| This article rebuilds the drought and floods grade of Shaanxi province's stations from 1470 to 2008, by using the historical documents and precipitation data. It analysis the basic features and evolution trend, and provides basis for forecast of drought and floods. There are five typical stations picked up that are Yulin, Yan'an,Xi'an, Hanzhong, Ankang. By analyzing 539 years drought and floods grade of five stations from 1470 to 2008, Yulin and Yan'an have the trend which is from drought to normal. Baoji and Xi'an has significant alternating of droughts and floods and the trend which is from drought to floods. The trend of Hanzhong and Ankang is mainly floods. The change points of drought and floods came out in southern, northern Shaanxi and Guanzhong in about 1640s. The change of southern Shaanxi is from drought to normal in about 1640. The change of Baoji and Xi'an is from drought to floods in about 1648. The change of Hanzhong and Ankang is from normal to floods. The time sequences of 539 years' drought and flood in 5 Shaanxi stations are decomposed by EOX. The first three EOF modes make a contribution accounting for 91% of the total variance. The first EOF makes a contribution accounting for 60.3%. The concordant form takes the leading position of all these years. The second EOF contributes 19.8%, it is the opposite type of drought and flood between south and north. The third EOF contributes 10.9%. |