The major variations of the annual PDI are found in Guangdong province of China, which is therefore the first region examined. A wavelet analysis suggests that the annual PDI has a 2-8-year oscillation which is partly related to the El Niño-Southern Oscillation phenomenon (ENSO). The alterations of the genesis locations and the preferred tracks associated with the ENSO events partly explain this interannual variation. The annual PDI also shows a significant 16-32-year oscillation, with distinct low and high PDI periods. The recent low PDI period in this region, beginning in 1997 and lasting to at least 2011, is related to the low TC activity over the western North Pacific and the decadal changes of the TC track pattern. Such changes are also found to be related to those in the PDI in Vietnam, East China as well as the Korea/Japan regions. The oceanic and atmosphere conditions associated with these changes have also been investigated and will be presented at the conference.