| Based on the related data of chorography, history and meteorology, with methods of linear fitting trend, least square method, Arcgis and Morlet wavelet, this paper study on level, frequency, space distribution and cycle of drought, flood, frost and snow disasters in Xihaigu Region. Studying on historical period meteorological disasters of Xihaigu Region has important scientific and practical significance.The main conclusions are as follows.(1) In period I, drought disasters of Xihaigu Region were 87 times and a drought disaster happened every 3.1 years on average. Drought disasters were divided into 3 levels including 7 times (level 1),68 times (level 2) and 11 times (level 3).Flood disasters were 98 times and a flood disaster happened every 2.7 years on average. Flood disasters were divided into 4 levels including 12 times (level 1),77 times (level 2),5 times (level 3) and 4 times (level 4).Frost and snow disasters were 43 times and a frost and snow disaster happened every 3.1 years on average. Frost and snow disasters were divided into 3 levels including 3 times (level 1),37 times (level 2) and 3 times (level 3).The occurrence frequency of three kinds of meteorological disasters of Xihaigu Region in period I were on the rise.(2) In period II, drought disasters of Xihaigu Region were 61 times and a drought disaster happened every 1.4 years on average. Drought disasters were divided into 4 levels including 4 times (level 1),19 times (level 2),26 times (level 3) and 19 times (level 4).Flood disasters were 51 times and a flood disaster happened every 1.7 years on average. Flood disasters were divided into 4 levels including 9 times (level 1),10 times (level 2),22 times (level 3) and 10 times (level 4).Frost and snow disasters were 41 times and a frost and snow disaster happened every 2.1 years on average. Frost and snow disasters were divided into 3 levels including 4 times (level 1),33 times (level 2) and 4 times (level 3).The occurrence frequency of drought disasters and flood disasters in period II were on the rise, but occurrence frequency of frost and snow disasters was on the contrary.(3) In period I, drought disasters of Xihaigu Region can be divided into 5 stages, respectively were 1644-1743,1743-1783,1784-1803,1804-1863 and 1863-1804, drought disasters of stages 1,3 and 5 were low incidence, however drought disasters of stages 2 and 4 were high incidence. Flood disasters can be divided into 5 stages, respectively were 1644-1743,1743-1783,1784-1803,1804-1863 and 1863-1804, flood disasters of stages 1,3 and 5 were low incidence, however drought disasters of stages 2 and 4 were high incidence. Frost and snow disasters can be divided into 6 stages, respectively were 1644-1743,1743-1783,1784-1823,1824-1863,1864-1883 and 1884-1912, frost and snow disasters of stages 1,3 and 5 were low incidence, however frost and snow disasters of stages 2,4 and 6 were high incidence.(4) In period â…¡, drought disasters of Xihaigu Region can be divided into 5 stages, respectively were 1913-1932,1932-1952,1953-1962,1963-1982 and 1983-2000, drought disasters of stages 1,3 and 5 were low incidence, however drought disasters of stages 2 and 4 were high incidence. Flood disasters can be divided into 4 stages, respectively were 1913-1942,1942-1952,1953-1962 and 1963-2000, flood disasters of stages land 3were low incidence, however drought disasters of stages 2 and 4 were high incidence. Frost and snow disasters can be divided into 3 stages, respectively were 1913-1942,1943-1982 and 1983-2000, frost and snow disasters of stages 1 and 3 were low incidence, however frost and snow disasters of stages 2 were high incidence.(5) The occurrence of three kinds of meteorological disasters in period I was in the south of Xihaigu Region. The occurrence of drought disasters was more in the north than the south, but occurrence of frost and snow disasters was on the contrary. Drought disasters occurred mainly in the middle of region.(6) In period I, cycle of drought disasters included short-term, medium-term and long-term, respectively 6a,14a and 37a.As well, cycle of flood disasters included 3 and 5a, 11a and 22a, cycle of frost and snow disasters included 6a,16a and 30a. The first main cycle of three kinds of meteorological disasters in period I was respectively about 14a, 11a and 6a.In period â…¡, cycle of drought disasters included 3a,9a and 19a.As well, cycle of flood disasters included 4a,12.5a and 21a, cycle of frost and snow disasters included 4a,7a and 19a. The first main cycle of three kinds of meteorological disasters in period I was respectively about 19a,12.5a and 7a.(7) In study periods dry climate events happened 6 times in Xihaigu Region, respectively in 1762-1772,1831-1838,1851-1857,1937-1943,1857-1953 and 1953-1953. Humid climate events happened 4 times, respectively in 1775-1780,1942-1947,1780-1992 and 1992-1992. Cold climate events happened 3 times, respectively in 1851-1855,1951-1960,1855-1974 and 1974-1974. The three kinds of climate events had the characteristics of long duration and large range of influence.(8) Factors of location, climate and less precipitation were the main cause of drought disasters. Factors of large ground slope, vegetation sparse, loose soil, precipitation concentrating in summer such as heavy rain were the main reason for the flood disasters. Anomalous monsoon activities in winter were the main cause of frost and snow disasters. |
