Abstract:

The purpose of this article is to reveal the climatic characteristics and trends of flood and drought in SichuanYunnan region.By using methods of linear regression,the fiveyear moving average,MannKendall nonparametric statistical tests,inverse distance weighted spatial interpolation,the time change trends and space distribution characteristics of temperature and precipitation were analyzed based on the monthly temperature and precipitation data collected from 70 meteorological stations in this area from 1961 to 2011.On this basis,droughtflood index model was constructed by using Z index,and the droughtflood time evolution was analyzed by using Morlet wavelet transform.Results showed that:temperature presented an increasing trend over the last 51 years in this area,with a rate of 0.21℃/10 a and a warming trend coefficient as high as 0.71; the temperature had a significant longterm warming trend; the annual average temperature was the lowest in west Sichuan plateau and the highest in the south of Yunnan; altitude was the most important factors affecting the temperature.The annually precipitation showed an decreased trend in the past 51 years in this area,with a rate of 10.76 mm/10 a.With the influence of southwest monsoon and altitude,the precipitation was comparatively low in west Sichuan plateau and the surrounding area of southwestern Sichuan Basin;the precipitation was relative abundant in Sichuan Basin,the precipitation was the most abundant in southwest of Yunnan.The SichuanYunnan region was experiencing climate warming and precipitation reducing period since the late nineteen ninties; the trend of climate warming and drying was clearly in this area.This area became increasingly dry in recent 51 years and 2000 was a turning point; this area was flood before 2000 and drought after 2000,being coherent with the temperature and precipitation changes in this area; increasing temperature and decreasing precipitation in this area led to intensified drought directly.The drought and flood had a strong interannual periodic variation in spring and winter.Z index showed an upward trend,precipitation was increased; the drought trend was obvious in summer and autumn; the periodic variation of drought and flood was strong in summer,the degree of drought and flood was intensified; the drought and flood periodic variation was not strong in autumn,it had a weak drought trend.There was an obvious waterlogging to drought transformation trend in summer and autumn of this area,and attention should be paid to the drought control work