Climatic Features of Rainfall in the Loess Plateau in China

Abstract

We have researched environmental monitoring to support anti-desertification activities in the Loess Plateau. In this thesis, the spatial distribution, the variance (stability) and the trend of annual precipitation were studied. In addition, the stability of precipitation in the summer rainy season was estimated from the viewpoint of seasonal features of precipitation. The sampling distribution of the mean of the annual precipitation was resampled by the Bootstrap method at each observation point, and the mean of the annual precipitation was estimated by interval estimation. The time series trend of the annual precipitation was analyzed by using the interval estimation mean of the annual precipitation. The stability of precipitation in the summer rainy season was analyzed from the relationship between the precipitation ratio and the precipitation stability index for the period of five days. It seems that the mean of annual precipitation was the lowest in the Tengeri Desert and the Wulanbu Desert. But the region on the Quilian mountain range at the west side of those deserts near Menyuan had much precipitation. The rainfall increased in low-latitude regions. The variation of annual precipitation was the largest in the northern Maowusu Desert, the northeastern Wulanbu Desert, and around Wugong. In contrast, the variations of annual precipitation were small around Menyuan. We could not see a trend for annual precipitation in the whole of the Loess Plateau from 1980 to 2000. However, it seems that there were significant trends at a few observation points. We proposed the rainy season stability index {RSS(j)} based on the relationship between the precipitation ratio PRP(t, j) and the precipitation stability index PSI(t, j). The analysis of the feature of precipitation by using RSS(j) clarified that the rainy season is not equally stable between the east side and the west side of the Loess Plateau, even if the annual precipitation is at the same level.