Precipitation Cycles in the Middle and Lower Yellow River

Based on the long-term precipitation series with annual time resolution in the middle and lower Yellow River and its four sub-regions during 1736-2000 reconstructed from the rainfall and snowfall archives of the Qing Dynasty,the precipitation cycles are analyzed by wavelet analysis and the possible climate forcings,which drive the precipitation changes,are explored. The results show that the precipitation in the middle and lower Yellow River has inter-annual and inter-decadal oscillations like 2-4a,quasi-22a and 70-80a. The 2-4a cycle is linked with El Nino events,and the precipitation is lower than normal year in the occurrence of the El Nino year or the next year; for the quasi-22a and 70-80a cycles,Wolf Sun Spot Numbers and Pacific Decadal Oscillation (PDO) coincide with the two cycle signals. However,on 70-80a time scale,the coincidence between solar activity and precipitation is identified before 1830,and strong (weak) solar activity is generally correlated to the dry (wet) periods; after 1830,the solar activity changes to 80-100a quasi-century long oscillation,and the adjusting action to the precipitation is becoming weaker and weaker; the coincidence between PDO and precipitation is shown in the whole time series. Moreover,in recent 100 years,PDO is becoming a pace-maker of the precipitation on 70-80a time scale.