Increased Frequency of Consecutive Positive IOD Events Under Global Warming

Consecutive positive Indian Ocean Dipole (pIOD) induces more severe climate impacts than a single pIOD because of multi-year accumulation of precipitation anomalies. Using CMIP6 outputs and reanalysis data, we show that the observed increasing trend of consecutive pIOD frequency will continue in future. The simulated frequency of consecutive pIOD increases by 131.3% over 1950-2100. More than 65% pIOD will manifest as consecutive pIOD events in the second half of this century. The increase in consecutive pIOD is dominated by the rise in mixed consecutive pIOD that contains both ENSO-pIOD and independent pIOD. Mixed consecutive pIOD that start with ENSO-pIOD increases fastest among all types of consecutive pIOD events. The increase is contributed by three factors: higher ENSO-pIOD frequency, weaker biennial component of ENSO forcing, and more active pIOD triggers that are independent from ENSO. Climate extremes associated with consecutive pIOD are therefore expected to occur more frequently under global warming. A positive Indian Ocean Dipole (pIOD) could induce droughts and floods in the eastern and western Indian Ocean countries, respectively. In consecutive pIOD events, the multi-year accumulation of precipitation anomalies leads to more severe and prolonged climate anomalies than that in a single pIOD event. Observations show that consecutive pIOD events have become more frequent under global warming. They occurred only twice in the last 50 years of last century and have already occurred three times in the first 20 years of this century. Model outputs suggest that the observed increasing trend of consecutive pIOD frequency will continue in future. The overall frequency of consecutive pIOD will increase by 131.3% over 1950-2100. More than 65% of pIOD will manifest as consecutive pIOD events in the second half of this century. Mixed consecutive pIOD that start with ENSO-pIOD increases fastest among all types of consecutive pIOD events. The increase in consecutive pIOD is contributed by higher ENSO-pIOD frequency, weaker biennial component of ENSO forcing, and more active IOD triggers other than ENSO. Climate extremes associated with consecutive pIOD events are likely to occur more often in the Indian Ocean surrounding countries due to more frequent consecutive pIOD events. The observed increasing trend of consecutive pIOD frequency will continue in future Mixed consecutive pIOD that start with ENSO-pIOD increases fastest among all types of consecutive pIOD events An increase in consecutive pIOD is caused by a higher frequency of pIOD, a weaker biennial component of ENSO, and more active IOD triggers