Characteristic analysis on climatological variation of precipitation days with heavy and above rain intensities overHetao region

Based on the daily precipitation data from 87 meteorological stations over Hetao region from 1961 to 2010, we analyze the temporal-spatial distribution characteristics and the climatological variation features of precipitation days with heavy and above rain intensities(PDHR) over Hetao region by using linear trend and Morlet wavelet analysis methods. Results indicate that PDHR is clearly more in thesoutheast and less in northwest of Hetao. The annual mean PDHR being more than 5.0 days can be found in the southeastern Hetao, includingsouthern Shanxi, northwestern Henan and southeastern Shaanxi. Over Hetao region, the PDHRs in July, August, from June to September andwhole year all are in decrease trend in general, and the annual change of the precipitation days has a clear fluctuation in which high and lowfrequency periods of heavy rain alternately occur. The annual mean PDHR has reduced in some parts but increased in other parts before andafter 1985. In the last 50 years, PDHRs in July, August, from June to September and whole year all have clear fluctuating period of 2-4 years,as well as fluctuating period of 6-8 years over Hetao region.