Sains Malaysiana 41(11)(2012): 1345–1353

Application of Loglinear Models in Estimating Wet Category in Monthly Rainfall

(Penggunaan Model Loglinear dalam Penganggaran Kategori Basah Hujan Bulanan)

Wahidah Sanusi*

Department of Mathematics, Faculty of Mathematics and Natural Science

Universitas Negeri Makassar, 90224, Parangtambung Makassa

Sulawesi Selatan, Indonesia

Kamarulzaman Ibrahim

School of Mathematical Sciences, Faculty of Science and Technology

Universiti Kebangsaan Malaysia, 43600, Bangi, Selangor

Received: 28 September 2011 / Accepted: 31 May 2012

ABSTRACT

Climate changes have become serious issues that have been widely discussed by researchers. One of the issues concerns with the study in changes of rainfall patterns. Changes in rainfall patterns affect the dryness and wetness conditions of a region. In this study, the three-dimensional loglinear model was used to fit the observed frequencies and to model the expected frequencies of wet class transition on eight rainfall stations in Peninsular Malaysia. The expected frequency values can be employed to determine the odds value of wet classes of each station. Further, the odds values were used to estimate the wet class of the following month if the wet class of the previous month and current month were identified. The wet classification were based on SPI index (Standardized Precipitation Index). For station that was analyzed, there was no difference found in the comparison between estimated and observed wet classes. It was concluded that the loglinear models could be used to estimate the wetness classes through the estimates of odds values.

Keywords: Loglinear models; odds; Standardized Precipitation Index (SPI); wet classification

ABSTRAK

Perubahan iklim merupakan isu yang banyak diperbincangkan oleh penyelidik. Salah satunya ialah tentang kajian perubahan corak hujan. Perubahan corak hujan membawa kesan terhadap keadaan kering ataupun basah sesebuah rantau. Dalam kajian ini digunakan model loglinear tiga dimensi untuk menyuaikan kekerapan dicerap dan untuk memodelkan kekerapan dijangka peralihan kelas basah pada lapan stesen hujan di Semenanjung Malaysia. Nilai kekerapan dijangka dapat digunakan untuk menentukan nilai kemungkinan kelas basah setiap stesen. Selanjutnya, anggaran nilai kemungkinan yang telah diperoleh dapat digunakan untuk menganggar kelas basah satu bulan ke hadapan, jika diketahui kelas basah bulan sebelum dan bulan semasa. Pengkelasan basah yang digunakan adalah berdasarkan indeks SPI (indeks hujan dipiawai). Bagi stesen hujan yang dianalisis, hasil bandingan antara anggaran kelas basah dengan cerapan didapati tidak ada perbezaan. Hasil kajian ini memperlihatkan bahawa model loglinear dapat digunakan untuk menganggar kelas kebasahan melalui anggaran nilai kemungkinan.

Kata kunci: Indeks Hujan Dipiawai (SPI); kemungkinan; model loglinear; pengelasan basah

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*Corresponding author; email: w_sanusi@yahoo.com