribution of the range of average rainfall intensity of Chabagou watershed was more dispersed.