Changes in Extreme Rainfall in New Capital of Indonesia (IKN) Based on 20 Years of GPM-IMERG Data

Abstract

The Indonesian government has decided to relocate the nation’s capital city from Jakarta on Java to the Nusantara Capital (IKN) on Kalimantan for political, socioeconomic, and infrastructure reasons, among others, including the threat of flood, earthquake, and land subsidence in Jakarta. However, IKN remains susceptible to hydro-meteorological disasters due to its equatorial location and high yearly rainfall amounts. In this article, we investigated changes in extreme rainfall in the IKN area over the last 20 years (2001- 2020) based on Integrated Multi-Satellite Retrievals for GPM (IMERG) version 6 data. Overall, extreme rain in the IKN area, especially in the Sepaku and Semboja sub-districts, has slightly declined in the last 2 decades, as shown by negative and positive Sen’s slopes of precipitation amount-based indices and the consecutive dry days (CDD), respectively. A decrease was also observed in RX1 day (annual maximum 1-day precipitation) and SDII (annual total rainfall divided by the number of wet days in the year) indices. This indicates that the IKN area is getting drier and could impact the availability of clean water in the future by increasing the intensity and duration of the drought. While the total amount of precipitation has decreased over the past 2 decades, there has been an increase in the intensity of more extreme precipitation events. This is evident from the rise in precipitation frequency-based indices (annual count of days with rainfall exceeding certain thresholds), such as R20mm and R50mm. The RX5day index (maximum 5-day precipitation) has also shown an increase. These changes increase the risk of flooding, so it is crucial to implement appropriate measures to mitigate the risk of floods in the IKN area. HIGHLIGHTS Extreme rain in the IKN area, especially in Sepaku and Semboja sub-districts, has slightly declined in the last 20 years. Increases were observed in the consecutive dry days (CDD) and some precipitation frequency-based indices. It is important to take appropriate measures to reduce the risk of floods and drought in the IKN areas. GRAPHICAL ABSTRACT