HEAVY RAINFALL CHARACTERISTICS AT SOUTH-WEST OF MT. MERAPI- YOGYAKARTA AND CENTRAL JAVA PROVINCE, INDONESIA

Heavy rainfall analysis is an important data for disaster management of flash floods and debris flows in mountainous areas. Those disasters may cause casualties and property damages. It is an urgent consideration to analyze the heavy rainfall characteristics in the area in order to gain well-planned disaster mitigation. Hourly rainfall data were analyzed over Mt. Merapi area especially those which are located in the Yogyakarta and Central Java Province. The rainfall data were collected from a number of automatic rainfall stations with 11 to 28 years of data length. Heavy rainfall is defined when the rainfall depth exceeds 50 mm per event. Heavy rainfall analysis at the study area indicates that heavy rainfall varies among the stations and it is likely occurred more often at the south-west of Mt. Merapi. Statistical analysis gives that maximum rainfall depth for an event varies from 99 mm at the south-east area to 282 mm at the south-west area of Mt. Merapi. Maximum rainfall intensity values show that at the south-west of Mt. Merapi have higher rainfall intensity than at the south-east area. The results indicate that orographic effects and west monsoon are important in determining the spatial distribution of heavy rainfall occurrences in Mt. Merapi area. Besides, heavy rainfall more frequent occurred from noon until late afternoon. The annual maximum heavy rainfall data at the southwest of Mt. Merapi was best fitted with the LN3 distribution.