The Precursors of High Rainfall Intensity During June in Southern Central Java: A Case Study of Flash Floods 18 June 2016 in Purworejo

Abstract

High rainfall intensity during the dry season can cause floods and landslides that cause a lot of loss of property and life as happened in Purworejo. Generally, the dry season with little rainfall, heavy rain in June is very rare, therefore disaster anticipation will be better if the precursor can be identified. This research aims to obtain high-intensity rain precursors in the south of Central Java, especially Purworejo. Identification used classifying rainfall for 10 years and related to atmospheric phenomena that impact to Indonesian rainfall variability. The results show that if there are very heavy rainfall and evenly distributed, precursors, can be identified in 3 days before the incident such as low OLR which value of <150 Wm-2. Moreover, an analysis of the average 3 days before the incident, the value of the OLR anomaly in the Central Java region is between –20 to –60 Wm-2. Meanwhile, the vertical humidity profile with more than 80% reached the 500 mb level, as well as spots where the temperature was more than 30.20C, three to four days before the incident with a value of more than 30.20C in the Indian Ocean adjacent to the southern part of Java Island. Existing low air pressure in the northern part of Kalimantan and in the southern part of Java, which persists for a long time, can support very heavy rains in June in Purworejo. Especially if the wind speed decreases to less than 4 m/s and occurs in phases 3 and 4 of the MJO.