The Change Trend Of Graded Precipitation In Nearly60Years In Three Urban Agglomeration Of China

Climate change and urbanization is two major factors that make humans more easily influence by disaster.These two major factors will be stack by urban agglomerations,and make it more vulnerable to disasters to cause major disruption.Due to its geographical size and complex topography,the spatial distribution of precipitation is very unevenly.The change of time and space distribution of rainfall as a result of global warming,must have a deeply influence on Socio-economy and livings of cities.This research use China481ground stations1951-2010years of daily rainfall data and analyzes the annual precipitation and the four seasons of rainfall at all levels days geographical distribution,have studied long-term trends of precipitation and the number of days at all levels of rainfall.The main studies are as follows:(1) In our country the precipitation and rainfall at all levels days in year and in the four seasons has the very clear regional variations.The overall trend is from the north east south west gradually increasing. With the rain strong increase, at all levels of the great number of rainfall in value center gradually from Sichuan basin to move the Yangtze river and the southeast coastal area, Sichuan basin maximum center greatly weakened and even gradually tend to disappear; and minimum zone to Qinghai-Tibet plateau, Qaidam Basin, Alxa Plateau area as the center expanded. At all levels of the great number of the four seasons of rainfall center value mainly distributed in the east of the qinghai-tibet plateau and the Yangtze river basin and regions south; Minimum area including the most parts of qinghai-tibet plateau, north-west, northern north China and northern Northeast China, which is in significantly greater than the number of regional rainfall distribution at all levels.(2) Nearly60years, the Beijing-Tianjin-Tangshan region November to next march rainfall have no obvious increase or decrease, May,June and October micro increased. July, August and September significantly reduced, lead to regional annual precipitation reduced tendency obvious, linear trend rate is-22.59mm/10a. From the Mid-1970s to20th century end, linear trend rate reached-78.42mm/10a. The Yangtze river delta region January-April, June has not significant increase or decrease in rainfall change, May, September declined obviously; On July August increased significantly, this made the regional annual precipitation to increase Increasing trend is not obvious;But from Mid-1950s to the Middle and Late1960s, Annual precipitation is decreased, linear trend rate is-313.23mm/10a, thereafter to the early1990s annual precipitation is increased, linear trend rate is-99.34mm/10a. In Pearl River Delta region winter half year and May, September has not significant increase or decrease in rainfall change, On June August increased significantly; annual precipitation in this region mainly increased and has significantly inter-decade scale change. It increase in1950s, from mild-1960s to mild-1970s and1990s; and decrease in1960s,1980s and beginning of21th.(3) Annual precipitation of the Beijing-Tianjin-Tangshan area changes is obvious in recent60years, and18years,10-year periodic variation in the past60years has always existed.In recent60years, the annual variation of annual rainfall of Yangtze River Delta area changes remarkably and greatly. And in this region,9-year periodic oscillation of annual rainfall is obvious in recent60years;14-year periodic oscillation is remarkably in the1970s and1980s. In Pearl River Delta region, there is7-year,12-year and21-year characteristic time scale periodic oscillation, and9-year periodic oscillation of annual rainfall has always existed in recent60years.(4) In recent60years, annual rain day of the Beijing-Tianjin-Tangshan region decreased from mild-1960s to mild-1970s, increased in1980s, and in1990s decrease significantly. The annual rain day of Yangtze river delta region significantly decreased from mild-1950s to late1960s, in1970s, the number of annual rain days first increased and then decreased, but after1980, have no obvious increase or decrease. The annual rain day of Pearl River Delta region significantly decreased, linear trend rate is-2.51day/10a. The number of annual rain day decreased significantly in early of1990’s, late1970s, and late1980s and beginning of21th.(5) In the Beijing-Tianjin-Tangshan region, the decrease of annual rain days result in annual precipitation increasing; The main cause of annual precipitation decreased is annual days of heavy rain and rainstorm and above have decreased. The annual light rain days in Yangtze river delta region decreased, annual heavy rain days increased, the annual rain days have no obvious increase or decrease. The annual light rain days in Pearl River Delta region decrease significantly, linear trend rate is-2.96day/10a. The days of moderate rain, heavy rain, and rainstorm and above relatively increased. And, heavy rain days, rainstorm and above rain days in the Beijing-Tianjin-Tangshan region have significantly decreased, Heavy rain or even exceptional heavy rain days in the Yangtze river delta and Pearl River Delta region presents the overall increase trend.