Tropical climate influences on drought variability over Java, Indonesia

We investigate relationships between Indonesian drought, the state of the equatorial Indian Ocean, and ENSO using three instrumental indices spanning 1884-1997 A.D.: 1. EQWIN, a zonal wind index for the equatorial Indian Ocean; 2. the Dipole Mode Index (DMI), an indicator of the Indian Ocean SST gradient; and 3. tropical Pacific Niño-3.4 SSTs. A regression model of the Java Sep-Dec Palmer Drought Severity Index (PDSI) using a combination of these indices provides significant predictive skill (ar^2 = 0.50). Both the DMI and EQWIN correlate strongly with Java droughts (r = 0.71 and 0.66, respectively), but weakly with wet events (r = 0.21 and 0.18, respectively), while the Niño SST index correlates moderately with both dry and wet events (r = 0.31 and 0.36, respectively). Our findings indicate that Java droughts are intensified during El Niños that coincide with negative EQWIN conditions, which are also linked to a strengthened Indian monsoon