Abstract
Mt. Merapi cold lava disasters in 2010 had caused a lot of public infrastructure and facilities in the area around Mt. Merapi were damaged, due to the occurrence of debris flows triggered by extreme rainfall. Analysis of extreme rainfall characteristics are conducted to determine the pattern of distribution of the amount of hourly rainfall in the slopes of Mt. Merapi. To reduce the negative impact caused by cold lava flood, it is necessary to plan an Early Warning System (EWS) and the proper evacuation measures. EWS based Rainfall intensity, can refer to the Critical Line Curve. The research results showed the greatest rainfall intensity occurred in the Mt. Maron station Pwith the cumulative relative frequency of rainfall intensity >20 mm/hr in between the years 1988 to 2010 with 6.74%. Analysis of the incidence of the most extreme hourly rainfall of 14 rainfall stations in the slopes of Mt. Merapi in 1988 to 2010 occurred in kemasan station in 2010 with 621.5 mm in January at 6:00 p.m. to 7:00 p.m. Critical Line Curve Kali Gendol rain station Batur, Deles and Sorosan, non-causing rainfall in the dangerous area is 24 events (13.79%), causing rainfall in the dangerous area is 4 events (2.30%) and non-causing rainfall in the safety area is 146 events (83.91%). Cumulative Relative frequency rainfall intensity >20 mm/hr at rainfall stations close to the Kali Gendol i.e. Batur, Deles and Sorosan rainfall station from the highest to the lowest are 2.74%, 2.33% and 1.70%, respectively.
Highlights
to the occurrence of debris flows triggered by extreme rainfall
Analysis of extreme rainfall characteristics are conducted to determine the pattern of distribution of the amount
reduce the negative impact caused by cold lava flood
Summary
Balai Penyelidikan dan Pengembangan Teknologi Kegunungapian (BPPTK) Yogyakarta, memperkirakan bahwa setelah erupsi Gunung Merapi tahun 2010 baru 10 persen dari sekitar 130 juta meter kubik material vulkanik yang terangkut oleh banjir lahar dingin. Karakteristik hujan sangat bervariasi pada setiap daerah [3]. Dengan data hujan yang ada, maka dilakukan analisis sebaran hujan dengan membandingkan berbagai sifat hujan yang meliputi intensitas hujan, durasi hujan, jumlah hujan jam – jaman dan hujan bulanan. Analisis karakteristik hujan ekstrim dilakukan untuk mengetahui pola sebaran jumlah hujan jam - jaman di wilayah lereng Gunung Merapi [4-5]. Untuk mengurangi dampak negatif akibat banjir lahar dingin, maka perlu direncanakan suatu sistem peringatan dini Early Warning System (EWS) dan tindakan evakuasi yang tepat. EWS berbasis intensitas hujan, dapat mengacu pada kurva garis kritis (Critical Line Curve) [6-7]
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