Spatiotemporal trends of precipitation on the Loess Plateau of China

Abstract

Spatiotemporal trend of precipitation potentially influences vegetation restoration and soil erosion on the Loess Plateau. Daily data at 100 meteorological stations in and around the area from 1957 to 2009 were used to analyze the spatiotemporal trends of precipitation and the return periods of the different types of precipitation classified in the study. Nonparametric methods (Mann-Kendall and Sen's slope estimation) were employed for temporal analysis and Kriging interpolation method, for spatial analysis. The annual precipitation was detected to have a slight decreasing trend at 0.1 significance level on the Loess Plateau and no change point existed. The decreasing rate changed from a negative value up to -3~-7 mma -1 in southeast to a positive value up to 1~2 mma -1 in northwest. The average annual decreasing rate was found to be -1.15 mm a -1 accounting for 0.26% of the average annual precipitation. The area with decreasing trend accounted to 86% of the total area of the Loess Plateau. Only except for the winter, the regional precipitation in other seven time series, i.e., spring, summer, autumn, wet season, dry season, EFP (early flood period), and LFP (late flood period), presented insignificantly decreasing trends. The areas for the seven time series were up to 70%, 72%, 83%, 84%, 90%, 56% and 89% of the total area, respectively. The shifts of the 150, 250, and 350 mm isohyets were not evident between the decades. The weighted average centers of the 450 and 550 mm isohyets moved 134 km eastwards and 213 km westwards from 1960s to 1990s. However, the two centers retreated 12.1 km westwards and 54.8 km northwards from 1990s to 2000s. The frequencies of the precipitation types defined with Moderate, Heavy, Rainstorm, and Heavy Rainstorm were detected to have decreasing trends from 1960s-2000s, based on the decadal analysis. The return periods of the four types of precipitation changed from 0.13, 0.39, 1.82, 19.80 a in 1960s to 0.15, 0.39, 2.34, and 26.88 a in 2000s. Results indicates a small drier precipitation change of no significance given by Mann-Kendall test, the shifted southward precipitation isohyets, a slightly delayed rainy season, and the prolonged return period especially in rainstorm and heavy rainstorm types in the last 53 years. Global climate change seemly did not influence the Loess Plateau of China greatly, but the variations of precipitation apparently took place both in spatial and temporal dimensions on the Loess Plateau from 1960s to 2000s.