Sains Malaysiana 49(10)(2020): 2573-2585

http://dx.doi.org/10.17576/jsm-2020-4910-23

Analisis Penskalaan bagi Kejadian Hujan Ekstrim di Semenanjung Malaysia

(Scaling Analysis for Extreme Rainfall Events in Peninsular Malaysia)

WAN ZAWIAH WAN ZIN*, ABDUL AZIZ JEMAIN, MARINA ZAHARI & KAMARULZAMAN IBRAHIM

Jabatan Sains Matematik, Fakulti Sains dan Teknologi, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor Darul Ehsan, Malaysia

Diserahkan: 19 Julai 2018/Diterima: 16 April 2020

ABSTRAK

Maklumat mengenai kehujanan ekstrim dalam skala masa berbeza diperlukan dalam pembinaan lengkuk keamatan-tempoh-kekerapan (IDF). IDF menjadi rujukan utama dalam pembinaan infrastruktur berkaitan hujan seperti sistem perparitan dan empangan. Seringkali, agak sukar untuk mendapatkan data dalam pelbagai skala seperti per minit, per jam dan per hari. Justeru, kajian ini menggunakan konsep penskalaan yang mengambil kira sifat kebersandaran antara data hujan ekstrim pada sub skala yang berbeza dalam mengkaji ciri-ciri hujan ekstrim. Dalam kajian ini, data hujan maksimum dalam tempoh sejam sehingga 48 jam dari tahun 1970-2008 di 43 buah stesen cerapan hujan di Semenanjung Malaysia telah diuji. Penentuan jenis penskalaan yang sesuai; sama ada penskalaan ringkas atau pelbagai diuji berdasarkan teori skala tak varians. Hasil mendapati bahawa 41 stesen kajian memenuhi syarat penskalaan ringkas dan seterusnya, faktor penskalaan eksponen bagi setiap stesen telah ditentukan. Ini diikuti dengan pemadanan taburan ekstrim yang paling sesuai dengan data kajian bagi setiap stesen memandangkan konsep pembangunan IDF berasaskan taburan statistik. Lima taburan ekstrim iaitu taburan Ekstrim Teritlak (GEV), Logistik Teritlak (GLO), Gumbel, Pareto Teritlak (GPA) dan Pearson 3-Parameter (P3) telah dipadankan kepada data hujan maksimum harian dan hasil mendapati padanan data dengan GEV dan GLO di kebanyakan stesen. Berdasarkan maklumat taburan terbaik, nilai-nilai ulangan dihitung untuk pelbagai skala masa dengan menggunakan maklumat daripada hanya satu skala masa sahaja. Hasil kajian ini ternyata membolehkan pengurusan data yang lebih cekap dalam pembangunan IDF kerana data daripada hanya satu skala masa sahaja sudah mencukupi untuk menganggar nilai pada skala masa yang berlainan.

Kata kunci: IDF; konsep penskalaan; lengkung keamatan-tempoh-kekerapan; taburan nilai ekstrim

ABSTRACT

Information on extreme rainfall at various time scales is needed in the construction of the Intensity-Duration-Frequency (IDF) curve. Thus, the concept of scaling which takes into account of the dependency property of extreme rainfall data at various time scales in studying the characteristics of extreme rainfall is investigated in this study. Maximum rainfall data in the scales of one-hour until 48-hour for the years 1970 to 2008 at 43 rain-gauge stations were analyzed. The determination of the suitable type of scaling, either the simple scaling or multi-scaling, was tested based on the scale-invariance property. The result shows that 41 stations satisfied the simple scaling property and the scaling exponent for each station was determined. IDF concept requires data to be fitted by a suitable statistical distribution, thus, five types of extreme distributions, namely the Generalised Extreme Values (GEV), Generalised Logistic (GLO), Gumbel, Generalised Pareto (GPA) and Pearson 3-Parameter (P3) were fitted to the maximum daily rainfall data and the results showed that most stations followed the GEV and GLO. Subsequently, based on the best-fitted distribution for each station and the estimated scaling factor, the return values for various time scales at each station can be calculated using information from only one time scale. The results of this study will enable the efficient management of data in the development of IDF as it only requires data from one time scale to estimate values at various other time scales.

Keywords: Extreme value distribution; intensity-duration-frequency curve; IDF; scaling concept

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*Pengarang untuk surat-menyurat; email: w_zawiah@ukm.edu.my