Sains Malaysiana 38(2): 149-158(2009)

 

Frequency Analysis of Maximum Daily Rainfalls via

L-Moment Approach

( Analisis Frekuensi Hujan Harian Maksimum Melalui

Kaedah L-Momen )

 

 Ani Shabri & Noratiqah  Mohd Ariff

Jabatan Matematik, Fakulti Sains, Universiti Teknologi Malaysia

81310 Skudai Johor, Malaysia

 

Received: 19 May 2008 / Accapted: 12 August 2008

 

ABSTRACT

Knowledge related to distributions of rainfall amounts are of great importance for the design of water related structures.  The greater problem facing hydrologists and engineers identifying the best distribution form for regional data. The main goal of the study is to perform regional frequency analysis of maximum daily rainfalls selected each year among daily rainfalls measured over stations in Selangor and Kuala Lumpur by using the L-moment method. Several distributions were taken into account in this study which include two-parameter normal (NOM),  lognormal (LN2), three-parameter lognormal (LN3), logistic (LOG), generalized logistic (GLO), extreme value type I (EV1), generalized extreme value (GEV) and generalized Pareto (GPA) distribution.  The most suitable distribution was determined according to the mean absolute deviation index (MADI), mean square deviation index (MSDI) and the L-moment ratio diagram.  The result of this study showed that the GLO distribution is the most suitable distribution to fit the data of maximum daily rainfalls for stations in Selangor and Kuala Lumpur.

Keywords: Flood frequency; L-moment ratio; maximum daily rainfalls; regional frequency analysis

 

ABSTRAK

Pengetahuan berkaitan taburan jumlah hujan adalah sangat penting untuk merekabentuk struktur-struktur yang mempunyai hubungan dengan hidrologi.  Masalah utama ahli hidrologi dan jurutera adalah mengenalpasti bentuk taburan terbaik untuk data serantau. Objektif utama kajian ini adalah untuk menganalisis frekuensi rantau terhadap data hujan harian maksimum bagi setiap tahun yang diukur pada stesen-stesen hujan di Selangor dan Kuala Lumpur menggunakan kaedah L-momen.  Beberapa taburan telah diambil kira dalam kajian ini termasuklah taburan dua-parameter normal (NOM), lognormal (LN2), tiga-parameter lognormal (LN3), logistik (LOG), logistic teritlak (GLO), nilai ekstrim Jenis I (EV1), nilai ekstrim teritlak (GEV) dan Pareto teritlak (GPA).  Taburan terbaik bagi mewakili data untuk setiap stesen ini dikenalpasti melalui sishan indeks min mutlak (MADI), sisihan indeks min kuasa dua (MSDI) dan rajah nisbah L-momen.  Hasil  kajian ini mendapati bahawa taburan GLO adalah taburan yang paling sesuai bagi mewakili data taburan hujan di stesen-stesen Selangor dan Kuala Lumpur.

Kata kunci:      Analisis frekuensi rantau; frekuensi banjir; hujan harian maksimum; nisbah L-momen

 

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