Discussion Of Precipitation Variation In Ningxia And Its Relationship With The Heating Field Of Tibetan Plateau

Drought is the most widely distributed natural disaster in Ningxia which causes most losses to agriculture. To study the variation law of precipitation in Ningxia and make better prediction on precipitation is beneficial for the social-economic development and disaster prevention and mitigation capabilities. There are too many factors that effect the precipitation in Ningxia, and the heating of Tibetan plateau is one of the most important factor, but studies of this region is rare. In this paper, we analyzed monthly precipitation data of 20 weather stations in Ningxia and the heating field data of Tibetan plateau during 1961-2012,and studied the relationship between seasonal variation of precipitation and heating field of Tibetan plateau, and also studied the effect of circulation and vapour transportation to the formation of precipitation in Ningxia. In order to eliminate the harmful effect of inhomogeneous distribution of precipitation, we divided Ningxia into three climatic regions. Firstly, we studied the variation trend of seasonal precipitation in the three regions, then induced variation characteristics of precipitation in Ningxia. Secondly, we analyzed time series of seasonal precipitation in three regions using Mann-kendall method and moving t-test method, and compared the two analysing results, then discovered the mutation period of precipitation in Ningxia. Thirdly, we studied the distribution law of precipitation of Ningxia using EOF method, and found out the distribution characteristics of precipitation, and also discovered the regions where the precipitation mutation most likely to emerge under different EOF modes. Finally, we analyzed correlation between Tibetan plateau heating field and monthly precipitation in each climatic region using correlated synthetic method.The main conclusions we got are as follows:1. The variation law of seasonal precipitation in three climatic regions were analyzed, the result shows: The precipitation in Ningxia was inhomogeneous; it decreased successively from south to north. Annual precipitation showed downward trend with fluctuant variation and most obviously in southern mountain area. Precipitation in summer and autumn decreased most obviously, and the autumn precipitation in southern mountain area decreased significantly with 9.58mm/10 a. Winter precipitation in three climatic regions increased slightly.2. The mutation of precipitation in Ningxia was analyzed by using Mann-kendall method and moving t-test method, then we compared the two analyzing results, and found that Mann-Kendall method is better than moving T-test method. The autumn average precipitation in whole region and precipitation in central arid area and southern mountain area all passed the test of significance; it accords with the obvious precipitation variation period and region. The precipitation mutation emerged in early 60 s, after that period precipitation in Ningxia varied from more to less.3. The distribution mode of precipitation in Ningxia was analyzed. There are three main precipitation distribution modes, in mode 1, the precipitation distribution was accordant in whole region of Ningxia; in mode 2, the precipitation distribution in southern and northern part of Ningxia was different; in mode 3, the precipitation distribution in central and southern and northern part of Ningxia was different. In different season, the distribution region and mutation centre was slightly different.4. There was good correlation between heating field of Tibetan plateau and monthly precipitation in Ningxia, picking typical month to make synthetic analysis of them, the result shows that the heating field intensity of Tibetan plateau during earlier period was accordant with the 500 hPa height field during later period in typical drought and flood year. The synthetic analysis of typical heating field of Tibetan plateau during earlier period and relative humidity and wind field in Ningxia during later period showed nice coherence between them, the result gave further verification to the conclusion that the variation of heating field of Tibetan plateau could indicate the variation of precipitation in Ningxia.