Impacts of the boreal summer intraseasonal oscillation on precipitation extremes in Indonesia

The relationship between boreal summer intraseasonal oscillation (BSISO) and precipitation extremes over Indonesia is investigated using observational datasets from 30 years (1987-2016) of rain gauge measurements and the gridded Asian Precipitation-Highly Resolved Observational Data Integration Towards Evaluation of Water Resources from 1998 to 2015. The results indicate that the frequency of daily extreme precipitation events in Indonesia (defined as total precipitation above the 95th percentile) during extended boreal summer (May-August) is significantly modulated by BSISO, especially over the western and northern regions. Under the influences of BSISO1, the probability of the precipitation extremes over Sumatra and Borneo increases by 20-120% (relative to the seasonal probability) during phases 1-3 and approximately 50-80% over the eastern part of Borneo and Sulawesi during phase 4. Under BSISO2, the probability of the extremes increases up to 40% over Sumatra during phases 1 and 2 and up to 140% over Borneo and Sulawesi during phases 2 and 3. The increase in the probability of extreme summer precipitation is associated with enhanced large-scale moisture flux convergence and upward moisture transport induced by the active phases of BSISO. These results provide potential information for medium- to extended-range predictions of summer precipitation extremes in Indonesia.

Automated summary

The relationship between boreal summer intraseasonal oscillation (BSISO) and precipitation extremes in Indonesia was studied using observational datasets from rain gauge measurements and gridded Asian Precipitation-Highly Resolved Observational Data Integration. The results show that the frequency of daily extreme precipitation events during extended boreal summer is significantly influenced by BSISO, particularly in western and northern regions. The probability of extreme precipitation increases during active phases of BSISO due to enhanced large-scale moisture flux convergence. These findings can provide valuable information for predicting summer precipitation extremes in Indonesia.