Extreme precipitation in urban Jakarta: historical and future trends

Extreme rainfall associated with Jakarta floods has been observed to increase significantly in the 130-year historical data. Rainfall in the category heavy, very heavy, and extreme shows a trend to increase significantly in frequency and intensity, while the number of days of rain events continues to decline. The increase is more obvious in the rainy season and in the short duration (< 3 hours duration) rainfall classes. This increase is also more pronounced in the rainfall event that occurs at night and in the morning, which is different from past climatic conditions where intense rainfall occurred in the afternoon. Meanwhile during that time, the surface air temperature in Jakarta also increased dramatically by 1.4 times faster than the increase in global temperature. The dew point was observed to rise slightly, but the humidity actually decreased significantly. This trend is related to environmental changes due to the development of urban areas and the continued increase in the urban population. Compared to rural areas, there is a strong indication of the urban heat island phenomenon in Jakarta. This thesis finds that changes in the character of rainfall events and extreme rainfall in Jakarta are closely related to the increase in surface air temperature. The trend of increasing urban air temperature has increased the 2-3% chance of extreme rainfall events that trigger floods such as the Jakarta flood in 2020 and 2015 in the recent climate compared to the climatic conditions of 100 years ago. The continued increase in surface air temperature is associated with an increase in extreme rainfall intensity by about 14% in the Clausius-Clapeyron relationship. This indicated that a 1℃ increase in surface air temperature will increase about 14% of the water vapor holding capacity in the atmosphere. Increasing air temperature and surface drying in urban Jakarta, combined with increased atmospheric moisture content, promote intensified atmospheric convection, which contributes to increased intense rainfall. The observed historical trends in the characteristics of urban extreme rainfall and future climate projections from urban climate modeling indicate that the continued increase in temperature, population, and urban development will continue to cause these extreme problems to become more serious and riskier in the future.