Extreme Precipitation’s Response To Climate Change And Risk Analysis Of Shanghai

The precipitation status caused by global climate change has become the focus of researches in many academic fields. Cities are not only the sensitive response areas, but also influence and contribute to global climate change greatly. Shanghai, as a typical city among The Yangtze river delta economic zone, its particular geography, climate, society and economy characteristics determine it will be influenced more complicated from the long-term perspective of precipitation changes.In this paper, the research data was selected from meteorology, geography, hydrology, atmospheric circulation sciences, besides, IPCC prediction data as well as extensive field survey data were also used. Strict quality controlling, data standardizing and pretreatment were made to guarantee its reliability and authenticity. Based on Matlab, Office and Arc GIS platforms, the precipitation indexes were selected, and the methods of cumulative departure, moving average, linear tendency estimation, DFA, percentile, frequency analysis, statistical downscaling, spatial analysis of GIS etc. were used to analyze precipitation change characteristics from perspectives of multi-time scale under the situation of the long-term and future climate change. At the same time, basing on the impact caused by extreme precipitation to Shanghai, using the method of scenario simulation, identify the extreme precipitation threshold of Shanghai from the perspective of climate statistics and risk assessment, and study the change characteristics of the extreme precipitation, risk level and risk assessment. The research results can not only enrich and develop the urban disaster risk evaluation theory system, but also can be referenced by the government to manage the water resources, prevent city water disaster and organize disaster reduction in Shanghai rationally. Research indicates that:1) Seasonal precipitation showed significant differences in different areas, precipitation of the urban is less than the suburan in spring and winter, while it is on t he contrary in summer and autumn, and more farther from the urban, more different it presented. As to the variation of seasonal precipitation, it declines unobvious in spring and autumn, while it increases significantly in summer and winter. However, the variation presents big value differences between different metrological sites, especially between the urban and suburban area. Take Xujiahui site as a standard, Minhang is as similar to Baoshan, Qingpu is as similar to Songjiang and Jinshan, Congming is as similar to Jiading, Fengxian and Nanhui.2) The variation of different level precipitation presented obvious regional differences in Shanghai. As to the index under rainstorm, there was no continuity in departure value among all metrological stations. As to rainstorm index, Baoshan, Xujiahui, Fengxian, Songjiang, Jinshan, Chongming and Nanhui stations convert into positive departure in 1980 s, Jiading in 1970 s, others in 1990 s. As to index above rainstorm, Xujiahui station kept negative departure until 2000 s, and the extreme value reaches 84.8mm, other stations appeared departure conversion in every 10 years, and the value is less than 40 mm.3) Precipitation in the future in Shanghai will increase compared to base time, but the precipitation-increase range is dropping in the next 3 different periods. It will present the biggest growth in 2020 s, and then the 2050 s, and least in 2080 s. Remarkable mutation of precipitation reduction will occur in 2070 s in Nanhui and Jinshan, while it will occur in 2060 s in other areas.4) Extreme precipitation frequency showed great spatial divergence in different areas by the method of DFA, while it showed little spatial differences by the method of percentile. The amount of extreme precipitation showed a fluctuating growth, sliding precipitation increasing rate was between 11.2-28.3mm /(10a), and the farther from the urban, the smaller the rate is.5) In historical scenario, the maximum inundation depth was around 120 mm after 15 minutes in 50 years return period, and it was around 150 mm in 100 years return period. The deepest inundation areas were mainly distributed in the inner outer ring along the east coast of Huangpu River, and on the whole, the inundation in east of Huangpu River was deeper than the west.6) In the middle of 21 st century scenario, the maximum inundation depth will be around 140 mm after 15 minutes in 50 years return period, and it will be around 160 mm in 100 years return period. Not only was the biggest depth deeper than historical period, but also was the spatial distribution more concentrated.7) In the end of 21 st century scenario, the maximum inundation depth will be around 140 mm after 15 minutes in 50 years return period, and it will be around 160 mm in 100 years return period. The high-deep inundation areas will be more concentrated in spatial distribution, the secondary deep inundation areas will be along east coast of Huangpu River, and both the high-deep and secondary deep inundation areas will spread a lot.8) According to the results of dynamic risk analysis, the high risk areas were mainly concentrated in the south of Chongming Island and north of Pudong in historical scenario of 50 years return periods, the west part of Huangpu River was mainly underi low risk level. When it comes to 100 years return periods, the high risk areas were spread to the whole Chongming Island and the whole Pudong, in addition, some regions of Fengxian, Jiading, Songjiang, Jinshan were also classified into high risk areas. In the middle of 21 st century scenario, high risk areas, different from historical period, will be mainly distributed in the southwest of Chongming Island and Jinshan area in 50 years return periods, and it will spread to three Chongming Islands, north Pudong, Jinshan and Songjiang in 100 years return periods. In the end of 21 st century scenario, the extreme precipitation will be similar as the historical period, but the high risk areas will be dropping, especially in Chongming Island, but the areas which will be the second higher risk level will enlarge a lot.