Analysis Of Extreme Climate Events And Its Causes In Yangtze River Delta Region

The extreme temperature and extreme precipitation change of Yangtze River Delta and its causes are analyzed and studied In this paper by using the1960-2012temperature and precipitation data of34meteorological stations, the NCEP/NCAR reanalysis data, the subtropical high index data and global sea surface temperature (SST) data provided by NOAA.The results show that:(1) in recent53years, the Yangtze River Delta region temperature having risen in both extreme high and low, but the extreme low temperature rising trend is more obvious, the extreme temperature rise of the fastest and most obvious area including Shanghai, Nanjing, Hangzhou city and the surrounding area.(2) The extreme precipitation in Yangtze River Delta area mainly concentrated in the5-9month, extreme precipitation index showed an upward trend, the trend is most obvious in Zhejiang area. North Jiangsu area, Eastern Zhejiang coastal and island stations precipitation will become more extreme in the future, more prone to heavy rains and floods, Sheyang and circumjacent area will become drier.(3) The extreme low temperature anomalies in atmospheric circulation difference as:Cold winter East Asian continent high latitude in the wave form of distribution for the "+-", most area of our country is controlled by low voltage; warm winter Eurasia mid high latitude in the wave form of distribution for the "-+-", large parts of China was controlled by high pressure. Extreme temperature index and the Western Pacific subtropical high intensity index is positively correlated, negatively correlated with the subtropical high ridge point index, the best correlation is August, El Nino year summer extreme temperature is low which is hot in summer, the Yangtze River Delta region of La Nina years summer extreme high temperature high is hot summer. Urbanization effect is an important reason why the extreme temperatures rising of the major city in the Yangtze River Delta.(4) When the Eurasian500hPa is East-West direction "+-+" wave pattern, low level wind is strong convection in East China area, southerly wind in the lower reaches of the Yangtze River and the confluence with the strong water vapor transport and other atmospheric conditions, the extreme precipitation in the Yangtze River Delta is much, on the contrary is extreme precipitation is less. There is a good positive correlation with extreme precipitation and the intensity of subtropical high index, also a good negative correlation with the subtropical high ridge, from the distribution of the global sea surface temperature, equatorial eastern Pacific and southern coastal waters of Peru, the sea surface temperature anomaly (SSTA) of southern waters of Cape of Good Hope in Atlantic and India ocean sustained high (low) is the obvious signal of extreme precipitation more (less) in Yangtze River Delta.This article believes that, changes in atmospheric circulation, intensity and western ridge point index of subtropical high including the urbanliztion effect are important factors of extreme temperature change; El Nino has certain instruction to the extreme temperature. Atmospheric circulation, intensity and western ridge point change of subtropical high, wind and water vapor transport are the direct causes of the extreme precipitation anomaly in the Yangtze River Delta region; the SSTA of part sea area has some indication.