Analysis on variation trend of summer precipitation in Henan province during the recent 40 years

Based on data at 111 basic meteorological stations in Henan province from 1971 to 2010, the spatial and temporal characteristics of summer precipitation events were analyzed. The results show that in the last four decades, the amount of summer rainfall in Henan province is increasing. The contribution level of each precipitation events for summer rainfall rate is in the following order:light rain, moderate rain, heavy rain and rainstorm. The contribution of light rain and moderate rain to summer precipitation is decreasing, while the contribution of heavy rain and rainstorm is increasing. In most regions, the amount of precipitation increases while the days of rainstorm decreases, indicating the more frequent of extreme precipitation events. Wavelet analysis shows that the precipitation, precipitation intensity and the number of days of heavy precipitation all have the oscillation period of 2-3a, and the cycles of precipitation and rain days are consistent. In order to explore the causes of precipitation change, in this paper we conducted an atmospheric circulation field synthetic analysis for the drought and flood years, respectively. Analysis shows that in drought years, the positive anomaly was in most regions of the east of 100°E at 500 hPa level, and most part of Henan province were located in the descending-motion zone. Therefore, water vapor is difficult to transport to Henan province. On the contrary, the negative anomaly and frequent short-wave activity were found in most regions in the east of 110°E during flood years. The region of the west of 110°E during flood years was controlled by the high pressure ridges, and the southerly wind in lower level carried the warm moist flow from the Bay of Bengal to Henan. Therefore, the strong convection and sufficient water vapor are beneficial to precipitation.