IO has its own climate variability, that is the IOD. IOD usually start to develop in boreal summer when the Asian summer monsoon starts, it peaks in fall and decay rapidly in early winter when the monsoon winds reverse. IOD is strongly modulated by Asian monsoon. Generally, IOD signal is weaker than ENSO and difficult to predict. But in the IO the SST is very warm, above 28C, and the convection is strong. Even small SSTA may induce large rainfall variations not only in local areas but also can affect the climate in far region through atmospheric bridge. So IOD prediction can be very important and beneficial to the society.