| The flood and mud-rock flow caused by extremely precipitation events influences a lot and cause large lost and damages to the society, economy and our lives. Further researches for investigating the variability and mechanism of the extremely precipitation events is helpful and important for forecasting the extremely precipitation events and can support us to reduce the lost and damages caused by flood and other subsequent destructions. By using the rainfall data of293stations in northern China from1959to2008and NCEP/NCAR daily circulation reanalysis data, the extreme precipitation threshold which was suitable for related stations in Arid and Semi-arid Areas in Northern China was put forward, the temporal and spatial characteristics of precipitation days and extreme precipitation events in recent50years were researched, the atmospheric circulation features were analyzed when extreme precipitation event occurred and analyzed the correlation between extreme precipitation event and climate factors, results show that:1) the total precipitation days and different intensity precipitation days in space are decreasing from east to west in northern China, and show increasing trend in West China, but have an decreasing tendency in other places,the light rain days have increased mutation in Northwest Western.2) the extreme precipitation threshold, extreme precipitation days and yearly extreme rainfall are gradually increasing from the northwest to the southeast in northern regions, and distributes in belts; the proportion of extreme precipitation days to total rain days, and the proportion of extreme rainfall to annual rainfall are also increased gradually from west to east in four climatic regions.3) the temporal changes of extreme precipitation days and yearly rainfall have the obvious differences in four climatic regions, the days of extreme precipitation and extreme rainfall mainly concentrates in summer; the extreme precipitation days and yearly rainfall show increasing trend in Northwest Western, but have an decreasing tendency in the east part of northwest, North and northeast three climate zones. 4) the circulation characteristics of extreme precipitation event when it appears in Northwest Western:the low trough Lake between Balkhash-Pamirs plateau extends to south of40°N, the India monsoon is stronger; the circulation characteristics of extreme precipitation event when it appears in Eastern Part of Northwest China:the low trough covers on the Eastern part of Northwest China, the deep low trough could extend south to30°N, the south of35°N area is controlled by high pressure,westerly and southerly wind prevails over the bay of Bengal, which is formed by combining the southeast air current from north part of Northwest Pacific subtropical high, and northward moving, the circulation characteristics of extreme precipitation event when it appears in the North China:the circulation situation is lower in west and higher in east over China, the low trough is extending from the northeast to Sichuan, the southwestly wind ahead of it is more stronger, Subtropical High Ridge Locates at30°N; the circulation characteristics of extreme precipitation event when it appears in Northeast China:the low pressure covers on the Northeast China, there is a southern trough over the bay of Bengal, the southwest air current front of the southern trough,which is formed by combining the southeast air current from west part of Northwest Pacific subtropical high, and northward moving,the amount of water vapor is transported to the Northeast China by them.5) there is a positive correlation between the extreme precipitation events of four climatic regions and subtropical high pressure intension index, South China Sea intensity index,and the position of the northern boundary; Western Northwest China climate zone and Nino4zone of the sea surface temperature is related to the best, the other three climate zone correlated best with Nino34zone of the sea surface temperature. |
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