关键词: 中国西南, 旱涝, 演变, 极端, 持续性

Abstract:

Using 44 stations temperature and precipitation data of day by day in Southwest China in 1953-2012, latency evaporation is calculated by Thornthwaite method, from inter-decadal, inter-annual, inter-seasonal variability, extreme and persistent characteristic of drought and flood analyzed over southwest China in past 60 years by homogenized drought-flood index of precipitation and latency evaporation. The results showed that: From the point of view of space trends to see, it displayed consistent drought trend in autumn and whole year over southwest China in past 60 years, but it displayed regional drought-flood trend feature in spring, summer and winter. Precipitation is main driven factor of drought-flood change in spring and summer, temperature is main driven factor of drought-flood change in winter and whole year, but driven function of precipitation and temperature are all notable in autumn. Therefore it is not objective to analyze drought-flood change only by precipitation, driven function of temperature must be considered. From the point of view of time evolution to see, it displayed drought trend by driven of temperature and precipitation double factor in spring, summer, autumn and winter over southwest China in past 60 years. By comparison, drought degree is strongest in autumn, but it is weakest in spring, and it is quite in spring and winter. However annual drought degree is stronger than that of seasons. From multiple time scales of view of extreme drought-flood to see, on interannual and decadal scales, extreme floods occur frequency gradually decreased, and extreme drought occur frequency gradually increased in past 60 years over southwest China. From inter-seasonal scales of view of extreme drought-flood to see, there is a greater probability of extreme drought in spring and winter, but it is smaller in summer, and there is a greater probability of extreme flood in summer, followed by spring ,but it is smaller in autumn. From month scales of view of extreme drought-flood to see, there is a greater probability of extreme drought on August, followed by February, but it is smaller in June, and there is a greater probability of extreme flood on August, followed by February, but it is smaller in January. Therefore it is most unusual month of drought-flood on August and February. From the point of view of persistent characteristic to see, from trend of persistent drought and flood event to see, duration of persistent drought event gradually lengthen, frequency gradually increased, intensity gradually strengthen, and it occurs mainly in winter and spring, but duration and strength of persistent flood event have not clear trend, frequency gradually decreased, and season of appearance have not significantly difference. In addition by comparing frequency of persistent drought and flood event to south China and southwest China in the past 60 years, nine times is consistent in the time of occurrence of persistent drought, especially it is entirely consistent autumn winter and spring drought in 1998, nine times is not consistent. Seven times is consistent in the time of occurrence of persistent flood, eleven times is not consistent, therefore affect system of persistent drought and flood is not entirely consistent over southwest and south China.

Key words: southwest China, drought-flood, evolution, extreme, persistent