Sains Malaysiana 38(2):  133-142(2009)

Trends of Wet Spells Over Peninsular Malaysia During Monsoon Seasons

(Trend Rentetan Hari Basah bagi Semenanjung Malaysia pada Musim Monsun)

Sayang Mohd. Deni

Center for Statistical Studies

Faculty of Information Technology and Quantitative Science

Universiti Teknologi MARA, 40450 UiTM Shah Alam, Selangor.

Suhaila Jamaludin

Department of Mathematics, Faculty of Science

Universiti Teknologi Malaysia, 81310, UTM Skudai, Johor , Malaysia .

Wan Zawiah Wan Zain & Abdul Aziz Jemain

School of Mathematical Sciences, Faculty of Science and Technology

Universiti Kebangsaan Malaysia, 43600, UKM Bangi, Selangor , Malaysia .

Received:  17 April 2008 / Accepted:  22 Julai 2008

ABSTRACT

This study attempts to trace changes in the wet spells over Peninsular Malaysia based on the daily rainfall data from 32 selected rainfall stations which include four sub-regions; northwest, west, south and east, for the period of 1975 to 2004.  Six wet spells indices comprising of the main characteristics (maximum, mean, standard deviation), the persistency of two consecutive wet days and the frequency of the short and long duration of wet spells will be used to identify whether or not these indices increase or decrease over Peninsular Malaysia during the monsoon seasons. The study indicates that the eastern areas of the peninsula could be considered as the wettest areas since almost all the indices of wet spells over these areas are higher than over the other regions during the northeast monsoon (NE).   The Mann-Kendall (MK) trend test revealed that almost all of the stations located in the eastern areas of the peninsula exhibited a positive trend in the mean, variability and persistency of wet spells indices during the NE monsoon, while a negative trend was observed during the southwest monsoon (SW) in these areas. Moreover, these indices showed a positive trend, and at the same time a decreasing trend was observed in the frequency of the long wet spells in most stations located over the west coast of Peninsular Malaysia during the SW monsoon for the period of 1975 to 2004. 

Keywords:  indices; Mann-Kendall trend test; persistency; wet spells

ABSTRAK

Kajian ini bertujuan menjejaki perubahan rentetan basah di dalam hujan harian bagi Semenanjung Malaysia berdasarkan data pemerhatian dari 32 buah stesen hujan yang merangkumi empat kawasan; barat laut, barat, selatan dan timur untuk tempoh 1975 hingga 2004.  Terdapat enam indeks rentetan basah yang terdiri dari rentetan yang paling maksima, purata, sisihan piawai, keberterusan hujan bagi dua hari berturut-turut serta frekuensi rentetan basah untuk tempoh jangka pendek dan jangka panjang akan digunakan di dalam menentukan sama ada indeks ini menunjukkan tren positif ataupun negatif bagi Semenanjung Malaysia pada musim monsun Timur Laut dan Barat Daya.  Hasil kajian mendapati kawasan di sebelah timur semenanjung adalah yang paling basah di mana hampir semua indeks rentetan basah bagi kawasan ini menunjukkan nilai yang lebih tinggi dari kawasan lain pada musim monsun Timur Laut.  Ujian tren Mann-Kendall (MK) pula mendapati bahawa hampir kesemua stesen hujan di sebelah timur semenanjung menunjukkan tren positif bagi indeks purata, sisihan piawai dan keberterusan rentetan basah pada monsun Timur Laut, sementara itu, indeks tersebut menunjukkan tren negatif pada monsun Barat Daya di kawasan ini.  Seterusnya, indeks-indeks tersebut menunjukkan tren menaik dan pada masa yang sama, tren menurun bagi frekuensi tempoh jangka panjang rentetan basah diperhatikan di kebanyakan kawasan di pantai barat Semenanjung Malaysia pada monsun Barat Daya untuk tahun 1975 hingga 2004.

Kata kunci:  Indeks;  keberterusan; rentetan basah; Ujian tren Mann-Kendall

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