Assessment On The Risk Of Extreme Weather In Chongqing Summer

In this study, risk index of extreme weather climate (storm, thunderstorm, high temperature) in Chongqing’s summer are computed on the basis of meteorological data obtained from1981to2010in34meteorological observation stations in Chonqing with information diffusion technology. Then the temporal-spatial patterns of extreme weather climate (storm, thunderstorm, high temperature) in Chongqing’s summer are analyzed by mathematical statistics and correlation coefficient method. Analytic hierarchy process (AHP) and weighted comprehensive evaluation method are applied in meteorological disaster assessment and regionalization research. Following conclusions are drawn in this study:(1) Climatic characteristics of extreme weather climate in Chongqing:the number of rainstorm days showed a significant downward trend. Except for the upward trend in Fuling station, the other three stations have the similar changing trend as the city. The average rainstorm days are usually2-5d in Chongqing and the distribution feature shows that value is lower in southern Chongqing than in northern regions. The essential feature of rainfall distribution is that region north of Yangtze River has more rainfalls than the region south of it. Annual average maximum temperature showed a rising trend in Chongqing area and increases linearly with the time. Zones with extremely high temperature are Qijiang, Wansheng, Beipei, Jiangjin and Tongliang in Western Chongqing, following by Fuling to Fengdu in central Chongqing, and KaixianCounty in northeast Chongqing. The extreme low temperature center locates in Youyang in southwest Chongqing. There are three regions with serious high-temperature days, which are Wansheng and Qijiang in western Chongqing, Fuling to Fengdu zone in central Chongqing, Wanzhou to Wushan in northeast Chongqing; the distribution of serious high temperature days (HTD) is consistent with that of extreme HTD, but HTD decreases gradually. Youyang-Xiushan zone in southeast Chongqing doesn’t have extreme HTD; the number of thunderstorm days (TD) in the city is36d. TD in the city and four stations decreases significantly. The average TD in Chongqing area has three levels and the TD increases with the decrement of latitude.(2) The risk probability curve of the heavy rain days (HRD) in four stations is unimodal.2-4d range takes the largest proportion. In spatial distribution map of HRD risk, we infer that HRD in the region south of the Yangtze River is significantly higher than that in the region north of the River. The high HRD center locates in Fengdu-Shizhu zone in central Chongqing. When HRD is4-6d, the spatial distribution is contrary to the first level. The HRD in the region south of the Yangtze River is lower than that in the region north of the River. The high HRD center locates in Yunyang in northeast Chongqing; High-risk center (7-10d) locates in KaixianCounty of northeast Chongqing.(3) Risk probability curves of rainstorm grades obtained at the4stations in Chongqing are basically consistent, which are unimodal type. This probability has strong uncertainty. The maximum probability occurs when rainstorm grade is60-70mm;and the probability is slim as the rainstorm grade exceeds150mm. The spatial distribution of rainstorm risks shows that the risk probability decreases with the increase of rainstorm grades. The risk region at the second level is quite contract to that at the first level. At the third level, the high value zones of risk probability are distributed in Yubei-Beipei in western Chongqing, Pengshui in southeast Chonqing, Wanzhou-Liangping in northeast Chongqing. With respect to high risk probability at the fourth level, except for the low-probability zones such as Bishan-Shapingba in western Chongqing, Liangping-KaixianCounty in northeast Chongqing and Qianjiang in southeast Chongqing, most of the regions in Chongqing are risk free.(4) The HTD risks in four regions in Chongqing area vary significantly. The probability curves at Wanzhou Station in northeast Chongqing and Fuling Station at central Chongqing are unimodal; the probability curve at Shapingba Station in western Chongqing is bimodal and the curve at Qianjiang Station in Southeast Chongqing is reverse S-type. The spatial distribution of HTD risks indicates that the risk distributions of HTD at the second level and third level are consistent and contrary to the first level. Their high-risk centers are Yunyang, KaixianCounty, Wushan and Wuxi in northeast Chongqing, Qijiang and Wansheng in western Chongqing. Youyang and Xiushan are low-risk area.(5) The risk probability curves of high temperature values at four stations are all inversed "S" type, with maximum value at36℃. High temperature events in the regions represented by Shapingba, Wanzhou and Fuling Stations have strong uncertainty. The region where Qianjiang Station locates has strong stability with low risk probability of high temperature events. From the spatial distribution of high temperature values, the risk values of high-temperature disasters are high and basically cover whole Chongqing area. When the increase of high temperature grades, the area of high-temperature affected regions is correspondingly reduces. Especially at extreme high temperature grade, Youyang, Xiushan and Qianjiang are risk free.(6) TD probabilities at four stations have strong uncertainty. The TD risk is high. With the increase of TD, the probability of lightening disasters decreases correspondingly. The risk center at first grade is Tongliang in Western Chongqing. The probabilities at the second and third grades are just the opposite. The low-value zone (Youyang-Xiushan) at second grade is high value zone at third grade. With respect to the distribution of high-risk probability at the fourth grade, the risk probability in the entire city is less than0.1. Hechuan-Beipei, Rongchang in Western Chongqing, Liangping-Dianjiang, Wuxi-Wushan in Northeast Chongqing are risk free.(7) This study computes the integrated meteorological disaster risk at34stations in Chongqing through the established integrated summer meteorological disaster risk model. Results show that the integrated meteorological disaster risks in Chongqing have significant regional differences. The risk value in western region is higher than that in eastern region. And the risk value in the region north of the Yangtze River is higher than that in the region south of the River.