Study On Flood Disaster And Hail Disaster In Yan'an Area During Ming And Qing Dynasties

Yan’an area is located in the northwest in China.There are all kinds of natural disasters occurred frequently since ancient times.Although drought is the main disaster in Yan’an area, the occurrence of flood and hail disasters is high, the damage caused by which should also not be ignored. Research on historical natural disasters not only has scientific significance to reveal its characteristics, rules and scale, but also has important practical significance for today’s disaster relief work.Based on widely collected data, and using mathematical statistics, the fractal structure method and wavelet analysis method, we study the frequency, level, seasonal variation, interannual variability, cycles, space distribution and the cause of the disaster of flood and hail disasters. The following conclusions can be drawn from the study:(1) The flood disaster of Yan’an area in Ming Dynasty happened 37 times, most of them were light flood disaster. The hail disaster of Yan’an area in Ming Dynasty happened 24 times, most of them were moderate hail disaster. The flood disaster of Yan’an area in Qing Dynasty happened 50 times, most of them were moderate flood disaster. The hail disaster of Yan’an area in Qing Dynasty happened 62 times, most of them were moderate hail disaster.(2) The flood disaster of Yan’an area in Ming Dynasty can be divided into four stages. The first stage was 1368～1368, the second stage was 1408-1487, the third stage was 1488～1547, the fourth stage was 1548～1644. The flood disaster in the first stage and the third stage were less and in the second stage and the fourth stage were more. The hail disaster of Yan’an area in Ming Dynasty can be divided into four stages. The first stage was 1368～1387, the second stage was 1388～1487, the third stage was 1488～1567, the fourth stage was 1568～1644. The hail disaster in the first stage and the third stage were more and in the second stage and the fourth stage were less.(3) The flood disaster of Yan’an area in Qing Dynasty can be divided into seven stages. The first stage was 1644～1703, the second stage was 1704～1743, the third stage was 1744～1763, the fourth stage was 1764～1803, the fifth stage was 1804～1843, the sixth stage was 1844～1883, the seventh stage was 1884～1911. The flood disaster in the first stage, the third stage, the fifth stage and the seventh stage were more. The flood disaster in the second stage, the fourth stage and the sixth stage were less. The hail disaster of Yan’an area in Ming Dynasty can be divided into six stages. The first stage was 1644～1723, the second stage was 1724～1763, the third stage was 1764～1803, the fourth stage was 1804～1843, the fifth stage was 1844～1883, the sixth stage was 1884～1911. The hail disaster in the first stage, the third stage and the fifth stage were less and in the second stage, the fourth stage and the sixth stage were more.(4) The frequency of flood and hail disasters occurred most was Fu county and Yan’an city of Yan’an area in Ming Dynasty. The frequency of flood and hail disasters occurred most was Zichang county, Yanchuan county and Yan’an city, least was Wuqi county and Huanglong county of Yan’an area in Qing Dynasty.(5) The frequency of flood disaster occurred most was in the autumn, then in the summer of Yan’an area in Ming and Qing Dynasty. The frequency of hail disaster occurred most was in the summer, then in the autumn of Yan’an area in Ming and Qing Dynasty.(6) The flood disaster of Yan’an area in Ming Dynasty had obvious periodic oscillations of 5a,7a,10a and 25a, the main period was about 25a. The hail disaster of Yan’an area in Ming Dynasty had obvious periodic oscillations of 3a,6a,9a,15a,19a and 38a, the main period was about 38a. The flood disaster of Yan’an area in Qing Dynasty had obvious periodic oscillations of 3a,10a,16a and 60a, the main period was about 60a. The hail disaster of Yan’an area in Qing Dynasty had obvious periodic oscillations of 3a,8a,15a and 59a, the main period was about 59a.(7) The humid climate events had occurred 5 times in Ming and Qing Dynasty were respectively from 1659 to 1665,1749 to 1756,1810 to 1815,1892 to 18938 and from 1905 to 1910. And the humid climate events mainly concentrated on Qing Dynasty which due to Ming Dynasty was more drought than Qing Dynasty.(8) There were two types of flood disaster in Yan’an area. One was the heavy rain and rainstorm caused by the uneven distribution of seasonal rainfall which lead to flooding. The other was the rainstorm and continuous rain caused by increased annual precipitation which lead to flooding. Yan’an area is located in mid-latitudes continental interior which has complex underlying surface and terrain. The temperature difference is bigger. In the summer, the ground by the strong solar radiation is easy to form strong convection movement is the main reason for the hail disaster in Yan’an area. Besides, the flood disaster was also affected by sunspot activity, ENSO events, subtropical ridge line position and amplitude variation of polar motion.