Regional rainfall variability in East Asia associated with climate trends

We performed an analysis of daily rainfall in East Asian region associated with low-frequency (decadal to multidecadal and global warming) climate trends which are identified primarily by monthly sea surface temperature (SST, 1880-2009). The global warming trend is first identified by applying the Hilbert-Huang Transform method to global SST data. It is then subtracted from the SST data. The detrended SST is further analyzed by the EOF method that reveals two dominants trends. One is the Pacific Decadal Oscillation /Inter-decadal Pacific Oscillation (PDO/IPO), the other is a multidecadal variability (MDV) near 60-year period. The climate trends in SST are further compared with sea level pressure data and WOA ocean temperature data to check their consistency. In this presentation, we focus on the extreme rainfall changes associated with climate trends. We first discuss the spatial circulation changes associated with the climate trends which are obtained through regressions of NCEP and ERA re-analyses data against the time series of climate trends. The associated features are compared with those of recent analyses of global monsoon changes and tropical general circulation changes. Then the yearly (annual cumulative), warm-season (seasonal cumulative), and extreme rainfall (top 95% and 99% rainfall cumulative over each year from daily station rainfall) in East Asian regions are regressed upon the climate trends. We first examined the rainfall data in Taiwan region. Overall, warming trend together with MDV can largely explain the trends in yearly rainfall, warm season rainfall and the extreme rainfall in the early period (before 1955) and recent years (after 2005). During the years in between, a nearly canceling effect of the warming trend and MDV makes rainfall changes small. During the period of 1985-1990, warming trend, MDV and PDO all contributed positively to a dramatic increase in rainfall, especially the more extreme rainfall. We also analyzed the rainfall variability at 20 stations. The results are consistent with the above results. Similar analysis of rainfall over China is being investigated and will be presented in the meeting.