Pentad Precipitation Changes During Recent 40 Years in Inner Mongolia

In order to study the characteristics of the pentad precipitation median changes in Inner Mongolia, the daily precipitation records of 44 meteorological stations from 1964 to 2003 in this area are analyzed. These 40 years are divided into two 20-year periods, one is from 1964 to 1983, and the other is from 1984 to 2003. From these daily precipitation data, the pentad (5 d) precipitations in each period are calculated and compared at 5-day interval (pentad), and then the clustering analysis is conducted.First, the optimal clustering number of the pentad precipitation change between the first period and the second period is determined by 4 determining indices, classifying the stations into 4 clusters. Then, based on the pentad precipitation differences between two periods, and k-means method, clustering analysis is conducted, so the spatial pattern of the clustered pentad precipitation differences are obtained. The lower temporal resolution data may mask some of the more subtle changes. Use of different time-resolution data can sometimes lead to different conclusions.The spatial uniformity of 11-day precipitation changes clustering is better than the 5-day result. This is most likely due to the different duration of the temperature and the precipitation process. Therefore, analyzing different climatic factors calls for different time-resolution data.By analyzing the polar plots of the pentad precipitations, it is clear that the patterns of the pentad precipitation change are different in different regions and seasons, and the spatial distribution of pentad precipitation change clusters shows that there is a zonation along the longitude. Meanwhile, medians of annual precipitations of the first period and the second period are compared, indicating that the annual precipitation has increased in the most parts of Inner Mongolia. It can be concluded that the seasonal and regional precipitation difference has increased.These changes reflects the correlation of the distribution and trends of precipitation with the intensity and trends of the East Asian monsoon, as well as the complexity of precipitation characteristics in the different climatic zones in Inner Mongolia.