Dalam kajian ini, pendekatan pengelompokan kabur Gustafson-Kessel (Gx) telah digunakan untuk mengelaskan 35 stesen hujan di Semenanjung Malaysia ke dalam rantau homogen. Pertama, algoritma pengelompokan kabur GK digunakan untuk mengenal pasti rantau awal. Kemudian, diuji keserasian dan kehomogenan rantau berkenaan. Akhir sekali, penyesuaian rantau dilakukan untuk mendapatkan rantau homogen. Hasil kajian mendapati 35 stesen hujan kajian boleh dibahagikan kepada enam rantau yang homogen. Rantau 1 meliputi bahagian barat laut dan utara Semenanjung Malaysia, rantau 2, 3 dan 4 meliputi bahagian barat, rantau 5 meliputi bahagian barat daya dan rantau 6 meliputi bahagian timur. Hasil kajian ini juga memperlihatkan bahawa berdasarkan nilai purata Indeks Kerpasan Piawai (sPi) skala masa satu bulan, rantau 2 lebih sering mengalami keadaan kemarau melampau. Walau bagaimanapun, berdasarkan sPi skala masa satu bulan, peristiwa kemarau terjadi secara rawak dalam semua rantau yang dianalisis , bahkan semua rantau tersebut pernah mengalami kejadian kemarau melampau dalam tempoh masa setahun. Hasil kajian ini turut menunjukkan bahawa pendekatan pengelompokan kabur Gustafson-Kessel boleh digunakan untuk membina rantau homogen.
Kajian ini bertujuan mendapatkan gabungan statistik untuk pemodelan hujan kelompok berstokastik Denyut Segi Empat Neyman-Scott (NSRP) yang mampu memberikan pemadanan terbaik bagi hujan di stesen hujan Semenanjung Malaysia. Enam set gabungan statistik, yang setiap setnya mengandungi gabungan statistik momen (1, 2 dan 3) dan kebarangkalian hujan dalam selang masa yang singkat (jam) dan panjang (harian), serta empat taburan yang berbeza bagi kelebatan sel hujan (Eksponen, Campuran Eksponen, Gamma dan Weibull) telah dikaji. Penyelidikan telah dilakukan ke atas sembilan stesen hujan yang mewakili rantau yang berbeza di Semenanjung Malaysia. Hasil mendapati bahawa statistik momen ke-3 (kepencongan) tidak memberikan sumbangan yang baik dalam menjayakan model. Selang masa 1, 6 dan 24 jam didapati yang terbaik bagi statistik momen kedua (variasi) bagi menjayakan model. Kajian ini juga mendapati bahawa taburan eksponen adalah yang terbaik bagi pemodelan hujan NSRP di Semenanjung Malaysia.
Kajian ini bertujuan untuk mengenal pasti model statistik terbaik bagi mewakili set data melampau untuk salah satu bahan pencemaran udara iaitu zarah terampai (PM10). Data dari enam buah stesen pengawasan kualiti udara di sekitar Lembah Klang dari tahun 2009 hingga 2011 digunakan dalam kajian ini. Dalam penentuan taburan terbaik, taburan parametrik dan taburan tak berparameter telah diuji. Dua siri data melampau yang digunakan ialah siri data maksimum bulanan dan siri data melangkaui ambang bagi PM10. Seterusnya, dua taburan parametrik iaitu Taburan Melampau Teritlak (GEV) dan Taburan Pareto Teritlak (GPD) masing-masing dipadankan kepada siri data maksimum bulanan dan siri data melangkaui ambang. Kaedah penganggaran parameter L-momen dan ujian kebagusan penyuaian Anderson Darling digunakan dalam pemilihan taburan parametrik terbaik yang juga menentukan kaedah pemilihan data melampau yang mana lebih baik. Bagi kaedah tak berparameter, penganggaran fungsi ketumpatan kernel (KDE) digunakan untuk menentukan taburan terbaik PM10 melampau. Hasil pengiraan ralat min kuasa dua (MSE) mendapati taburan tak berparameter merupakan taburan terbaik bagi data melampau PM10 di kebanyakan stesen kajian. Taburan terbaik bagi setiap stesen kajian seterusnya digunakan bagi menghitung tempoh ulangan PM10 yang sangat berguna bagi pihak yang terbabit.
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.
This study investigated the spatial pattern and trends of the daily rainfall data in Peninsular Malaysia based on seasonal rainfall indices. Five rainfall indices which describe the main characteristics of rainfall, the total amount of rainfall, frequency of wet days, rainfall intensity, extreme frequency, and extreme intensity, were employed in this study. The statistics of rainfall indices were calculated in terms of their means for four regions in Peninsular Malaysia for the period 1975 to 2004. The findings indicate that the southwest monsoon had the greatest impact on the western part of the Peninsula, particularly in characterizing the rainfall pattern of the northwest region. During this season, the northwest region could be considered as the wettest region since all rainfall indices tested are higher than in other regions of the Peninsula. Otherwise, the northwest region is denoted as the driest part of the Peninsula during the northeast monsoon period. The northwest region is less influenced by the northeast monsoon because of the existence of the Titiwangsa Range, which blocks the region from receiving heavy rainfall. On the other hand, it is found that the lowlands areas such as the eastern part of the Peninsula are strongly characterized by the northeast monsoonal flow. Based on the results of the Mann-Kendall test, as the trend of the total amount of rainfall and the frequency of wet days during the southwest monsoon decrease at most of the stations, the rainfall intensity increases. In contrast, increasing trends in both the total amount of rainfall and the frequency of wet days were observed at several stations during the northeast monsoon, which give rise to the increasing trend of rainfall intensity. The results for both seasons indicate that there are significantly decreasing trends in the frequency of wet days during the extreme events for most of the stations on the peninsula. However, a smaller number of significant trends was found for extreme intensity.
Kajian ini bertujuan mengenal pasti pola taburan kehujanan di Semenanjung Malaysia menggunakan Indeks Kerpasan Piawai bagi skala masa yang berbeza iaitu sebulan, enam bulan dan dua belas bulan. Data kajian adalah data hujan harian dari 75 stesen tadahan hujan yang merangkumi empat zon iaitu Barat Laut, Barat, Barat Daya dan Timur untuk 33 tahun; 1975 – 2007. Hasil kajian mendapati nilai serakan bagi frekuensi keberlakuan keadaan basah/kering bertambah dengan peningkatan skala masa. Kajian pemboleh ubah berkaitan iaitu tempoh, keparahan dan selang ketibaan mendapati wujud peningkatan dalam nilai-nilai maksimum, purata dan sisihan piawai di setiap zon dengan bertambahnya skala masa yang digunakan. Seterusnya, zon Barat Daya secara konsisten mengalami tempoh keadaan basah yang lebih lama berbanding tempoh keadaan kering manakala zon Barat pula menghasilkan nilai sisihan piawai yang paling tinggi berbanding dengan zon lain untuk kesemua pemboleh ubah kajian kecuali intensiti.
This study investigates the relationship between land use types and sedimentary characteristics of fluvial bed at three
rivers in Selangor, Malaysia; namely Sungai Tengi, Selangor and Langat. The diversity in population density and land
development at the adjacent river banks gives associated dominant land use type as forest, agriculture and urban for
Tengi, Selangor and Langat, respectively. Field sampling was conducted at consistent spatial locations for Tengi and
Selangor, whereas for Langat, the bed sediment was taken at non-uniform spatial points due to limited access. Statistical
analysis of the sediment bed mixture shows that forest dominated land gives finer bed sediment size at < 200 µm.
Agriculture-type of land use increases the mean sediment size to medium sand, whereas bed material near to urbanized
areas has coarser sediment size with > 650 µm. Correlation analysis proved that there is a relationship between types
of land use with the mean sediment size. No distinctive correlation can be observed for sorting, skewness and kurtosis
of the sediment with the types of land use.