Understanding Variability of Rainfall Extremes in Jakarta and Surrounding Regions

© 2021 Sopia LestariFor many years, megacity Jakarta has had to deal with floods associated with heavy rainfall. Despite the major impacts of these events, there is a general lack of research in understanding the factors that can influence the nature of heavy rainfall in the region. This thesis investigates the effect of large-and local-scale drivers on mean rainfall and rainfall extremes (REs) and how they vary in topography, seasonally and diurnally. By using high temporal and spatial resolution datasets including rain gauges, disdrometer, and weather radar (1974-2020), it has been found that topography plays a vital role in rainfall organisation in this region. Large-scale climate variability modulates rainfall in the region. The El Nino-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) have strong relationships with an increase of REs in the dry season during La Nina and negative IOD. However, the impact of IOD on REs is larger than the ENSO effect. In contrast, the Madden Julian Oscillation (MJO) is associated with variations of REs in the wet season, with a stronger variation is found over the mountains compared to the coast and inland regions. Characteristics of sub-daily rain-rate are also highly inhomogeneous spatially and seasonally. However, high rain-rates persistently occur over the mountains in all seasons. In the wet season, hourly rain-rate has a distinct character different to all other seasons with a higher occurrence of smaller rain-rates and a lower intensity of mean rain-rate. The spatial distribution of hourly rain-rate also differs with the highest intensity REs found to be to the northeast coast of the radar domain in all seasons. Hourly rain-rate features are highly variable between each MJO phase and with topography. The most distinct characteristic is that during the active phase of MJO (phase 5), overall, the mean hourly rain-rate over the northern coast and ocean has increased compared to the suppressed MJO phases (phases 1-3 and 7-8) and the study-period mean. Also, in phase 5 of MJO, over the western part of inland, the morning hourly rain-rate contributes most to the daily mean rain-rate. This thesis serves as a base for future studies demonstrating the usefulness of high spatial and temporal resolution datasets, particularly in regions of complex topography. Indeed, high resolution of both observational datasets and model simulations is necessary in understanding the nature of rainfall over the Maritime Continent (MC). To represent the changes of rainfall properly over the MC, the role of topography needs to be incorporated in global climate models. Further study of the Cross-Equatorial Northerly Surge impact on local REs might also be required in the future as over megacity Jakarta, this phenomenon is also known to increase rainfall in the wet season