Sains Malaysiana 45(1)(2016): 87–97

The Use of BLRP Model for Disaggregating Daily Rainfall Affected by Monsoon in Peninsular Malaysia

(Penggunaan Model BLRP untuk Mengasingkan Curahan Hujan Harian Terjejas oleh Monsun di Semenanjung Malaysia)

HARISAWENI, ZULKIFLI YUSOP* & FADHILAH YUSOF

Centre for Environment Sustainability and Water Security (IPASA)

Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310 Skudai,

Johor Darul Takzim, Malaysia

Received: 16 July 2014/Accepted: 14 November 2014

ABSTRACT

Rainfall intensity is the main input variable in various hydrological analysis and modeling. Unfortunately, the quality of rainfall data is often poor and reliable data records are available at coarse intervals such as yearly, monthly and daily. Short interval rainfall records are scarce because of high cost and low reliability of the measurement and the monitoring systems. One way to solve this problem is by disaggregating the coarse intervals to generate the short one using the stochastic method. This paper describes the use of the Bartlett Lewis Rectangular Pulse (BLRP) model. The method was used to disaggregate 10 years of daily data for generating hourly data from 5 rainfall stations in Kelantan as representative area affected by monsoon period and 5 rainfall stations in Damansara affected by inter-monsoon period. The models were evaluated on their ability to reproduce standard and extreme rainfall model statistics derived from the historical record over disaggregation simulation results. The disaggregation of daily to hourly rainfall produced monthly and daily means and variances that closely match the historical records. However, for the disaggregation of daily to hourly rainfall, the standard deviation values are lower than the historical ones. Despite the marked differences in the standard deviation, both data series exhibit similar patterns and the model adequately preserve the trends of all the properties used in evaluating its performances.

Keywords: Bartlett Lewis rectangular pulse model; daily to hourly; disaggregation; Inter-monsoon; monsoon

ABSTRAK

Keamatan hujan adalah pemboleh ubah input utama dalam pelbagai analisis hidrologi dan pemodelan. Malangnya, kualiti data hujan selalunya lemah dan rekod data yang boleh dipercayai diperoleh pada jangka masa kasar seperti tahunan, bulanan dan harian. Rekod hujan selang pendek adalah terhad kerana kos yang tinggi serta kebolehpercayaan pengukuran yang rendah dan sistem pemantauan. Salah satu cara untuk menyelesaikan masalah ini adalah dengan mengasingkan selang kasar untuk menghasilkan yang pendek menggunakan kaedah stokastik. Kertas kerja ini menghuraikan penggunaan model segiempat denyut Bartlett Lewis (BLRP). Kaedah ini digunakan untuk mengumpul data 10 tahun setiap hari untuk menjana data setiap jam dari 5 stesen hujan di Kelantan sebagai kawasan wakil dipengaruhi oleh tempoh monsun dan 5 stesen hujan di Damansara dipengaruhi oleh tempoh antara monsun. Model dinilai berdasarkan keupayaan mereka untuk menghasilkan semula statistik model piawai dan hujan melampau yang diperoleh daripada rekod lampau ke atas penyampaian simulasi pengasingan. Pengasingan daripada setiap hari untuk hujan setiap jam dihasilkan melalui cara bulanan dan harian dan perbezaan yang rapat sepadan dengan rekod lampau. Walau bagaimanapun, bagi pengasingan daripada setiap hari untuk hujan setiap jam, nilai sisihan piawai adalah lebih rendah daripada rekod lampau. Walaupun perbezaan ketara dalam sisihan piawai, kedua-dua siri data menunjukkan corak yang sama dan model mengekalkan trend semua sifat secukupnya yang digunakan dalam menilai prestasinya.

Kata kunci: Antara-monsun; harian kepada jam; model segiempat denyut Bartlett Lewis; monsun; pengasingan

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*Corresponding author; email: zulyusop@utm.my