Indicators Establishment And Risk Assessment Of Double-cropping Rice Flood Disaster In Hunan Province

The middle and lower reach of the Yangtze River region is one of the most waterlogged area in China. Hunan is located in the middle reaches of the Yangtze River, rice is the main food crops of in Hunan, and double-cropping rice is its main planting patterns. Floods occurs in every period of early rice and late rice in Hunan province. The production of cropping is affected and restricted by the flooding for a long term. Meteorological indicators and risk assessment of double-cropping rice flood disaster is recognized to be of realistic importance to the rice high and stable production management.The research is based on the integrating daily precipitation data (1961 to 2010) from 68 meteorology stations, flood disaster historical data and double-cropping rice phenophase data (1984-2015) in Hunan province.385 early rice and 125 late rice flood rainfall amount data samples have been built respectively from double-cropping rice flood disaster sample sets based on different rice growth stages (transplanting-jointing, booting-blooming, milk-maturity stage of early rice; transplanting-tillering, jointing-booting stage, blooming-maturity stage of late rice) and flood level (light, moderate, severe).The rainfall thresholds of double-cropping rice flood level indicators in different growth periods are defined by K-S test method and confidence intervals of Student t-distribution, and verified by independent samples.Temporal-spatial characters of double-cropping rice flood disaster were analyzed in Hunan province based on the constructed flood level indicators and ArcGIS.The risk, exposure, vulnerability, flood disaster prevention and mitigation capabilities models are built from the four factors perspective of disaster risk, thus the double-cropping rice flood integrated risk model are established and used for risk evaluation. Main results of the paper shows:(1) The thresholds of early rice flood disaster are 129mm,154mm, and 241mm in transplanting-jointing stage for light, moderate and severe flood. It became in sequence 135mm,170mm and 260mm for booting-blooming stage, and 145mm,190mm,295mm for milk-maturity stage, respectively. Late rice flood disaster thresholds are 131mm,181mm, and 251mm in transplanting-tillering stage for light, moderate and severe flood. It became in sequence 133mm,190mm and 264mm for jointing-booting stage, and 137mm,209mm,277mm for blooming-maturity stage, respectively. Flood indicators were detected to be basically consistent with the historical occurrence levels of rice flood disasters.(2) Total flood and severe flood disaster frequency of early rice showed an increasing tendency since 1961, while those of late rice showed a decreasing tendency. To early rice:severe flood mainly located in northern Yueyang and southern Chenzhou, south and east of Hunan was detected with high frequency of flood in transplanting-jointing stage, booting-blooming stage flood mainly happened in east and mid region of Hunan while milk-maturity flood occurred mainly in the north region of Hunan. To late rice:severe flood mainly located in Linwu, Guidong and mid-region of Hunan, high frequency of transplanting-tillering stage flood was detected in southeast of Hunan, jointing-booting stage flood mainly happened in Chenzhou and northern Yongzhou while blooming-maturity flood occurred mainly in western Shaoyang.(3) The high value area of early rice flood risk mainly distributed in east and south region of Hunan, while those of late rice flood risk mainly distributed in southeast of Hunan. The double-cropping rice districts that mostly exposed to flood disasters are Yueyang, Xiangyin, Zhuzhou, Wugang and Xinning. Zhuzhou, eastern and southern Chenzhou, northern and southern Yongzhou, Wugang, Xinning and Yueyang region are the most vulnerable area in early rice vulnerability assessment. Late rice vulnerability assessment results show that Xiangxiang and northern Yongzhou are the most vulnerable area. The place with better flood disaster prevention and mitigation capabilities mainly located in the central-north region of Hunan. Integrated flood risk centers of early rice are Yueyang, Pingjiang, Zhuzhou, Chaling, Yizhang, Jianghua, Xinning and Wugang, while those of late rice located in Yueyang, Taoyuan, Xiangxiang, midwest Shaoyang, mideast Chenzhou, Linwu, Anren, Leiyang and Zhuzhou region.