Observed Increase of Urban Extreme Rainfall as Surface Temperature Rise: The Jakarta Case

Sub-daily extreme precipitation in Jakarta exhibits trends related to local temperature, seasonal tropical monsoon circulations, and other environmental drivers. Analysis of 81 years of hourly rainfall between 1900-2010 shows a significant increase of about doubling the number of short-duration rainfall events in the wet season. In recent decades, rainfall is found to be higher in intensity and shorter in duration relative to preceding decades. These short-duration rain showers develop typically between afternoon and late night or during early morning hours. Changing short-duration rainfall characteristics throughout the last century are partly attributed to changes in the surface environment of urban Jakarta. A recent temperature increase and land surface drying in the city, in combination with a small increase of the atmospheric moisture content, promote intensified atmospheric convection. A combination of rain gauge data with upper-air observations collected during 2002-2016 reveals that surface warming in the urbanized city accompanied by enhanced availability of moisture results in an increase of convective available potential energy (CAPE), which contributes to enhanced intense precipitation. Super Clausius-Clapeyron scaling (CC) of high-intensity rainfall is attributed to high near-surface temperature and atmospheric moisture content in the morning. This super CC scaling is present in a relatively small range of surface temperature values. Results of this study are in agreement with earlier findings exploring the intensification of extreme morning precipitation and a temporal shift of the diurnal convective maximum from late afternoon to late night/early morning in response to local warming. For a delta city such as Jakarta with abundant convection and heavy precipitation, a well-maintained rainfall database is crucial to assist urban flood early warning.