Sains Malaysiana 41(11)(2012): 1377–1387

Comparisons between the Window-Based and Storm-Event Analysis

(Perbezaan antara Analisis Berdasarkan Tingkap dan Analisis Kejadian Ribut)

Noratiqah MohdAriff* & Abdul Aziz Jemain

School of Mathematical Sciences,Faculty of Science and Technology,

Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia

Diserahkan: 17 Oktober 2011 / Diterima: 29 Mei 2012

ABSTRACT

Rainfalls data have been broadly used in researches including in hydrological and meteorological areas. Two common ways in extracting observations from hourly rainfalls data are the window-based analysis (WBA) and storm-event analysis (SEA) approach. However, the differences in the qualitative and quantitative properties of both methods are still vaguely discussed. The aim of studying these dissimilarities is to understand the effects of each approach in modelling and analysis. The qualitative difference is due to the way the two analyses define the accumulated rainfalls for observations which are referred to as rainfall and storm depths, respectively. The repetitiveness of rainfall depths provide nested structure while the storm depths are considered independent. The quantitative comparisons include their statistical and scaling properties that are linked by the self-similarity concept from simple scaling characteristics. If self-similarity concept holds, then the rainfall or storm depths follow simple scaling and the analysis would be simplified. The rainfall depths showed clearer simple scaling characteristics compared to the storm depths. Though the storm depths do not yield self-similarity for a large range of storm duration but the characteristics of simple scaling can be observed for a reduced range of the considered duration. In general, the context of the research and the region of the time interval and duration will be important aspects to consider in choosing which method is best to use for analyzing the data.

Keywords: Rainfalls analysis; self-similarity concept; simple scaling; storm events

ABSTRAK

Data hujan telah diguna pakai dalam pelbagai kajian termasuk dalam bidang hidrologi dan meteorologi. Terdapat dua kaedah yang biasa digunakan untuk mengekstrak maklumat daripada data hujan setiap jam iaitu analisis berdasarkan tingkap dan analisis kejadian ribut. Walau bagaimanapun, perbezaan secara kualitatif dan kuantitatif kedua-dua analisis belum pernah dibincangkan dengan jelas. Tujuan mempelajari kelainan ini adalah untuk memahami kesan setiap kaedah tersebut terhadap permodelan dan analisis hujan. Perbezaan kualitatif antara kedua-dua analisis adalah disebabkan cara hujan terkumpul didefinisikan. Hujan terkumpul ini masing-masing ditulis sebagai kedalaman hujan dan kedalaman ribut. Pengulangan data yang digunakan dalam analisis berdasarkan tingkap menyebabkan kedalaman hujan mempunyai struktur bersarang manakala kedalaman ribut dianggap sebagai pemboleh ubah tak bersandar. Perbandingan kuantitatif pula terdiri daripada ciri statistik dan ciri berkala yang berkait rapat melalui konsep serupa daripada struktur berkala mudah. Jika konsep serupa diri ini dipenuhi, ini bermakna kedalaman hujan atau ribut itu mengikut sifat berkala mudah dan analisis akan menjadi lebih senang. Kedalaman hujan menunjukkan ciri berkala mudah yang lebih jelas berbanding pemboleh ubah kedalaman ribut. Walaupun kedalaman ribut tidak mempamerkan sifat serupa diri bagi julat tempoh ribut yang besar, tetapi sifat berkala mudah ini dapat dilihat pada pemboleh ubah tersebut jika julat ini dikecilkan untuk tempoh tertentu. Secara keseluruhannya, konteks kajian dan julat selang masa hujan atau tempoh ribut adalah aspek penting yang perlu diambil kira dalam memilih kaedah yang paling sesuai untuk menganalisis data hujan.

Kata kunci: Analisis hujan; berkala mudah; kejadian ribut; konsep serupa diri

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*Pengarang surat-menyurat; email: tqah@ukm.my