Probabilistic trend of anomalous summer rainfall in Beijing: Role of interdecadal variability

The interdecadal variability of summer precipitation in Beijing from 1724 to 2005 is analyzed using a filter, keeping the true trends at time series ends. A probability distribution, Pearson type III, was applied to the summer precipitation series to estimate the probability of anomalous rainfall. This study includes the correlation between the interdecadal variations of the summer precipitation in Beijing and those of the indices of Northern Atlantic Oscillation (NAO), Southern Oscillation (SOI), Pacific Decadal Oscillation (PDO), and summer monsoon (SMS) of East Asia indices are computed. A methodology is thus developed to forecast the probable distribution of precipitation intensities in Beijing. Results show that the probability of drought in Beijing has greatly increased since the middle of the 1960s. The interdecadal variability of NAO, PDO, and SMS are extremely important for the low-frequency forecast of anomalous summer rainfall in Beijing. The method developed here seems appropriate to estimate the probability of future anomalous summer rainfall.