Abstract: Droughts and floods are the most severe disasters in China, featuring wide spread, high occurrence and tremendous economic damage. Based on the analysis of documentation and observation data, the inter-decadal changes of drought-and-flood in south China indicated that the yearly and inter-decadal changes of d-and-f disaster have been becoming more and more obvious corresponding to the process of global warming. Jiangxi province is located in the central area of southern red soil region. In recent decades, Jiangxi suffered from the harm of frequent droughts and floods. Moreover, Jiangxi is one of the provinces famous for its farming production. Therefore, frequent droughts and floods have resulted in enormous economic losses in this region. Hence, studies about the inter-annual variation of droughts and floods in Jiangxi province are helpful for the early warming of droughts and floods. In this study, the monthly mean meteorological data during 1961-2010 including monthly mean temperature, maximum temperature, minimum temperature, relative humidity, wind speed and sunshine data in five meteorological stations such as Ganxian, Ji'an, Nancheng, Nanchang and Jingdezhen in Jiangxi province were collected from China Meteorological Data Center (CMDC). Based on these data, reconnaissance drought index (RDI) was adopted and calculated and the changes of droughts and floods in Jiangxi in recent fifty years (1961~2010) were looked into with the help of the Mann-Kendall test. Moreover, main driving factors for such changes in droughts and floods have been investigated with the help of multiple regression analysis method. The results suggested that an increase break point of the inter-annual scale RDI_st value of Jiangxi province occurred in 1969 years during 1961-2010, suggesting that the drought level increased but flood level declined during this period. It was indicated that an increase break point of the RDI_st value in spring occurred in 1967 years, indicating that the drought level gradually increased but flood level gradually decreased in spring in Jiangxi province since 1967 years. It was suggested that an increase break point of the RDI_st value in fall occurred in 1971 years, indicating that the drought level gradually increased but flood level gradually decreased in fall in Jiangxi province since 1971 years. No break points existed in the RDI_st value of Jiangxi province in summer and winter during 1961-2010 as indicated by the Mann-Kendall test, which suggested that drought level or flood level in summer and winter during 1961-2010 showed no increasing or decreasing trends. The inter-annual scale or seasonal-time scale of RDI was significantly positive correlated with rainfall and relative humidity, but negative correlated with sunshine (p < 0.01). The contribution rates of rainfall to the changes in droughts and floods were highest, accounting for 42%~58%, followed by mean temperature and relative humidity accounting for 11%~19% and 7%~19%, respectively. The contribution rates of mean wind speed and sunshine to the changes in droughts and floods were small. Inter-annual scale and spring standardized RDI displayed an increasing trend during 1961~2010, caused by increases in rainfall and relative humidity and decrease in sunshine. However, summer, fall and winter standardized RDI showed no increasing or decreasing trends during 1961~2010.

Key words: Droughts and floods, Reconnaissance drought index, Penman-Monteith, Driving factors, Jiangxi Province