Climate trends and rainfall patterns in the Ciliwung watershed, West Java of Indonesia

Abstract

Jakarta city is one of the capitals that prone to frequent flooding. The objective of this study was to reveal climate trends and rainfall patterns upstream that were deemed to contribute to the flooding. Based on the daily climate data over 35 years from 1985 to 2019 and by applying Mann-Kendall Test and Gumbel distribution model, the watershed has become hotter and drier as indicated by a significant increase of air temperature (between 0.48 °C – 1.26 °C) and decrease of the relative humidity (over 2.9%). While the annual rainfall ranged around 3158±432 mm and did not indicate any changes. There were 5 extreme rainfalls in 1992 amounted to 4104 mm, 1995 (3758 mm), 2000 (3593 mm), 2012 (3779 mm), and 2013 (4283 mm). The maximum daily rainfall tended to increase at the slope of 0.94 mm/year, but the trend was not considered significant. The most probable event (63%) of the maximum daily rainfall was 98 mm with its return period of 1.6 years. The largest maximum daily rainfall was 245 mm in 2007 with its return period of 187 years causing the heaviest flooding with the highest casualty. There were clear indications that the rainfalls upstream considerably correlated with flooding.