HEAVY RAINFALL CHARACTERISTICS AT SOUTH-WEST OF MT. MERAPI- YOGYAKARTA AND CENTRAL JAVA PROVINCE, INDONESIA
Keywords:
heavy rainfall, West monsoon, Debris flow, Flood warning, Heavy rainfallAbstract
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 south-
west of Mt. Merapi was best fitted with the LN3 distribution.