PENENTUAN BATAS ATAS NORMAL DAN BAWAH NORMAL CURAH HUJAN BULANAN SETARA TERCILE DENGAN KOEFISIEN REGRESI LINIER SEDERHANA
DOI:
https://doi.org/10.31172/jmg.v15i1.175Keywords:
Tercile, Uji-t berpasangan, Metode Kuadrat Terkecil, Faktor Skala, Paired t-test, Least Square Method, Scale FactorAbstract
WMO mendefenisikan kategori sifat hujan Atas Normal (AN) dan Bawah Normal (BN) berdasarkan nilai Tercile (P66 dan P33). Sedangkan BMKG menggunakan kategori 1.15Ẍ dan 0.85Ẍ sebagai batas AN dan BN. Penelitian dilakukan di 120 stasiun BMKG menggunakan data curah hujan bulanan. Uji-t berpasangan (α = 0.01) digunakan untuk menguji 1.15 Ẍ dengan P66 dan0.85 Ẍ dengan P33. Hasilnya 1.15Ẍ berbeda dengan P66 pada 6 stasiun dan 0.85 Ẍ berbeda dengan P33 pada 108 stasiun. Regresi Linier Sederhana dengan metode kuadrat terkecil dilakukan antara Ẍ (peubah bebas) dengan P66 dan P33 (peubah tak bebas) sehingga didapatkan koefisien regresi βɑ dan βƅ. Selanjutnya dipilih nilai tengah dari setiap kelas distribusi frekuensi βɑ dan βƅ yang disebut sebagai faktor skala terbaik β*ɑ dan β*ƅ. Uji-t berpasangan kembali digunakan untuk menguji β*ɑẌ dengan P66 dan β*ƅẌ dengan P33. Hasilnya pada tingkat kepercayaan 99% β*ɑẌ tidak berbeda dengan P66 dan β*ƅẌ tidak berbeda dengan P33 untuk 120 stasiun. Sehingga β*ɑẌ dan β*ƅẌ direkomendasikan sebagai batas AN dan BN yang lebih mendekati standar WMO.
WMO defines a category for above normal (AN) and below normal (BN) as Tercile (P66 dan P33). On the other hand, BMKG uses 1.15Ẍ and 0.85Ẍ to determining AN and BN respectively. Monthly rainfall data in 120 BMKG’s stations are used in this research. A paired t-test (α = 0.01) is used for determining 1.15Ẍ and P66 as well as 0.85Ẍ and P33. As a result, 1.15Ẍ is not equivalent to P66 in 6 stations and 0.85Ẍ do not equal to P33 in 108 stations. The least-square method in Simple Linear Regression is examined between Ẍ as an independent variable and P66 as well as P33 as the dependent variable. Therefore, βɑ and βƅ have been found as coefficient regression. The next step is choosing β*ɑ, β*ƅ as a median for classes of frequency distribution βɑ and βƅ. β*ɑ and β*ƅ are the best scale factor. Finally, a paired t-test is used also to determining β*ɑẌ and P66 and β*ƅẌ and P33. As a result, β*ɑẌ is the same as P66and β*ƅẌ equals to P33 in 120 stations for confidence level 99%. Consequently, β*ɑẌ and β*ƅẌ are strongly recommended as new above normal and below normal which are similar to WMO standards.
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